B 
 
 m 
 
THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
 
OUTLINES 
 
 HUMAN PHYSIOLOGY. 
 
 BY 
 
 HERBERT MAYO, F.R.S. F.G.S. 
 
 rnoFrsscm OF ANATOMY IN KING'S COLLEGE, LONDON; 
 
 SURGEON TO THE MIDDLESEX HOSPITAL; 
 
 FORMERLY 1'ROFESSOU OF ANATOMY AND SURGERY TO THE KOYAf, COLLF.GE OF 
 
 SURGEONS. 
 
 THE THIRD EDITION. 
 
 LONDON : 
 
 BURGESS AND HILL, GREAT WINDMILL STREET. 
 MDCCCXXXIII. 
 
*2^A ^ 
 

 CONTENTS. 
 
 CHAPTER I. 
 
 OF LIFE AND ORGANIZATION. 
 
 Mtfe 
 
 Meaning of the Term Life .................................................... 2 
 
 Organized Matter, how characterized ....................................... 3 
 
 Spontaneous Decomposition of Organized Matter ........................ 4 
 
 Of Antiseptic Substances ...................................................... 5 
 
 Of the Phenomena of Life .................................................. 6 
 
 Of Nutrition ...................................................................... 7 
 
 Of Generation .................................................................. 8 
 
 Of the Properties of Life ...................................................... .9 
 
 Of the Motion of the Sensitive Plant ........................................ 10 
 
 Phenomena of the Growth of Plants ........................................ 13 
 
 Sensitive and Vegetative Functions combined in Animals ............... 14 
 
 CHAFFER II. 
 
 OF THE BLOOD. 
 
 Of the Course of the Blood .................................................. 18 
 
 Proofs of the correctness of the Harveian Theory ........................ 19 
 
 Differences of Arterial and Venous Blood ................................. 20 
 
 Changes, which supervene in freshly drawn Blood ....................... 21 
 
 Of the Serum and of the Fibrin of the Blood .............................. 22 
 
 Of the Colouring Matter of the Blood ....................................... 23 
 
 Causes which promote Coagulation ........................................... 24 
 
 Causes which retard Coagulation ............................................. 25 
 
 Causes which prevent Coagulation ........................................... 26 
 
 Final causes of the Coagulation of the Blood ........... , .................. 27 
 
 Inflammatory State of the Blood ............................................ 28 
 
 Its rapid alternation with the ordinary state ............................... 29 
 
 CHAPTER III. 
 OF MUSCULAR ACTION. 
 
 Appearance and Chemical Composition of Muscles ........................ 31 
 
 Of the Minute Structure of Muscles ....................................... 32 
 
 Phenomena of Muscular Relaxation .......................................... 33 
 
 Phenomena of Muscular Action .................................. ........... 34 
 
 Condition of the Fibres of a Muscle when in action ..................... 35 
 
 Of the Tone of Muscles ............................................ . ............ 36 
 
 R/I385J09 
 
VI CONTENTS. 
 
 Pftye 
 
 Of Muscular Fatigue 37 
 
 Rigidity of Muscles after Death 38 
 
 Proximate Cause of Muscular Contraction 39 
 
 Distribution of Muscles in two classes 40 
 
 CHAPTER IV. 
 OF THE FORCES WHICH CIRCULATE THE BLOOD. 
 
 Means of increasing the Depth of the Chest 44 
 
 Means of increasing the Breadth of the Chest 45 
 
 Means of increasing the Height of the Chest 46 
 
 Of the Pleura and Pericardium 48 
 
 Of the Lungs 49 
 
 Effect of the Resiliency of the Lungs 50 
 
 Of the Muscular Structure of the Heart 51 
 
 Use of the Mitral and Tricuspid Valves 52 
 
 Use of the Semilunar Valves 53 
 
 Of the Structure of Arteries and Veins 55 
 
 Of the Flow of Blood into the Auricles 56 
 
 Suction produced by the Resilience of the Lungs ..,. * 57 
 
 Influence of Breathing on the Circulation 58 
 
 Of the action of the Auricles and Ventricles 59 
 
 Force of the Left Ventricle 60 
 
 Action of the Heart not produced by Nervous Influence 61 
 
 Action of the Heart influenced through the Nerves '. 62 
 
 Frequency of the Action of the Heart 63 
 
 Of a Circulation without a Heart 64 
 
 Of the Nature of the Capillary Vessels G5 
 
 Of the Arterial Pulse 66 
 
 Evidence that Arteries are Irritable 67 
 
 Relaxation of Arteries the Cause of Local Action 68 
 
 Cause of the Tortuousness of certain Veins 69 
 
 Influence of Gravity on the Circulation 70 
 
 Of the Circulation in the Brain 71 
 
 CHAPTER V. 
 
 OF THE PULMONARY CIRCULATION. 
 
 Cause of the Entrance of Air into the Lungs 73 
 
 Different Degrees of Inspiration 74 
 
 Volume of Air inhaled at a single Inspiration... 75 
 
 Average Quantify of Air contained in the Lungs 76 
 
 Changes produced in Atmospheric Air by Breathing 77 
 
 Absorption and Production of Nitrogen 79 
 
 Respiration of other Gases than Atmospheric Air 80 
 
 Pulmonary Exhalation find Absorption 81 
 
CONTENTS. Vll 
 
 Page 
 
 Influence of the Phrenic Nerves in Breathing- 82 
 
 Influence oftheNervi Vagi 83 
 
 CHAPTER VI. 
 OF THE CIRCULATION THROUGH THE BODY. 
 
 Of Fainting 85 
 
 Of Asphyxia 86 
 
 Effects of breathing Nitrous Oxide 87 
 
 Effects of Air, 8fc. injectedinto the Veins 88 
 
 Of Secretion in general 89 
 
 Of Nutritive Secretion 90 
 
 Influences ivhich modify Nutritive Secretion 91 
 
 Of Functional Secretion 92 
 
 Influences which modify Functional Secretion 93 
 
 Heat liberated when the Blood becomes venous 94 
 
 Quantity thus produced comparatively trivial 95 
 
 Opinions respecting* the Source of Animal Heat 96 
 
 Phenomena of Venous Absorption referable to Transudation 9/ 
 
 CHAPTER VII. 
 OF DIGESTION. 
 
 SECTION 1. OF HUNGER AND THIRST J OF THE MASTICATION OF 
 FOOD, AND OF DEGLUTITION. 
 
 Of the Fauces, ,., .,...., 104 
 
 Chemical Composition of Teeth ... ., 105 
 
 Number and Shape of Human Teeth 106 
 
 Different hinds of Teeth 107 
 
 Movements of the Lower Jaw 108 
 
 Of the Muscular Structure of the Tongue 109 
 
 Quantity of Saliva formed at each Repast 110 
 
 Use of the Saliva , Ill 
 
 Use of the Soft Palate , 112 
 
 The Aperture of the Larynx how protected U3 
 
 Of Pharyngeal Deglutition , , 114 
 
 SECTION II. OF THE NATURE OF THE ALIMENTARY CANAL FROM 
 THE OESOPHAGUS DOWNWARDS, AND QF THE FLESHY VISCERA 
 CONNECTED WITH IT. 
 
 Of the Structure of the Alimentary Canal 116 
 
 Of the Irritability of its Muscular Fibres 117 
 
 Triple division of the Alimentary Canal 118 
 
 Shape and Situation of the Stomach 119 
 
 Of the Gastric Secretion, 120 
 
 Of Spontaneous Vomiting 121 
 
 Of Spasmodic Vomiting 122 
 
 Of the Pylorus 123 
 
Vlll CONTENTS. 
 
 Pa^e 
 
 Of the small Intestines 124 
 
 Of the Great Intestines 125 
 
 Of the Spleen 126 
 
 Of the Pancreas 127 
 
 Of the Liver 128 
 
 Bile formed from Arterial and from Venous Blood 1 29 
 
 Experiments of M. Simon 130 
 
 SECTION III. OF THE FUNCTION OF THE STOMACH. 
 
 Of the Valve at the Cardia 131 
 
 Food digested in the Stomach 132 
 
 Formation of Chyme .... 133 
 
 Varieties of Chyme 134 
 
 Ordinary period of the Formation of Chyme 135 
 
 Causes which retard Chymi/ication 136 
 
 Influence of the Nerves upon Digestion 137 
 
 SECTION IV. OF THE FORMATION OF CHYLE. 
 
 Appearance of the Chyle in the small Intestines 1 39 
 
 Researches of Tiedemann and Gmelin t and of Leuret and Lassaigne 
 
 on Digestion 140 
 
 Function of the Colon 147 
 
 SECTION V. OFFICE OF THE GHEAT INTESTINES. 
 
 Analysis of the Contents of the Ctecum 148 
 
 Analysis of the Contents of the Colon 149 
 
 Analysis of the Contents of the Rectum 150 
 
 SECTION VI. OF THE VARIOUS SUBSTANCES EMPLOYED AS FOOD. 
 
 Of the various Articles of Food 151 
 
 CHAPTER VIII. 
 
 OF THE LACTEAL AND LYMPHATIC VESSELS. 
 
 Of the Conglobate Glands 157 
 
 Absorbent Vessels either Lacteals or Lymphatics 1 59 
 
 Researches of Lippi 160 
 
 Of Lymph 161 
 
 Researches of Tiedemann and Gmelin 162 
 
 Nature of Chyle and Lymph 163 
 
 Origin of the Lacteals 164 
 
 Hunteriitn Experiment upon Lacteal Absorption 1 65 
 
 Evidence that Lymphatics absorb 166 
 
 Of the Lymphatics 167 
 
 CHAPTER IX. 
 
 OF THE URINARY ORGANS. 
 
 Structure of the Kidney 169 
 
 Of the Urethra ,,.', 170 
 
CONTENTS. IX 
 
 Page 
 
 Nature of the Urine 171 
 
 Absorbed Substances easily detected in the Urine 1 72 
 
 Effect of removing the Kidneys 1/3 
 
 CHAPTER X. 
 
 OF THE SKIN. 
 
 Of the Cutis 176 
 
 Of the Nerves and of the Absorbents of the Skin . 177 
 
 Analogy between the Skin and Mucous Membranes 1 78 
 
 Of Cutaneous Transpiration 179 
 
 Of the Standard Pleat of the Body 180 
 
 Difference observed in very young Animals 181 
 
 Effects of extreme Cold 182 
 
 Effects of great Heat on the System 184 
 
 CHAPTER XI. 
 
 ON THE FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 SECTION I. OF THE MENTAL PHENOMENA IN MAN AND ANIMALS. 
 
 Of Sensation and Perception 186 
 
 Of Volition 188 
 
 Of Instinct 189 
 
 Of modified I istincts 193 
 
 Of Conception and Memory in Animals 194 
 
 Of Imitation and Attention 195 
 
 Of the observation of direction shown by Animals 1 96 
 
 What tee term in Animals rational 197 
 
 Professor Glennie's account of James Mitchell 1 98 
 
 Of Conception, Memory, Attention, Comparison 200 
 
 Analysis of Belief 201 
 
 Of the Moral Sense 204 
 
 Of Taste 205 
 
 Of Talent and Disposition 206 
 
 Of the Active Principles of our Nature 207 
 
 Tne Mind not the Result of Organization 208 
 
 Of Sleep 209 
 
 Influence of the Will over the Voluntary Muscles not suspended 
 
 during Sleep 210 
 
 Of Somnambulism 212 
 
 Of false Perception 213 
 
 Case of Nicolai 214 
 
 Distinction between Delirium and Madness 217 
 
 Of the Decay of the Mind 218 
 
 Of Failure of Recollection 219 
 
 SECTION II. OF THE ELEMENTS OF A NERVOUS SYSTEM. 
 
 Nervous System of Radiated Animals 221 
 
X CONTEN 7 TS. 
 
 Page 
 
 Nervous System of Articulated Animals 222 
 
 Nervous System of Mollusca - 223 
 
 Nervous System of Vertebral Animals 225 
 
 First Appearance of a Brain 227 
 
 Of the Functions of the Chord 228 
 
 Importance of the Medulla Oblongata 229 
 
 The Spinal Chord an assemblage of independent segments 23 1 . 
 
 SECTION III. OF THE SPINAL CHORD. 
 
 Independence of the different Segments of the Chord 233 
 
 Markings upon the Spinal Chord ... .. 234 
 
 Disposition of the Grey Matter in the Chord 235 
 
 Functions of the interior and Posterior Fasciculi , *. 236 
 
 SECTION IV. OF THE ENKEPHALON 1 . 
 
 Of the Shape of the Medulla Oblongata 237 
 
 Of the Origin of the Anterior Pyramids 23S 
 
 Shape and Connections of the Cerebellum 239 
 
 Reil's Exposition of the Structure of the Cerebellum ... 240 
 
 Of the Structure of the Cerebrum 241 
 
 Distribution of the Fasciculi of the great Commissure 242 
 
 Theory of Dr. Foville 243 
 
 Experiments on the Cerebellum 244 
 
 Experiments on the Tubercles 246 
 
 Experiments on the Cerebrum 247 
 
 Relation of the size of the Brain to Mental Power 249 
 
 Of the Brains of the Cetaceous Mammalia 250 
 
 Other relations of the size of the Brain ,, 251 
 
 SECTION V. OF THE FUNCTIONS OF THE NERVES. 
 
 Nerves. Their Structure, Origin, and Termination 252 
 
 Of Plexuses and Ganglia 253 
 
 Of the Origin of the Spinal Nerves 254 
 
 Of the First and Second Cerebral Nerves 255 
 
 Of the soft portion of the Auditory Nerve... ,. 256 
 
 Of the third, fourth, fifth, and ninth Cerebral Nerves 267 
 
 Origin of the Fifth Cerebral Nerve 258 
 
 Sir Charles BeWs Experiments 259 
 
 Experiments showing the true Function of the Facial Branches of 
 
 the Fifth and Seventh Nerves 260 
 
 Uses of the remaining parts of the Fifth Nerve 262 
 
 Of the Pneumogastric Nerve ,. 263 
 
 Of the Sympathetic Nerve 264 
 
 Plate of the Origins of the Cerebral Nerves 266 
 
 Of the Cerebral Nerves 26? 
 
 Principle observed in the Origin of Nerves 268 
 
 Nerves probably Media of Transmission only 269 
 
 What Nerves are distributed to the Electric Organs 270 
 
CONTENTS. XI 
 
 Page 
 
 CHAPTER XII. 
 OF THE ORGANS OF THE SENSES. 
 
 SECTION I. OF THE ORGAN OF VISION. 
 
 Of the Nature of Light 272 
 
 Of Reflection and Refraction 273 
 
 Of Colour. Of Complementary Colours 274 
 
 Of defective Vision of Colours 275 
 
 Perception of the Blood-vessels of the Retina 276 
 
 Fundamental Law of Vision 277 
 
 Use of the Inversion of the Picture on the Retina 278 
 
 Further Offices of the Humours of the Eye 279 
 
 Of Myopic and Presbyopia Eyes 280 
 
 Experiment of Schemer 281 
 
 Of the Humours of the Eye 282 
 
 The Eye Achromatic 283 
 
 Of the Knowledge directly obtained by Vision 284 
 
 Case mentioned by Cheselden 285 
 
 Knowledge of the Magnitude and Distance of Objects, how obtained. 286 
 
 Convergence of the Optic Axes ,. 288 
 
 Use of the Pigmentum Nigrum 289 
 
 The Action of the Iris in certain Animals distinctly voluntary 290 
 
 State of the Pupil in Death 292 
 
 The Eye adjusts itself to Vision at different Distances 293 
 
 Mechanism by wh iek the Eye alters its focal Length , 294 
 
 The Eye adjusts itself to different Distances 296 
 
 Extent of the Field of Vision 297 
 
 Retina insensible to the ordinary Impressions of Light 298 
 
 Remarkable simultaneous Affection of both Retince 299 
 
 Of the Action of the Recti Muscles 302 
 
 Of the Action of the Obliqui 303 
 
 Intricacy of the Nerves of the Orbit considered 304 
 
 Of Squinting 305 
 
 Of the Eyelids and Tunica Conjunctiva 306 
 
 Of the Tears 307 
 
 SECTION II. OF THE ORGAN OF TOUCH. 
 
 Of the Sensation of Touch 308 
 
 Of Sensations of Heat and Cold 309 
 
 Influence of the Nerves of Touch over Nutrition 310 
 
 Influence of the Nerves of Touch 311 
 
 SECTION III. OF THE ORGAN OF TASTE. 
 
 Of the Organ of Taste 312 
 
 Impressions included under the term Taste 313 
 
Xll CONTENTS. 
 
 SECTION IV. OF THE ORGAN OF SMELL. 
 
 Of Odorous Impressions ........................................................ 315 
 
 Form of the Nostrils ........................................................... 316 
 
 Experiments on the Olfactory Nerves ...................................... 317 
 
 SECTION V. OF THE ORGAN OF HEARING. 
 
 Of the Nature of Sound ....................................................... 318 
 
 Of the Organof Hearing ..................................................... 320 
 
 Of the Tympanum ............................................................... 321 
 
 Of the External Ear ............................................................ 322 
 
 Of the Nerve of Hearing ..................................................... 323 
 
 CHAFi'ER XIV- 
 
 OF VOLUNTARY MOTION. 
 
 SECTION I. ON THE ATTITUDES AND MOVEMENTS OF MAN. 
 
 Of the different kinds of Bones ...................... . ....................... 325 
 
 Chemical Composition of Bone ................................................ 326 
 
 Of the Joints ..................................................................... 327 
 
 Nature of Sinovia ............................................................... 328 
 
 Analogical Design in the Skeleton ........................................... 329 
 
 The Skeleton fitted for the Erect Posture ................................. 331 
 
 Of the Strength of the Skeleton ............................................. 332 
 
 Of the Joints of the Atlas and Dentata .................................... 333 
 
 Of the Muscles, which move the Frame .................................... 334 
 
 Use of Tendons illustrated ..................................................... 335 
 
 Of Antagonist Muscles ........................................................ 337 
 
 Instances of the different kinds of Levers .................................. 338 
 
 Strength in the Human Frame sacrificed to Velocity ..................... 339 
 
 Of the Erect Posture and of Locomotion .................................... 340 
 
 Of Physiognomy ................................................................. 341 
 
 SECTION II. OF THE MECHANISM OF SPEECH. 
 
 Various means of producing Sound .......................................... 342 
 
 Of the Production of Sound by the Lips .................................... 343 
 
 The Chordee Vocales comparable to the Lips .............................. 344 
 
 Of the Structure of the Larynx ............................................... 345 
 
 Action of the Muscles of the Glottis ........................................ 348 
 
 State of 'the Rima Glottidis in Vocalization ................................. 349 
 
 Tension of the Ligaments in Vocalization .................................. 350 
 
 Vocalizing Position of the Ligaments ....................................... 351 
 
 Use of the Windpipe in Vocalization .................... . ................... 352 
 
 Of the Compass of the Human Voice ........................................ 353 
 
 Of Articulation .................................................................. 354 
 
COM'KNTS. XII 1 
 
 Page 
 
 Of the Vowel Sounds 355 
 
 Of Consonantal Sounds 356 
 
 Of Stammering 357 
 
 Of Coughing', Hiccupping, Sneezing 358 
 
 Of the Mechanism by which the Larynx is closed 359 
 
 Of the Larynx in reference to Deglutition 360 
 
 Of Spasmodic Closure of the Glottis 361 
 
 Closure of the Glottis necessary for muscular Efforts 362 
 
 CHAPTER XV. 
 
 OF GENERATION. 
 
 SECTION I. OF THE DIFFERENCE OF THE SEXES, AND OF IMPREG- 
 NATION. 
 
 Of true and of equivocal Generation 364 
 
 Of the Female Organs of Generation 365 
 
 Of the Male Organs 366 
 
 Influence of the Genital Organs on the Frame 367 
 
 Of Puberty 369 
 
 Of Menstruation 370 
 
 Period at which Menstruation begins 371 
 
 Appearance of the Ovulum, after Baer 372 
 
 Production of Corpora Lutea 573 
 
 Condition essential to Impregnation 374 
 
 Place in which the Ovum is fertilized 375 
 
 Influence on Immature Ovula 376 
 
 SECTION II. ON THE DEVELOPMENT OF THE EMBRYO. 
 
 State of the Ovulum after Impregnation 3/8 
 
 Of the Germinal Membrane in the Egg 379 
 
 Division of the Germinal Membrane into Layers 380 
 
 Folding of the three Layers 381 
 
 Appearance of the Heart ; 332 
 
 Of the Vascular Area 383 
 
 Of the Vascular Area in Mammalia , 384 
 
 Development cf the Brain and Spinal Chord 385 
 
 Of the Spinal Chord 386 
 
 Of the Medulla Oblmgata 337 
 
 Of the Cerebellum and Tubercles 388 
 
 Development of the Cerebrum 389 
 
 Of the Nerves 390 
 
 Of the Muscles 391 
 
 Of the Eye 390 
 
 Of the Organ of Hearing 393 
 
 Of the Development of the Bones 394 
 
 Of the Progress of Ossification 395 
 
XIV CONTENTS. 
 
 Pages 
 
 Of the Ossification of Epiphyses 396 
 
 Of the Shape of the Embryo , 397 
 
 Of the Integuments > 398 
 
 Of the Growth of the Limbs 399 
 
 Production of the Amnios 400 
 
 Of the Intestinal Vesicle 401 
 
 Of the Fauces and Stomach 402 
 
 Of the Intestines 403 
 
 Of the Salivary Glands 404 
 
 Of the Liver and Gait-bladder 405 
 
 Of the Lungs 406 
 
 Of the Wolffian Bodies.... 407 
 
 Of the Kidneys, and of the Spleen 409 
 
 Of the Bladder 410 
 
 Of the Testes and Ovaries 411 
 
 Of the Vascular Layer 413 
 
 Of the Vascular Area 414 
 
 Of the Heart 415 
 
 Of the Septum of the Heart 416 
 
 Of the Vascular Arches derived from the Aorta 417 
 
 Transmutation of the Single Aorta into Aorta and Pulmonary Artery. 418 
 
 Of the Allanto'is 420 
 
 Of the Navel String 422 
 
 Of the Chorion 423 
 
 Of the F(tal Placenta 424 
 
 SECTION III. OF THE SOURCE OF THE NOURISHMENT OF THE HUMAN 
 EMBRYO, AND OF ITS CONNECTION WITH THE UTERUS. 
 
 Source of the Nourishment of the Embryo 425 
 
 Of the Cotyledon in Ruminants 426 
 
 Of the Decidua: 42/ 
 
 Of the Maternal Placenta 428 
 
 Of Foetal Digestion 430 
 
 Period of Utero-gestation 431 
 
 Of Labour 433 
 
 Of the Mamma 434 
 
 CHAPTER XVI. 
 OF GROWTH AND OF REPARATION. 
 
 Of the Growth of Teeth 437 
 
 Influence of the Nerves 438 
 
 Of the Temporary Teeth 439 
 
 Of the Permanent Teeth 440 
 
 Of the Growth of Hoofs and Horns 441 
 
 Of the Nails and Epidermis 442 
 
CONTENTS. XV 
 
 Pages 
 
 Of Reunion of Soft Parts 443 
 
 Of the Reunion of Tendons 444 
 
 Of the Reunion of Nerves : 445 
 
 Of the Reunion of Cartilage 446 
 
 Of the Reunion of Bone 447 
 
 Of Fracture of the Neck of the Femur 448 
 
 Of Fractures of the Cranium 449 
 
 Nerve divided in the Cranial Cavity 450 
 
 CHAPTER XVII. 
 OF THE VARIETIES OF THE HUMAN SPECIES. 
 
 The Human Race descended from one Stock 452 
 
 Of differences of Colour in different Nations 453 
 
 OfAWmoes 454 
 
 Of Differences in the Texture of the Hair 455 
 
 Of Differences in the Shape of the Cranium 456 
 
 Distribution of the different Races of Mankind 458 
 
 Of the ^Ethiopian Variety 459 
 
 Of the Yoloffs 460 
 
 Of the Tibboo 461 
 
 Of the Copts 462 
 
 Of the Hottentots 463 
 
 Of the Papuas of New Guinea , 464 
 
 Of the New Hollanders 465 
 
 Of the Inhabitants of Van Dieman's Land 466 
 
 Of the Inhabitants of Europe 467 
 
 Of the Arabs 468 
 
 Of the Hindoos 469 
 
 Of the South Sea Islanders , 4/0 
 
 Of the Calmucks 471 
 
 Of the Tungusians , 472 
 
 Of the Japanese 473 
 
 Of the Inhabitants of the Continent of America 474 
 
 CONCLUSION.. 477 
 
 ERRATA. 
 
 Page 2, line 2, for continuation read combination. 
 
 354, .. 9, . . narrowing .... temporary obstruction. 
 
 356, .. 6, .. k q g ....k g ng. 
 
 357, ..12,.. Italy .... modern Italy. 
 384, .. 5 .. yolk, body . yolk bag. 
 
" In the study of anatomy, every man proceeds on the maxim, that 
 nothing in the body of an animal was made in vain ; and when he meets 
 with a part of which the use is not obvious, he feels himself dissatisfied, 
 till he discovers some at least of the purposes, to which it is subservient. 
 * I remember (says Mr. Boyle) that, when I asked our famous Harvey what 
 were the things that induced him to think of a circulation of the blood ? 
 he answered me, that when he took notice, that the valves in the veins of 
 so many parts of the body were so placed, that they gave a free passage to 
 the blood towards the heart, but opposed the passage of the venal blood 
 the contrary way ; he was incited to imagine, that so provident a cause as 
 Nature had not placed so many valves without design ; and no design 
 seemed more probable, than that, since the blood could not well, because 
 of the interposing valves, be sent by the veins to the limbs, it should be 
 sent through the arteries, and return through the veins, whose valves did 
 not oppose its course that way.' " 
 
 STEWART'S OUTLINES OF MORAL PHILOSOPHY. 
 
OUTLINES 
 
 OF 
 
 HUMAN PHYSIOLOGY 
 
 CHAPTER I. 
 OF LIFE AND ORGANIZATION. 
 
 THE globe of the earth is formed of what are termed mineral 
 substances, existing either in a solid, or in a liquid, or in a 
 gaseous form. Upon or near its surface are found other 
 bodies, which either live, or, being dead, preserve some re- 
 mains of that shape and structure which they possessed 
 during life. Living bodies are either plants or animals. 
 The varied and elaborate mechanism calculated to perform 
 determinate functions, which admits of being displayed in 
 the greater number, has obtained for the whole the common 
 appellation of organized bodies. Mineral substances, on 
 the other hand, which taken individually consist of mere 
 aggregations of similar particles, are termed unorganized. 
 
 Mineral bodies have been incorrectly characterized as 
 inert. The properties of unorganized matter are continually 
 producing important changes. The surface of the earth is 
 perpetually undergoing alteration, through chemical or me- 
 chanical agency. The oxygen of the atmosphere is in con- 
 stant consumption, and is as constantly reproduced. The 
 waters, which in various ways become polluted, are restored 
 to a state of purity when they rise in vapour : the purified 
 element, subsequently recondensed, falls in rain, or hail, or 
 snow, and becoming impregnated with atmospheric air, is 
 
2 Meaning of the Term Life. 
 
 again distributed over the earth, to diffuse fertility and 
 health ; a continuation of phenomena, which correspond in 
 a remarkable manner with the functions of respiration and 
 of the circulation of the blood in animals. The properties of 
 inert matter again determine the alternations of night and 
 day, the recurrence of the seasons, the motions of the pla- 
 netary system ; a series of changes which may be termed 
 the Life of the World. 
 
 In the preceding illustration of its meaning, the term 
 Life is employed figuratively. In its direct sense it denotes 
 other changes, which occur exclusively in organized bodies. 
 It is important, however, to remark, that in either instance 
 the force of the term is the same : in its direct as well as in 
 its figurative application, the word life is no more than 
 a collective expression for a series of phenomena. 
 
 The aim of natural philosophy is to verify and to accu- 
 mulate facts relating to the phenomena of the universe, and 
 to trace their mutual relations and dependence. As soon as 
 by observation and experiment the conditions have been 
 rigorously ascertained, under which given classes of phe- 
 nomena manifest themselves, the physical cause of such 
 phenomena, or the law which regulates them, is said to be 
 discovered ; and some general expression is made use of, 
 which strictly indeed denotes no more than the invariableness 
 of the sequence of events, however it may figuratively appear 
 to attribute causation to matter or to mind. The terms pro- 
 perty and principle are commonly considered in natural phi- 
 losophy equivalent to the term already used : yet each has 
 its peculiar shade of meaning, fitting it to convey a different 
 relation of the same idea. The word law serves to express 
 the conditions essential to a change : the word property, to 
 attribute to a substance the power of producing a change 
 under ascertained conditions; while the word principle, 
 fitted for a ruder state of science, is used like the final 
 letters of the alphabet in algebraic calculations, to denote 
 an unknown element, which when thus expressed may be 
 more conveniently analyzed. Consistently with the expla- 
 nation given, we state as the law of gravity the ratio in 
 which masses of matter are reciprocally attracted ; or we 
 
Organized Matter, how characterized. 3 
 
 observe that masses of matter possess a property of reci- 
 procal attraction ; or we speak of the principle of electricity, 
 or of the principle of magnetism, as the unknown causes of 
 phenomena that are as yet imperfectly understood. Hitherto 
 the laws of life, or the properties of living matter, have not 
 been determined with precision ; and physiologists have 
 shown themselves reluctant to disuse the vague term, "a 
 Principle of Life," to which an imaginary and delusive 
 meaning is attached by many, who forget that terms of this 
 nature have no real value, except as generalized and ri- 
 gorous expressions of facts. 
 
 Organized bodies are distinguished from mineral sub- 
 stances, not less by their physical character, than by exclu- 
 sively exhibiting the phenomena of life. Animals and plants 
 are distributed in species, each of which has a limited bulk 
 and peculiar form. Mineral substances on the contrary 
 appear to have no limit assigned to their magnitude or va- 
 riety of figure. The former are generally composed of dissi- 
 milar parts, the latter are homogeneous. The former have 
 in most instances curvilinear surfaces ; the latter are com- 
 monly bounded by right lines. The former, which consist 
 of materials produced in the laboratory of the living body 
 by delicate combinations of mineral elements, are preserved 
 from decomposition by the vital influence alone ; and as 
 soon as life has ceased, slowly or rapidly revert to the con- 
 dition of inert matter. The latter, which derive their cha- 
 racter from causes of a more permanent nature, have less 
 tendency to change. 
 
 The materials of which organized bodies are wrought, are 
 termed their proximate principles. They may for the most 
 part be obtained separately by very simple processes. Thus, 
 if a ductile paste be formed by the gradual addition of a 
 small quantity of water to flour ; and the paste be kneaded 
 by the hand and washed by a slender stream of water, it 
 becomes a grey, tenacious, and highly elastic substance, 
 termed gluten. The water employed in the process is ren- 
 dered turbid and milky : a white matter remains suspended 
 in it, which is starch. When meat has been boiled for a 
 time in water, oil is observed to separate and float upon the 
 
 B 2 
 
Spontaneous Decomposition of Organized Matter. 
 
 surface : another substance separated from the meat exists 
 dissolved in the water; this substance becomes solid on 
 cooling, and is termed gelatin : the tasteless shreds which 
 remain are termed fibrin. Gluten and starch are instances 
 of the proximate principles of plants ; 'as are oil, fibrin, and 
 gelatin, of the proximate principles of animal matter. 
 
 The proximate principles of organized bodies are again 
 individually resoluble into definite combinations of the 
 simple elements of inert matter. According to Thenard, the 
 three substances most used in the construction of the human 
 body may be shown to consist of the following combinations 
 of simple bodies : 
 
 Carbon. Oxygen. Hydrogen. Nitrogen. 
 
 Fibrin, of 53.365 19.865 7.021 19.934 
 
 Albumen 52.883 23.872 7.540 15.705 
 
 Gelatin 47.881 27.207 9.914 16.988 
 
 The tendency to decomposition in dead animal or vegeta- 
 ble matter depends upon the nature of its proximate prin- 
 ciples. In many instances changes supervene, which have 
 the effect of retarding complete resolution. Thus various 
 sorts of fermentation furnish products remarkable for the 
 length of time they may be preserved unchanged. Where 
 nitrogen is present, as in most animal and in some vegeta- 
 ble substances, the process of decomposition, characterized 
 by its rapidity, itsjetor, and the extrication of ammonia, is 
 termed putrefaction. Within a short period after death, the 
 human frame, as a step in this process, undergoes an evi- 
 dent change ; the features become sharper ; the cornea loses 
 its brightness ; the eyes sink. Then the neck and abdo- 
 men become discoloured ; the body softens and exhales an 
 offensive odour; the skin, from which the cuticle separates, 
 turns successively green, and blue, and black ; the corpse 
 slowly dissolves, part combining with the atmosphere, part 
 reduced to a liquid state, part mouldering to earth. 
 
 In order that putrefaction may take place, the body must 
 be exposed to the conjoined influence of an elevated tem- 
 perature, of moisture, and of atmospheric air or air contain- 
 ing oxygen. If either of these agents be excluded, the 
 progress of decomposition is arrested. Frozen provisions 
 
Of Antiseptic Substances. 5 
 
 will keep for an indefinite period, with little change except 
 a diminution of their flavour. A dissected limb suspended in 
 a current of air, loses its moisture by evaporation, becomes 
 hard and of a brown colour, and subsequently remains for a 
 length of time without undergoing further alteration. And 
 a method has been successfully tried of preserving the 
 flesh of animals for many months free from taint, by in- 
 closing it directly after boiling in metal cases accurately 
 soldered. 
 
 Certain substances are termed antiseptic, with which 
 when animal matter is impregnated, the ordinary mode of 
 decomposition is prevented, and another change substituted : 
 after which, any further alteration is greatly retarded. An- 
 tiseptic substances are either of an aromatic nature, such as 
 camphor, resins, volatile oils, and bitumens, which have 
 been at various times employed in the process of embalming: 
 or acids, sugar, certain neutral salts, as nitre and muriate of 
 soda, which are principally used for culinary purposes, but 
 some of which are serviceable in anatomy. A saturated 
 solution in water of three parts of nitre to one of salt, or of 
 nitre alone, injected into the blood-vessels, is found to retard 
 decomposition sufficiently long to allow time for the ordi- 
 nary process of dissection. Of the substances that remain, 
 alcohol, which when diluted produces less change than any 
 other antiseptic fluid in the appearance of parts immersed 
 in it, is peculiarly fitted for the preservation of anatomical 
 preparations. 
 
 What, it may next be inquired, are those changes, which, 
 exhibited for a period by all organized bodies, constitute 
 the phenomena of life. 
 
 The mucors and confervse, the lowest of plants in the 
 scale of organization, may be adduced as the simplest ex- 
 amples of vitality. 
 
 The conferva rivularis, to select an individual instance,; is 
 a green filament, finer than a hair, which is found in streams 
 and in stagnant waters. It has no distinct root or leaves : 
 it is attached by means of a disk to stones in the bank or 
 at the bottom. Its structure is uniformly cellular, the shape 
 of the cells being oblong. 
 
 The conferva rivularis, when living, is observed to- in- 
 
6 Of the Phenomena of Life. 
 
 crease in length, and to throw out filaments like branches. 
 
 The added parts are similar in structure and composition to 
 
 the first. 
 
 ^ These phenomena, in which nearly all that is known of 
 
 the vitality of the plant is comprised, imply several distinct 
 
 operations. 
 
 The plant, in its increase in size and weight, borrows 
 something from the medium in which it lives. 
 
 The material borrowed, which is supposed to be little 
 more than water, is converted into vegetable matter, or is 
 assimilated to the chemical nature of the living body which 
 contains it. 
 
 The newly assimilated matter is laid down as a part of 
 the plant in a determinate shape and structure. 
 
 The assumption of food, its assimilation, and the depo- 
 sition of the assimilated matter as a part of the frame, are 
 the steps by which growth is accomplished, or in which 
 nutrition consists. In the instance which has been given, 
 the occurrence of these three operations is indeed established 
 less by direct observation than by analogical reasoning; but 
 in the higher plants, each part of the process admits of 
 being shown : the imbibition of fluid by the radicles ; its 
 ascent in the vessels of the alburnum to the leaf, where its 
 assimilation is accomplished ; the subsequent descent of the 
 assimilated fluid by the vessels of the liber to be used in 
 the growth and nourishment of the plant, are demonstra- 
 able by experiment. At the same time an additional phe- 
 nomenon presents itself: the growing plant is continually 
 eliminating water, and carbon or carbonic acid. Wherever 
 vitality is active, a constant elimination of carbon takes 
 place; and the exposure of the living plant or animal to at- 
 mospheric air or to air containing oxygen, is observed to 
 be a necessary condition for effecting the separation of the 
 superfluous element. 
 
 In the higher animals, other principles besides water and 
 carbonic acid, are continually in process of being thrown 
 out of the system ; these are contained in the urine, the 
 perspiration, and other excretions. Further, there is satis- 
 factory evidence, that in the early periods of life, if not 
 during their whole existence, the frame of animals is under- 
 
Of Nutrition. 7 
 
 going an internal change and renovation. The nutriment 
 which they take is believed to be used, not merely to add 
 to their bulk, but to replace in each part of the frame the 
 materials which have hitherto composed it; the old con- 
 stituent elements being supposed to be simultaneously re- 
 moved by a process of molecular or interstitial absorption, 
 and to be afterwards in part or wholly expelled. 
 
 In the higher plants again, and in animals, an extrication 
 of heat occasionally or continually takes place. It would 
 be reasonable to view this function as an accidental result 
 of the chemical changes which are in operation throughout 
 the frame, were it not for the remarkable precision with 
 which it is performed in the higher animals. In the perfect 
 animal economy, what is termed a standard temperature is 
 rigorously maintained : provision is made, not merely for 
 getting rid of any accidental superfluity of heat, but like- 
 wise for furnishing an additional supply of caloric, when 
 under opposite circumstances the animal heat may happen 
 to be too rapidly abstracted. The importance of these provi- 
 sions is shown by the consequences of exceeding their limits. 
 If the temperature of the body be for any considerable time 
 raised above, or lowered beneath the standard, the animal 
 perishes. 
 
 Growth by nutrition is characteristic of life. In the 
 higher animals it is usual to consider the process of internal 
 renovation already adverted to, as an essential part, if not as 
 the main object, of nutrition ; but to what extent, or with 
 what interruptions this renovating process goes on, remains 
 uncertain. Several parts in the living frame once formed 
 from assimilated matter (the teeth for example), continue alive 
 through their simple adhesion to organs in which renovation 
 is presumed to take place : and there are instances even of 
 entire organized bodies, that retain vitality for a length of 
 time during the total suspension of every internal motion. 
 The seeds of plants and eggs of animals, if adequately pro- 
 tected against air and moisture and extremes of temperature, 
 continue alive for months and years. The vibrio tritici, a mi- 
 mite animalcule, which is the cause of the ear-cockles in 
 wheat, when dried is to all appearance dead ; but, after being 
 kept for many days in this state, on being moistened, re- 
 
Of Generation. 
 
 vives, and moves in a lively manner*. The same fact is well 
 authenticated of many of the infusorial animals. A leech 
 frozen and gradually thawed will sometimes live. After the 
 preceding facts, it will appear less surprising, that a part 
 of a warm-blooded animal, which has been frozen so as to 
 chip, when thawed will bleed and inflame, but live. 
 
 Living beings are produced by a modification of that 
 process which brings them to maturity. Generation in 
 plants and animals consists in the formation of a germ, 
 which in time separates from the surface upon which it 
 grew, and becomes an independent living being. It was 
 discovered by Trembley, that the nais at one period of its 
 existence spontaneously divides into two unequal parts : to 
 the posterior segment, which is a third of the length of 
 the animal, a head is formed, to the fore part a tailf. The 
 growth of a germ or embryo upon a definite surface in a 
 plant or animal, with its subsequent separation, presents no 
 feature that essentially distinguishes it from the preced- 
 ing marvellous instance. 
 
 Upon a strict analysis of the phenomena above enume- 
 rated, two properties admit of being indistinctly shadowed 
 out, which concur with the laws common to living and to 
 dead matter in their production. 
 
 I. The changes wrought upon the ingesta during assimi- 
 lation may be ascribed to a principle of^ Vital Affinity. In 
 order to give this term an equal value with the term gravity, 
 physiologists require to ascertain the conditions, which es- 
 sentially precede changes in the chemical nature of the ele- 
 ments which compose a living body. As the phenomena 
 here adverted to strikingly correspond with known effects 
 of chemical agency, it is highly probable, that both will 
 eventually be found to depend upon modifications of the 
 same general law. 
 
 II. The assumption of foreign matter, and its propulsion 
 through the tubes of a living body, may be partially pro- 
 duced or promoted by capillary attraction, by elasticity, by 
 impulse communicated from without, by gravity, by elec- 
 trical attraction or repulsion. In the majority of instances, 
 
 * Phil. Trans, vol. cxiii, p. 9. 
 
 f Me"moires pour 1'Histoire d'un Genre de Polypes, p. 221. 
 
Of the Properties of Life. 9 
 
 however, another principle is distinctly in operation. Va- 
 rious parts in animals and plants alternately contract and 
 expand, or shorten and elongate themselves, or change from 
 a straight to an incurvated figure, or from the state of re- 
 laxation to that of tension, under circumstances which 
 prevent our referring these phenomena to the agency of 
 the causes above enumerated. The tendency inherent in 
 certain living textures to pass alternately from one of these 
 states to the opposite, is termed Irritability. We call the 
 fibre of which the heart is composed irritable ; and we sup- 
 pose from the many instances in which the fact admits of 
 proof, that the nutritive fluids in all living bodies have 
 motion communicated to them by the contraction of the 
 containing vessels. 
 
 All the phenomena of vegetable life may be explained 
 upon the assumption of two vital properties, such as have 
 been described. Even the sensible motions of plants, and 
 the discrimination which some evince in the direction of 
 their growth, imply no further agency. On these occasions 
 we sometimes, perhaps, feel half-persuaded that plants ex- 
 hibit an obscure degree of consciousness ; but on candidly 
 examining the phenomena, however closely they may cor- 
 respond with the effects of sensation and instinct, it appears 
 very certain that they flow from simpler principles. By 
 such analogies, in which Nature especially delights, the 
 vast interval that exists between minerals and plants is ren- 
 dered less apparent ; and the yet wider break between beings 
 that have life alone, and those which both live and feel, is 
 so artificially concealed, that we can scarcely determine at 
 what point in the creation it occurs. 
 
 I examined, with Mr. Gilbert Burnett, in the summer of 
 the year 1826, the motion of the leaves of the mimosa pu- 
 dica. Many of the facts which we noticed had been al- 
 ready described by Dr. Dutrochet, and were discovered 
 many years earlier by Mr. Lindsay : an account of some of 
 them will serve to illustrate the preceding remarks. 
 
 The sensible motions of the mimosa pudica are confined 
 to the joints, 1, of the leaf-stalk or petiole with the stem 
 or branch ; 2, of the sub-petioles with the leaf-stalk ; 3, of 
 the sub-leaflets with the sub-petioles. During the day-time 
 
10 
 
 Of the Motion of the Sensitive Plant. 
 
 the leaf-stalk is raised, the leaflets diverge, and the sub- 
 leaflets are expanded, in the manner shown in the adjoined 
 sketch 
 
 Fig. 1. 
 
 In a plant sickly from exposure to cold, this position of 
 the leaves is permanent; and no sensible motion follows 
 
 any kind of excitement that may 
 be employed. When the plant 
 is healthy, on the contrary, it is 
 difficult to approach it without 
 causing several of the leaves to 
 fall. If the plant be shaken, all 
 drop at once at their joints ; at 
 the same time the leaflets ap- 
 proach each other, and the sub- 
 leaflets become folded in pairs, 
 after the manner represented in 
 Fig. 2. 
 
 If the stimulus applied be par- 
 tial; if, for instance, it consist 
 in cutting a single sub-leaflet, 
 that sub-leaflet instantly rises 
 with its fellow; then the next 
 pair, and so on in succession, till 
 all upon the same leaflet are 
 
 Fig. 2. 
 
Of the Motion of the Sensitive Plant. 1 1 
 
 folded : the leaf-stalk then drops at its joint; and afterwards 
 all the remaining leaflets close. If a sub-leaflet have been 
 burnt, the excitement extends from one leaf to those 
 adjoining ; or if applied to the stem, or to the flower, which 
 in themselves have no motion, it will thence be propagated 
 to the leaves. 
 
 A few points among these phenomena deserve to be more 
 particularly remarked. 
 
 1. The motion, which takes place at the articulation, is 
 produced by an excess of force, not on the side towards 
 which the leaf is bent, but on the opposite. This is proved 
 by cutting a notch in the intumescence of the joint ; upon 
 which the leaf-stalk becomes permanently bent towards the 
 wounded side. 
 
 The effects of this experiment, which was first made by 
 Mr. Lindsay, Dr. Dutrochet well explains, by comparing 
 the action of the predominant side of the intumescence to 
 that of a curved spring, which has been temporarily held in 
 an extended position by an antagonist force, and is allowed 
 to resume its incurvated figure. Or the intumescence may 
 be said to consist of four such springs opposed to one 
 another, of which the two that form the upper surface, 
 distinctly possess irritability. 
 
 2. The substance, which conveys the excitement from 
 one part to another, has been proved by original experiments 
 of Dr. Dutrochet, not to be the bark or the pith, but the 
 wood. 
 
 3. Mr. Burnett observed, that when a single leaf with its 
 
12 Of the Motion of the Sensitive Plant. 
 
 leaf-stalk is removed with great gentleness from the plant, 
 the irritability of the separated part remains for a time as 
 lively as before. The detached leaf spreads its leaflets as 
 soon as it has recovered from the shock attending its re- 
 moval ; upon the re-application of a stimulus it again closes 
 them ; after a time it again expands them. 
 
 4. It appears by facts which have been mentioned, that 
 the leaf-stalk is depressed by the action of the upper portion 
 of the intumescence, a [fig. 1 and 2] : and that if any part 
 of the plant is sufficiently irritated, this effect follows. But 
 I discovered that there is one part better calculated than the 
 rest to receive impressions; or on which impressions tell, 
 that are too slight to produce action in the irritable sub- 
 stance of the plant, when applied elsewhere. This suscep- 
 tible part is the under half of the intumescence b [fig. 1 
 and 2] : it is of a darker colour than the upper surface, and 
 covered with strong short hairs. A steel point may be 
 gently moved over, and even pressed against the upper sur- 
 face without producing any sensible effect ; but the instant 
 that it is applied with the slightest contact to the under 
 half, the leaf-stalk falls. Thus the intumescence has two 
 surfaces possessing different properties : the one irritable, 
 the other especially fitted to receive impressions, through 
 which the irritability of the first is brought into action. 
 
 A similar provision exists at the articulation of the sub- 
 leaflets. If the surface at c [fig. 1] be slightly touched, 
 the sub-leaflet instantly rises through the action of the 
 posterior part of the intumescence, d [fig. 2] : but when 
 the experiment is reversed, and the surface d in an ex- 
 panded leaflet is irritated, no sensible effect follows. 
 
 It is impossible not to be struck with the close analogy 
 which holds between the phenomena last described and 
 many of the instinctive motions of animals. In animals, as 
 in the mimosa, one organ being stimulated, another and a 
 different part acts : when a particle of dust, for example, 
 is driven against the surface of the eye, the orbicular muscle 
 closes the eyelids ; when a brighter light falls upon the 
 retina, the iris contracts. The two cases are nevertheless 
 essentially different. In the first, sensation being excited 
 
Phenomena of the Growth of Plants. 13 
 
 upon one surface of a living animal frame, an instinctive ac- 
 tion follows in another part. In the second, all that we 
 know amounts to this, that one part of a plant being irri- 
 tated, a physical impression is conveyed from it through 
 the vegetable substance to another, which being thus excited 
 assumes an incurvated figure. 
 
 The discrimination seemingly evinced by plants is a sub- 
 ject no less curious than the preceding. Climbing plants 
 stretch towards objects calculated to support them : a shrub 
 growing upon a wall, when it has exhausted the nourishment 
 which its situation afforded, has been known to drop a long 
 root to the soil below. The daisy, in rank grass, bears a 
 flower upon a long stalk : on a close shaven lawn, its flower 
 is sessile. These and similar instances have again been oc- 
 casionally ascribed to an instinct in plants : but nothing can 
 be looser than the analogy upon which this conclusion is 
 founded. In animals, instinct is a part of consciousness : 
 and although it serves as a guide in the selection of proper 
 nourishment, yet it exerts no direct influence upon growth. 
 When, for example, an animal is transported from a colder 
 to a warmer climate, the change which in some instances 
 takes place in the character of the integuments, fitting the 
 animal for its new abode, is not wrought by instinct. How 
 illogical would it evidently be to attribute instinct to plants, 
 in order to account for classes of phenomena, which in be- 
 ings, that unquestionably possess it, result from another prin- 
 ciple. Is it not more reasonable to suppose, that the growth 
 of plants is determined by physical impressions alone, such 
 as variations of moisture or temperature, and exposure to or 
 deprivation of light ; and that Nature, instead of impart- 
 ing sense and perception to plants as their guiding princi- 
 ples, has attained her purpose by another method, having 
 so framed and endowed the vegetable economy in accord- 
 ance with the circumstances in which it is placed, that the 
 common accidents of the elements and of the seasons are 
 certain to bring it to perfection ? Several remarkable ex- 
 amples go to prove the correctness of the preceding views, 
 out of which it may be sufficient to adduce the following. 
 
 It is well known, that in whatever position a seed is laid in 
 
14 
 
 Sensitive and Vegetative Functions 
 
 the ground, the plumule inva- 
 riably rises towards the surface 
 of the soil, while the radicle, 
 on the contrary, shoots down- 
 wards, something in the manner 
 shown in the adjoined figures. 
 Upon the hypothesis that phy- 
 sical impressions determine the 
 growth of plants, we should 
 expect to find that gravitation 
 is in this instance the influen- 
 tial cause; or that the growth 
 of the radicle necessarily fol- 
 lows the direction of an at- 
 tracting force, that of the plu- 
 mule the reverse. 
 
 Mr. Knight ascertained this 
 solution to be just, by an ex- 
 periment in which another force 
 was made to supersede that 
 of gravity. Numerous seeds of 
 the garden bean, which had 
 been previously soaked in wa- 
 ter, were attached at short dis- 
 tances along the circumference 
 of a vertical wheel, which was 
 made to perform more than 150 
 revolutions in a minute. In a 
 few days the seeds began to 
 germinate : the plumule of each 
 tended towards the axis of the 
 wheel ; the radicle grew in the 
 contrary direction. In an- 
 other experiment, beans simi- 
 larly prepared were attached to the circumference of a hori- 
 zontal wheel, which was then set in rapid motion : the re- 
 sult was not less conclusive than in the former instance : the 
 plumule from each seed was observed to grow in a direction 
 upwards and inwards, while the radicle tended downwards 
 
combined in Animal Ldfe. 15 
 
 and outwards, that is to say, in the diagonal of the two 
 forces, by both of which, according to the hypothesis, it 
 should have been blindly influenced *. 
 
 From these and similar instances it appears reasonable to 
 conclude, that the vital endowments of plants are limited 
 to two ; irritability namely, and some modification of che- 
 mical affinity. What an immeasurable interval between 
 their mode of existence and that of animals ! 
 
 The hydra viridis, a polype, which in complexity of or- 
 ganization is infinitely below the higher plants, in its ani- 
 mal functions is placed as far above them. It is observed 
 to move spontaneously from place to place, to attach itself 
 in preference to the sunny side of the vessel of water in 
 which it is exposed to the study of the curious, to seize 
 its prey by means of filamentous tentacula and to force it 
 into its digestive cavity ; in short, to exhibit a succession 
 of actions, which compel us, if we would not deny con- 
 sciousness to the dog and to the elephant, to attribute sen- 
 sation and volition to this little gelatinous bell. 
 
 In the polype, life and consciousness are equally distri- 
 buted through one uniform texture. An unbroken chain of 
 improving organization may be traced from this zoophyte 
 upwards to man : digestive organs, a vascular system, a 
 respiratory apparatus, successively appear in the more 
 elaborate frame. While these parts are produced, which 
 are appropriated to nutrition or to the functions of vege- 
 tative life, the nervous system is developed, which becomes 
 the exclusive seat of consciousness. 
 
 If a polype be divided (and this phenomenon extends 
 much higher in the scale), it becomes two living animals. 
 But as the type of organization further improves, the animal 
 becomes individualized : if divided, its separate portions are 
 found to be incapable of independent existence : the animal 
 now consists of a single series of organs, the functions of which 
 exert a reciprocal influence, and combine to sustain life. 
 
 It is usual to arrange the functions distinguished in the 
 human economy under the two classes above adverted to, 
 
 * Phil. Trans, vol. cvi, p. 108. 
 
16 Sensitive and Vegetative Functions. 
 
 one as the vegetative or organic class, the other as the 
 animal or sensitive. 
 
 By the former, nutritious matter is separated from the food, 
 is conveyed through the lacteals into the veins, becomes 
 blood, and is circulated through the body, which grows and 
 lives through its influence : or component particles of the 
 body are absorbed, thrown into the circulation, and what are 
 useless eliminated : or the embryo is formed and foecun- 
 dated, and having attained to foetal maturity, is born. 
 
 By the latter, the human being, through sensation, 
 becomes acquainted with the world around him, is led to 
 the instinctive gratification of his appetites, or under the 
 guidance of reason directs a succession of voluntary efforts 
 towards higher purposes. 
 
 The preceding division is not, however, strictly applica- 
 ble to the plan of a systematic work upon Physiology. 
 Almost every function is partly sensitive, partly vegetative. 
 Thus we discriminate the quality of food by sensation, and 
 swallow it voluntarily to allay an appetite ; but of its diges- 
 tion we are unconscious, and cannot by an effort of the will 
 directly accelerate or retard it. 
 
 In this dilemma, it is obvious that the adoption of a very 
 rigorous method is impracticable, or would serve to give 
 about as clear a notion of life, as a separate description of 
 the single threads in a piece of tapestry would of its design. 
 Among the circle of functions, again, it is difficult to de- 
 termine with which to begin; but where selection is not 
 easy, it may be presumed that the advantages of different 
 plans are so equally balanced, as to leave it a matter of 
 small importance, which is chosen. 
 
CHAPTER II. 
 OF THE BLOOD. 
 
 IF any subject is fitter than another to occupy the first 
 place in a physiological treatise, it is the history of the 
 blood. From this fluid the body is formed ; by its influ- 
 ence life is immediately sustained. It consists, on the one 
 hand, of new materials freshly elaborated from the food, and 
 on the other, of the old constituent elements of the frame that 
 have been returned to it through the function of molecular 
 absorption. The frame that was, the body that is to be, 
 may be said therefore, without too bold a figure, to exist in 
 solution in the blood. 
 
 The student in Physiology may begin with imagining the 
 body to be permeated in every part by tubes or vessels 
 which transmit blood. The minutest of these vessels, 
 which are cognizable to our senses, are -y^w of al * i ncn i n 
 diameter; they are termed capillaries, and are so numerous, 
 and so universally distributed, that when they are success- 
 fully filled with size and vermilion, the part that has been 
 injected appears of as bright and uniform a colour, as if it 
 had been dyed scarlet. Dr. Marshall Hall* has lately 
 published some interesting observations on the capillary 
 vessels in cold-blooded animals, which he has shown 
 by their freedom of communication to form a tubular net- 
 work. Into this network of capillaries pervading every 
 part, florid scarlet blood is conveyed by minute arteries, 
 which are derived through successive subdivisions from a 
 single arterial trunk, which issues from the left cavity of 
 the heart, and is called ihe aorta. 
 
 In the capillary system of the body, the blood changes 
 
 * Dr. Marshall Hall on the Circulation. 
 
 c 
 
18 Of the Course of the Blood. 
 
 its hue from scarlet to a deep purple. It leaves this system 
 by nieans of the veins, which, each originally formed by 
 the union of several capillaries, unite together to form 
 larger and larger trunks : these end at last in three great 
 vessels, which open into the right cavity of the heart, and 
 pour the dark blood into it. 
 
 Scarlet blood is called arterial, because blood of this 
 colour is usually found in the arteries of the body. Dark 
 coloured blood, again, is called venous, because the veins 
 of the body commonly contain dark blood. These terms, 
 however, are only just, when applied to the blood in 
 the systemic vessels. In the pulmonary circulation the 
 facts are reversed. The single vessel by which the black 
 blood is thrown out of the right cavity of the heart, 
 is in structure an artery, and its branches are distributed 
 in the lungs in the same manner as those of the aorta are 
 distributed through the entire frame. After many subdi- 
 visions the branches of the pulmonary artery terminate in a 
 network of capillaries : in these the blood again changes its 
 colour ; but from dark it now becomes florid. 
 
 This phenomenon appears at first sight a very simple one. 
 When black blood that has been drawn from a vein is ex- 
 posed to atmospheric air, the surface exposed acquires a 
 florid scarlet colour : at the same time it is found, that the 
 oxygen of the air so employed has been converted into car- 
 bonic acid. In this experiment it is evident that the oxygen 
 of the air combines with the carbon of the blood, and ab- 
 stracting it, leaves the blood of a brighter colour. Breath- 
 ing may be considered as a process through which a parallel 
 effect is produced upon the purple blood in the living body. 
 In the capillaries of the lungs, the venous blood is con- 
 tinually exposed to the influence of fresh atmospheric air, 
 drawn in at each inspiration. In consequence of this, 
 the venous blood loses its dark hue : at the same time 
 oxygen disappears from the air which is breathed, and 
 carbonic acid is left in its place. 
 
 The blood, purified of its superfluous carbon in the lun^s, 
 is finally transmitted by the pulmonary veins to the left 
 cavity of the heart ; in other words, it is brought back to the 
 
Evidence of the Harveian Theory. 19 
 
 point at which we began to trace its course. Thus is the 
 blood alternately thrown through the whole frame which it 
 vivifies and nourishes, but in which its composition and its 
 properties become impaired, and through a single organ in 
 which it is renovated by exposure to the atmosphere, and 
 rendered fit for the support of life. 
 
 The name of Harvey has been immortalized by the dis- 
 covery of the circulation. The simple and conclusive argu- 
 ments which our great Physiologist adduced in support 
 of his theory may be thus stated. 
 
 An animal may be drained of blood by opening either 
 the large arteries or the large veins. The blood therefore 
 must naturally flow from one of these sets of vessels into 
 the other. 
 
 If an artery be tied, and then punctured on both sides 
 of the ligature, the blood rushes violently and by jets from 
 the puncture nearest the heart, but flows without force 
 from the remoter puncture. It follows, that the current of 
 the blood in the arteries sets from the heart. 
 
 If a vein be obstructed by pressure, it swells or fills with 
 blood on the side remote from the heart, while the part 
 between the point of obstruction and the heart does not swell. 
 It follows, that the current of the blood in the veins sets 
 towards the heart. 
 
 Finally, the valves in the veins are so placed that " they 
 give a free passage to the blood towards the heart, but 
 oppose the passage of the venal blood the contrary way." 
 
 To this body of proof may now be added the fact, that 
 in transparent parts of living animals, the blood may be 
 seen to flow in a continued stream from the arteries through 
 the capillaries into the veins. 
 
 Blood when flowing from a vessel of the living body is an 
 unctuous liquid, of a faint odour and saline taste, of the 
 temperature of 98 of Fahrenheit's thermometer : its specific 
 gravity varies from 1038 to 1059*. 
 
 Dr. Davy ascertained that the temperature of arterial 
 blood in a living animal is about a degree higher than that 
 
 * Dr. Davy's Observations, &c., Edinburgh Medical Journal, 
 vol. xcv, p. 246 ; and Dr. Scudarnore on the Blood, p. 36. 
 
 c 2 
 
20 Differences of Arterial and Venous Blood. 
 
 of venous blood. The temperature of blood when flowing 
 from the carotid artery of a lamb was found to be 105, from 
 the jugular vein 104. In lambs killed by the division of 
 the great vessels in the neck, the temperature of the left 
 side of the heart was 106, that of the right side 105.5. 
 In oxen that had been knocked down, the blood being of 
 the same colour in the arteries and veins, the temperature 
 of the arterial blood was found to be 101 or 101.5: 
 that of the venous blood, 100. In a sheep, in which 
 the specific gravities of arterial and venous blood were 1049 
 and 1051, the relative capacities of the two fluids for caloric 
 were 913 and 903*. 
 
 When venous blood is detained in a vein, its colour 
 becomes darker. 
 
 When arterial blood is kept at rest in a living vessel, it 
 gradually acquires the properties of venous blood ; as may 
 be seen on slackening a tourniquet after an amputation, 
 when the first blood that issues from the divided arteries is 
 of a dark colour. If arterial blood is placed in vacuo, or is 
 exposed to nitrogen, hydrogen, or carbonic acid, it loses its 
 florid huef. The blood has been found of a dark colour 
 upon opening the temporal artery of persons labouring 
 under the effects of opium. Extravasated arterial blood 
 remains florid for several minutes ; after an interval it is 
 found to have coagulated, and to have acquired a dark 
 colour J. 
 
 Blood flowing from a vein has been observed, when faint- 
 ing has supervened, to lose its usual appearance, and to 
 become of a florid hue. 
 
 A halitus is seen to rise from the surface of blood recently 
 drawn, upon the same principle that a sensible evaporation 
 takes place from other liquids at an elevated temperature. 
 
 Blood, that after having been drawn has stood a few 
 minutes, is observed to be covered with a thin pellicle, and 
 afterwards the whole quantity gradually becomes a ge- 
 
 * Phil. Trans, vol. civ, p. 593, et seq. 
 
 f- Thomson's System of Chemistry, vol. iv, p. 615. 
 
 J Hunter on the Blood, p. 68. 
 
 Hewson's Experimental Inquiries, p. 25. 
 
Changes, which supervene in freshly drawn Blood. 21 
 
 latinous solid. This change is termed the coagulation of 
 the blood. On an average it commences about three or four 
 minutes after blood is drawn, and is completed in seven or 
 eight. Dr. Gordon found the coagulating portion of a 
 quantity of blood warmer than the rest by 6 of Fahrenheit's 
 thermometer. On repeating the experiment upon blood 
 drawn from a person labouring under inflammatory fever, 
 the rise of the thermometer is said to have been no less 
 than 12*. But there is reason to suspect that some error 
 had crept into these observations. Mr. Hunter detected no 
 extrication of heat during the coagulation of the blood of a 
 turtle, the temperature of which was the same as that of the 
 air. Dr. Davy mentions, that he has repeated Mr. Hunter's 
 experiment with the same negative results, upon the blood 
 both of the turtle and of the shark. Dr. Davy remarks as 
 a parallel phenomenon to the present, that when serum is 
 coagulated by means of dilute nitric acid, no perceptible 
 alteration of temperature occurs. 
 
 Mr. Brande observed, that during the coagulation of the 
 blood carbonic acid is disengaged : this appeared to happen 
 to an unusual extent in blood drawn soon after a mealf. 
 Dr. Davy, however, adduces several observations in oppo- 
 sition to those of Mr. Brande ; and denies the existence of 
 free carbonic acid in the blood. 
 
 In a short time after coagulation, drops of a yellowish 
 liquid are seen to exsude from the clot, which goes on thus 
 spontaneously to separate into two elements ; the solid part 
 is termed the crassamentum, the fluid part the serum of 
 the blood. The crassamentum is usually estimated to be a 
 little less in quantity than the serum. The proportion of 
 serum is greater in persons of a debilitated habit of body 
 than in those who are strong : it is greater again when 
 coagulation takes place under a low degree of temperature. 
 The slow contraction of the coagulum has not entirely 
 ceased till the fourth day. 
 
 Serum, when exposed to a temperature of 160, and still 
 
 * Thomson's Annals, vol. iv, p. 139. 
 t Phil. Trans, vol. ex, p. 6. 
 
22 Of the Serum and of the Fibrin of the Blood. 
 
 more readily at 212, is converted into a white coherent 
 mass, from which a fluid termed the serosity may be obtained 
 by pressure. The coagulated part is albumen. The same 
 principle exists in the serosity, but is suspended by the pre- 
 sence of an alkali. Atmospheric air in contact with serum 
 does not lose oxygen and acquire carbonic acid, as when in 
 contact with blood. The component parts of serum, ac- 
 cording to Dr. Marcet, are, 
 
 Water 900.00 
 
 Albumen ; 86.80 
 
 Muriates of potash and soda 6.60 
 
 Muco- extractive matter 4.00 
 
 Subcarbonate of soda 1.65 
 
 Sulphate of potash 0.35 
 
 Earthy phosphates 0.60 
 
 1000.00 
 
 The specific gravity of serum is 1028. Albumen, which 
 forms so large a part of the serum of the blood, is the prin- 
 cipal element in the composition of the skin, and of the 
 cellular and vascular tissues. 
 
 When the crassamentum has been repeatedly washed, it 
 becomes a glutinous and fibrous mass of a . grayish colour : 
 the water employed is rendered red. The grayish substance 
 is termed fibrin, and appears to be of the same nature with 
 the material left after muscle has been boiled for a conside- 
 rable length of time. It forms the tough substance which 
 is met with after death in the cavities of the heart and great 
 vessels, and in aneurysmal sacs in which it is disposed in 
 layers. Dr. Davy found the specific gravity of the fibrin of 
 the blood, examined in three different instances, to be 1046, 
 1057, and 1060. The quantity of dry fibrin that may be 
 obtained from blood varies from .13 to .47 per cent. 
 
 The colouring matter of the blood resides in innumerable 
 particles, which are readily discovered with the assistance of 
 a microscope, upon examining serum, in which a portion of 
 the coloured clot has been broken down. The form of these 
 
() 
 
 Qf the Colouring Matter of the Blood. 23 
 
 particles may be compared to that of a silkworm's egg : 
 they are circular, and extremely thin, with rounded edges, 
 and a central depression on either flat surface : their dia- 
 meter is very exactly -s-oVo- of an inch. They are flexible, 
 and when rolling upon their edges are often bent in such 
 a manner that they appear to consist of a central nucleus 
 projecting from a thin disc. Their specific gravity Dr. Davy 
 estimates at about 1087. 
 
 The adjoined figure repre- 
 sents six squares of a glass mi- 
 crometer, each side of a square 
 being -^ of an inch. In the 
 squares marked 1, 2, and 3, 
 different appearances of the par- 
 ticles of human blood are deli- 
 neated, showing their diameter, 
 their central depression, and 
 various positions in which they 
 may be seen when rolling down 
 an inclined surface. I made 
 
 this drawing from particles of the blood as seen in a micro- 
 scope which I possess, made by Dollond, having achro- 
 matic object glasses. The true shape of these bodies was, 
 I believe, discovered by Dr. Young, who describes it in an 
 essay published in his Medical Literature. Figs. 4, 5, 6, 
 represent the particles of the blood of a skate : they appear 
 to differ from the particles of human blood principally in 
 being of a much larger size, in their oval outline, and in the 
 oval figure of their central depression. 
 
 When immersed in water the particles of the blood lose 
 their colouring matter, and with it much of their specific 
 gravity, so that they float ; their diameter likewise becomes 
 reduced by one- third, and their figure becomes spherical. 
 
 Mr. Brande discovered, that the colouring matter of the 
 blood is an animal substance of a peculiar nature, suscepti- 
 ble, like the colouring matter from vegetables, of uniting with 
 bases, and applicable to the art of dyeing. The most effectual 
 mordaunts for the colouring matter of the blood are salts 
 of mercury, especially the nitrate and corrosive sublimate. 
 
24 Causes which promote (Coagulation. 
 
 Mr. Brande ascertained that iron does not exist in greater 
 proportion in one element of the blood than in another*. 
 
 The coagulation of the blood and its separation into serum 
 and crassamentum are phenomena, which may be regarded 
 as the result of its chemical composition no less than its pre- 
 vious continuance in a fluid state. The circumstances under 
 which the blood exists vary, and the reciprocal attraction 
 of its elements is changed. Our knowledge upon this sub- 
 ject is, however, very imperfect, and amounts but to a bare 
 enumeration of instances, in which the coagulation of the 
 blood takes place readily, or slowly, or is entirely prevented. 
 
 The tendency of the blood to coagulate, when drawn 
 from the living body, is not affected by moderate differences 
 in temperature "f*. Blood at 67 and 105 coagulates in the 
 same time as at 98: as readily J when exposed to azote, 
 nitrous gas, nitrous oxide, carbonic acid, and hydrocarbon, 
 as when exposed to atmospheric air. 
 
 Blood coagulates quickly when placed in a receiver, from 
 which the air is immediately exhausted ; when drawn from a 
 small orifice into a shallow vessel ; when exposed to atmo- 
 spheric air at a temperature of 120 ; more rapidly when 
 the body is exhausted by hemorrhage, than when it exists in 
 strength and vigour. 
 
 The coagulation of the blood admits of being delayed : 
 1. By freezing. A portion of the jugular vein of a rabbit 
 tied between two ligatures was removed with the blood con- 
 tained in it, and frozen : when thawed, the blood became 
 liquefied, and coagulated. 2. By low temperatures above 
 the freezing point. Mr. Hewson placed blood in oil at a 
 temperature of 38 : at the expiration of six hours it con- 
 tinued fluid ; but being then allowed to attain a warmer 
 temperature, it became coagulated in twenty-five minutes. 
 3. By mixture with certain neutral salts. If half an ounce 
 of Glauber's salt be mixed with six ounces of fresh blood, 
 the mixture does not coagulate : but on the addition of a 
 double quantity of water coagulation takes place. 
 
 * Phil. Trans, vol. cii, p. 90. 
 
 f Hewson, 1. c. J Hunter, 1. c. 
 
 Researches on Nitrous Oxide, by Sir H. Davy, p. 380. 
 
Causes which retard Coagulation. 25 
 
 Other circumstances retard coagulation. Blood coagu- 
 lates slowly when drawn from a large orifice into a deep 
 vessel; when taken from a person in vigorous health, or 
 from one labouring under inflammation ; when detained at 
 rest in a vein of a living animal between two ligatures. On 
 a repetition of the last observation, Mr. Hewson found the 
 blood two-thirds fluid after three hours and a quarter had 
 elapsed : the blood being then exposed, entirely coagulated, 
 When the experiment was varied by blowing air into the 
 vein, the blood was found to have coagulated in a quarter of 
 an hour. Mr. Hunter mentions, that two leeches which 
 had been applied were subsequently preserved ten weeks. 
 At the expiration of that time they contained a considerable 
 quantity of blood, which appeared like blood recently drawn 
 from a vein, and coagulated when exposed. The following 
 incident is to the same purpose. On tapping a hydrocele, a 
 small vessel was wounded, and the blood escaped into the 
 sac : when the tapping was repeated sixty-five days after, 
 the blood came out thickened, but then coagulated and se- 
 parated into different parts *. Blood, extravasated through 
 the rupture of vessels, often remains for a considerable time 
 in a fluid state. 
 
 In some instances a modified coagulation takes place. 
 Mr. Hewson found, that if blood was kept at a tempera- 
 ture of 38 for twenty-four hours, it had become thick and 
 viscid, but did not coagulate on regaining a higher tem- 
 perature. In torpid bats, Mr. Cornish found the blood 
 thickened, but it soon recovered its fluidity on motion and 
 heat. 
 
 The blood does not coagulate when the causes that are 
 capable of delaying the process have continued to operate 
 beyond a certain period. If blood freshly drawn be kept 
 for some time in very brisk motion by being stirred, it will 
 not coagulate at all. In persons killed by lightning, by 
 hanging, by blows on the stomach, by the bite of venom- 
 ous serpents, or through the influence of acrid vegetable 
 poisons, or in persons dying from violent mental emotion, 
 
 * Hunter on the Blood. 
 
26 Causes, which prevent Coagulation. 
 
 the blood is said to be found fluid, and the muscles not to 
 become rigid. A temporary change in the nature of the 
 blood of a like kind is found in certain diseases. Mr. Hew- 
 son mentions, that a woman was bled in a fever which came 
 on soon after delivery : her blood did not coagulate on being 
 exposed to the air, but appeared like a mixture of the red 
 globules and serum only, the globules having subsided to 
 the bottom in the form of a powder. She died three days 
 after; and upon examination the blood was observed to 
 have coagulated in the vessels, and a tough white clot was 
 found in each auricle of the heart : the blood that had been 
 taken during her life did not coagulate till at the heat of 
 160. The blood excreted in healthy menstruation does not 
 coagulate. 
 
 In reviewing these phenomena, it cannot but appear 
 deserving of notice, that the circumstances, which are found 
 in physiological experiments the most efficient in retarding 
 the coagulation of the blood, are conditions essentially 
 present during life. These are, motion, and the contact of 
 living surfaces. The blood at a temperature near its 
 standard temperature, and unexposed to any very active 
 agent, is sure to coagulate, unless both of these conditions 
 be present. Thus in a living vessel in which the blood is 
 detained at rest by ligatures, it clots, although slowly ; and 
 when blood has been drawn in the usual manner from 
 a vein, if it be kept in gentle motion only, it yet co- 
 agulates. 
 
 I suppose it is to the retarding or preventive influence of 
 the contact of living surfaces, that we may attribute the 
 facts, that blood drawn into a deep vessel and in a large 
 quantity coagulates slowly ; and that the blood of those who 
 are destroyed in full health by sudden and violent death, un- 
 attended with hemorrhage, as by hanging or through the 
 action of prussic acid, does not coagulate at all. In the 
 latter class of instances, although consciousness is suddenly 
 extinguished, yet the unexhausted animal tissues probably 
 retain for several hours a residuum of vitality. In such 
 cases again it is remarkable that, as in life, the blood spee- 
 dily coagulates, if through rupture of a vessel it becomes 
 
Final causes of the Coagulation of the Blood. 27 
 
 extravasated : what remains in the vessels is through their 
 vitality prevented coagulating for so long a time, that the 
 tendency has ceased, before it can have been exerted. 
 
 The final causes of the coagulation of the blood, or the 
 objects attained by it in the vital economy, are very strik- 
 ing. In a common incised wound in which no large vessels 
 are divided, the blood which flows, clotting between the 
 cut surfaces, glues them together ; and then by a wonder- 
 ful process, the thin intervening layer contributes to produce 
 a renewal of vascular continuity between the newly adherent 
 parts. To serve this purpose entirely, however, the interven- 
 ing layer of blood must be the thinnest film : a sensible 
 quantity of clot intervening may indeed for a time unite the 
 wound, but after a few days, instead of becoming organized 
 it loses its hold and is thrown off. Nevertheless, a con- 
 siderable clot of blood adhering to a vascular surface is oc- 
 casionally found to have received blood into a series of 
 irregular tubes, which appear to form spontaneously within 
 the coagulum. These tubes Sir Everard Home supposed to 
 be wrought by the extrication of bubbles of carbonic acid 
 during the process of clotting. 
 
 Another use of the coagulation of the blood, is to stop 
 hemorrhages resulting from the giving way of large vessels. 
 An essential element in this process is the clotting of the 
 blood in the extremity of the ruptured vessel : and it cannot 
 but excite admiration, that this important change is hurried 
 on by Nature, in proportion as the danger increases, and as 
 the frame is nearer complete exhaustion. The experimental 
 proof, that the tendency of the blood to coagulate is directly 
 increased by loss of blood, has been already given. 
 
 During derangement of health, the blood exhibits various 
 peculiarities. 
 
 The serum has been found to have the appearance of 
 whey ; to have streaks upon its surface like a cream ; to 
 have been as white as milk, the coagulum retaining its 
 usual appearance. Mr. Hewson attributed the colour of the 
 serum in the preceding instances to the presence of very 
 minute globules. Mr. Hunter observed the serum in one 
 case separate from, and swimming upon, the uncoagulated 
 
28 Inflammatory State of the Blood. 
 
 fibrin immediately after the blood had been drawn. In 
 jaundiced persons the serum is yellower than ordinary. 
 
 The crassamentum is sometimes found straw or size- 
 coloured and semi-transparent, to a greater or less depth 
 upon its upper surface. This appearance is termed the buff, 
 or, from its ordinary cause, the inflammatory crust of the 
 blood. In general the sizy part is firmer than the rest of 
 the clot, and its edges are drawn inwards, so as to render 
 the upper surface concave, which is then said to be cupped. 
 
 It is not easy to say by what internal arrangement of 
 parts the colourless size is produced : for although it be 
 true that inflammatory blood coagulates more slowly than 
 healthy blood, yet it is known from the experiments of 
 Mr. Hewson, that neither the serum nor the coloured par- 
 ticles of either sort of blood differ in specific gravity ; and 
 from those of Dr. Davy, that the fibrin of inflammatory 
 blood is even heavier than that of healthy blood : that 
 healthy blood when slow in coagulating does not form a 
 size ; and that inflammatory blood in half a minute after 
 it is drawn exhibits a blueish transparency upon its surface, 
 which shows that already the colour of the upper part is 
 discharged. We seem therefore left to conclude, as the 
 likeliest means of accounting for the speedy descent of the 
 colouring matter from its surface, that inflammatory blood 
 is less viscid than healthy blood. 
 
 Dr. Davy ascertained that there is no constant relation 
 between the appearance of a size in blood, and the quantity 
 of fibrin. 
 
 The rapidity with which the healthy and inflammatory 
 appearances of the blood may alternate, is remarkable, and 
 well illustrated in the following case. 
 
 A young man of an athletic habit was bled during a fe- 
 brile attack. Upon opening a vein the blood flowed very 
 slowly, or merely trickled down his arm : this appeared to 
 result from the timidity of the patient ; for after closing the 
 wound for a few seconds and encouraging him) upon re- 
 moving the finger the blood flowed copiously. Three ounces 
 were then received into a second cup ; an equal quantity 
 was immediately caught in a third cup. The patient now 
 
Its rapid alternation with the ordinary State. 29 
 
 became faint, was laid upon the floor, and a few drachms 
 more of blood were taken into a fourth cup. 
 
 Of these four quantities of blood, that which was taken 
 away the last was coagulated in three minutes ; that first 
 taken was coagulated in twelve minutes ; that taken in the 
 second cup was not completely coagulated in twenty-two 
 minutes ; neither of the three had an inflammatory crust. 
 But the blood received into the third cup began in five 
 minutes to appear transparent on its surface, was not com- 
 pletely coagulated at thirty-five minutes, and exhibited a 
 remarkably thick and tough size*. 
 
 * Hewson, 1. c. 
 
CHAPTER III. 
 
 OF MUSCULAR ACTION. 
 
 VARIOUS textures in animals are observed to exist at suc- 
 cessive periods in two different states, to be at one time 
 elongated, at another shortened. The change from the one 
 state to the other is the beginning of motion. The phe- 
 nomena attending the greater number of cases in which 
 motion is thus produced, have common points enough to 
 authorize us in ascribing them to one property, which has 
 been termed Irritability. They are certainly not effects of 
 elasticity or of gravitation, nor are they expansions and 
 contractions of bodies caused by changes of temperature ; 
 and although they correspond in some respects with the 
 results of galvanic action, yet the analogy is as yet too 
 loose and incomplete to warrant any confident expectation 
 that the movements of irritable parts will be proved to de- 
 pend upon a modification of the electric principle. 
 
 The parts of the human frame which possess irritability 
 are, .muscular substance, the substance of the uterus, the 
 fibrous coat of arteries, the unattached margin of the iris, 
 some parts of the skin, and perhaps the dense texture which 
 is employed in forming excretory tubes. In the phenomena 
 of muscular action alone, which form the subject of the 
 present chapter, a surprising diversity exists. 
 
 Muscular substance is what is commonly called flesh in 
 animals ; varying in different genera and species, in different 
 individuals of the same species, in different parts of the 
 same body, both in firmness and colour, it presents in 
 every instance the common point of a fibrous structure. 
 Nevertheless, in the same animal the deeper colour and 
 
Appearance and Chemical Composition of Muscles. 3 1 
 
 firmer texture of a single muscle or class of muscles may be 
 taken as a proof, that it has been more frequently and 
 powerfully exerted than others, and through use has ac- 
 quired greater strength. 
 
 The flesh of the human frame is of a reddish brown 
 colour in the muscles of the trunk, head, and limbs, and in 
 the heart ; of a pale gray in the muscular coat of the ali- 
 mentary canal and of the bladder. But upon maceration 
 in water it is found in each case to be reduced to little more 
 than a colourless fibrin. The water that has been employed 
 contains albumen, gelatin, extractive matter, and various 
 salts. Perhaps the most remarkable circumstance, which 
 has come to light in this investigation, is that nitrogen ex- 
 ists in larger proportion in the muscles of animals with red 
 blood, which possess the greatest variety of functions and 
 enjoy them in the most perfect state, than in those of fish 
 or reptiles. The same difference is observed in the muscles 
 of animals of the same species, between the adult and 
 the young *. In young animals, it appears that the 
 muscles as well as the membranes and bones contain a con- 
 siderable quantity of gelatin ; but as they advance in age 
 the gelatin disappears, and is replaced by albumen. Fat, 
 or oil contained in delicate membranous cells, is found in 
 the substance of muscles, more coarsely wrought into the 
 texture of some than of others, and in age than in youth. 
 
 The muscular tissue consists of flattened bands or lacerti 
 of soft flesh, connected together by a thin elastic transparent 
 membrane. Each of these bands admits of separation into 
 slender strips or fibres, which again may be resolved into 
 others yet finer. All the fibres are individually invested 
 and joined together by processes of the same membrane 
 which clothes the lacerti. 
 
 Within the last few years it has been very generally be- 
 lieved, on the authority of Meckel, Home, Bauer, and 
 Dr. H. M. Edwards, that the muscular fibre is ultimately 
 composed of globules combined in a linear arrangement. 
 More recent investigations, made by Dr. Hodgkin and 
 
 * Bostock's Elementary System of Physiology, vol. i, p. 152. 
 
32 Of the Minute Structure of Muscles. 
 
 Mr. Lister with the aid of the achromatic compound mi- 
 croscope in the possession of Mr. Lister, have shown this 
 appearance to be an optical illusion. The following extract 
 from the observations of these gentlemen contains the re- 
 sult of their inquiries. 
 
 " The muscular tissue may be easily seen with the naked 
 eye, or with the assistance of a comparatively feeble lens, 
 to be composed of bundles of fibres, held together by a 
 loose and fine cellular membrane ; and these fibres are again 
 seen to consist of more minute fibrillee. It is difficult to 
 push the mechanical division much further ; for the softness 
 of the muscular substance is such, that it is either crushed, 
 or breaks off rather than admit of further splitting. If a 
 piece of one of the most delicate of the fibrillse last arrived 
 at, be placed on a piece of glass in the field of the micro- 
 scope, lines may be seen parallel to the direction of the 
 fibre, which show a still further division into fibres. 
 
 " Although no trace of globular structure can be detected, 
 innumerable very minute, but clear and Jine parallel lines or 
 strife, may be distinctly perceived transversely marking the 
 fibrilla. In some instances these seem to be continued 
 nearly or quite at right angles, completely across the fibril ; 
 but frequently the strise in one part are opposite to the 
 spaces in another, by which arrangement a sort of reticu- 
 lated appearance is produced. The striae are not in all 
 specimens equally distant ; but this may, perhaps, be owing 
 to the elongation or contraction of the fibre. We have dis- 
 covered this peculiar and very beautiful appearance in the 
 muscles of all animals which we have yet examined ; and, 
 as we have seen it in no other tissue, we have been induced 
 to view it as a distinguishing feature of muscle*." 
 
 Muscular parts receive a large supply of blood. The 
 veins in muscles have numerous valves. Lymphatics have 
 not been traced to any distance in the substance of muscles. 
 
 Nerves are distributed to all muscles, but in a larger pro- 
 portion to some than to others, to the voluntary than to the 
 involuntary: their disposition is thus described by MM. Pre- 
 
 * Philosophical Magazine and Annals, Aug. 1827. 
 
Phenomena of Muscular Relaxation. 33 
 
 vost and Dumas. The trunk of a nerve and its first branches 
 penetrate between the muscular fasciculi in a tortuous 
 course, the exact direction of which appears indifferent. 
 But the minute filaments, in which each branch ends, are 
 found invariably to traverse the muscular fibres at a right 
 angle and at short distances from each other, and then 
 either to return to the same nerve, or to join a neighbour- 
 ing; branch : thus a nerve terminates in muscles by innume- 
 
 o > 
 
 rable delicate loops ; or the nervous filaments distributed 
 transversely through muscular substance, communicate 
 equally at either end with the brain or spinal chord. This 
 disposition of parts is not observed without difficulty in the 
 opaque flesh of warm-blooded animals, but is readily seen 
 in the thin transparent muscles of frogs. Several partial 
 instances of a like nature have been long known to anato- 
 mists. The branches of the portio dura are found to unite 
 by slender twigs with those of the three divisions of the 
 fifth nerve upon the face ; and in the tongue the union is 
 equally distinct of twigs of the ninth nerve with twigs of the 
 gustatory. It is remarkable that in many of these familiar 
 instances the junction that takes place is between sentient 
 nerves and nerves of motion. 
 
 It has been already observed, that muscular parts are 
 found during life in one or other of two conditions, which 
 naturally alternate, in relaxation or tension, in repose or 
 in action. 
 
 A muscle when relaxed is soft and pliant, yields readily 
 to lateral pressure, and is easily extended in the direction 
 of its fibres. At the instant of becoming relaxed, muscular 
 fibres always exhibit some degree of elongation, which, 
 however, in many instances is extremely slight. It is 
 uncertain from what cause this effect proceeds : under 
 ordinary circumstances, some external force contributes to 
 produce it, at least when it occurs in voluntary muscles : 
 but in the heart, the forcible elongation of fibre, that takes 
 place upon its relaxation, clearly results from some inherent 
 property, which, in the want of proof, we may suppose to be 
 either elasticity, or a part of irritability. On the other 
 hand, muscular fibres, during the state of relaxation, are 
 
34 Phenomena of Muscular Action. 
 
 capable of becoming shorter. If we bend the elbow of 
 an infant when lying asleep, the bicipital flexor becomes 
 shorter in proportion as its attachments are approximated, 
 but continues still disposed in a straight line between the 
 shoulder and the elbow. The latter instance, however, 
 should perhaps rather be considered as an effect of that low 
 degree of action called the tone of a muscle, than as a phe- 
 nomenon of relaxation. 
 
 A muscle, when in action, is hard, rigid, resists extension, 
 and has a forcible tendency to shorten in the direction of its 
 fibre. The rigidity depends less on the degree of shortening 
 produced than on the force exerted. If a heavy body be 
 held out nearly at arm's length, the palm of the hand being 
 directed upwards, and the elbow slightly bent, the bicipital 
 flexor will be found considerably more rigid than when using 
 less effort we completely bend the elbow joint and supinate the 
 wrist. A muscle in action, if counteracted by an equal force, 
 has its tendency to shorten neutralized, and remains tense 
 without any diminution of its length : and if opposed by 
 a force superior to its own, admits even of being elongated 
 during its most powerful action. 
 
 The relaxation of muscles seldom contributes directly to 
 the performance of a function, or only contributes to this 
 end by permitting the influence of other forces to be fully 
 exerted. The action of muscles, on the contrary, has the 
 most extensive, important, and direct application in the 
 animal oeconomy. By muscular action, for example, the joints 
 are knit, and the frame of the skeleton is sustained in fixed 
 positions or is carried forward in locomotion, or the cavities 
 of the trunk are alternately enlarged or contracted, or the 
 contents of the hollow viscera are expelled. 
 
 Action may be produced in all muscles during life or 
 soon after death by various stimuli ; by mechanical irri- 
 tation, as for instance by the simple contact of a foreign 
 body, and still more forcibly by cutting, tearing, or pinching 
 the exposed fibre ; by chemical excitement, as upon the ap- 
 plication of diluted acid or alkaline fluids, and of different 
 neutral salts ; or by electricity. 
 
 A muscle in action, if allowed to become shorter, gains 
 
Condition of the Fibres of a Muscle when in action. 35 
 
 exactly in thickness what it loses in length. This I as- 
 certained to be the case by the following experiment. The 
 ventricular portion of the heart removed from a large dog 
 immediately after death by hanging, was immersed in warm 
 water contained in a glass vessel, which was closed below 
 with a ground glass stopper, and terminated above in an 
 open vertical tube one-third of an inch in diameter. The 
 ventricles continued alternately to contract and dilate for a 
 considerable length of time, during which the water stood 
 at the same level in the tube, not sensibly rising and 
 falling by the varying condition of the muscular fibre*. 
 
 The change in form, which muscular fibres assume during 
 their action, is thus described by Dr. Hales. 
 
 " If," says he, " the skin be removed from the belly of a 
 live frog, and the abdomen opened on each side, so as that 
 its straight muscles may by drawing a little on one side 
 have a strong focal light cast on the inside of them ; if in 
 this posture these muscles be viewed through a good micro- 
 scope, the parallel fibres of the muscles are plain to be seen, 
 with the blood running alternately up and down between each 
 fibre in capillary arteries so fine, that only a single globule 
 can pass them. If the muscle happens to act while thus 
 viewed, then the scene is instantly changed from parallel fibres 
 to series of rhombo'idal pinnulae, which immediately disappear 
 as soon as the muscle ceases to act. It is not easy to get a 
 sight of this most agreeable scene, because that on the action 
 of the muscle the object is apt to get out of the focus of the 
 microscope ; but those who are expert in the use of these 
 glasses may readily move them accordingly. I have found 
 small frogs best for this purpose, namely, such as are not 
 above a third or a fourth of their full growth. Stimulating 
 the foot of a frog will sometimes make it contract these 
 muscles. The frog must be fixed in a proper frame. If 
 repeated observations were made on the muscles thus in 
 action, it might perhaps give some farther insight into the 
 nature of muscular motionf." 
 
 The recent researches of MM. Prevost and Dumas ex- 
 
 * Anatomical and Physiological Commentaries, vol. i, p. 12. 
 f Hsemastatics, p. 59. 
 
 D 
 
36 Of the Tone of Muscles. 
 
 plain the change in form of each single fibre, from which 
 the preceeding appearance results. The ventral muscle of 
 a frog so placed in a frame that a current of the galvanic 
 fluid might at pleasure be directed through it, was examined 
 in a microscope. When excited to contract, the fibres were 
 seen to become bent at numerous angles into zigzag lines. 
 When the stimulus was discontinued, the part regained its 
 former length, and the fibres their straight direction. The 
 angles were observed to be placed at nearly equal distances, 
 and corresponded exactly with the point of intersection of 
 nervous filaments. These circumstances are stated to have 
 been made out in the muscles of warm-blooded animals, 
 and no less in the muscles of the trunk and limbs than in 
 those of the hollow viscera*. 
 
 When the ovary of the frog is full of spawn, the ab- 
 dominal muscles are extended considerably beyond their 
 habitual length. Upon being detached from the body, 
 when in this condition, they are found to lose at once a 
 third of their accidental elongation : but during this 
 shortening, the fibres, according to Messrs. Prevost and 
 Dumas, preserve their straight direction ; and only when 
 subsequently excited by galvanism to further action, are 
 thrown into zigzag lines. 
 
 The retraction of the detached- muscle in the preceding 
 instance, is one of several phenomena which are said to 
 depend upon muscular tone. Through this cause, if quickly 
 after death a muscle in its medium state of extension be 
 divided transversely, the separate portions instantly recede 
 to some distance from each other. The same result of 
 course ensues upon the division of a muscle in the living 
 body ; and as Bichat ascertained, the retraction is equally 
 prompt and energetic, whether the nerves of the part have 
 been previously cut through or not. It is remarkable that 
 the separate portions which have retracted, if excited, 
 shorten further, and then again become elongated to their 
 last dimension. There are other instances, to which the 
 term muscular tone has been applied, which depend upon a 
 different cause. If the nerves of the face are divided, the 
 * Magendie, Journal de Physiologic, vol. iii, p. 301, et seq. 
 
Of Muscular Fatigue. 3? 
 
 features no longer remain supported in their usual expres- 
 sion; their muscular tone is gone, and they drop from 
 their weight. On the other hand, the contraction by which 
 a muscle accommodates itself to the flexion of a joint, or 
 to the shortening of a bone that has been broken and ill 
 set, is certainly independent of its nerve. 
 
 Repeated or continued exertion of muscular parts exhausts 
 their irritability. When fatigued, we are conscious that 
 our muscular frame has become temporarily weaker. 
 A muscle repeatedly stimulated in a physiological ex- 
 periment at length ceases to act. Dr. Wilson Philip 
 ascertained, that this mode of exhaustion ensues even sooner 
 when the part is left in communication with the brain, than 
 when its nerves have been previously divided*. After 
 unusual exertion, a period of repose seems necessary to 
 enable a muscle to recover its full capability of acting upon 
 excitement. 
 
 Sir A. Carlisle discovered, that in several animals, which 
 are remarkable for the slowness of their muscular move- 
 ments, the main artery of each limb is abruptly divided into 
 numerous trunks, which pursue a parallel course and freely 
 communicate. In the fore leg of the lemur tardigradus, as 
 many as sixty brachial arteries are thus formed^. One 
 effect of this provision must be to lessen the force of the 
 blood circulating in the muscles of the limbs ; but its 
 relation to the habits and muscular power of the animal 
 is unknown. In this, as in other instances, we are wholly 
 unacquainted with the qualities in the organization of 
 muscles, which diversify their mode of irritability. 
 
 The rigidity of muscles, which ensues soon after death, 
 should tend to elucidate the nature of their action during 
 life. The period at which this change begins, as well as its 
 degree and the term of its continuance, are very indefinite, 
 but appear to have some relation to the degree of physical 
 exhaustion which the body has previously undergone. The 
 muscles of those killed by lightning are said, but I believe 
 erroneously, not to become rigid. In animals that have 
 
 * Experimental Inquiry, p. 100. 
 f Phil. Trans., vol. c, p. 99. 
 
 D 2 
 
38 Ridigity of Muscles after Death. 
 
 been hunted or driven hard before slaughtering, the muscles 
 stiffen in a few minutes; but the rigidity is incomplete, 
 and disappears sooner than in other cases. 
 
 In sheep and oxen the joints have ordinarily begun to 
 stiffen in half an hour after death : in about twenty-four 
 hours the ridigity appears complete, and the flesh when 
 divided does not retract : but it seems that during the first 
 three or four days it continues gradually to acquire more 
 firmness. In hot weather the flesh of slaughtered animals 
 never becomes perfectly rigid, and, till decomposition 
 begins, retracts in some degree when divided. Warmth 
 appears directly to prolong the phenomena of irritability in 
 dead muscular parts. A heart that has ceased beating will 
 even resume its action when immersed in warm water. It 
 may be observed, that under circumstances nearly similar, 
 like parts in different animals of the same species vary re- 
 markably in respect to the duration of their irritability after 
 death. In two cats destroyed by hanging, the heart of the 
 one had entirely lost its irritability in half an hour ; in the 
 heart of the other the auricles continued, at the expiration 
 of four hours, occasionally to contract. In one instance 
 the voluntary muscles, in another the involuntary muscles, 
 first lose the capacity of being excited by stimuli. If the 
 surface of the flesh be exposed within a few minutes after 
 death, the fibres are seen to describe a right line, unless 
 their attachments be brought near to each other, when they 
 lie in folds : after a minute or two, slight convulsive actions 
 are to be remarked of the separate fibres, both in the heart, 
 and in the muscles of the trunk and limbs : these last for a 
 few minutes, and are capable of being re-excited by 
 sprinkling salt upon the surface. Rigidity is produced 
 almost instantaneously if warm water be injected into the 
 arteries of a muscle. The flesh under these circumstances 
 becomes pale, increased in bulk, and suddenly hardens. 
 
 The operation of crimping fish consists in dividing the 
 muscular fibre before it has become rigid, and immersing it 
 in spring water. A small part treated in this manner, con- 
 tracts and hardens within five minutes ; a larger part takes 
 a longer period. Sir A. Carlisle observed, that crimped 
 
Proximate Cause of Muscular Contraction. 39 
 
 flesh gains both in weight and in specific gravity. Crimp- 
 ing only takes effect if performed before the natural stiffen- 
 ing has been completed. Sea-fish intended for crimping, 
 are usually struck on the head when caught, which is said 
 to preserve them for a longer period fit for the purpose. 
 No doubt this expedient, which is fortunately merciful, 
 operates by preventing the fish from exhausting its muscles 
 in convulsive efforts. 
 
 The preceding details illustrate generally the nature of 
 muscular action. A muscle is, it appears, so constituted, 
 that upon a given impression certain points in each fibre 
 are suddenly attracted towards each other with increased 
 force. We have yet to learn whether the attraction be 
 exerted equally by every integrant molecule of the fibre, 
 or whether it operate from definite points at appreciable 
 intervals. Either supposition appears compatible with the 
 change already described from the right line to a zigzag, 
 which is observed to take place when the fibre is shortened 
 beyond certain limits. 
 
 Muscular parts are found to vary among themselves, as 
 regards their natural condition in the absence of special 
 impressions, the duration of their action and of the intervals 
 of repose which they require, the kind of stimulus calcu- 
 lated to excite their action, and the degree of sensation 
 attending their use. 
 
 When we seek for some broad and leading distinction 
 among parts of this nature, a phenomenon presents itself, 
 which serves to distribute the different varieties of muscular 
 irritability under two heads. It is to be understood that 
 every voluntary muscle receives a nerve, upon the division 
 of which its action is paralized : nerves of this class are 
 generally called voluntary nerves. Now I ascertained that 
 after any voluntary nerve whatsoever is cut through, either 
 in a living animal or immediately after death, mechanical 
 irritation of the part of the nerve disconnected with the 
 brain, as for instance the pinching it with forceps, causes a 
 single sudden action of the muscle or muscles it supplies. 
 On the other hand, a like effect cannot be produced by 
 
40 Distribution of Muscles in two Classes. 
 
 irritating mechanically the nerves distributed to those mus- 
 cles, over which the will has indisputably no influence, 
 Yet it must be admitted that the phenomenon which I 
 have described is not exclusively confined to those muscles 
 which are allowed at all hands to be voluntary; nor in 
 truth is it shown in all the muscles which seem at first 
 sight to be directly under the control of the will. But 
 it is not easy in various instances to determine whether 
 muscular actions are voluntary or not ; while the point of 
 distinction, which is here proposed, has at all events the 
 recommendation of being readily verifiable. Setting aside 
 therefore in the first instance the question of the influence 
 of the will, let us be satisfied with observing what muscles 
 act when a divided nerve that enters their substance is 
 mechanically irritated, and what do not : we may after- 
 wards trace the collateral differences of the two classes of 
 muscles, which are thus distinguished. 
 
 The parts whieh are susceptible of this mode of excite- 
 ment, are the muscles of the trunk, head, and limbs, of the 
 tongue, of the soft palate, of the larynx, of the pharynx and 
 oesophagus, and of the lower outlet of the pelvis. The op- 
 posite class comprehends the heart, the stomach, the small 
 and great intestines, and the bladder. 
 
 The collateral differences which characterize either class, 
 are, with exceptions afterwards to be adverted to, the 
 following. 
 
 Of the muscles, whieh act when a nerve distributed 
 through them is mechanically irritated, it may be re- 
 marked ; 
 
 1. That they admit of being thrown into action by an 
 effort of the will. 
 
 2. That with sufficient attention and resolution, their 
 action may be refrained from. 
 
 3. That their action is attended with a conscious effort, 
 and is guided by sensation. 
 
 4. That if divided, the separate parts retract instanta- 
 neously to a certain distance, and subsequently undergo no 
 further permanent shortening. 
 
Distribution of Muscles in two Classes. 41 
 
 5. That when mechanically irritated, a single and momen- 
 tary action of their fibres alone ensues. 
 
 6. That they remain relaxed, unless excited by special 
 impressions, both in the living body and before the loss of 
 irritability after death. 
 
 7. That their action in the living body habitually results 
 from an influence transmitted from the brain or spinal chord 
 through the nerves. 
 
 The exceptions to be made against this statement, if ap- 
 plied generally, are, that the three first affections are not 
 easily brought home to the muscular fibres of the oeso- 
 phagus, or of the lower part of the pharynx ; but it deserves 
 at the same time to be considered, that the lower part of 
 the pharynx and the oesophagus are in the peculiar situa- 
 tion of parts employed upon one object alone instinctively 
 and habitually, on the recurrence of one impression; a 
 condition which would soon reduce a strictly voluntary 
 muscle to a state apparently removed from the control of 
 the will. 
 
 Muscles of the preceding class, if we except the fasciculi 
 belonging to the pharynx and oesophagus and urethra, are 
 so disposed as to extend from one piece to another of the 
 solid framework of the body: they enlarge or straighten 
 the cavities of the trunk ; they produce the phenomena of 
 the voice ; they close the excretory passages ; the greater 
 number are employed to move the limbs upon the trunk, 
 the frame upon the ground. Muscles of the second class 
 are used, like the exceptions in the preceding, as tunics to 
 the hollow viscera, the cavities of which they diminish in 
 their action, and thus serve to give motion to their con- 
 tents. The oesophagus, indeed, appears to partake of the 
 nature of both classes of muscles; when the nervi vagi are 
 pinched, one sudden action ensues in its fibres, and presently 
 after, a second of a slower character may be observed to 
 take place. 
 
 Of the muscles which do not act upon the mechanical 
 irritation of any nerve distributed through them, it may be 
 remarked ; 
 
42 Distribution of Muscles in two Classes. 
 
 1. That the will cannot instantaneously or directly pro- 
 duce action in them. 
 
 2. That the resolution to abstain from their action is in- 
 sufficient to repress it. 
 
 3. That their action is not attended with a conscious 
 effort, and seldom has reference to sensation. 
 
 4. That if divided, the retraction which follows is in 
 most instances slow and gradual. 
 
 5. That if they are mechanically irritated, not one, but a 
 series of actions, ensues. 
 
 6. That their natural state, in the absence of external 
 impressions, is not continued relaxation. When the heart 
 and bowels are removed from the body of an animal imme- 
 diately after death, they continue for a time alternately to 
 contract and to dilate. 
 
 7. That an impression transmitted through the nerves 
 does not appear the usual stimulus to their action. 
 
 The exceptions to be found to these remarks are more 
 numerous than in the preceding class, and their considera- 
 tion would lead me into details unfitted for this part of the 
 work, in which my object has been to convey a general 
 notion only of muscular action. Let me conclude the pre- 
 sent chapter by observing, that the leading distinction 
 pointed out among different modes of irritability appears 
 applicable to other textures, besides those which are 
 strictly termed muscular. The irritable portion of the iris 
 I found would in some animals contract instantaneously, 
 upon the mechanical irritation of the third nerve. On the 
 other hand, the calibre of arteries is not diminished when 
 their nerves are pinched : and the uterus and the skin, it 
 is probable, are equally insensible to this mode of excite- 
 ment. 
 
CHAPTER IV. 
 OF THE FORCES WHICH CIRCULATE THE BLOOD. 
 
 THE stream of florid blood, collected from innumerable 
 vessels in the lungs, flows to every part of the body. The 
 stream of black blood collected from the capillary vessels of 
 the whole body flows again into the lungs. The former 
 passes through the left cavity of the heart ; the latter 
 through the right. The structure of the heart is muscular ; 
 its action gives motion to the blood, which through the 
 operation of valves, that preclude its retrograde course, 
 flows uniformly in one direction. 
 
 But in order to understand the mechanism of the circu- 
 lation, it is necessary not merely to examine the disposition 
 of the muscular lacerti and of the valves in the heart, and 
 the structure and properties of arteries and veins, but in ad- 
 dition, to consider the nature and influence of the cavity in 
 which the heart is placed, and of the dilatable and elastic 
 viscera with which it is surrounded. 
 
 The thorax of a skeleton is a hollow conoid, broad below, 
 narrow above, where it is obliquely truncated : its axis is 
 inclined obliquely upwards and backwards : it is composed 
 of the dorsal vertebrae, the ribs, and sternum. The twelve 
 dorsal vertebrae form a column so bent as to be concave 
 forwards, and which in reference to changes of figure in the 
 chest, may be considered as fixed. The twenty-four ribs 
 are individually moveable upon the spine in every direction, 
 but to a degree extremely limited. The seven uppermost 
 on either side, or the true ribs, are let in by slips of carti- 
 lage into oval fossulae along the side of the sternum, which 
 
44 Means of increasing the Depth of the Chest. 
 
 they support. The five lower or the false ribs, are attached 
 each to that above. The ribs and sternum are slight and 
 fragile bones. In composition they derive strength from 
 their external convexity, and from their numerous and 
 yielding joints. 
 
 An imaginary plane carried through the first dorsal 
 vertebra, through both arti- 
 cular extremities of the first 
 rib of either side, and through 
 the upper part of the sternum, 
 would slant obliquely down- 
 wards and forwards. By a 
 movement of each first rib 
 upon its spinal joint suffi- 
 cient to raise the upper 
 margin of the sternum to the 
 height of the first dorsal ver- 
 tebra, the imaginary plane 
 would become horizontal. In 
 man this motion of the first 
 rib is very limited ; but it is 
 obvious, that in proportion as 
 it takes place, the vertical 
 distance of the sternum from 
 the spine, or the depth of 
 the chest, becomes increased. 
 The six lower true ribs ad- 
 mitting of the same kind of 
 motion upon their vertebral 
 joints contribute to raise and 
 carry forward the middle and 
 lower part of the sternum for 
 the same purpose. 
 
 By this provision all the muscles of the trunk, the lower 
 attachment of which is to the ribs, are rendered capable of 
 increasing the depth of the chest, or its diameter from 
 before backwards ; and the opposite class of muscles, of 
 diminishing the area of the chest in the same dimensions. 
 
Means of increasing the Breadth of the Chest. 45 
 
 All the ribs, but the first, admit of a limited degree of 
 
 rotation upon their vertebral 
 and sternal joints. Nature 
 marks, even in the foetal 
 state, the limited degree of 
 motion, which the first rib is 
 intended to enjoy, by form- 
 ing its cartilage of one piece 
 with the sternum, to which 
 the cartilages of the succeed- 
 ing ribs are already articu- 
 lated, by moveable joints; 
 and by disposing all its parts 
 in one plane. If an oblique 
 plane were imagined to pass 
 through the four joints of 
 any pair of ribs between 
 the second and tenth inclu- 
 sively, great part of the shafts 
 and cartilages of the pair of 
 ribs would fall below it. If 
 i the intermediate part of these 
 ribs be raised towards the 
 imaginary plane by the rota- 
 tion of each upon its sternal 
 and vertebral joints, it is ob- 
 vious that the transverse dia- 
 meter or breadth of the chest 
 becomes increased. The ad- 
 vantage derived from the mo- 
 tion of the ribs on both their 
 articular extremities is in- 
 tended to be explained by 
 the adjoined figure. 
 
 By this provision the same muscles, which contribute to 
 enlarge the depth of the thorax, are rendered capable of 
 adding to its breadth, and the same which diminish its 
 
46 wfte ^ Means of increasing 
 
 area in the first dimension, are fitted to diminish it in the 
 second. 
 
 The chest is closed above, by a fascia or layer of con- 
 densed cellular membrane, which extends across from the 
 spine to the sternum, and from the first rib of one side to 
 the opposite, and is perforated by the windpipe, by the 
 oesophagus, by nerves, and by the great vessels. The in- 
 tervals between the ribs are closed by the oblique fibres of 
 the intercostal muscles, which in their action draw towards 
 each other adjoining ribs, and are capable of contributing 
 either to the enlargement or to the diminution of the area 
 of the thorax. 
 
 The floor of the chest is formed by the diaphragm, or 
 muscular partition, which separates it from the abdomen. 
 
 The diaphragm consists of three parts. 1. Of a central 
 thin tendon of the shape of a trefoil leaf, of greater breadth 
 than depth, which, although in a degree concave down- 
 wards, yet may be regarded as spread out horizontally at 
 the level of the ninth dorsal vertebra, or of the lowest part 
 of the fifth rib. 2. Of muscular fibres derived from the 
 anterior and lateral margins of the central tendon, which 
 slope downwards to be inserted into the ensiform cartilage 
 and into the inner and lower part of the seven lowest ribs, 
 and are called the greater muscle of the diaphragm. 3. Of 
 other muscular fibres which descend from the posterior edge 
 of the centrum tendinosum to the lumbar vertebrae, and are 
 called the lesser muscle. The diaphragm gives height by 
 its action to the cavity of the chest. In an ordinary inspi- 
 ration, the lateral parts, or the greater muscle, alone sen- 
 sibly descend, something in the manner, but not to the 
 degree represented by the dotted lines in the adjoined 
 sketch. 
 
the Height of the Chest. 
 
 47 
 
 
 Except during the deepest inspiration, the lungs do not 
 reach lower than the sixth rib in front, and the eighth 
 dorsal vertebra behind ; laterally below this level, the dia- 
 phragm lies in contact with the ribs, or rather the pleura 
 diaphragmatica with the pleura costalis. The diaphragm 
 gives passage to different vessels and nerves ; and it is re- 
 markable, that while the oesophagus, the aorta, and thoracic 
 duct pass through muscular apertures, the pressure of which 
 they are calculated to resist or to profit by, the great ascend- 
 ing venous trunk passes through an opening in the central 
 tendon, with the margin of which its substance is inter- 
 woven, so that the vein is perpetually held open by the 
 whole tonic force of the greater and lesser muscle. 
 
 The abdominal muscles are the antagonists of the dia- 
 phragm, which upon becoming relaxed admits of being 
 raised through their lateral pressure upon the bowels. 
 
 In the cavity of the chest, thus amply furnished with the 
 means of alternate expansion and diminution, are placed 
 the lungs, one on either side, with the heart between. 
 
 A lung is an organ composed of a light cellular flesh, 
 
 
48 Of the Pleura and Pericardium. 
 
 fitted to the varying form of the chest, not less by its 
 original figure than by its great elasticity. Each lung is at- 
 tached to the spine by its root, at which part blood-vessels 
 and nerves, lymphatics, and a branch of the windpipe, enter 
 its substance. Each lung is covered by a fine transparent 
 membrane termed a pleura, which reflected from the root 
 of the lung towards the sternum and towards the spine, 
 afterwards lines the diaphragm, the ribs, and intercostal 
 muscles. 
 
 The pleura is one of a class of parts termed serous mem- 
 branes : these a're for the most part closed sacs, one half or 
 one portion of which forms the investing tunic of a viscus, 
 while the other is attached to the parts adjoining. The 
 outer surface of a serous membrane coheres with the cellular 
 texture of the organs which it covers : the inner surface is 
 unattached, and kept moist with a fluid resembling the 
 serum of the blood. Serous membranes are employed to 
 facilitate the movements of viscera upon the neighbouring 
 parts by the interposition of two lubricated surfaces, and to 
 isolate adjacent organs from one another. Sometimes there 
 is a dirFerence in the character of the visceral and reflected 
 portions of a serous membrane. In the present instance 
 there is none : but the pleura covering the lung is termed 
 pleura puhnonalis, the reflected portion pleura costalis, 
 pleura diaphragmatica, or pleura peri cardiac a, in reference 
 to the surfaces to which it is applied. That part of the 
 pleurae, which extends from the sternum to the spine, 
 constitutes the septum or mediastinum of the chest, be- 
 tween the two layers of which the heart is contained. 
 
 The substance of the heart is covered with a serous mem- 
 brane termed the pericardium, which is reflected from the 
 great vessels to form the sac, in which the heart plays. 
 The reflected portion coheres firmly with the centrum ten- 
 dinosum of the diaphragm, upon which the heart rests : it 
 has great strength, and is divisible into a thin internal 
 layer, the true continuation of the pericardium covering the 
 heart, and a thick outer adventitious membrane. Dr. Baillie 
 met with an instance, in which the pericardium was defi- 
 cient, and the heart invested by the pleurge. The heart is 
 
Of the Lungs. 49 
 
 fixed at its base ; from whence proceed, the vena cava in- 
 ferior to descend through the diaphragm, the vena cava 
 superior and aorta to ascend towards the neck, where their 
 branches are distributed, and the pulmonary artery and 
 veins to extend transversely outwards into either lung. 
 
 The form and dimensions of each lung, while the chest is 
 entire, are determined by the atmospheric pressure. A lung is 
 laid out in cells, into which the windpipe opens. The windpipe 
 or trachea, continuous through the larynx with the fauces, is a 
 tube nearly cylindrical, and about ten lines in diameter, consist- 
 ing of from fifteen to twenty incomplete rings of cartilage, the 
 deficiency of which at the back part is made up by transverse 
 muscular fibres, and by an elastic membrane, which serves 
 at the same time to connect each ring with those adjoining 
 it. The tube is lined by a vascular and sensible membrane, 
 continued from the lining membrane of the fauces, and 
 termed a mucous membrane from the nature of its secretion. 
 The trachea descends from the throat into the chest, and 
 opposite to the third dorsal vertebra divides into two smaller 
 tubes termed bronchi : of these the right is the shortest and 
 most capacious ; for the right lung is larger than the left, 
 the greater part of the heart being placed upon the left side. 
 The left lung is divided into two lobes, the right lung into 
 three, by fissures extending to the root of each. The bron- 
 chus divides into a branch for each lobe; and in the sub- 
 stance of the lung, these branches, after a few subdivisions, 
 lose all trace of the imperfect cartilaginous rings which be- 
 long to the first parts of the respiratory tube, and become 
 membranous. The branching air-tubes terminate in minute 
 cells at every point in the lung, each lobe of which is subdi- 
 vided into innumerable lobules. 
 
 The cells of the lungs, while the chest is entire, are 
 always distended beyond their natural limits. The sub- 
 stance of the lungs is elastic, but its resistance is of no 
 effect against the disproportionate pressure of the atmo- 
 sphere. If at an intercostal space the skin, muscles, and 
 pleura reflexa be cut through, atmospheric air enters the 
 chest through the aperture, the lung recedes from the ribs, 
 and shrinks to a smaller dimension. By this well-known 
 
50 Effect of the Resiliency of the Lungs. 
 
 experiment the atmospheric pressure is equalized upon 
 either surface of the lung, and the organ takes a volume 
 determined by its elasticity and weight. Dr. Carson in- 
 geniously contrived to measure the resistance of the lungs 
 in the most contracted state of the chest to the atmospheric 
 pressure, by observing the height to which a column of 
 water must be raised in order to force air into the lungs, 
 after the opening of the intercostal spaces, in sufficient 
 volume to fill the cavity of the chest as before. He em- 
 ployed a hollow glass globe, to one side of which a tube 
 was let in, that admitted of being securely fastened into the 
 trachea of a slaughtered animal ; to the other was attached 
 a vertical tube, bent near its junction with the globe, into 
 which water was poured, after openings had been made be- 
 tween the ribs, and the lungs had contracted. Though the 
 means of this apparatus Dr. Carson ascertained, that in 
 calves, sheep, and large dogs, the resiliency of the lungs 
 is balanced by a column of water varying in height from 
 one foot to a foot and a half; and in rabbits and cats, 
 by a column of water varying in height from six to ten 
 inches*. 
 
 If the lungs were inelastic, but admitted of being un- 
 folded to an indefinite extent on the enlargement of the 
 chest, the pressure of the atmosphere upon the inner surface 
 of the chest would be the same as elsewhere ; but it is 
 clear, that in proportion as the lungs have a tendency to 
 resist the atmospheric pressure, or in other words to recede 
 from the pleura reflexa, the weight of the atmosphere must 
 be lessened upon all the parts against which the lungs are 
 applied. Thus it happens that the outer surface of the heart 
 is not at any time exposed to the same degree of pressure 
 with parts external to the chest; and that the degree of 
 pressure is yet further reduced, when upon the dilatation of 
 the chest the lungs become further expanded, and their 
 elastic resiliency increased. 
 
 The heart is of a conical figure : the septum, which di- 
 vides its cavities, is disposed nearly in its long axis, but 
 
 * Phil. Trans, vol. ex, p. 42. 
 
 M* 
 
Of the Muscular Structure of the Heart. 51 
 
 gives the apex of the heart to the left ventricle exclusively. 
 The shape of each chamber of the right cavity is triangular, 
 that of the left oval; the contents of each are about two ounces. 
 The auricles are of a thin substance ; the ventricles are of 
 considerable thickness ; the muscular fibres of the right 
 auricle are disposed in parallel lacerti prominent inwards, 
 called musculi pectinati : a like appearance is not seen in 
 the left auricle. In the appendage of each auricle the 
 lacerti are reticularly interwoven. The external layer of 
 muscular fibres in the left ventricle, extends spirally from 
 the base and superior longitudinal furrow forward and to- 
 wards the left, and turning round the margin of the heart 
 reaches the longitudinal furrow upon its under surface. The 
 external layer of muscular fibres upon the right ventricle, 
 extends in a like manner from the right transverse and infe- 
 rior longitudinal furrows obliquely forward to the superior. 
 In the middle layer no regular disposition seems observed. 
 The lacerti of the inner layer again intersect each other re- 
 ticularly, without any exact order, except that in the left 
 ventricle two fleshy columns, and in the right three or 
 four, project towards the auricle. The aperture of either 
 ventricle towards the artery, which springs from it, is per- 
 fectly smooth. 
 
 Either cavity of the heart is lined with a thin transparent 
 membrane, which is readily separable from the inner surface 
 of the auricles and ventricles, and is found to be continued 
 along the artery, which terminates the latter, and along the 
 veins that open into the former. This membrane is in a de- 
 gree firmer and more opaque upon the left side of the heart 
 than upon the right. In the arteries it appears of a more 
 brittle texture than in the veins : it is everywhere in con- 
 tact with the blood, and is usually classed among the serous 
 membranes. ' 
 
 At the opening of the inferior cava into the right auricle, 
 the inner membrane is raised along the left margin of the 
 vein, so as to form a crescentic fold, which is termed the 
 Eustachian valve. By this provision, useful only in the 
 fcetal state, the inferior cava is made to open exactly op- 
 posite to the fossa ovalis. Muscular fibres are often con- 
 tained in the Eustachian valve. At the opening of the 
 
 
52 Use of the Mitral and Tricuspid Valves. 
 
 common coronary vein, another semilunar fold of membrane 
 forms a valve to guard its oblique aperture, and to prevent 
 the regurgitation of blood from the auricle into the vein. 
 No valve is placed upon the entrance of the superior cava 
 into the right auricle, or of the pulmonary veins into the 
 left. 
 
 The valve between each auricle and ventricle is a re- 
 duplicature of the inner membrane, thickened by intervening 
 fibrous substance. Its floating margin is irregular, and 
 presents three points in the right, two in the left ventricle ; 
 whence the former is termed the tricuspid, the latter the 
 mitral valve. The floating edge of the valve is attached by 
 short tendinous threads, called chordae tendinese, to the 
 fleshy columns of the ventricle. Each fleshy column 
 receives all the tendinous chords from the opposite edges of 
 two adjoining points of the valve. The valve at its broadest 
 parts is about eight or nine lines in depth, intermediately 
 about five. The margin of the valve is strengthened by 
 numerous little granular bodies, called corpora sesamoidea. 
 
 The action of the mitral and tricuspid valves may be 
 easily understood, when the parts forming either valve are 
 displayed in their entire state, either by opening the ven- 
 tricles from the aorta and pulmonary artery, or by removing 
 the apex of the heart. 
 
54 
 
 Use of the Semilunar Valves. 
 
 The first figure of the two preceding represents the 
 semilunar valves half raised, as they appear upon slitting 
 open the aorta or pulmonary artery. Fig. 2 represents the 
 ventricular surface of the valves when thrown down. I am 
 tempted to add another drawing from a specimen which I 
 recently met with. Instead of three crescentic folds, the 
 semilunar valve of the aorta consisted but of two ; yet 
 though monstrous, the construction of the valve was perfect, 
 each of the two flaps being proportionately larger than 
 usual, and strengthened by a central band extending 
 towards the sesamoid body. The valve at the root of 
 the pulmonary artery in this heart presented no uncommon 
 appearance. 
 
 The heart is supplied with blood from the two coronary 
 arteries, which are the first branches of the aorta ; it has a 
 large supply of lymphatic vessels ; its nerves are derived 
 from the sympathetics and nervi vagi. 
 
 An artery is a cylindrical and highly elastic tube; its 
 thick texture is separable into, 1. An inner serous coat: 
 2. A middle fibrous coat, of a yellow colour in the larger 
 trunks, of a redder hue in the smaller branches, composed 
 of fibres, which are disposed transversely, but seem in some 
 degree interwoven ; they are very elastic, and at the same 
 
Use of the Semilunar Valves. 53 
 
 Fig. 1 represents the passive state of the mitral valve, while 
 the blood is flowing from the auricle into the ventricle. 
 Fig. 2 represents the state of the valve when acting : its 
 edges are in that case drawn together so as nearly to meet by 
 the action of the fleshy columns. If the heart be opened in 
 either of the methods described above, it is only necessary 
 to imitate the natural action of the fleshy columns by pull- 
 ing upon them in a proper direction, and the valve will be 
 seen to close in the manner represented. Fig. 3 is a dia- 
 gram, giving another view of the mitral valve when closed. 
 These figures are erroneous in the following respects ; they 
 represent the edges of the valve as meeting more closely 
 than they do in nature ; and they represent the two points 
 of equal depth, whereas the right process, or that next the 
 opening into the aorta, is considerably deeper than the other. 
 The tricuspid valve acts upon exactly the same principle 
 with the mitral valve. 
 
 The valves at the root of the aorta and of the pulmonary 
 artery are of a different description ; they consist of three 
 semilunar folds of the inner membrane, attached by their 
 convex margin, each along a third of the circumference of 
 the artery. They are so disposed, that when blood issues 
 from the ventricle, they are thrown up, and lie in contact 
 with the parietes of the artery : but upon the reflux of the 
 blood towards the heart, they are thrown down and sac- 
 culated, while their floating margins, the centre of each of 
 which is strengthened by a sesamo'id body, meet as tense 
 chords, describing three radii of the circular aperture of the 
 vessel. These valves are termed the sigmoi'dal or semilunar 
 valves of the aorta and pulmonary artery. 
 
 y V , 
 
Of the Structure of Arteries and Veins. 55 
 
 time so brittle, that the pressure of a ligature tied 
 upon an artery cuts through the fibrous together with the 
 inner coat: and, 3. An outer cellular coat, consisting of 
 tough white elastic fibres closely interwoven, which the 
 pressure of a ligature does not divide. Dr. Hales as- 
 certained that the force required for bursting one of the 
 carotids of a dog, is equal to that of a column of water 
 one hundred and ninety feet high. He does not remark 
 that the artery became dilated, but observes that with this 
 pressure the artery burst at once. 
 
 A vein is a flexible tube of great strength, but of little 
 elasticity, separable into an inner serous tunic, and a dense 
 external coat of white and closely interwoven fibres. The 
 inner coat is thrown at intervals into semilunar folds that 
 occur in pairs, and are attached by their convex margins 
 each to half the circumference of a vein : as the blood 
 flows towards the heart, these valves lie against the sides 
 of the vessel ; upon its reflux they are thrown down and 
 their edges meet. Valves are not found in the venae cavae 
 
 o 
 
 or in the veins of the abdominal viscera : they are found 
 in the iliac veins, in the veins of the neck and head, and 
 of the extremities, and in the pulmonary veins. Dr. Hales 
 found the jugular vein of a mare to burst with a force equal 
 to that of a column of water one hundred and forty-four 
 feet high*. 
 
 When an artery divides, the two branches have a com- 
 mon area larger than that of the trunk, and in most in- 
 stances diverge at an acute angle ; the same is observed 
 of veins. The arterial and venous trunks generally are 
 distributed together : the largest arteries have one ac- 
 companying vein, the smaller arteries two. In the neck 
 and extremities superficial venous trunks are found besides 
 those which accompany the arteries. The area of the venous 
 system is greater than that of the arterial, in the proportion 
 of four to one, according to Borelli. The ratio between 
 the capacity of individual arteries and veins in different 
 parts, is very various : between the carotid and internal 
 
 * Hsemastatics, p. 151. 
 
56 Of the Flow of Blood into the Auricles. 
 
 jugular 196 : 441, between the subclavian artery and vein 
 81 : 196, between the crural artery and vein 3844 : 7396, 
 between the aorta and vena cava 9 : 16, between the sple- 
 nic artery and vein 156 : 676*. 
 
 Arteries and veins have their vasa vasorum, and are 
 supplied with nerves derived from the sympathetic, the 
 nervi vagi, and the spinal nerves, if not indiscriminately 
 from all but the first, second, third, and fourth, and the 
 soft portion of the seventh. 
 
 * If the chest and pericardium be laid open in an animal 
 immediately after death, the heart is found to continue 
 beating : the action of the auricles and ventricles is seen 
 to alternate, the two auricles being simultaneously relaxed 
 at one instant, the two ventricles at the next. The passive 
 state of each chamber of the heart is termed its diastole, 
 the contrary state its systole. 
 
 During the systole of the ventricles, the blood which 
 is expelled from their cavities and thrown into the arteries 
 urges on that before contained in either arterial trunk, and 
 in its branches, in the capillary vessels, and in the veins, 
 towards the auricle of the opposite side of the heart. 
 During the succeeding diastole the direct influence of the 
 ventricles is suspended ; but many forces continue to 
 operate, the general effect of which is to diminish the 
 area of the vascular system : and as the blood is prevented 
 returning into the ventricles by the semilunar valves, they 
 serve to propel it onwards towards the auricles. These 
 forces consist in the elasticity and tone of the arteries 
 themselves, in the compression of surrounding elastic 
 organs, in the contraction of muscular parts, in the pres- 
 sure of the atmosphere. 
 
 Various causes again combine to give effect to these 
 forces in filling the auricles with blood, which operate by 
 taking off or diminishing the atmospheric pressure upon 
 their outer surface. The auricle during its diastole spon- 
 taneously expands ; the elasticity of the lungs constantly 
 tends to draw apart the walls of the auricle ; and at the 
 
 * Haller, Elementa Physiologise, vol. i, p. 131. 
 
Suction produced by the Resilience of the Lungs. 57 
 
 time of each inspiration, while the area of the chest is 
 enlarging, the heart is probably relieved of external at- 
 mospheric pressure in the same manner as the lungs, 
 although in a less degree. 
 
 The spontaneous expansion of the auricles is perhaps 
 of no great effect; but of the three causes assigned to 
 facilitate the entrance of the blood into their cavities, this 
 is apparently the only one in operation during the foetal 
 state, or when the circulation is kept up, after laying open 
 the chest, by means of an artificial respiration. 
 **** The extent to which the elastic resilience of the lungs 
 contributes to diminish the atmospheric pressure upon the 
 outer surface of the auricles is shown by the experiments 
 of Dr. Carson, which have been already detailed ; but its 
 effects are perhaps more strikingly illustrated by subsequent 
 researches of the same author. It has always excited 
 surprise that the arteries are comparatively empty after 
 death, and that the blood accumulates exclusively in the 
 veins and in the heart. In expectation of elucidating this 
 phenomenon, Dr. Carson killed a dog by opening both 
 sides of its chest. The body being examined several hours 
 afterwards was unusually turgid with blood, the mem- 
 branes appeared as if injected, the muscles bled when 
 divided, and there were coagula of blood in the arteries*. 
 But these uncommon appearances were produced by equal- 
 izing, before the circulation ceased, the atmospheric pres- 
 sure upon the mucous and serous surfaces of the lungs ; 
 or, in other words, by preventing the suction which the 
 resilience of the lungs usually produces after death, and 
 which this experiment proves to be a cause sufficient to 
 account for the empty state of arteries observed on dis- 
 section after ordinary death. 
 
 The effect of the dilatation of the thorax on the circu- 
 lation of the blood, has been recently placed in a strong 
 light by the experiments of Dr. Barry. One of these 
 experiments consisted in tying the jugular vein of a horse, 
 and inserting into the vein on the side open towards the 
 
 * Medico-Chirurgical Trans, vol. xi, p. 165. 
 
58 Influence of Breathing on thq Circulation. 
 
 heart, a flexible tube communicating with a spiral tube of 
 glass, which stood in a vessel of coloured water. Each 
 time that the animal inspired, the fluid was seen to ascend 
 in the spiral tube*. 
 
 But other phenomena, several of which with their true 
 explanation have long been familiar to physiologists, satis- 
 factorily illustrate the same principle, and show that the 
 influence of the state of the thorax upon the circulation 
 is felt at every part of the system. During expiration, or 
 in other words when the internal area of the thorax is un- 
 dergoing contraction, the flow of the blood into the chest 
 is shown to be retarded by the swelling of the superficial 
 veins of the neck. Under the same circumstances the 
 brain, when an opening has been made in the cranium, is 
 observed to be lifted up by the blood accumulating in it. 
 Through the same principle, blood flows in a stronger gush 
 from a divided artery during expiration, or even from a 
 vein that after having been tied is punctured on the side 
 remote from the heart f. During inspiration, on the other 
 hand, the phenomena referred to are found to be exactly 
 reversed ; the suction towards the chest upon the vascular 
 system is indeed so strong at this period, that it has hap- 
 pened, that where the jugular vein has been opened in an 
 operation and not secured, air has been inspired through 
 the vein into the heart in sufficient quantity to destroy life. 
 
 The auricles being filled with blood through the influence 
 of various causes that have been enumerated, contract: 
 the blood expelled by their action, is partly thrown back 
 upon the veins, and in its reflux from the right auricle 
 produces a pulse sometimes visible in the internal jugular 
 veins of thin persons, in part enters the ventricles, which 
 spontaneously dilate to receive it. 
 
 The auricles then become relaxed, and the ventricles act, 
 and drive back upon the auricles part at least of the blood 
 situated behind their valves, the tricuspid or the mitral : 
 and it is worthy of remark, how completely the elements 
 
 * Recherches Experimentales, par D. Barry, M.D. p. 19. 
 f Magendie, El&nens de Physiologic, tome ii, p. 423. 
 
 
Of the action of the Auricles and Ventricles. 59 
 
 of the blood must become mixed and blended together, as 
 the stream first rushes into each auricle, then is in part 
 thrown back into the veins, is again carried into the auricle, 
 and then thrown upon the ventricle ; is again in part thrown 
 back into the auricle, and at last reaching the interior of 
 the ventricle, and driven along all the irregular channels 
 and hollows of its surface, is eventually propelled into the 
 artery. 
 
 The action of the auricles is gentle, often partial, and some- 
 times repeated before the action of the ventricle takes place : 
 the action of the latter is strong and sudden. In animals, 
 rendered insensible by prussic acid, in which the action of 
 the heart is displayed by opening the chest, the ventricles 
 are sometimes seen to act alone, supporting a languid cir- 
 culation without the assistance of the auricles. 
 
 Upon listening to the action of the heart, two strong 
 sounds are distinctly heard about the time of each arterial 
 pulse ; the first, which is the loudest, is nearly synchronous 
 with the arterial pulse : it is instantly followed by the other. 
 In some experiments made by Dr. Hope, which I witnessed, 
 it was satisfactorily shown, that the first of the two sounds 
 occurs at the systole of the ventricle, the second at the com- 
 mencement of its diastole. A pause precedes each repeti- 
 tion of the ventricular systole, during which the auricle 
 acts. 
 
 At the moment when the ventricles act, the apex of the 
 heart is thrown upwards against the side of the chest. Va- 
 rious solutions have been proposed of this phenomenon; of 
 which the most ingenious attributes it to the extension of 
 the curve of the aorta upon the rush of blood from the left 
 ventricle. But it is questionable whether the cause sup- 
 posed would produce the effect which it is employed to ex- 
 plain ; and it is certain that when its influence is wholly 
 removed, the movement of the apex of the heart may take 
 place as before. I ascertained that if the heart of a dog 
 recently killed, while yet palpitating, be placed upon a 
 table, the apex continues to be lifted up at each contraction 
 of the empty ventricles. In this instance it is obvious that 
 the, movement of the apex of the heart must either depend 
 
60 Force of the Left Ventricle. 
 
 upon the direct action of the exterior fibres of the ventricle, 
 which tend when the base of the heart is fixed (as on this 
 occasion by its weight alone) to raise the apex ; or be in- 
 directly produced through the reaction of the surface, upon 
 which the heart rests when contracting. 
 
 The force with which the different chambers of the heart 
 contract is not easily computed. But some experiments 
 made by Dr. Hales throw considerable light upon this sub- 
 ject, and furnish us with an approximation to the average 
 pressure upon the blood during the systole of the left ven- 
 tricle. In some of the experiments of Dr. Hales, tubes were 
 inserted into the arteries of living animals, and the height 
 observed to which the blood ascended in them. In a glass 
 tube a sixth of an inch in diameter, fixed into the crural ar- 
 tery of a mare, the blood rose eight feet three inches above 
 the level of the left ventricle of the heart ; but it did not 
 attain its full height at once : it rushed up about half way 
 in an instant, and afterwards gradually at each pulse, 
 twelve, eight, six, four, two, and sometimes one inch : when 
 it was at its full height, it would rise and fall at and after 
 each pulse two, three, or four inches, and sometimes it 
 would fall twelve or fourteen inches, and have there for a 
 time the same vibrations up and down, at and after each 
 pulse, as it had when at its full height, to which it would 
 rise again after forty or fifty pulses. When the glass tube 
 was taken away, the greatest height of the jet of blood was 
 not above two feet. Horses were found to expire when 
 after continued hemorrhage the blood stood only at two 
 feet in the tube. Upon a measurement of the area of the 
 left ventricle, and comparing it with the height at which the 
 blood stood in the tube in the preceding experiment, 
 Dr. Hales concludes that the left ventricle of the horse 
 exerts a force in propelling the blood equal to 113.22 
 pounds. 
 
 " If we suppose," observes Dr. Hales, " that the blood 
 would rise 7| feet high in a tube fixed to the carotid artery 
 of a man, and that the internal area of the left ventricle of 
 the heart is equal to fifteen square inches, these multiplied 
 into 7f feet, give 1350 cubic inches of blood, which press 
 
Action of the Heart not produced by Nervous Influence. 61 
 
 upon that ventricle when first it begins to contract, a weight 
 equal to 51.5 pounds*." 
 
 The alternate action and relaxation of the muscular fibres 
 of the heart appear not, like similar phenomena in the dia- 
 phragm, to depend upon a series of impressions transmitted 
 from the brain or spinal chord. I have ascertained that the 
 heart being taken from the body of an animal immediately 
 after death, if the blood be carefully washed from its in- 
 ternal surface, or if the auricular part be separated from 
 the ventricles by a clean section, the alternate states of 
 action and relaxation continue for a time to succeed each 
 other in each part as before. For the brief period, during 
 which it is reasonable to suppose that the heart retains its 
 perfect organization, no stimulus seems required to excite 
 it to contract. The alternation of action and repose seems 
 to be natural to its irritable fibre, or to be the immediate 
 result of its structure. 
 
 It is remarkable that if the heart yet beating be placed in 
 warm water, it continues to act more briskly and for a 
 longer time than if exposed to the air. On the other hand, 
 if water be injected into its blood-vessels, its flesh becomes 
 pale and swollen, and after two or three beats hardens per- 
 manently. If the fibres of the heart be transversely cut 
 through, their action is stopped at once. 
 
 In the first of the preceding instances the heart is sub- 
 jected to some of the conditions, under which it exists in the 
 living body. With a little contrivance every influence to 
 which it is habituated during life, excepting that derived 
 from the nervous system, may for a short space after death, 
 be kept up upon the heart. The researches of Mr. Brodie 
 have successfully elucidated the phenomena which ensue 
 upon sustaining in dead animals an artificial respiration, ex- 
 tending to some very curious results presently to be noticed 
 respecting secretion and the source of animal heat, the origi- 
 nal experiment of Vesalius and of Hooke. If the chest be 
 alternately inflated with and emptied of atmospheric air, 
 the blood which passes through the lungs acquires a florid 
 
 * Haemastatics, p. 21 and 39. 
 
62 Action of the Heart influenced through the Nerves. 
 
 hue ; the heart's action does not sink as when black blood 
 is contained in both its cavities ; and a complete circula- 
 tion of the blood may thus be preserved for the period of 
 two hours and a half after death. Under other circum- 
 stances the heart's action ceases in from five to ten minutes 
 after apparent death. The preceding phenomena were 
 observed when the head had been removed after tying the 
 vessels in the neck. Dr. Wilson Philip found that in 
 warm-blooded animals the circulation might be kept up 
 after death by means of artificial respiration equally well, 
 whether the brain and spinal chord had been left or re- 
 moved ; and that in frogs it spontaneously continues for a 
 considerable period after the same degree of mutilation*. 
 Molae again are occasionally developed in the uterus, which 
 have neither brain, nor spinal marrow, in which, never- 
 theless, a circulation has existed. 
 
 But while the fact appears thus established, that the 
 heart needs no specific irritation through the nerves to 
 cause it to contract, it must not be lost sight of that the 
 brain and spinal chord influence remarkably the frequency 
 and vigour of its action. How promptly mental emotions 
 affect the heart is too familiarly known to need illustration. 
 The effect of physical impressions upon the brain and spinal 
 chord is not less decided. The experiments of Le Gallois 
 and Dr. Wilson Philip sufficiently prove this assertion. 
 When spirit of wine, in the experiments of Dr. Wilson 
 Philip, was applied to the surface of the brain in a stunned 
 rabbit, or to the cervical or dorsal part of the spinal chord, 
 the heart was observed to beat more quickly than before ; 
 this effect, however, gradually subsided, and the heart beat 
 again as at first. When an infusion of opium was em- 
 ployed, the heart's action was found to be at first rendered 
 stronger ; it then became enfeebled ; but on washing off the 
 poison the heart recovered itself. On a large portion of the 
 brain or spinal chord in a rabbit being suddenly crushed 
 with a steel instrument, the heart's action was observed to 
 be immediately enfeebled, if not stopped entirely. On the 
 
 * Phil. Trans, vol. ci, p. 39. 
 f Experimental Inquiries, p. 75. 
 
Frequency of the Action of the Heart. 63 
 
 brain of a frog being crushed, the heart was observed to 
 perform a few quick and weak contractions ; it then became 
 quite still for about half a minute : after this its beating re- 
 turned, at first imperfectly, but in ten minutes afterwards it 
 was sufficiently restored to support the circulation, but with 
 less force than before the destruction of the brain. The 
 spinal chord was then crushed at one blow ; the heart again 
 beat quickly and feebly for a few seconds, and then seemed 
 entirely to have lost its power of acting. Dr. Wilson Philip 
 remarked that the heart's action in these experiments was 
 rendered quicker or slower, stronger or more feeble, but 
 never rendered irregular* 1 . 
 
 The heart in adults beats in general from seventy to 
 seventy-five times in a minute ; in infants of two years of 
 age, a hundred to a hundred and ten times ; in infants of 
 one year, a hundred and twenty times ; at birth a hundred 
 and forty times ; at puberty about eighty times ; towards old 
 age the heart acts at longer intervals, and the pulse does 
 not exceed sixty in a minute. 
 
 During health the contractions of the ventricles generally 
 take place at equal intervals, and with the same degree 
 of force, or in other words are regular and equable. But 
 there are some persons, in whom, when in perfect health, 
 the pulse is habitually irregular; and only regular when 
 they labour under febrile excitement, 
 
 The quantity of blood in the body of an adult is estimated 
 on an average at from thirty to forty pounds : between one 
 and two ounces are supposed to be propelled at each con- 
 traction of the left ventricle into the aorta, with a velocity 
 of 120 feet in a minute ; and as the contraction of the ven- 
 tricle occupies a third only of the period from one systole to 
 another, the mean velocity of the blood in the aorta may be 
 computed at eight inches in a second f. 
 
 The force, with which the blood is propelled, appears 
 employed in overcoming the friction of the innumerable 
 capillary tubes which it traverses. In the capacious venous 
 
 * Experimental Inquiries, p. 36. 
 f Young's Medical Literature, p. 609. 
 E 2 
 
64 Of a Circulation without a Heart. 
 
 trunks the blood moves slowly onwards in an equable 
 stream, and with an impulse so moderate, as to rise in a 
 vertical tube, according to the experiments of Hales upon 
 the horse, to the height of six inches only. In the smallest 
 arteries the flow of the blood per saltum appears to be lost, 
 a phenomenon which is included under the following general 
 proposition in mechanics, that an intermittent motion may 
 be changed into a continuous motion by employing the 
 force, which produces it, to compress a spring, the reaction 
 of which is constant*. 
 
 From the preceding details, the motion of the blood 
 would seem to be entirely derived from the action of the 
 heart. But there are animals in which a circulation seems 
 to take place that have no heart ; and molse, or imper- 
 fect human foetuses, sometimes attain considerable matu- 
 rity with a circulation carried on by arteries and veins alone. 
 Mr. Brodie examined a foetus of this description, born, how- 
 ever, as usual a twin ; it had grown to the height of thirteen 
 inches ; and although many organs were deficient or mal- 
 formed, yet the brain and spinal chord appeared to be com- 
 plete; the principal parts of the abdominal viscera were 
 found, and the body had nearly the natural form. The 
 umbilical chord contained a vein with a single artery, the 
 structure of which seems to have presented nothing unusual. 
 The vein opened into the vena cava, from which branches 
 passed to every part of the body : the artery opened into the 
 left internal iliac, from which was derived an aorta, having 
 no arch at its upper part, but terminating in branches to the 
 head and arms. No communication existed between the 
 trunks of the arterial and venous systems, and we may sup- 
 pose that the blood was returned from the placenta along 
 the artery, was distributed through its branches to every 
 part of the body, was conveyed back by the veins of the 
 body to the umbilical vein, and thence to the placenta 
 again f. 
 
 In this and similar cases, it is presumed that motion,, 
 
 * Magendie, Etemens de Physiologic, tome ii, p. 388. 
 f Phil. Trans, vol. xcix, p. 163. 
 
Of the Nature of the Capillary Vessels. 65 
 
 limited to one direction by the valves in the venous system, 
 is given to the blood by the contraction of the arteries and 
 of the capillary vessels. Upon a like supposition the fact 
 has been explained that after the removal of the heart, if 
 transparent parts of the body be examined in a microscope, 
 the blood is seen to flow for a time in the minute vessels. 
 In an experiment of Dr. Marshall HalPs, which I witnessed, 
 a ligature was tied round all the vessels passing to and from 
 the heart of a frog. Under these circumstances, the blood 
 continued to flow with some rapidity in the arteries of the 
 web of the foot : but, after a few seconds, it became slower, 
 then stopped, when a retrograde rush of the blood took place. 
 After this its ordinary flow was resumed : then again a reflux 
 took place : and in this manner for a considerable time the 
 blood continued to flow alternately backwards and forwards 
 in the vessels. 
 
 Little is known of the nature of the capillaries : their ex- 
 istence even is only a matter of inference ; the particles of the 
 blood are seen traversing the web of the frog's foot in single 
 files, and are supposed to move in tubes of a similar nature 
 to the arteries. These channels are capable of enlarging, 
 and of admitting more blood at one time than at another. 
 If an irritant, as diluted liquor ammonise, be applied to the 
 web of the frog's foot, the small vessels speedily become 
 dilated, the blood flows more slowly through them, and here 
 and there its course is entirely arrested : bathed with cold 
 water, the part slowly recovers itself, and the vessels con- 
 tract. A particle of dust resting within the eyelids, pro- 
 duces in a few seconds an appearance of a fine vascular 
 network upon the white part of the eye ; it is supposed that 
 this results from the sudden enlargement of vessels, which 
 were before too minute to be coloured. But more is known 
 by direct observation of the properties of the larger arteries, 
 and the phenomena of the capillary circulation are only to 
 be explained by reasoning upon analogy. 
 
 The first phenomenon which attracts attention in the 
 larger arteries of the body, is their sensible pulsation ; it is 
 
 * Young's Medical Literature, p. 605. 
 
66 Of the Arterial Pulse. 
 
 synchronous with the action of the left ventricle, and re- 
 sults from the impulse communicated by the fresh jet of 
 blood from the heart. The velocity of a pulsation, according 
 to Dr. Young, is sixteen feet in a second * ; and consistently 
 with this estimate, the throb of the arteries appears to be 
 simultaneous in every part. 
 
 In a curved artery, as for instance in the temporal, the 
 pulse is visible ; the artery, if not elongated at each systole 
 of the left ventricle, is moved from its place, to which it re- 
 turns during the succeeding diastole. But if a straight ar- 
 tery be examined, as for instance the common carotid, when 
 exposed in the neck of an ass, no motion whatever or change 
 of figure is distinguishable, as long as the animal remains 
 free from alarm or suffering. And in order to perceive the 
 pulse, it is necessary, as Dr. Parry observed, to indent with 
 the finger the artery > so as to oppose it to the rush of blood. 
 
 M. Magendie mentions, however, that the aorta is visibly 
 dilated at each systole of the left ventricle, and that the 
 same change may be shown in the crural artery by the 
 following experiment. If a ligature be passed behind the 
 crural artery and vein round the thigh of a dog, and drawn 
 tight, so that the circulation be sustained through the two 
 crural vessels alone, upon compressing the artery between 
 the finger and thumb, it gradually contracts on the side 
 remote from the heart ; but upon removing the finger and 
 thumb, the artery, according to M. Magendie, while be- 
 coming distended to its former dimension, at each pulse is 
 visibly dilated. 
 
 The preceding appearances in arteries admit perhaps 
 of being referred to the acknowledged elasticity of their 
 textures. But on other occasions partial changes are 
 observed in the calibre of arteries, while the pressure of 
 the circulation is equal upon every pait, which seem to 
 result from another principle, which can be produced by 
 blind physiological experiments, or occur in the order of 
 nature for definite and important objects. 
 
 Mr. Hunter observed, that when a large artery, as for 
 
 * Young's Medical Literature, p. 606. 
 
.IK Evidence that Arteries are Irritable. 67 
 
 instance the crural artery of a dog, is exposed for some 
 time to the air, its diameter becomes gradually diminished. 
 Dr. Parry observed further, that if a ligature be placed 
 upon an exposed artery so as merely to lie in contact with 
 its surface without the knot being drawn, the vessel con- 
 tracts where the foreign body touches it, but preserves its 
 full size upon either side of the ligature. When a por- 
 tion of an artery is removed from a living animal, it slowly 
 contracts during the first minute or two to less than half 
 its first diameter. 
 
 By the experiments which have been mentioned, arterial 
 contraction is produced. The following method I dis- 
 covered would cause the partial dilatation of an artery. 
 If a large artery in the living body, as for instance the 
 carotid in an ass, or the crural artery of a dog, be rubbed 
 for half a minute between the finger and thumb, its 
 diameter at the part so treated becomes sensibly increased. 
 The ampullated appearance thus produced upon the artery 
 subsides in a quarter of an hour if the wound be closed. 
 If before it has again contracted, the ampullated part be 
 removed and examined, the enlargement of the vessel is 
 clearly seen to be dilatation, not thickening. 
 
 Hemorrhage from a small artery, that has been divided, 
 becomes slackened in a short time; and before it can 
 be supposed that faintness and a languor of the circula- 
 tion can have taken place. This spontaneous cessation 
 of arterial hemorrhage seems to occur more readily in 
 animals than in human beings. If in an experiment 
 upon a horse or ass a muscular artery of the size of a 
 crow-quill be divided, and the subsequent changes watched, 
 the jet of blood is seen to diminish gradually in volume, 
 and the distance to which it is projected to become less and 
 less ; at length the blood merely trickles over the adjoining 
 surface, then but slightly oozes, then stops. These pheno- 
 mena distinctly result from the contraction of the extremity 
 of the divided artery. Cold, which has so remarkable an 
 effect in producing contraction of the skin, serves to arrest 
 hemorrhage. Warmth and moisture, which relax the skin, 
 encourage the continuance of hemorrhage. 
 
68 Relaxation of Arteries the Cause of Local Action. 
 
 When the main artery is tied in a part, the blood finds 
 its way more freely than before through collateral vessels, 
 which speedily become dilated. If the facts which have 
 been already mentioned are sufficient to show that arteries 
 in warm-blooded animals are irritable parts, it is easy to 
 account for this phenomenon. We have but to suppose 
 that the tone of the collateral vessels is lowered on this 
 occasion : their usual resistance to the force of the blood 
 being thus diminished, they yield and are dilated by it. 
 
 The vascular turgescence of various parts is found to be 
 sometimes disproportionately increased during perfect health. 
 The class of phenomena, to which I advert, are said to re- 
 sult from local action. The following is an instance. The 
 uterus and ovaria in a rabbit, killed when the animal is 
 hot, are found to be turgid and black with blood ; if in- 
 jected in this state with size and vermilion, they are ren- 
 dered much redder than usual. The vessels have become 
 enlarged and admit more of the colouring matter than 
 they before would have done. The suffusion of the coun- 
 tenance in blushing is a phenomenon of the same nature 
 with the preceding. The simplest explanation of both is 
 to suppose the vessels irritable parts, the tone of which is 
 lowered when a larger draught of blood is required in any 
 part. The opposite hypothesis, that a sudden constriction 
 at any part of the capillary system is the cause of the dila- 
 tation of the vessels on the side next the ventricle, may 
 be considered untenable, since it is opposed to analogy. 
 If a large artery be tied, it does not become more capa- 
 cious on the side next the heart. 
 
 The opinion, which I advocate, that the flow of blood in 
 increased quantity to a part results from the relaxation of the 
 coats of its small arteries, is remarkably confirmed by what 
 is noticed respecting the larger vessels, wherever local ac- 
 tion frequently occurs, or happens to exist for a consider- 
 able period. The arteries of such parts gradually become 
 elongated and tortuous. This is the character of the 
 arteries of the testis, of the uterus, of the mammae towards 
 the latter period of and after utero-gestation, of the face 
 and temples. The latter instance, perhaps, requires an 
 
Cause of the Tortuomness of certain Veins. 69 
 
 explanation to show its coincidence with the three former. 
 In a child the temporal arteries are straight ; in proportion 
 as life advances they become more and more tortuous ; but 
 as life has advanced, the sources of passion and excitement 
 have multiplied, and the face has flushed and burnt, and 
 the temples have throbbed with an increased flow of blood 
 on countless occasions. Let me endeavour to show in 
 what manner the tortuous form, which arteries acquire in 
 such cases, is consistent with the explanation of local 
 action which I have adopted. 
 
 We may presume that an artery, at the average tone 
 of arteries, would be affected in the same manner by an 
 unusually forcible contraction of the left ventricle, as a 
 relaxed artery under the ordinary pressure of the blood. 
 The former case is easily obtained. It has been already 
 mentioned, that the carotid artery laid bare in the neck 
 of an ass lies without any visible pulse or change, as soon 
 as the animal becomes composed. But if the animal be 
 then alarmed, as by holding its nostrils for a few seconds, 
 the heart acts violently, and the carotid artery leaps from 
 its place, and becomes elongated and tortuous at each 
 stroke of the ventricle. It follows, that if the coats of the 
 same vessel were specially relaxed, a like phenomenon would 
 ensue during the ordinary action of the heart. 
 
 It appears, therefore, that the phenomena of local action, 
 whether in large or in small arteries, may be accounted for, 
 by assuming as their common cause, a spontaneous re- 
 laxation of the coats of these vessels *. But where local 
 action exists, the veins likewise become tortuous. To what 
 principle is this change to be referred ? 
 
 It is not likely that veins are irritable; the effect of 
 their valves, which act by their mechanical adjustment 
 to a given area, would be defeated were that area readily 
 capable of enlargement. 
 
 What are termed varicose veins are tortuous and dilated 
 veins. They are frequently observed below the integu- 
 ments of the thigh and leg. No doubt is entertained 
 
 * I am aware of the solecism of calling that process local action, 
 which I represent as depending upon relaxation. 
 
70 Influence of Gravity on the Circulation. 
 
 that the veins of the leg often become varicose through 
 the pressure of the column of blood in the descending 
 cava, which by a gradual process of dilatation renders each 
 pair of valves in succession useless. The same pressure, 
 which gradually dilates the veins, naturally tends to elon- 
 gate them. Pressure, then, upon the inner surface of a 
 vein, tends to enlarge and elongate it. 
 
 Varicose veins of the legs are again produced by liga- 
 tures tied below the knee ; the superficial veins are in this 
 instance observed to be continually swollen, and gradually 
 to become tortuous, ' as if knotted. The swollen state of 
 the veins shows the internal pressure to which they are 
 subjected : but this internal pressure is the force of the 
 blood propelled from the left ventricle. 
 
 Now by my hypothesis, the blood during local action 
 would arrive in the veins through larger channels than 
 before ; its force therefore would be less broken ; its pres- 
 sure would be increased upon the veins. But increased 
 pressure upon the inner surface of the veins has just been 
 shown to enlarge and elongate them ; and thus the state 
 of the veins in parts subject to local action tends to sup- 
 port the theory which I have advanced. 
 
 Blood is not returned to the heart so readily from a 
 dependent part, as from parts whence it has to descend. 
 The circulation in the lower extremities always appears 
 more sluggish than in the upper part of the body. If the 
 hand be held up, it becomes whiter and less in bulk ; if 
 it hang down, it becomes swollen and darker. In the one 
 case the weight of the blood favours its return by the veins 
 to the heart ; in the other case its weight is opposed to its 
 ascent along the veins. The veins of the lower extremities 
 have coats as thick as those of arteries : the arteries are 
 perfectly straight, in order that there may be no unneces- 
 sary waste of the impulse derived from the heart. 
 
 The arteries distributed to the human brain are four 
 in number, the two internal carotids and the two ver- 
 tebrals. The brain is an organ of so slight and delicate 
 a texture, as to suffer more readily than any other from 
 an unusual force of the blood in the arteries, or from its 
 
Of the Circulation in the Brain. 71 
 
 accumulation in the veins. Accordingly in some animals, 
 as for instance in the common ox, the internal carotid 
 artery, upon entering the skull, divides into many 
 branches, which subsequently re-unite and form a trunk, 
 in which the force of the blood must be greatly diminished. 
 This contrivance is termed the rete mirabile. In human 
 beings another provision is employed for the same purpose : 
 each of the four arteries of the brain is bent twice at an 
 abrupt curve just before or after entering the cranium : and 
 as a proof how sufficient this contrivance must be to break 
 the rush of blood upon the brain, the arteries distributed 
 in that viscus are found to have thinner and weaker coats 
 than other arteries of the same calibre. 
 
 Some physiologists confound the original and permanent 
 curvature of the cerebral arteries with the superinduced 
 curvature of the temporals, and suppose the cause and pur- 
 pose of the two phenomena to be the same. The preceding 
 remarks will have led the reader to view these phenomena 
 as utterly and essentially dissimilar. 
 
 The veins of the brain, instead of being collected into large 
 trunks of the ordinary description, open into cylindrical 
 or triangular canals in the dura mater of great strength and 
 thickness which are termed sinuses, and terminate after 
 circuitous routes in the internal jugular vein of either side. 
 The oblique entrance of the veins of the brain into the 
 sinuses, the undilatable nature of the latter, their long 
 and winding course, are circumstances that tend to prevent 
 the reflux of venous blood upon the brain, when its en- 
 trance into the chest is impeded. 
 
;f CHAPTER V. 
 
 OF THE PULMONARY CIRCULATION. 
 
 THE blood probably suffers some alteration at every instant 
 in every part of the vascular system: but the principal 
 changes which it undergoes appear to take place in the ca- 
 pillary vessels. 
 
 In the human body there essentially exist two sets of 
 capillary vessels, the one interposed between the pulmonary 
 artery and the pulmonary veins, the other between the 
 branches of the aorta and the veins which return blood 
 to the right side of the heart. 
 
 Each lung is a tissue of air-cells, with which the wind- 
 pipe communicates in a manner already described, and upon 
 which the capillaries of the pulmonary artery ramify. 
 
 If a lung be inflated and dried, its substance when di- 
 vided, independently of the arteries and veins cut through, 
 appears uniformly porous. The larger pores appear sec- 
 tions of tubes, the lesser are shallow cups, being segments 
 of air-cells. The air-cells are smaller, as M. Magendie 
 observed, in infants than in adults, in adults than in persons 
 advanced in age. In the lungs from a body about five 
 years of age, I found the air-cells vary in size, but on an 
 average to be -r^- of an inch in diameter, and to be nearly 
 circular. In the lungs from a body about fifty years of 
 age, their form seemed not to be as regular or uniform as in 
 the preceding instance : their diameter varied from -gV to ^v 
 of an inch. The extent of the internal sflirface of the lungs 
 is less in proportion as the air-cells are larger. 
 
 The pulmonary artery divides into a branch to each lung, 
 which subdivides into branches for each lobe, and for each 
 lobule. These vessels are accompanied by similar ramifica- 
 tions of the pulmonary veins. In the root of each lung the 
 
Cause of the Entrance of Air into the Lungs. 73 
 
 artery extends transversely outwards, the veins being situ- 
 ated before and below it. The bronchus descends obliquely 
 behind the blood-vessels. If coloured water be thrown into 
 the pulmonary artery, it passes into the pulmonary veins, 
 but in part escapes into the air passages. 
 
 Each lung receives for its nourishment two or three vessels 
 from the aorta, termed bronchial arteries, which are distri- 
 buted with the bronchi. The pulmonary nerves are princi- 
 pally derived from the nervi vagi, which pass behind the 
 root of each lung, and throw a plexus of branches round it : 
 their final distribution has not been traced. The lymphatic 
 vessels from the substance and superficies of the lungs are 
 received into a vast number of conglobate glands disposed 
 around the bronchi and the bifurcation of the trachea. They 
 are remarkable for the black colour, which' they begin to 
 assume in childhood, and which increases though not uni- 
 formly with ag;e. The lung itself, of a pink colour in infancy, 
 gradually becomes in like manner mottled with black. The 
 experiments of Dr. Pearson on the nature of the colouring 
 matter in these instances seem to prove that it is carbona- 
 ceous*. 
 
 Through the windpipe atmospheric air finds its way into 
 the cells of the lungs : it is first inhaled the instant after 
 birth, and is continually changed and replaced by fresh 
 draughts through the operation of muscles, which alternately 
 expand and contract the cavity of the chest, as long as life 
 remains. If the lungs were inextensible and of a sufficiently 
 firm texture, and the muscles which enlarge the chest were 
 to act with unlimited force, no air would enter the lungs at 
 each attempt to inspire, but a vacuum would be formed be- 
 tween the pleura pulmonalis and pleura reflexa. As, how- 
 ever, the lungs are readily extensible, atmospheric air rushes 
 into and dilates their cells in exact proportion to the expan- 
 sion of the area of the chest, and holds the two surfaces of 
 the serous membrane in strict contact: yet the same 
 points are not always in apposition : when the chest enlarges, 
 the surface of the lung during its expansion slides upon the 
 
 * Phil. Trans, vol. ciii, p. 166. 
 
74 Different Degrees of Inspiration, 
 
 pleura reflexa, as is shown by the elongation of the shreds 
 of lymph by which the two layers of pleura are often found 
 joined together after inflammation. 
 
 The passage of air into the lungs is so free, that the 
 muscles which dilate the chest are not opposed by the atmo- 
 spheric pressure in a greater degree than those which move 
 the limbs ; but they have to overcome the resiliency of the 
 lungs, the elasticity of the abdominal parietes, and the resist- 
 ance of the joints of the ribs, which all favour the state of 
 expiration. 
 
 The term breathing, or respiration is employed to signify 
 both the mechanical operation of renewing the air within 
 the lungs, and the changes to which its presence there con- 
 tributes. 
 
 The mechanism, by which the chest admits of being alter- 
 nately enlarged and diminished, has already been described : 
 every provision which it contains is employed in a greater 
 or less degree at every repetition of breathing. The dif- 
 ference between a moderate and a deep inspiration is in the 
 extent only to which the diaphragm and the muscles that 
 elevate the ribs contract. But it may be observed, that for 
 the fullest enlargement of the chest, the scapula and clavicle 
 are raised and carried backward by the trapezius, levator 
 scapulse, and rhomboid muscles, so as to give greater effect 
 to the action of the serratus magnus and pectoralis minor ; 
 and that to yield a freer passage to the air, the nostrils are 
 dilated, the larynx descends, and the rima glottidis is 
 enlarged : during each strong expiration the rima glottidis 
 is narrowed. Ordinary breathing takes place between the 
 limits of forced inspiration on the one hand, and forced ex- 
 piration on the other. 
 
 Numerous experiments have been made to ascertain the 
 quantity of air alternately drawn into and thrown out of the 
 chest, in ordinary breathing. Those of Dr. Menzies, which 
 coincide nearly in their result with the researches of Jurin 
 and Fontana, are commonly esteemed deserving of credit ; 
 but they differ remarkably from the observations of 
 Sir H. Davy and of Messrs. Allen and Pepys. Differences 
 in the relative size of the thorax in different persons, a dif- 
 
Volume of Air inhaled at a single Inspiration. 75 
 
 ference in the frequency with which breathing is performed, 
 and perhaps other causes, may have combined to produce 
 this discrepancy. The frequency of respiration ranges be- 
 tween fourteen and twenty-seven times in a minute, but 
 is commonly from seventeen to twenty. 
 
 Dr. Menzies employed two processes in estimating the 
 quantity of an ordinary inspiration. A healthy man five feet 
 eight inches in height, and somewhat more than three feet 
 about the chest, stood immersed in warm water to above his 
 breast, in a vessel which narrowing at the upper part allowed 
 an accurate estimate to be made of the level to which the 
 water alternately rose and fell while he breathed. His pulse, 
 both before and after immersion, beat sixty-four or sixty- 
 five times, and his respirations were fourteen or fourteen and 
 a half in the space of a minute ; and they continued the 
 same during two hours and upwards that he remained in 
 the vessel without suffering inconvenience. The quantity 
 of air thrown out at each expiration averaged at 46.76 cubic 
 inches. The same person afterwards was employed to fill a 
 cow's allantoid, a membranous sac well calculated for such 
 a purpose, by repeated expirations. The allantoid was 
 found to contain 2700 cubic inches of air, and was filled in 
 many trials with fifty-eight expirations, which gives 46.55 
 cubic inches as the quantity of air expired each time. The 
 same trials repeated upon a man five feet and an inch in 
 height, whose pulse beat seventy-two, and the number of 
 whose respirations was eighteen in a minute, gave from 
 thirty -eight to forty cubic inches as the measure of a com- 
 mon expiration. Repeating the experiment himself, Dr. Men- 
 zies filled an allantoid containing 2400 cubic inches by 
 about fifty-six expirations, giving 42.8 cubic inches as the 
 average quantity of each ; and found that he exhausted the 
 allantoid, when previously filled with atmospheric air, by an 
 equal number of inspirations *. Sir H. Davy estimates the 
 quantity of a single inspiration at thirteen or seventeen cubic 
 inches : Messrs. Allen and Pepys at sixteen and a half; 
 Mr. Kite at seventeen ; Mr. Abernethy at twelve. 
 
 Dr. Menzies observed that many individuals were capable 
 
 * Menzies on Respiration, p. 21 et seq. 
 
76 Average Quantity of Air contained in the Lungs. 
 
 by a forced expiration of throwing out an additional seventy 
 cubic inches ; and that the difference between an extreme 
 inspiration and an extreme expiration often exceeded two 
 hundred cubic inches. The lungs after death under ordi- 
 nary circumstances are probably reduced to the same com- 
 pass as by a forced expiration during life. Messrs. Allen 
 and Pepys found that the lungs of a stout man about five 
 feet eight inches high after death contained nearly one 
 hundred cubic inches of air. Of this quantity 31.58 cubic 
 inches were expelled by the resilience of the lungs upon 
 opening the thorax*.- 
 
 Dr. Bostock estimates the quantity of air, which may be 
 voluntarily expelled fron the lungs after an ordinary expira- 
 tion, at 160 or 170 cubic inches, from trials made upon him- 
 self and others. Adding to this quantity 120 cubic inches 
 for the residual air in the lungs, he supposes 290 cubic 
 inches to be the entire contents of the lungs in their natural 
 state, to which about forty cubic inches more are added by 
 an ordinary inspiration. According to this calculation, 
 one-eighth of the whole contents of the lungs is changed by 
 each respiration f. 
 
 Atmospheric air consists of seventy-nine parts of nitrogen 
 and twenty-one of oxygen, A small proportion of both ele- 
 ments, which has been variously estimated J, is found to 
 have disappeared at each expiration : but this phenomenon 
 loses interest when compared with the curious circumstance, 
 that a disproportionate quantity of oxygen has disappeared, 
 and has been nearly or completely replaced by carbonic 
 acid. In the elaborate experiments of Messrs. Allen and 
 Pepys, from 8 to 8.5 per cent, of carbonic acid were ob- 
 served to be produced by each respiration. When the 
 breathing was more rapid than usual, a larger quantity of 
 carbonic acid was emitted in a given time, but the propor- 
 tion at each expiration remained the same. The proportions 
 of carbonic acid in the first and last portions emitted after 
 a deep inspiration differed as widely as from 3.5 to 9.5 
 per cent. On an average it appeared that about 27.5 cubic 
 
 * Phil. Trans, vol xcix, p. 411. 
 
 f Bostock's Elements of Physiology, vol. ii, p. 34. 
 
 J By Sir H Davy at T V to -rfo. Researches, &c. p. 431. 
 
Changes produced in Atmospheric Air by Breathing. 77 
 
 inches of carbonic acid are produced per minute, or 39534 
 in twenty-four hours ; a quantity which contains about 
 eleven ounces troy of solid carbon *. 
 
 If a series of experiments conducted with great skill and 
 caution, and leading to a theory the most simple, were suf- 
 ficient to decide a question in physiology, the researches 
 of Messrs. Allen and Pepys would set at rest every doubt 
 respecting the changes produced in the air and upon the 
 blood in breathing. They go to establish the facts, that 
 in respiration the nitrogen of atmospheric air remains un- 
 altered, and that the carbonic acid produced exactly equals 
 the volume of oxygen which disappears. But by former 
 experiments Messrs. Allen and Pepys had ascertained, that 
 in the formation of a given volume of carbonic acid during 
 combustion an equal volume of oxygen is consumed : and it 
 is admitted that the change wrought upon the blood in the 
 pulmonary circulation is apparently no more than might re- 
 sult from the abstraction of carbon. Thus the essential 
 phenomena of respiration appear contained in, or consistent 
 with, the simple expression, that the carbon of the blood 
 unites in the lungs with the oxygen of the atmosphere to 
 form carbonic acid. 
 
 Facts are not wanting to illustrate every step of the 
 process. Plants as well as animals deteriorate atmospheric 
 air by substituting carbonic acid for oxygen ; and it has been 
 proved by the experiments of M. Huber and of Mr. Ellis, 
 that when a plant growing in a closed vessel has consumed 
 all the oxygen of the atmospheric air which it contained, 
 the nitrogen, which remains undiminished in quantity, be- 
 comes carburetted ; as if carbon spontaneously separated 
 from the living body in a form fitted to combine with either 
 element of the atmosphere, and in the absence of oxygen 
 might for a time continue to be eliminated and to unite with 
 another principle. 
 
 But it is evident that the preceding theory rests upon the 
 position that the carbonic acid produced in breathing ex- 
 actly equals the volume of oxygen lost. Now although this 
 
 * Phil. Trans, vol. xeviii, p. 277. 
 F 
 
78 Changes produced in Atmospheric Air by Breathing. 
 
 position be supported by the able researches of Messrs. Allen 
 and Pepys, and has been advocated by Mr. Ellis, M. Magen- 
 die, and others, it cannot be admitted to be universally true. 
 
 In the experiments of Lavoisier and Seguin, the propor- 
 tion of oxygen consumed exceeded that necessary for the 
 production of carbonic acid in the ratio of about 100 to 81.5; 
 a result which exactly coincides with the observations of 
 Sir H. Davy. In the recent experiments of Dr. Edwards, in 
 which small animals were immersed for a definite period in 
 large quantities of air, the general fact of the surplus quan- 
 tity of oxygen lost is. abundantly proved : at the same time 
 the apparently conflicting opinions of preceding physiolo- 
 gists are reconciled by the essential variableness of the re- 
 sults, which the experiments alluded to exhibit. Dr. Ed- 
 wards's general conclusion is, that the excess of oxygen 
 consumed in breathing above the volume of carbonic acid 
 produced, varies from nearly one-third of the oxygen that 
 disappears to almost nothing; that the variation depends 
 upon the species of the animal employed, upon its age, or 
 some peculiarity in its constitution ; and also that it varies 
 considerably in the same individual at different times *. 
 
 Upon these grounds we must adopt a different theory of 
 respiration. Part of the oxygen that disappears we must 
 suppose to be absorbed in the lungs, and the rest may com- 
 bine with the carbon of the blood to form carbonic acid ; or 
 the whole may be absorbed, and the expired carbonic acid 
 may be a new secretion. Dr. Edwards adopts the latter 
 opinion, and supports it by the following curious facts. If 
 frogs during the month of March are confined for the period 
 of eight hours in pure hydrogen after the previous exhaus- 
 tion of their lungs by pressure, they continue to breathe, 
 although less and less vigorously, till near the close of the 
 experiment, during which a volume of carbonic acid nearly 
 
 * De Plnfluence des Agens Physiques, &c., p. 418. See likewise 
 Dr. Bostock's remarks upon this subject ; Elements of Physiology, vol. 
 ii, p. 97 and 110. He concludes that a man under ordinary circum- 
 stances consumes about 45000 cubic inches of oxygen, and produces 
 about 40000 cubic inches of carbonic acid in the space of twenty-four 
 hours. 
 
Absorption and Production of Nitrogen. 79 
 
 equal to the bulk of the animal employed is given out. A 
 similar result ensued in experiments upon kittens. The 
 young of many species of warm-blooded animals can exist for 
 some time after birth without the contact of air : after two 
 or three minutes, voluntary motion ceases : but from time 
 to time deep inspirations are drawn, accompanied with yawn- 
 ings and movements of the whole trunk. A kitten three or 
 four days old was placed in a receiver containing pure hy- 
 drogen, and performed in nineteen minutes about as many 
 inspirations. Upon examining the air in which the animal 
 had been immersed, it was found to contain twelve times as 
 much carbonic acid as could be accounted for by the resi- 
 dual air in the lungs at the beginning of the experiment*. 
 
 We are, however, far from having attained conclusions 
 that are perfectly satisfactory upon this subject. The fol- 
 lowing is one of several anomalous facts, which are incon- 
 sistent with any received theory of respiration. 
 
 Dr. Edwards found, that the quantity of carbonic acid, 
 produced by frogs breathing in hydrogen during eight hours, 
 is equal to that furnished in twenty- four hours by frogs im- 
 mersed in atmospheric air : a curious result, which seems to 
 show that the principles of the atmospheric air have pos- 
 sibly no influence, direct or indirect, upon the separation of 
 carbonic acid. 
 
 The experiments of Dr. Edwards have thrown light upon 
 another question, upon which opposite opinions have been 
 entertained. M. Cuvier and Sir H. Davy have maintained 
 that a portion of nitrogen is absorbed during respiration. 
 Jurine, on the contrary, was induced to conclude, from the 
 results of his experiments, that nitrogen is generated by 
 respiration : and similar results were obtained by Berthollet 
 and Nystenf. Dr. Edwards found, by immersing small 
 animals in a large quantity of air for a limited period, that 
 in many instances there was an evident increase in the 
 quantity of nitrogea, while in, others there was a loss of 
 it. He observed, that the former change took place when 
 the experiment was performed in spring and summer, or 
 
 * De 1'Influence, &c., p. 456 et seq. 
 f Bostock, 1. c. p. 105. 
 
 F 2 
 
80 Respiration of other Gases than Atmospheric Air. 
 
 when young animals were employed, while the latter re- 
 sult was obtained when the circumstances of the experiment 
 were reversed. 
 
 The production of carbonic acid varies in the same person 
 at different times : Lavoisier found it greatly increased by 
 exercise and during digestion : Dr. Prout observed it to be 
 increased and diminished periodically. The maximum, es- 
 timated as equal to 4.1 per cent, of the oxygen inspired, 
 occurred about noon : the minimum, equal to 3.3 per cent., 
 occurred towards eight in the evening ; from which time till 
 half past three in the morning there was no change. 
 
 Atmospheric air is probably the only gas which can be 
 breathed for an indefinite period with impunity. But other 
 gases, as a mixture of oxygen with hydrogen in the propor- 
 tions of atmospheric air, or nitrous oxide, or oxygen, may 
 be breathed for a time without producing mischief. When 
 oxygen nearly pure is breathed, the air expired, according 
 to Messrs. Allen and Pepys, contains above 10 per cent, of 
 carbonic acid : a proportion of nitrogen likewise makes its 
 appearance in the room of an equal bulk of oxygen. In 
 some recent experiments by Mr. Broughton the proportion 
 of carbonic acid formed by animals immersed in jars of oxy- 
 gen appeared to be smaller. At the same time some very 
 interesting observations were made upon the poisonous 
 efiects of the long continued breathing of this gas. After 
 a period extending from one hour to four or five, rabbits 
 and young cats and dogs began to breathe quick and pant, 
 the heart acting violently. They then fell into a state of 
 debility, and became insensible : the diaphragm then gra- 
 dually ceased to act : but the heart continued to act 
 strongly for some time afterwards. Some of the stronger 
 animals, after having become insensible, recovered when 
 restored to the atmosphere. In those which were opened, 
 the blood was found equally bright and crimson everywhere, 
 in the veins, the heart, the arteries. 
 
 Other gases, as carburetted hydrogen, sulphuretted hy- 
 drogen, carbonic oxide, and perhaps nitrous gas, when 
 breathed occasion death immediately ; but at the same time 
 they produce certain changes in the blood, and therefore kill 
 
Pulmonary Exhalation and Absorption. 81 
 
 not merely by depriving the animal of air, but by their spe- 
 cific properties *. 
 
 Other gases again, hydrogen namely, and nitrogen, occa- 
 sion death when breathed, simply by depriving the animal 
 of atmospheric air. 
 
 The preceding sorts of gases have been termed respirable, 
 inasmuch as they admit of being drawn into the lungs. 
 One other kind still remains, which is termed irrespirable. 
 Carbonic acid, and possibly acid and alkaline gases in ge- 
 neral, are of this description. The instant that a draught 
 of carbonic acid comes in contact with the aperture of the 
 glottis, the latter is spasmodically closed, so that the at- 
 tempt to inspire is ineffectual. The same thing happens 
 when an animal is drowned in water or in quicksilver ; and 
 in each case the lungs are found emptied to an extraordi- 
 nary degree, by the expirations which the animal makes be- 
 fore each renewed and fruitless effort to inspire. 
 
 The air thrown out of the chest in ordinary breathing 
 contains an aqueous vapour, or carries off by evaporation 
 the liquid which lubricates the inner surface of the air-cells 
 and bronchi, of the trachea, the larynx, and the fauces. 
 According to Dr. Hales, the quantity of fluid from this 
 source amounts to about twenty ounces in the twenty-four 
 hours : according to Dr. Menzies, to six ounces : according 
 to Mr. Abernethy, to nine ounces : according to Dr. Thom- 
 son, to nineteen ounces. M. Magendie has ascertained 
 that a large proportion of this vapour is derived from the 
 membrane lining the mouth and fauces, and mentions that 
 its quality is readily modified by changes in the state of the 
 blood. If odorous substances be placed in a serous cavity 
 or injected into a vein, the breath acquires their odour. If 
 a solution of phosphorus in oil be thrown into the veins of 
 a dog, its expirations are luminous in the dark, and in the 
 light appear loaded with a thick white vapour, which con- 
 sists of phosphoric acidf. 
 
 The fine membranous texture of the lungs, which appears 
 to allow an instantaneous passage to the gaseous fluids that 
 
 * Thomson's Chemistry, vol. iv, p. 602. 
 
 t Magendie, El&nens de Phys. tome ii, p. 348. 
 
 
82 Liftuence of the Phrenic Nerves in Breathing. 
 
 are absorbed by or separated from the blood, is readily per- 
 meated by the substances which the air holds in solution. 
 Thus the vapour of turpentine, when inhaled, finds its way 
 into the blood, the urine acquiring in a short time that smell 
 of violets, which characterizes the absorption of turpentine. 
 Thus the fumes of tobacco find entrance into the system : 
 and by the same channel are perhaps admitted those mias- 
 mata, which are of so delicate a nature, that their exist- 
 ence is detected only by the influence which they exert 
 upon the human frame. 
 
 Respiration has a remarkable consent with the action of 
 the heart. When the pulse is frequent, the breathing is 
 hurried ; when the pulse is slow and gentle, respiration is 
 scarcely to be observed : when, for experiment's sake, we 
 breathe more frequently than usual, the pulse becomes 
 more frequent ; when the breathing falls back to its usual 
 rate, the heart's action again gradually subsides. . The 
 means by which this consent is established are unknown. 
 
 Respiration is remarkably modified by different affections 
 of the mind. In some states of highly-wrought emotion 
 the breathing is hurried and difficult ; at the same time the 
 voice is observed to fail. Perhaps both phenomena result 
 from the spasmodic action of the muscles which close the 
 glottis. After violent bodily exertion breathing is more fre- 
 quent and the inspirations are deeper. 
 
 Each act of inspiration requires a special impression 
 through the nerves upon the muscles which dilate the chest. 
 When the spinal chord is divided without violence above 
 the origin of the phrenic nerves, respiration ceases at once, 
 while the heart's action continues without undergoing any 
 immediate change. When the phrenic nerve is irritated in 
 an animal immediately after death, the diaphragm acts. 
 When the phrenic nerves are divided in a living animal, the 
 diaphragm is in great measure paralyzed ; but respiration 
 continues through the alternate action of the muscles which 
 raise and depress the ribs. Respiration is always performed 
 with a conscious effort during our waking hours ; but we 
 seem not to regulate the frequency of its recurrence or its 
 limits : nevertheless, we can at will enlarge or diminish the 
 
Influence of the Nervi Vagi. 83 
 
 area of the chest, and stop, accelerate, or retard the act of 
 respiration. When we attend to our breathing, or regulate 
 its rate, it quickly becomes fatiguing ; but the same hap- 
 pens with any voluntary and habitual action, if we attempt 
 to perform it analytically by directing the attention to every 
 step in its progress. 
 
 The influence of the nervi vagi on breathing is imperfectly 
 understood. In general, when these nerves are divided 
 about the middle of the neck, respiration immediately be- 
 comes laboured, or hurried and irregular, and the animal 
 dies in a few hours. This speedy death probably ensues in 
 consequence of the muscles, which tend to open the passage 
 of the glottis, being paralysed by the experiment, while the 
 opposite class remains unaffected by the division of the 
 nerves. In an ass in which laboured breathing was pro- 
 duced by cutting through the par vagum, I found the re- 
 spiration become easy and natural upon opening the trachea ; 
 it continued so for three hours, beyond which the existence 
 of the animal was not prolonged. In a dog in which the 
 par vagum was divided in the neck, the animal survived 
 three days : there was dyspnoea with frequent vomiting, 
 and the stomach was found to have become inflamed. Ac- 
 cording to the observations of Mr. Brodie, after the division 
 of the par vagum a less quantity of carbonic acid is evolved, 
 the respirations are much diminished in frequency, and the 
 blood in the arteries assumes a darker hue ; but its natural 
 colour may be restored by artificially inflating the lungs *. 
 Dr. W. Philip mentions that the dyspnoea produced ill dogs 
 and rabbits by the division of the par vagum in the neck, 
 may be relieved by the continued application of galvanism 
 to the chest : the animals nevertheless die : but the surface 
 of the lungs, though reddened generally, appeared to 
 Dr. Philip in this experiment not to show the patches of 
 red, nor the bronchial cells the quantity of frothy mucus, 
 usually observed after the division of the nervi vagi. 
 
 * Phil. Trans, vol. cii, p. 390, 
 
CHAPTER VI. 
 OF THE CIRCULATION THROUGH THE BODY. 
 
 ALL the phenomena of the circulation, which we have 
 hitherto considered, may be viewed as preparatory to orie 
 important object, the transmission of arterial blood 
 through the capillary vessels of the aortic system, in which 
 it conduces immediately to the support of life. It is here 
 that the blood becomes deteriorated ; when having lost its 
 florid hue and become venous, it has to toil back to the 
 heart and through the lungs to re-acquire its vivifying pro- 
 perties. 
 
 The phenomena dependent upon the circulation through 
 the body, may be classed under the heads of excitement, 
 secretion, the distribution of heat, and absorption. 
 
 I. The functions of the nervous and muscular systems 
 appear to flag if arterial blood be not propelled in adequate 
 quantity and with sufficient force through their capillary 
 vessels ; and although the term excitement may be an im- 
 proper term to denote the influence which the blood in this 
 instance exerts, and which may be but a part of nutrition, 
 yet the phenomena are so remarkable as well to merit sepa- 
 rate consideration. Perhaps they are of the same nature 
 with the following circumstance observed by Dr. Edwards. 
 When frogs are deprived of their hearts, they continue for a 
 time to exhibit voluntary motion ; if they are plunged in 
 water, however, they quickly lose all appearance of life, and 
 remain motionless and insensible under mechanical lesion ; 
 but upon withdrawing them from the water as soon as they 
 have fallen into this state, they revive and move sponta- 
 neously. The exciting or invigorating influence of the at- 
 
Of Fainting. 85 
 
 mosphere in this case may serve to illustrate the action of 
 arterial blood upon the organs of warm-blooded animals*. 
 
 1. When from hemorrhage, or from feebleness of the 
 heart's action, arterial blood is thrown with less force and 
 in less volume than usual upon the brain, fainting is ushered 
 in by sensations of languor and feebleness, the ears ring, 
 giddiness ensues, consciousness is lost. If in such a case 
 the nervous system be excited by ammonia held to the nos- 
 trils, the heart beats more vigorously ; and if the patient be 
 laid in a horizontal posture, the flow of arterial blood to the 
 brain is facilitated : by these means the conditions which 
 produce syncope are removed, and the fainting person re- 
 vives. It deserves to be remarked, that continued faintness 
 after hemorrhage is to be encouraged as a salutary provision 
 in cases where we cannot directly command the flow of 
 blood ; while faintness lasts, the tendency of the blood to 
 coagulate is considerably increased, upon the effects of 
 which the prevention of a return of hemorrhage greatly 
 depends. By repeated or profuse hemorrhage, an exsangui- 
 nated condition of the body is produced, with alarming 
 debility, which perhaps authorize, as Dr. Blundell has re- 
 cently pointed out, the transfusion of blood in such cases 
 from the veins of a healthy person. The original experi- 
 ment of Lower, performed about the year 1660, consisted 
 in connecting by means of a tube an artery of one animal 
 with the vein of another ; in one instance a healthy man 
 thus received into his system about nine ounces of the blood 
 of a young sheep without suffering from it: but subse- 
 quently the operation being employed medicinally met with 
 some notable failures and fell into disrepute. Dr. Blundell 
 has made it appear that the transfusion of blood in animals 
 of different species may be fatal ; but has shown that in 
 animals of the same species, if the operation be performed 
 with sufficient adroitness and celerity, the blood may be 
 successfully transferred by means of a syringe f. 
 
 * De 1 'Influence, &c., p. 7. 
 
 t Medico-Chirurgical Trans, vol. ix, p. 50 j and vol. x, p. 269. 
 
86 Of Asphyxia. 
 
 2. When any cause prevents the introduction of atmo- 
 spheric air or of air containing oxygen into the lungs, the 
 blood is returned unchanged to the left side of the heart, 
 venous instead of arterial blood is thrown into the brain, 
 and consciousness is suspended. This state is termed as- 
 phyxia ; the feelings with which it commences were ascer- 
 tained by Pilatre de Rosier, who placed himself in irrespi- 
 rable air by entering into a brewer's tub while full of car- 
 bonic acid evolved by fermentation. A gentle heat mani- 
 fested itself in all parts of his body, and occasioned a 
 sensible perspiration. A slight itching sensation constrained 
 him frequently to shut his eyes. When he attempted to 
 breathe, a violent feeling of suffocation prevented him. He 
 sought for the steps to get out, but not finding them readily, 
 the necessity of breathing increased, he became giddy, and 
 felt a tingling sensation in his ears. As soon as his mouth 
 reached the air, he Breathed freely, but for some time he 
 could not distinguish objects ; his face was purple, his limbs 
 were weak, and he understood with difficulty what was 
 said to him. But these symptoms soon left him. He 
 repeated the experiment often, and always found that as 
 long as he continued without breathing, he could speak and 
 move about without inconvenience ; but whenever he at- 
 tempted to breathe, the sensation of suffocation came on*. 
 
 Symptoms very similar appear to have been produced in 
 one experiment of Messrs. Allen and Pepys, when the same 
 three hundred cubic inches of atmospheric air were passed 
 and repassed from eight to ten times through the lungs : 
 the operator became insensible. It deserves remark, that 
 the air which had been employed was found to have gained 
 only ten per cent, of carbonic acid ; so that life, it appears, 
 would probably be lost before the entire consumption of the 
 air of a confined space. Lavoisier found, however, that by 
 repeatedly withdrawing an animal and reviving it, it might 
 be made to consume nearly all the oxygen of a given quan- 
 tity of atmospheric air before death. Otherwise birds die 
 
 * Journal de Phys. xxviii, p. 418. 
 
Effects of breathing Nitrous Oxide. 87 
 
 before two-thirds, and mice and Guinea pigs before three- 
 fourths of the oxygen of the air are destroyed. 
 
 When the influence of causes which produce asphyxia is 
 prolonged, the face becomes bloated and livid, the efforts at 
 respiration cease, and the heart's action gradually fails. 
 The first attempt to be instantaneously made in such a case 
 is to inflate the lungs, either with fresh atmospheric air 
 blown with bellows into the nostril, or with air thrown 
 from the lungs of an assistant into those of the asphyxi- 
 ated person. The body as a general rule should be kept 
 warm ; but in cases from the burning of charcoal, the ap- 
 plication of cold is said to be useful. 
 
 The period is not determined at which the power of re- 
 suscitation is lost after breathing has been wholly prevented : 
 it probably does not much exceed four or five minutes : 
 about this time life may be considered irrecoverably gone, 
 not merely in consequence of the continued suspension of 
 the energy of the brain, but because the heart appears to 
 lose its irritability when florid blood is not circulating in its 
 vessels. The experiments of Mr. Brodie and of Dr. Wilson 
 Philip, which have been already mentioned, show that after 
 the removal of the brain and spinal chord the heart will 
 continue to act for a length of time, if by means of an arti- 
 ficial respiration it continues to receive florid blood ; but if 
 this excitement be withheld, the tendency of the heart to 
 alternate action and relaxation quickly ceases. 
 
 3. When nitrous oxide is breathed, although it is uncer- 
 tain in what degree and by what means the nature of the 
 blood is modified, yet its effects upon the brain are remarka- 
 ble, and illustrate in a different manner the stimulating 
 effect of the blood. In this instance its power of excitation 
 is increased ; and phenomena occur resembling considerably 
 those of intoxication ; a degree of vertigo is experienced ; 
 the spirits are exhilarated ; the muscular force appears in- 
 creased, and a tendency to violent bodily exertion ensues. 
 When a mixture of oxygen with hydrogen is breathed, a 
 sedative effect appears to be produced. On breathing 
 oxygen nearly pure for a short time, a general glow over 
 
88 Effects of Air, #c. injected into the Veins. 
 
 the body, with gentle perspiration and quickened pulse, has 
 been observed to take place. 
 
 4. When warm water is injected into the veins of an 
 animal after an equal quantity of blood has been drawn 
 from its body, the animal becomes enfeebled, and its nervous 
 energy diminished. Magendie found the excitement of 
 rabies temporarily subdued by this means. 
 
 5. If air be thrown into the jugular vein of an animal 
 suddenly and in large quantity, a peculiar sound is heard in 
 the chest; the animal utters cries expressive of suffering 
 and quickly perishes. If air, however, be introduced gra- 
 dually into the veins, it frequently happens that no symptom 
 follows. The fatal effects of air becoming mixed with the 
 blood suggests a caution in reference to operations in the 
 neck, by which the external jugular vein may be opened. 
 It has happened in such a case that air has been drawn 
 during inspiration through the open vein into the right 
 cavity of the heart; faintness, cold perspiration, with a 
 peculiar noise in the chest, ensued, and the patient expired 
 in a quarter of an hour*. 
 
 Medicinal substances introduced into the blood in small 
 quantities act promptly and violently ; they are thus admi- 
 nistered in the veterinary college at Copenhagen. Oily and 
 viscid substances introduced into the blood produce death 
 rapidly, by obstructing the pulmonary capillaries. An 
 American physician, it appears, tried in his own person the 
 injection of a small quantity of castor oil into the blood. 
 Nausea, with a taste of oil in the fauces, an indescribable 
 sensation ascending towards the head, faintness, with spasm 
 of the muscles of the jaws and an imperfect articulation, 
 griping with tenesmus, ensued, and the imprudent experi- 
 mentalist did not regain his health for several weeks f. 
 
 II. From the blood in the capillary vessels of the aorta 
 the various substances of which the body consists, or which 
 are thrown out upon its surfaces, appear to be separated or 
 
 * Magendie, Journal de Physiologic, tome i, p. 193. 
 f Magendie, Ele'mens de Physiologic, tome ii, p. 431. 
 
Of Secretion in general. 89 
 
 secreted*. It is not known whether apertures exist in the 
 capillaries specially organized for this purpose, or whether 
 the different elements transude through an uniformly porous 
 texture. When size and vermilion have been thrown into the 
 aorta so as to inject the whole body, there is found in the 
 serous cavities a quantity of colourless size, which must have 
 been strained through very minute orifices, and is supposed to 
 illustrate the mechanism of secretion. But in truth we know 
 very little respecting the intimate nature of this phenomenon. 
 Nor does it much aid our inquiries to classify its products 
 according to their chemical relations : but it is interesting 
 to remark, that although the elements of one secreted sub- 
 stance are readily distinguishable in the blood, while those 
 of another have properties totally unlike that fluid, yet that 
 the quantity of secretion always has reference to the quan- 
 tity of blood circulating in a part : that when the former is 
 increased, as from the mamma after parturition, the arteries 
 of the part are enlarged : and conversely, that in order to 
 check the increase of a vascular tumour, it has occasionally 
 been found sufficient to tie the main artery leading to it. 
 
 Secretion furnishes products that are of two kinds ; those, 
 namely, which belong to the constitution of organs, being 
 either solid or fluid ; and such as are poured out in variable 
 quantities upon the skin or on mucous surfaces, from which 
 they are mostly mechanically removed before their function 
 is attained. The former are instances of nutritive, the lat- 
 ter of functional secretion. 
 
 * There are probably two exceptions to this statement. The bile 
 appears to be secreted from the capillaries of the vena portae ; and the 
 aqueous vapour of the lungs is perhaps in part supplied from the ca- 
 pillaries of the pulmonary artery. The reader will likewise observe, 
 that in describing secretion and venous absorption in connection with 
 the circulation of the body, 1 ain using an arrangement purely arbitrary, 
 and which 1 adopt only because the instances of pulmonary secretion 
 and absorption are confined to one or two cases. The capillaries of 
 the pulmonary artery imbibe substances that enter the lungs with 
 the air we breathe, as for example the vapour of turpentine; and in 
 the opinion of many physiologists the same vessels continually se- 
 crete carbonic acid. The pulmonary capillaries seem naturally as 
 well fitted for both the functions adverted to, as the aortic capillaries. 
 
90 Of Nutritive Secretion. 
 
 1 . No special organization appears necessary for nutritive 
 secretion, or for the separation from the blood of the ele- 
 ments by which the body grows. Capillary vessels that 
 carry red blood are distributed with considerable minuteness 
 in every organ ; and it is not improbable, reasoning from the 
 phenomena of inflammation, that channels exist yet finer 
 than the diameter of a coloured particle, with the influence 
 of which we are wholly unacquainted. Plants share this 
 function with animals ; and accordingly it seems in great 
 measure independent of the influences peculiar to animal 
 life. The hair and riails are said to grow after death : in a 
 paralyzed limb, growth and the common phenomena of re- 
 production take place. When the fifth pair of nerves had 
 been divided upon the petrous portion of the temporal line 
 in a rabbit, upon breaking off the crown of an incisor 
 tooth, I found the part reproduced as rapidly as in an 
 animal in which the nerves were entire. The human mola 
 is sometimes found to have attained considerable develop- 
 ment without either brain or spinal chord. Dr. Clarke met 
 with a case, in which after the birth of a perfect foetus, 
 another substance was expelled, inclosed in a distinct bag 
 of membranes. The membranes consisted of deciduse, 
 chorion, and amnios, and had a placenta belonging to 
 them, which was attached to the placenta of the per- 
 fect child. The mola itself was about four inches in 
 length and three in breadth, of an oval figure, and at- 
 tached to the placenta by a small and thin funis. There 
 was no vestige of head or neck, no ribs, nor clavicle, nor 
 scapula: it had four projecting parts, of which one bore 
 an imperfect resemblance to the foot of a child. The 
 surface was covered with the common integuments : the 
 soft parts consisted of an homogeneous fleshy texture, but 
 without any regular or distinct arrangement of muscular 
 fibres, and was very vascular throughout : it contained an 
 os innominatum and an os femoris of the natural size at 
 birth, with a tibia and fibula shorter than natural. A por- 
 tion of small intestine with a peritoneal covering and 
 mesentery was found, but no glandular substance. It had 
 neither ^heart nor lungs ; neither brain, spinal marrow, nor 
 
Influences which modify Nutritive Secretion. 91 
 
 nerves. The umbilical cord consisted of an artery and 
 vein. Before the internal structure was examined, the 
 navel-string of the perfect foetus was injected ; from 
 whence the injection passed through both placentae, and 
 then into the substance of the mola*. 
 
 Nevertheless it has been proved, in the instance of one 
 organ of very delicate fabric, that its nutrition is disturbed 
 upon the division of one of the nerves which supply it. 
 M. Magendie found, that when the fifth nerve is divided 
 in the cranial cavity of a rabbit close upon its appa- 
 rent origin, the surface of the eye inflames at its upper 
 part, and the upper segment of the cornea becomes 
 clouded. And what is still more remarkable, as tending to 
 show conjointly with the preceding experiment that the 
 influence of nerves upon nutrition is in part independent 
 of the brain, M. Magendie found that if the fifth nerve be 
 destroyed upon the petrous portion of the temporal bone, 
 where its destruction involves that of the ganglion of Gasser, 
 the entire cornea becomes opaque in twenty-four hours, and 
 the opacity daily increases : on the second day the tunica 
 conjunctiva reddens and secretes pus, and the iris becomes 
 inflamed and covered with lymph; about the eighth day 
 the cornea begins to ulcerate in its centre and at its edges, 
 the eye bursts, and the humours being discharged, wastes 
 and shrinks to a small nodule f. 
 
 The inflammation of the stomach, which ensues upon the 
 division of the par vagum in animals that survive the 
 operation for three or four days, is probably a phenomenon 
 of the same kind as the preceding. 
 
 Nutritive secretion has a strict reference to the physical 
 impressions made upon a part. When any part of the 
 frame happens to be habitually used in an employment 
 requiring an exertion of strength, the muscles of that 
 part become larger, firmer, and more powerful, the bones 
 enlarge, the sinews become stronger. If continued pres- 
 
 * Phil. Trans, vol. Ixxxiii, p. 154. 
 
 t Magendie, Journal de Physiologic, tome iv, p. 302, et 176. 
 
92 Of Functional Secretion. 
 
 sure be made upon a bone, such for instance as is sometimes 
 made upon the lower jaw through the use of instruments in 
 weakness of the spine, an exostosis is liable to rise from 
 the" bone, over which the skin is not tensely extended, but 
 grows so as to form a loose capsule containing it. If the 
 pressure be now discontinued, the tumour wastes and dis- 
 appears. Thus again if a limb be kept absolutely at rest, 
 its different textures are found to waste, becoming dimi- 
 nished in bulk and in strength. Medicines seldom appear 
 directly to affect nutritive secretion ; yet mercury in some 
 instances appears to -act locally in reducing the thickening 
 of parts that has followed inflammation ; liquor potassae 
 taken internally sometimes answers the same purpose ; and 
 iodine has been thought to exert a specific influence in 
 reducing the enlarged thyreoi'd gland. 
 
 2. The saliva, the bile, the urine, the perspiration, are 
 instances of functional secretion. They are liquids which 
 exude upon mucous surfaces, or upon the skin ; they are 
 formed, as occasion requires, in variable quantities, and 
 they are speedily removed from the surfaces on which they 
 are produced for some purpose in the vital ceconomy. 
 Some of these fluids, as for instance the perspiration and 
 the urine, are probably wholly excrementitious : others, as 
 the saliva, are perhaps wholly re-absorbed; a third set, 
 including the bile, seems to partake of both these characters. 
 
 The kind of organ in which functional secretion takes 
 place is greatly diversified. In one instance, as in the skin, 
 an uniform vascular superficies appears to pour out the 
 fluid. In another, as in the stomach of the ostrich, numerous 
 orifices are seen upon a surface, each of which leads into a 
 sac of membrane lying in intricate folds, so as greatly to 
 increase the vascular superficies. The lacuna of the 
 urethra, which are plain shallow pouches of mucous mem- 
 brane, are among the simplest secreting organs of this 
 description. In a third instance, as in the pancreas, a 
 fleshy substance presents itself, consisting of numerous 
 similar and coherent particles, which is termed a conglome- 
 rate gland. From each separate molecule of the gland, one 
 
Influences which modify Functional Secretion. 93 
 
 excretory tube at least issues, the mode of communication 
 of which with the arteries and veins of the part has hitherto 
 eluded satisfactory investigation. In general the excretory 
 tubes of a conglomerate gland coalesce to form a common 
 trunk. Each elementary portion of such a gland resolves 
 itself into blood-vessels and excretory tubes with nerves 
 and lymphatics. Upon the whole, it appears probable that 
 a vascular membrane is all which is requisite for secretion, 
 and that the other contrivances, which have been described, 
 are but methods of conveniently packing a large extent of 
 surface in a small compass. 
 
 Functional secretion is to a remarkable degree influenced 
 through the nerves. Upon one affection of the mind the tears 
 flow, upon a second the urine, upon another the saliva : 
 yet I found upon cutting the nerves of the kidney in a dog, 
 that in half an hour afterwards a quantity of urine had 
 accumulated in the pelvis of the kidney, and in the ureter, 
 which had been tied. In this as in the first kind of secre- 
 tion, physical impressions made upon the secreting organ 
 directly influence the rate of production. Upon the re- 
 moval of the young from its mother the secretion of milk 
 after a short time entirely ceases, in circumstances where 
 the gland would, if the demand for milk had continued, 
 have continued its action for several months. The influence 
 of medicines tells immediately upon functional secretion. 
 Many classes of drugs derive their names from the power 
 which they possess of increasing the flow of saliva, of the 
 urine, and the like ; and their value in therapeutics, from 
 the connection which exists between the rate of any one 
 secretion and the condition of the whole body. Mr. Bro- 
 die ascertained that the secretion of urine does not take 
 place in animals, in which after decapitation the circulation 
 of the blood is sustained by an artificial respiration*. 
 
 Three suppositions present themselves, as to the place 
 in which the secretions are formed : either they may be 
 produced in the blood while circulating in the system at 
 large, and be simply separated through the intervention of 
 
 * Phil. Trans, vol. ci, p. 48. 
 G 
 
94 Heat liberated when the Blood becomes venous. 
 
 secreting organs, or the entire process of secretion may 
 take place in the capillaries in each part, or the elements 
 of the different secretions may spontaneously develop them- 
 selves to a certain extent in the blood at large, yet require 
 the influence of the capillary tubes in the part where they 
 are separated, for their complete elaboration. The princi- 
 pal fact with which we are acquainted upon this subject 
 is the observation of MM. Prevost and Dumas, that after 
 both kidneys have been removed, an animal survives several 
 days, during which the characteristic .element of the urine 
 accumulates in considerable quantity in the blood. 
 
 III. When the resemblance was ascertained between the 
 effects of combustion and of respiration upon atmospheric 
 air, the lungs, which were previously supposed to act in 
 cooling the heart, were invested by physiologists with the 
 office of producing animal heat. The difficulty of account- 
 ing on this supposition for the equal diffusion of warmth 
 throughout the body was evaded by, and served to confirm 
 the beautiful theory of Crawford. By careful experiments 
 Crawford became satisfied that arterial blood has a greater 
 capacity for heat than venous blood, in the ratio of 114.5 
 to 100. The heat therefore liberated in the lungs during 
 the conversion of oxygen into carbonic acid might instantly 
 again become latent, forming an unobserved element of arte- 
 rial blood in its flow through the body ; till at the subsequent 
 conversion of arterial into venous blood in the capillaries, 
 it would become liberated at each point in the system. Nu- 
 merous observations, which have successfully established that 
 the vital heat in different animals, in the same individual, and 
 even in plants, has a close relation to the quantity of oxygen 
 consumed by them, seemed to place the theory of Crawford 
 beyond the reach of innovation. Recent inquiry concurs 
 with former experience upon the point before us. Dr. Ed- 
 wards has ascertained, that young animals consume in pro- 
 portion less oxygen than adults, and have a less power of 
 generating heat; and that young animals differ among 
 each other in the power of producing heat, something in 
 the ratio of the oxygen which they destroy. Where re- 
 spiration is imperfect, as in asthmatic patients, the tempera- 
 
Quantity thus produced comparatively trivial. 95 
 
 ture of the body is lower. Where pure arterial blood does 
 not circulate through the body, as in those in whom a com- 
 munication exists between the right and left cavities of the 
 heart, the temperature is below the usual standard. 
 
 But the experiments of Mr. Brodie have shown the pre- 
 ceding argument to be fallacious, and prove that Crawford 
 must have overrated the difference in the capacities for heat 
 of arterial and venous blood, upon which his theory rested. 
 Two rabbits, as nearly alike as possible, were destroyed by 
 decapitation after securing the vessels in the neck : in one 
 the circulation was kept up by means of an artificial respi- 
 ration ; the other was left untouched in the same room at 
 the same temperature. Of these two dead rabbits the first 
 was observed to cool more rapidly than the second : yet in 
 the first the chemical influence of respiration was perfectly 
 sustained, the blood circulating through the lungs from a 
 dark hue assumed the arterial character, that circulating 
 through the body became venous ; and the air respired was 
 deteriorated exactly as by the breathing of a living rabbit. 
 Nevertheless, heat was not derived in sufficient quantity 
 from this source to make up for the lowering of temperature 
 produced by the fresh draughts of cool air into the lungs of 
 the dead animal : the thermometer at the expiration of 
 thirty minutes stood at 97 in the rectum of the first, at 98 
 in the rectum of the second rabbit*. Subsequent researches 
 upon this subject by Dr. W. Philip and Dr. Hastings tend 
 to show, that the rapid cooling of the first animal in the 
 experiment detailed may have resulted in part from too 
 large an inflation of the chest; that upon avoiding this 
 excess, the process of cooling appears even to be retarded 
 by artificial respiration, but not to a degree that invalidates 
 Mr. Brodie's experiments. 
 
 But although the theory of Crawford be thus set aside, 
 it remains possible that arterial blood may prove by some 
 other method the source of animal heat. A general ratio 
 seems to exist between the temperature of parts and the 
 afflux of arterial blood ; and the following experiment by 
 Dr. Wilson Philip may serve to show how the decomposi- 
 * Phil. Trans, vol. ci, p. 36, et seq. ; and vol. cii,. p. 380. 
 
 G 2 
 
96 Opinions respecting the Source of Animal Heat. 
 
 tion of the latter through an agency, in many instances 
 analogous to the nervous influence, may produce heat. 
 Upon applying the galvanic influence to arterial blood im- 
 mediately upon its being drawn, an evolution of heat amount- 
 ing to 2 or 3 took place, while the blood assumed a venous 
 hue. The trial was made with the arterial blood of a rabbit, 
 the rise of temperature ceased to show itself in two minutes 
 after the blood began to flow from the vessel, but the 
 change in colour continued to be produced, accompanied 
 with an extrication of gas through the galvanic influence. 
 No rise of temperature could be produced in venous blood 
 by the same means*. 
 
 Physiologists at present incline to the belief that the 
 production of animal heat depends upon the nervous in- 
 fluence : yet the best evidence which we possess shows only 
 that temperature may be modified through the nerves, like 
 every other physical endowment of the body. Sir Everard 
 Home found, that upon the division of the nerves distributed 
 to the growing antler, its temperature fell immediately 
 several degrees, but rose again a few days afterwards even 
 higher than the temperature of the opposite horn*f*. 
 Sir Everard mentions on the same occasion some curious 
 instances of a partial extrication of heat, which he refers to 
 nervous agency : the oviduct of a frog ready to spawn is 
 two degrees hotter than the heart ; and it appears on the 
 assertion of Dr. Granville, that during labour the heat of 
 the uterus is sometimes raised to 120 ; but a very similar 
 phenomenon has been observed to occur in plants, in which 
 no organs analogous to a nervous system have been traced : 
 M. Hubert observed, that when the temperature of the 
 atmosphere stood at 21 cent, a thermometer surrounded 
 with spadices of the arum cordifolium during the process 
 of fecundation stood at 42 . 
 
 Upon the whole, we must admit that the source of vital 
 heat remains unknown. Its remarkable influence in the, 
 human ceconomy will be subsequently considered. 
 
 IV. The facts which we possess respecting imbibition by 
 
 * Inquiry, &c., p. 242. f Phil. Trans, vol. cxv, p. 7- 
 
 J Ellis on Respiration, &c. p. 204. 
 
Phenomena of Venous Absorption. 97 
 
 means of the blood-vessels are principally owing to the 
 researches of M. Magendie, from which I extract most of 
 the following observations. 
 
 The thigh of a dog, which had previously been stupefied 
 by Opium, was separated from the body by the division of 
 every part but the crural artery and vein ; into each of 
 these vessels a quill was introduced and tied with two 
 ligatures, between which the vessel was divided : thus a 
 channel was provided for the circulation of the blood, and 
 all other communication between the body and the limb 
 was cut off. Two grains of the upas tieute were then 
 inserted into a wound in the foot of the separated limb. 
 The poison manifested its effects upon the system in the 
 ordinary time, that is, in about four minutes ; and we are 
 given to understand that the animal died within the tenth 
 minute. 
 
 A fold of small intestine (this experiment, though 
 founded upon M. Magendie's, was made by M. Segalas) 
 was drawn out of a wound in the belly of a dog. All the 
 blood-vessels passing to and from it were tied but one large 
 artery. A vein punctured upon the mesentery allowing the 
 escape of blood prevented congestion. The lacteal vessels 
 and the nerves were left entire. The fold of intestine was 
 then tied at both extremities, was opened, and an aqueous 
 solution of the alcoholic extract of nux vomica poured into it. 
 During the hour which followed, the poison produced no 
 symptoms. The ligature being then removed from one of 
 the veins, blood was allowed to return to the heart after 
 circulating through the previously isolated portion of bowel. 
 In six minutes from this time the poison took effect. 
 
 The preceding phenomena admit of two hypothetical ex- 
 planations. We may suppose either that the veins possess 
 a special power of absorption through some mechanism not 
 as yet discovered ; or that a poisonous substance may find 
 its way into the blood through the coats of the vessels, by 
 virtue of that imbibition or trans udation of a nature partly 
 chemical partly mechanical, which takes place in dead 
 organized matter, and which it is analogically probable 
 takes place in living matter as well. The latter supposition 
 
98 Phenomena of Venous Absorption 
 
 has the recommendation of assuming nothing. The follow- 
 ing facts appear to me to support it. 
 
 If a piece of beef be put in salt, in a few days the saline 
 fluid penetrates the whole mass. 
 
 If an animal be opened some time after death, the parts 
 adjoining the gall-bladder are found to be deeply tinged 
 with bile. 
 
 If the theca vertebralis of an animal be opened during 
 life or soon after death, a quantity of fluid is found in it ; a 
 like quantity of fluid is not found if the examination be 
 delayed till some time after death. 
 
 If half an ounce of acidulated water be introduced into 
 the pericardium of a dog killed twelve hours before, and 
 warm water be injected in a continued stream through the 
 coronary arteries, so as to flow into the right auricle of the 
 heart, in four or five minutes it gives unequivocal evidence 
 of containing acid. 
 
 In an animal that had been killed by the wound of a 
 Javanese poisoned arrow, the parts around the wound 
 became of a brownish yellow colour for the depth of several 
 lines, and took the bitter flavour belonging to the poison. 
 
 The preceding instances establish the fact, that in dead 
 animal matter a free imbibition or transudation takes place ; 
 so that a substance introduced into it, if capable of being 
 dissolved by its juices, would find its way into the cavities 
 of its blood-vessels. 
 
 If a drop of ink be placed upon the peritoneum of a 
 living animal, it sinks into it and forms a large circular 
 stain, which at first is confined in depth to the serous mem- 
 brane, and takes a much longer time to penetrate the sub- 
 jacent textures. 
 
 If a small quantity of ink be introduced into the pleura 
 of a puppy (the experiment succeeds better upon smaller 
 animals), in an hour the pleura, the pericardium, the in- 
 tercostal muscles, and the surface of the heart itself, assume 
 a sensibly black tinge. 
 
 If the jugular vein of a living puppy be raised from its 
 place without interrupting the circulation, a slip of card 
 being introduced between it and the adjoining parts, and 
 
referable to Transudation. 99 
 
 the vein be carefully denuded of the surrounding loose tex- 
 ture, and a thick aqueous solution of the alcoholic extract 
 of nux vomica be placed upon the middle of the card so as 
 to surround and bathe the vein, in less than four minutes 
 the effects of the poison show themselves ; at first faintly, 
 but soon after so actively as to require the employment of 
 artificial respiration in order that life may be preserved. 
 
 On comparing these results with the preceding series, it 
 appears impossible to doubt that they depend upon a like 
 transudation taking place in the living body to that which 
 occurs in the dead. But various circumstances have been 
 ascertained to prevent, or retard, or accelerate this mode of 
 absorption ; and it is remarkable that they are consistent 
 with, if they do not materially strengthen, the hypothesis 
 which we have adopted. 
 
 Imbibition takes place more readily upon serous than 
 upon mucous membranes, more readily upon very vascular 
 surfaces than upon those which are less so. 
 
 The method common among barbarous nations of ex- 
 tracting poison from wounds by suction, is consistent with 
 the supposition that it makes its way into the system by 
 mechanical imbibition. 
 
 If a ligature be applied around a limb bitten by a ve^ 
 nomous serpent, no symptoms appear as long as the pres- 
 sure is kept up. The ligature stops the circulation of the 
 blood, and thus is calculated to prevent the poison being 
 conveyed to the heart and to the brain, when it has pene- 
 trated by transudation the cavities of the vessels and be- 
 come mixed with the blood. If it be true that continued 
 pressure of a ligature, though insufficient wholly to stop the 
 circulation, yet destroys the effect of the poison, this result 
 may be attributed to the gradual introduction of the poison 
 into the system in quantities too small to produce any 
 symptoms. 
 
 The interesting experiments of Dr. Barry upon the ab- 
 sorption of poisons are to be explained upon the same prin- 
 ciple. Dr. Barry found that the usual effect of introducing 
 prussic acid, strichnine, or the upas tieute into the subcu- 
 taneous tissue of animals is prevented, if a cupping-glass be 
 
100 Phenomena of Venous Absorption 
 
 applied over the wound, or in its immediate vicinity. If 
 the cupping-glass be applied for a short time only, and then 
 removed, the symptoms of poisoning show themselves; but 
 disappear again upon the reapplication of the pressure. If 
 the cupping-glass be kept on for a considerable length of 
 time, upon its removal the poison is found to have lost its 
 effect ; and in this manner poisoning may be arrested, and 
 prevented, after the symptoms have began to show them- 
 selves. The application of the cupping-glass has this 
 among other important advantages over the ligature, that it 
 not merely stops the- flow of the blood from the part, but 
 even draws the liquids in its vicinity within or towards its 
 circumference, causing them, in fact, even to exude, if the 
 cupping-glass be applied over the wound. If the cupping- 
 glass be applied in the neighbourhood of the wound, an in^ 
 cision between the edge of the cupping-glass and the 
 wound allows the poison to act by interrupting the natural 
 derivation of the fluids towards the part from which the 
 atmospheric pressure has been removed*. 
 
 If an animal be placed in a state of artificial plethora 
 by injecting a large quantity of warm water into its veins, 
 a poison introduced into the pleura, which ordinarily shows 
 its effect in two minutes, in half an hour produces no 
 symptoms. Upon drawing a large quantity of blood from a 
 vein, the effects of the poison discover themselves. 
 
 If a quantity of blood be drawn from an animal, and be 
 replaced with an equal quantity of water, poisoning takes 
 place as rapidly as if the blood were not thus diluted. 
 
 If a quantity of blood be drawn from an animal and no 
 substitution be made, a poison which naturally operates 
 in two minutes produces symptoms in thirty seconds. 
 
 In these cases it appears that the degree of distension of 
 the vessels influences the facility with whicji a poison is 
 introduced into the system : but the same result should 
 take place on mechanical principles, if the mode by which 
 the poison makes its way be mechanical transudation 
 through the coats of the blood-vessels. 
 
 * Memoire sur 1'Absorption, par David Barry, M. D. 
 
referable to Transudation. 101 
 
 In therapeutics the principle is well established, that 
 medicines act with increased and more rapid effect after 
 venesection. 
 
 If a solution of prussiate of potass be injected into the 
 pleura, and a solution of sulphate of iron be introduced into 
 the abdomen of a living animal, in general five or six 
 minutes are required for their communication through the 
 diaphragm. But this communication M. Fodera found to 
 be instantaneous, if a current of the galvanic fluid be di- 
 rected through the diaphragm, a phenomenon curiously 
 consistent with the effects of a similar influence upon the 
 transmission of liquids through inert capillary tubes. 
 
 Such is the mass of evidence by which it appears to be 
 well established, that a kind of transudation takes place in 
 living as well as in dead textures, and is the principle 
 through which foreign matter in contact with a vascular 
 surface finds its way into the circulation. 
 
f 
 
 CHAPTER VII, 
 OF DIGESTION. 
 
 THE matter lost by cutaneous and pulmonary transpiration, 
 by the urine, and by other secretions, which are wholly or in 
 part eliminated from the body, is a perpetual drain upon 
 the blood. To supply this waste, a fluid is elaborated from 
 the food, which in essential qualities nearly resembles the 
 blood, which is absorbed and poured into the veins by a 
 distinct set of vessels, and, mixing with the blood, in a 
 short time ceases to be separately distinguishable in it. 
 The process by which the nutritious element is extracted 
 from the food is termed Digestion. 
 
 In the lowest animals digestion is a very simple process. 
 The polype, which consists of a bell-shaped sac, seizes the 
 insects on which it preys with its tentacula, and thrusts 
 them into its cavity ; the business of digestion immediately 
 commences : great part of the insect that has been swallowed 
 disappears, having been first dissolved and then absorbed : 
 the refuse matter is afterwards expelled through the same 
 orifice at which it was received. 
 
 In the ascending scale of organization from the lowest ani- 
 mals to the highest, the digestive organs gradually become 
 more and more complex : the alimentary canal becomes laid 
 out into a series of chambers, in which the food undergoes 
 successive changes antecedently to its separation into nu- 
 tritive and excrementitious matter ; and the gradual assimi- 
 lation of the food is wrought, not by the influence of these 
 several chambers and their products alone, but in great 
 part through the chemical agency of copious secretions, 
 that are formed in glandular parts in the neighbourhood, 
 
Of Digestion. 103 
 
 and are afterwards conveyed into the different chambers of 
 the digestive apparatus. 
 
 The regular employment of these important organs, so 
 essential to the continuance of individual existence, has not 
 been left by Providence to the risk of being neglected 
 through caprice or accident : but strong desires have been 
 implanted in us, by which we are instinctively and irresisti- 
 bly led to their proper use. Our first inquiries may be 
 directed to that part of the process of digestion, with 
 which consciousness has to do ; or to the nature of those 
 parts which are thrown into action in order to gratify a 
 sense, yet in which at the same time the assimilation of the 
 food commences. 
 
 SECTION I. 
 
 Of Hunger and Thirst ; of the Mastication of Food, and 
 of Deglutition. 
 
 We are led to take food by the appetites of hunger and 
 thirst. If hunger be not gratified, an uneasy sensation of 
 gnawing or dragging occurs, which is referred to the epi- 
 gastrium,- if thirst be not slaked, the mouth and throat 
 become dry and parched. It is usual to attribute hunger 
 to an affection of the nerves of the stomach, and thirst to 
 an impression upon the nerves of the fauces and pharynx. 
 But it is far from certain that either of these suppositions is 
 just. Nausea is habitually referred to the stomach, upon 
 the same grounds with the sensation of hunger ; yet, ac- 
 cording to the experiments of Magendie, after the removal 
 of the stomach in an animal, nausea and retching may be 
 produced by the injection of tartar emetic into the veins ; 
 and Dr. Gairdner remarked, that in the case of a man who 
 had cut through the oasophagus, several buckets-full of 
 water were swallowed daily, and discharged through the 
 wound, without quenching thirst. The thirst, in this in- 
 stance, it was afterwards found, admitted of being allayed 
 
104 Of the Fauces. 
 
 ' '> v 
 
 by the injection of spirits diluted with water into the 
 
 stomach*. It is, therefore, not impossible that a person 
 might be hungry without a stomach, and thirsty without 
 a throat. 
 
 Hunger frequently remains for half an hour or an hour 
 after a hearty meal. Sleep allays it; violent emotions of 
 the mind prevent it. Hunger recurs at stated periods 
 through the influence of habit. If the gratification of the 
 appetite be withheld, it ceases, and a degree of nausea 
 takes its place, with languor and exhaustion ; then hunger 
 returns with painful sensations at the stomach, and as a 
 violent craving, which gets the better of every feeling of 
 aversion and abhorrence, and the vilest food is swallowed 
 with avidity. 
 
 We may now proceed to examine the parts into which 
 the food is first received. 
 
 The fauces form an organ iii which the solid food is 
 divided into fragments, and rubbed down with a fluid to 
 the consistence of a pulp; that it may leave its entire 
 flavour upon the neighbouring sentient surfaces, and be 
 readily conveyed in equal portions along the gullet in the 
 act of deglutition. 
 
 The vaulted roof of the fauces is formed by the hard palate, 
 around which are set the teeth in their sockets : this part may 
 be considered as fixed during mastication. The lower jaw re- 
 presents the alveolar processes of the upper maxillary bones, 
 with which it contains an equal number of teeth, and against 
 which it is capable of being pressed in various directions, 
 so that the edges and grinding surfaces of the different 
 teeth may tell upon the food. The tongue, contained within 
 the hollow of the lower jaw, forms the floor of the fauces, 
 and when the mouth is shut, presents a convex upper sur- 
 face in contact with the vaulted part of the palate. Three 
 glands on either side, the parotid, the submaxillary, and 
 the sublingual, pour saliva into the mouth, the inner sur- 
 face of which is lined with a mucous membrane that is 
 continuous at the lips with the skin; and many smaller 
 
 * Edinburgh Medical and Surgical Journal, vol. xvi, p. 355. 
 
Chemical Composition of Teeth. 105 
 
 glandular bodies within the lips and the muscles of the 
 cheek, termed glandules labiales and buccales, contribute 
 perhaps to the same office. 
 
 The teeth are thirty-two small bones, of which the crown 
 or base, or body, is covered with enamel, and appears above 
 the gum : the neck of a tooth is that part to which the gum 
 adheres ; the root or fang of each tooth is firmly wedged 
 into the substance of the jaw. A tooth is fixed by its fang 
 and neck ; the crown is employed in dividing the food, and 
 in articulating vocal sounds. 
 
 By means of a longitudinal section the cavity of a 
 tooth is shown ; which is naturally open at the extremity of 
 the fang, and ascends through the neck into the crown of 
 the tooth, representing very faithfully its outward form< 
 The cavity is seen to be wrought in the duller-coloured sub- 
 stance, or bone of the tooth ; and the glistening enamel 
 appears disposed in a thin layer, thickest upon the cutting 
 edge or grinding surface of the crown, and vanishing upon 
 the neck of the tooth. 
 
 If a tooth be steeped in diluted muriatic acid, it retains 
 its form, but becomes flexible ; the acid dissolves the earthy 
 matter, and leaves the animal substance with which it was 
 combined. 
 
 The following is the composition of the bone of teeth : 
 
 Animal matter 28.0 
 
 Soda with muriate of soda 1.4 
 
 Carbonate of lime 5.3 
 
 Phosphate of lime , 61.95 
 
 Fluate of lime 2.1 
 
 Phosphate of magnesia 1.25 
 
 100.00 
 The following is the composition of enamel : 
 
 Animal matter 2.0 
 
 Carbonate of lime '. 8.0 
 
 Phosphate of lime 85.3 
 
 Fluate of lime 3.2 
 
 Phosphate of magnesia 1.5 
 
 100.0 
 
106 Number and Shape of Human Teeth. 
 
 If a section be made through a tooth and the alveolar 
 process which contains it after a successful injection, 
 neither the enamel nor bony part of the tooth appear in 
 any degree reddened ; but a very vascular membrane is seen 
 to enter at the aperture of the fang and to line the whole 
 of the cavity of the tooth. Branches from the ganglionic 
 portion of the fifth pair of nerves may be traced to the cavity 
 of the fang, upon which the sensibility of a tooth depends. 
 
 In this manner the teeth cohere with neighbouring vas- 
 cular parts. Their mode of life and growth will be after- 
 wards described. At present we have only to consider 
 their mechanical agency in comminuting the food. 
 
 The four front teeth in each jaw are termed incisors : the 
 crown has a cutting edge extending transversely, and is 
 wedge-shaped : the fang is single : the two central incisors 
 in the upper jaw are larger than the rest, so as to throw 
 the remaining teeth of the upper jaw rather without or be- 
 hind those of the lower, till the smallness of the last grinder 
 in the upper jaw causes them to terminate at the same ver- 
 tical plane. 
 
 A cuspidatus, canine, or eye-tooth is found on each side 
 next to the incisors : a canine tooth is pointed, and larger 
 than an incisor : its fang is single but of great length, and 
 frequently bent at the extremity. 
 
 The two sets of cuspidati and incisors form two curved 
 blades, which meet like those of scissors bent upon the flat; 
 the incisors and cuspidati of the upper jaw generally fall 
 before those of the lower. 
 
 The two teeth, which immediately follow each cuspidatus, 
 have two points upon the crown, one without the other, 
 and the largest external ; they are called bicuspides : they 
 have one broad fang fluted at its sides. 
 
 The three remaining teeth on each side of each jaw are 
 called molares or grinding teeth; their crowns have five 
 points. The molares of the lower jaw have two fangs, one 
 behind the other : the molares of the upper have three, two 
 of which are external : they rise in a slanting direction. 
 This disposition of the fangs of the upper molares is in- 
 tended to avoid the antrum of Highmore ; but it often hap- 
 
Different kinds of Teeth. 107 
 
 pens that one fang, and that more generally one of those of 
 the second molaris, extends into the antrum. In the mu- 
 seum of Albinus there is an instance of the crown of a 
 molar tooth growing into the cavity of the antrum, the di- 
 rection of the fangs being reversed. The first molaris is the 
 largest ; the posterior, or dens sapientige, is small : its fangs 
 grow together, and are short. The grinding surfaces of 
 the two sets of molar teeth are exactly opposed to each 
 other. 
 
 The strictest relation exists between the form of the teeth 
 and the habits of animals. Thus in the horse, which crops 
 the herbage by bruising and snapping it across, the incisors 
 have broad cutting edges, which meet like the blades of 
 pincers : in the incisor teeth of the beaver, which gnaws 
 through the hardest vegetable fibre, a sharp chisel-like edge 
 is preserved by the disproportionate distribution of enamel 
 upon the fore part : in the lion the incisors are pointed: in 
 the elephant, front teeth grow from the upper jaw only, and 
 are prolonged into tusks, by the aid of which, with its 
 trunk, the animal tears up the plants that serve for its food. 
 The cuspidati are remarkably large in carnivorous quadru- 
 peds to enable them to hold and rend their prey ; and the 
 character of the head in this class is determined by the pro- 
 minence of the zygoma to give room for the thick temporal 
 muscle by which the jaws are closed, and by the shortness 
 of the jaws themselves, which saves expenditure of power 
 in closing them. 
 
 The molares are best developed in graminivorous animals ; 
 on this occasion a third substance termed the crusta 
 petrosa, having less hardness than the bone, as the bone 
 has less than the enamel, is wrought into their composition ; 
 and as each of these three substances is exposed upon the 
 grinding surface, the latter derives a permanent inequality 
 from their different degrees of hardness, favourable to the 
 comminution of the food. The form of the heads of grami- 
 nivorous quadrupeds is characterized by the length of the 
 jaws in which the massive grinding teeth are set; by the 
 long and flat zygoma, and by the depth and breadth of the 
 
108 Movements of the Lower Jaw. 
 
 branches of the lower jaw, to which muscles are attached, 
 that move it forward and laterally. 
 
 The lower jaw consists of the curved piece of bone in 
 which the sixteen teeth are set, and of a process or branch 
 on either side which rises nearly at a right angle < to be 
 articulated by means of its condyle with the glenoid fossa of 
 the temporal bone. Each branch is of such a length, that 
 when the lower jaw is fully raised, the two rows of teeth are 
 equally pressed against each other, the front teeth locking, 
 the molar teeth simply meeting. 
 
 The elementary motions of the lower jaw consist in its 
 simple elevation or depression, in its horizontal movement 
 forwards or backwards and from side to side. 
 
 1. During the depression or elevation of the lower jaw, 
 the centre of motion falls about the middle of its branches. 
 Or the lower jaw in rising or falling performs part of a 
 vertical revolution upon an imaginary axis extending from 
 side to side through the middle of its branches. In the 
 depression of the jaw the angle is carried upwards and 
 backwards, the condyle forwards and downwards sliding 
 upon the interarticular cartilage which is interposed be- 
 tween it and the os temporis. The temporal muscles 
 directly raise the lower jaw : the digastricus and other 
 muscles which depress it, at the same time retract it, and 
 thus admit of being brought into play even during the ele- 
 vation of the jaw, in order to modify the action of the 
 masseter and internal pterygoid muscles which tend to 
 carry the jaw forwards as well as upwards. 
 
 2. The lower jaw may be carried forwards in a plane 
 parallel to that of the alveoli of the upper jaw, by the action 
 of the external pterygoid muscles, aided by the masseters 
 and internal pterygoid muscles, if the tendency of the latter 
 to raise the jaw be prevented by the digastrici and various 
 other muscles attached to the os hyoides. The muscles 
 last alluded to are calculated simply to retract the jaw, 
 when their tendency to depress it is neutralized by the tem- 
 poral, masseter, and internal pterygoid muscles. 
 
 3. The lower jaw may rotate horizontally round an 
 
Of the Muscular Structure of the Tongue. 109 
 
 imaginary centre, which falls in the middle of a right line 
 joining the two condyles : the masseter of the same side 
 and the pterygo'idei of the opposite concur in giving the jaw 
 this movement, assisted by the digastrici and various other 
 muscles attached to the os hyoi'des, the action of which 
 preserves the movement horizontal. 
 
 By differently combining these simple motions, all the 
 variety of pressure which the teeth make upon the food is 
 produced. 
 
 The os hyoi'des is composed of three slight pieces of bone, 
 a base and two cornua, forming a small horse-shoe figure, 
 within and behind the more capacious curve of the lower 
 jaw : upon this bone the mass of flesh which forms the 
 tongue is supported. The central and largest muscle of the 
 tongue is termed the genio-hyo-glossus : it extends from 
 the symphysis of the jaw to the os hyoi'des in one direction, 
 and to the tip of the tongue in the other. Other muscles 
 descend obliquely, from the lower jaw to the os hyoi'des, 
 which, with the preceding, raise the os hyoi'des, and 
 carry the tongue forward or laterally. The linguales 
 shorten the tongue, the stylo-glossi give it breadth and 
 concavity, the hyo-glossi render it convex: so ample is 
 the provision for moving this organ to different parts of the 
 fauces, whether to bruise the softer parts of the aliment 
 against the palate, to mix it with the saliva, to place it 
 under the pressure of the teeth, to assist in bringing out the 
 taste and other sensible qualities of bodies in contact with 
 the finely organized papillae on its mucous surface, to urge 
 the masticated food towards the pharynx, or to give articu- 
 lation to vocal sounds. 
 
 The saliva is a limpid fluid like water, but much more 
 viscid : it has neither smell nor taste : its specific gravity ac- 
 cording to Dr. Thomson is 1.0038. Its constituents accord- 
 ing to Berzelius are as follows : 
 
 Water 992.9 
 
 Peculiar animal matter 2.9 
 
 Mucus J.4 
 
 Alkaline muriates 1.7 
 
 Lactate of soda and animal matter 0.9 
 
 Pure soda 0.2 
 
 1000.0 
 
110 Quantity of Saliva formed at each Repast. 
 
 The glands that secrete saliva are three in number on 
 each side : they are of an ochrey colour, and are composed 
 of numerous molecules of different sizes, connected together 
 by a very firm cellular texture. 
 
 The parotid gland is the largest of the three : it occupies 
 the hollow between the mastoid process of the temporal 
 bone and the branch of the lower jaw ; its duct, which is 
 commonly termed the Stenonian duct, passes across the 
 masseter muscle to perforate the buccinator and open upon 
 the membrane of the fauces opposite to the middle molaris 
 of the upper jaw. A small gland termed the socia parotidis 
 adheres to the Stenonian duct in its passage over the mas- 
 seter. The portio dura traverses the substance of the 
 parotid gland, which appears to derive nerves from this 
 source, from the superficial temporal branch of the third 
 division of the fifth, and from the second cervical nerve. 
 
 The submaxillary gland is of an oval form : it is placed 
 above the digastricus between the lower jaw and the mylo- 
 hyo'ideus muscle : its duct, termed the duct of Wharton, 
 opens upon the mucous surface of the fauces at the side 
 of the frsenum linguae. The nerves of this gland are 
 branches from the gustatory, upon which a ganglion is 
 formed. 
 
 The sublingual gland is frequently continuous with the 
 posterior portion of the submaxillary gland, is oblong, and is 
 placed between the mylohyoideus and the membrane of the 
 mouth : its principal ducts or duct open into the duct of 
 Wharton ; several smaller ducts open from it into the fur- 
 row by the side of the tongue ; its nerves are derived from 
 the gustatory. 
 
 In the case described by Dr. Gairdner, to which I have 
 already referred, from six to eight ounces of saliva were 
 observed to be discharged during a meal, which consisted 
 of broth injected through the divided oesophagus into the 
 stomach: the quantity is probably greater which is pro- 
 duced under the stimulus of ordinary mastication. With 
 this fluid the food is mixed while undergoing comminution 
 in the fauces. The food acquires at the same time the 
 temperature of the blood. 
 
Use of the Saliva. Ill 
 
 It does not appear that any notable effect is produced 
 upon the aliment through the conjoined influence of the 
 saliva and an elevated temperature. M. Krimer held in his 
 mouth a slice of ham weighing a drachm for three hours. 
 At the expiration of this time the morsel had become white 
 upon its surface, and had gained twelve grains in weight*. 
 Perhaps the qualities of the saliva are simply calculated to 
 produce a ready mixture of the various kinds of food tritu- 
 rated with it. 
 
 The nature of sensations of taste will be afterwards de- 
 scribed. The gratification of the sense of taste seems but 
 to whet the appetite of hunger : to allay which deglutition 
 instinctively follows. The morsel is thrown by the tongue 
 to the back part of the fauces, and we swallow it as soon 
 as its sapid juices have been diffused through the mouth, 
 and its altered consistence shows it to have attained a state 
 fit for deglutition: a capacious sac termed the pharynx 
 receives it. 
 
 The pharynx communicates at the fore part with the 
 cavities of the nostrils, with the fauces, with the larynx : 
 it is lined by a prolongation of the mucous surface common 
 to these three parts : it is suspended to the basilar process 
 of the occipital bone, and attached laterally to the pterygoid 
 processes of the sphenoid and to the cornua of the os hy- 
 oi'des ; thence it becomes narrower to the first ring of the 
 trachea, where the alimentary canal assumes a cylindrical 
 form, and receives the name of oesophagus. 
 
 The muscles which raise the os hyoides raise the pharynx 
 with it : at the commencement of deglutition all the parts of 
 the throat visibly ascend : the pharynx is drawn upwards to 
 receive the morsel thrust towards it by the pressure of the 
 tongue : and one muscle, the stylo-pharyngeus, which con- 
 curs in producing this movement, seems specially intended 
 in addition to expand the pharynx. 
 
 Three muscles throw their fibres round the pharynx, 
 which are termed its upper, middle, and lower constrictors : 
 their action is such as to compress any substance that has 
 
 Versuch einer Physiologic des Blutes. Lcipsig, 1820. 
 
 H 2 
 
112 Use of the soft Palate. 
 
 found entrance into the pharynx,- and thus to expel it. But 
 the pharynx is open towards several passages, and the 
 contrivances are remarkable, and well deserve attention, 
 which limit the progress of the food to one direction only, 
 and force it to descend towards the oesophagus, instead 
 of making its escape by the nostrils, the fauces, or the 
 larynx. 
 
 What is termed the soft palate is a flap of flexible elastic 
 substance about one-fourth of an inch in thickness and an 
 inch in depth, which hangs as a loose curtain from the 
 posterior edge of the palatine plate of the palate bones. 
 The centre of its unattached margin is prolonged to form 
 the uvula. Laterally two crescentic folds of mucous mem- 
 brane are reflected from the soft palate to the sides of the 
 tongue and pharynx : between these arches the tonsil, a 
 mucous gland, is placed on either side, Each crescentic 
 fold contains muscular fibres; the anterior contains the 
 constrictor isthmi faucium ; the posterior, the palato- 
 pharyngeus; these muscles depress the soft palate, and 
 narrow the .aperture leading from the fauces into the pha- 
 rynx. 
 
 By these means the communication with the fauces is so 
 straitened, that the pressure of the tongue readily precludes 
 the return of the food into the mouth when the constrictor 
 superior pbaryngis .contracts. 
 
 But the principal office ,of the soft palate in deglutition 
 consists in protecting the posterior openings of the nostrils : 
 for this purpose it is necessary not merely that this flap of 
 yielding flesh be carried before the food to the back of the 
 pharynx ; but that adequate tension be given to it to enable 
 it sufficiently to resist the pressure of the constrictor .superior 
 pharyngis and of the tongue upon the morsel swallowed. 
 Two muscles are provided in addition to those already 
 described to give the tension required to the soft palate, 
 namely, the levator palati mollis and the circumflexus 
 palati : both descend obliquely forwards, the cartilaginous 
 part of the Eustachian tube being interposed between them, 
 from the extremity of the petrous portion of the os temporis : 
 but while the former is directly expanded into the substance 
 
The Aperture of the Larynx how protected. 113 
 
 of the soft palate, the latter is previously reflected round 
 the hamuiar process of the sphenoid bone, and re-ascends to 
 its insertion : the two muscles thus become opposed in their 
 action, and drawing in different ways upon the soft palate 
 contribute to extend it over the pharynx behind the open- 
 ing into the nostrils. Something of the effect of these parts 
 in deglutition may be seen on pressing down the tongue with 
 the handle of a spoon, and conveying the instrument 
 towards the root of the tongue and the tonsils, when the 
 peculiar sensibility of the back part of the fauces is excited, 
 and an instinctive and irresistible action of deglutition 
 ensues. 
 
 It sometimes happens that infants are born with a natural 
 fissure of the soft palate in the median plane. When this is 
 the case deglutition is commonly performed imperfectly, 
 part of the aliment swallowed finding its way into the nos- 
 trils. However, many persons thus originally malformed, 
 gradually acquire a power of swallowing food with precision ; 
 for this purpose it is requisite that they swallow each 
 morsel not hurriedly but leisurely. It is curious to observe 
 the mechanism in action by which the imperfect palate is 
 rendered capable of performing its functions justly : the 
 means by which this is done may be seen on desiring the 
 patient to perform the act -of deglutition with the fauces 
 empty, and the lips sufficiently apart to disclose the soft 
 palate. At the moment of swallowing, the two parts of the 
 velum pendulum palati are seen to be drawn downwards 
 and inwards by the action of the circumflex muscles, so as 
 nearly to meet. This circumstance is favourable to the success 
 of the operation of staphyloraphe, as it tends to diminish 
 the strain upon the sutures during deglutition. 
 
 The mode in which the respiratory tube is protected 
 during deglutition can only be well understood in connec- 
 tion with the anatomy of the larynx. The epiglottis, a thin 
 portion of elastic cartilage, rises vertically at the root of 
 the tongue, and is broad enough when carried backwards 
 to cover the aperture of the glottis : and there is no doubt 
 that in ordinary deglutition this cartilage is pressed down 
 by the food towards the orifice of the larynx. But the epi- 
 
114 Of Pharyngeal Deglutition. 
 
 glottis was removed from animals in experiments by 
 M. Magendie, and it has been lost by disease in human 
 beings, without any essential prejudice to deglutition. The 
 security of the larynx, as M. Magendie discovered, depends 
 upon the contraction of the muscles which close its aper- 
 ture, namely, the ary tsenoideus transversus and the aryteeno'i- 
 dei obliqui. While these preserve their power of motion, 
 the loss of the epiglottis is not felt : but if they be paralyzed, 
 as through the division of the nervi laryngei interni, a part 
 of the food finds its way into the larynx, and violent cough- 
 ing is produced each time that deglutition is attempted, 
 even though the epiglottis have been left entire. I have at 
 this time a patient under my care in the Middlesex Hospital, 
 who, in an attempt to destroy himself, has made a deep 
 wound into the throat between the os hyo'ides and thyreoi'd 
 cartilage. The incision is close upon the latter, so that 
 the epiglottis is shorn off, and you look into the pharynx, and 
 directly upon the front of the arytsenoid cartilages. Each 
 time that this patient swallows liquid, a small quantity 
 escapes by the wound, but none appears to enter the larynx j 
 nor is coughing produced or any other symptom of laryn- 
 geal irritation. 
 
 Deglutition consists of three stages ; the passage of the 
 food from the mouth into the pharynx, from the pharynx 
 into the oesophagus, from the oesophagus into the stomach. 
 The action of pharyngeal deglutition may at any time 
 be performed through a deliberate exertion of the will : 
 at times it seems to take place, if not independently of 
 volition, at all events uncontrollably. If the action of 
 deglutition be voluntarily performed several times in succes- 
 sion, and nothing but saliva swallowed, the parts become 
 fatigued, and the operation cannot be immediately repeated. 
 The action of the lower part of the pharynx and of the 
 fibres of the oesophagus is not consciously voluntary. 
 
Of the Structure of the Alimentary Canal. 115 
 
 SECTION II. 
 
 Of the Nature of the Alimentary Canal from the (Esophagus 
 downwards, and of the Fleshy Viscera connected with it. 
 
 THAT part of digestion, which the will directly controls, is 
 limited to the fauces and pharynx : below the latter mus- 
 cular action ceases to be voluntary, and common sensation 
 is speedily lost. The elaboration of the food now proceeds 
 rapidly ; it loses its original qualities, and assumes different 
 characters, as it is successively submitted without our con- 
 sciousness to the influence of many viscera. It will help to 
 simplify our present inquiries, if I prefix a general account 
 of the nature of these viscera to the description of the dif- 
 ferent steps of the assimilative process, which are conducted 
 in them. 
 
 The alimentary canal below the pharynx constitutes a mem- 
 branous tube of from five to six times the length of the 
 body, the several parts of which are the oesophagus, the 
 stomach, the small and the great intestines. 
 
 When we consider this lengthened tube (for the purpose 
 of yet further simplification) as a single organ, disregarding 
 the differences of shape and structure which characterize its 
 several parts, we remark that notwithstanding its thin and 
 membranous structure, it throughout admits of being sepa- 
 rated into three distinct layers or tunics. 
 
 The innermost, or mucous coat, so called from the nature 
 of the secretion which exsudes upon it, is indeed so delicate 
 as not to allow of being displayed as a separate continuous 
 membrane, till the part has acquired firmness by maceration 
 in alcohol. The unadherent surface of the mucous coat is 
 not plain, but presents a superficies like that of plush or 
 velvet, being covered with a delicate pile, which where the 
 individual shreds are larger and more distinct is called a 
 villous structure. 
 
 The second layer is called the nervous or submucous coat; 
 its thickness is about one-fifteenth of an inch, and it serves to 
 give to the mucous coat, to which it closely adheres, the 
 
116 Of the Structure of the Alimentary Canal. 
 
 strength it would otherwise want. The intestinal glands 
 are seated in the submucous coat : they consist of flat 
 pouches, from two lines in diameter to microscopic minute- 
 ness, and are disposed singly and in clusters : each gland 
 opens by a single orifice upon the mucous surface. 
 
 The third tunic consists of muscular fibres, of which 
 there are two layers ; an inner, disposed in transverse or 
 circular fasciculi ; an outer, the direction of which is longi- 
 tudinal. The inner or circular fibres form with one excep- 
 tion a coat of tolerably equal thickness throughout the 
 whole of the alimentary canal. The longitudinal fibres on 
 the other hand are only well developed towards each ex- 
 tremity. The oesophagus and the rectum have a thick un- 
 interrupted covering of longitudinal fibres, which in the 
 former instance are spread out and lost upon the stomach, 
 while in the latter they extend the entire length of the 
 colon in the form of three narrow bands : upon the inter- 
 mediate three-fifths of the whole tube, longitudinal fibres 
 are not constantly found, and when found are but partially 
 distributed along the unattached surface of the bowel, and 
 are so slender in their texture as scarcely to admit of being 
 detached from the peritoneum which covers them. 
 
 The reason of the very partial disposition of longitudinal 
 fibres upon the alimentary canal I suppose to be this. 
 It is towards the extremities alone of the canal that its 
 contents are of solid consistence ; in the central part 
 they are fluid. Now the mode in which the contents 
 of the bowel 'are propelled is the following; the circular 
 fibres of the part which is to be emptied contract, the 
 fasciculi immediately behind remaining in action to prevent 
 the retrograde passage of the food, those before being relaxed 
 to offer no resistance to its progress. The action of the cir- 
 cular fibres of the bowel is commonly called their peristaltic 
 action ; or it is said to be vermicular, from the progressive 
 displacement of the bowel which attends it, resembling the 
 motion of an earth-worm. We may reasonably suppose, 
 that when the peristaltic action is employed in propelling a 
 fluid, which would readily insinuate itself into the next and 
 relaxed portion of the canal, no great strain would be made 
 
Of the Irritability of its Muscular Fibres. 117 
 
 upon the texture of the part, or more than its elasticity 
 alone would redress. The case is altered when we consider 
 this action applied to solid substances, such as are the im- 
 perfectly masticated food, which is frequently bolted down 
 the oesophagus, or the solid faeces, which are contained in 
 the great intestine : and we recognize at once, in the super- 
 added series of longitudinal fibres in these parts, a provision 
 necessary to prevent their elongation or their rupture. 
 
 In the abdomen, the alimentary canal receives a fourth 
 coat from the great serous membrane of that cavity. With 
 partial exceptions, the peritoneum is so attached as to allow 
 the viscera, which it covers, considerable latitude of motion. 
 This provision is doubtless of service in facilitating the 
 commodious packing of the viscera in different positions of 
 the body, and during their alternate states of emptiness and 
 repletion; but its principal object has reference to the 
 peristaltic action of the bowels, which would seem to be 
 imperfectly performed when the portions of the alimentary 
 tube cease to be disconnected with and to have the means 
 of freely moving over each other. Trifling causes are 
 known to produce the severest symptoms of obstruction of 
 the bowels, when the folds of the intestines have become 
 glued together by the effusion of lymph. 
 
 The muscular fibres of the alimentary canal seem to re- 
 ceive no direct excitement from the will ; accordingly, 
 when the nerves distributed to them are mechanically irri- 
 tated, no sensible effect follows * : and if a portion of bowel 
 in an animal recently killed be stimulated, the action which 
 follows is not sudden and immediate, and confined to the 
 point that was irritated ; but commences after an interval, 
 and gradually extends to some distance along the neigh- 
 bouring fasciculi. It is probable that the natural stimulus 
 to the action of the bowel is the pressure of its contents ; 
 and that these, according to their nature, may have a more 
 or less stimulating quality ; and that the bowel at different 
 periods, and under different circumstances, may be more or 
 less irritable. 
 
 * The oesophagus offers an exception to this rule : refer back to 
 chapter Hi. 
 
118 Triple division of the Alimentary Canal. 
 
 The sensibility of the alimentary canal in the healthy 
 state appears to be very moderate : common sensation is 
 probably limited to the oesophagus, which is supplied by 
 the eighth nerve; and to the extremity of the rectum, 
 which receives nerves from the sacral plexus ; the interme- 
 diate parts, which are principally supplied with nerves from 
 the sympathetic, appear to have no feeling when handled or 
 even wounded ; immoderate distension alone seems capa- 
 ble of exciting pain in these parts in the healthy state. 
 
 To take a different, but not less useful, view of the entire 
 alimentary canal, let us next consider it as naturally divided 
 into three parts : 1. The fauces, pharynx, and oesophagus; 
 2. The stomach and small intestines ; 3. The great in- 
 testines. 
 
 In the first portion, we are conscious of sensation and 
 voluntary action ; in the second, these affections are want- 
 ing ; in the third, they re-appear. 
 
 In the first portion the food is prepared for its subsequent 
 elaboration by being rubbed down with saliva to the con- 
 sistence of a pulp ; in the second, the nutritious element is 
 separated from it; in the third, the refuse matter under- 
 goes some farther changes. 
 
 The first portion is throughout lined with a fine but dis- 
 tinct cuticle : in the second, the mucous membrane is ex- 
 traordinarily vascular, and the large and distinct villi which 
 everywhere characterize it, have obtained for the lining 
 membrane of that portion the name of villous coat: the 
 third is remarkable for its plain internal mucous surface, 
 and for the sacculations into which it is thrown through the 
 shortness of the longitudinal fibres. 
 
 The series of circular fibres which belong to each of these 
 three leading divisions of the alimentary tube, terminates 
 with it. The circular fibres of the oesophagus are lost upon 
 the cardiac extremity of the stomach : the circular fibres of 
 the stomach and small intestines commence at the fundus 
 of the stomach, and terminate at the valve of the colon : the 
 circular fibres of the great intestine begin at the root of the 
 appendix of the caecum, and are interrupted only by termi- 
 nating at the anus. 
 
 Finally, each of these portions is characterized by being 
 
Shape and Situation of the Stomach. 119 
 
 disproportionately capacious at its commencement; the 
 fauces and pharynx, the stomach, the head of the colon, 
 have a larger internal area than the parts of the tube which 
 immediately follow : near the commencement again of each 
 portion, secretions are most liberally furnished, and the 
 glandular apparatus is more complex : near the fauces are 
 the salivary glands ; with the stomach and the first four 
 inches of the small intestines are connected the spleen, the 
 liver, and the pancreas ; and the caecum has a larger share 
 of submucous glands than the colon. 
 
 When we turn our attention to the subdivisions of the 
 alimentary tube, we may remark of its whole length, from 
 the fauces downwards, that the two inner coats are appa- 
 rently more capacious, or have less power of retraction, 
 than the muscular coat which contains them, so that they 
 lie in folds, which have a different character in different 
 parts ; these are lessened in proportion as the canal is dis- 
 tended, but never to the extent of becoming obliterated, 
 except perhaps in the oesophagus and the stomach. The 
 folds of the inner tunics of the oesophagus are longitudinal ; 
 the rugse in the stomach are disposed with great irregularity, 
 so as to intercept innumerable areolse of diversified shapes 
 and sizes ; the folds in the small intestine, each a quarter of 
 an inch in depth, are uniformly disposed transversely; 
 they are termed valvulae conniventes: they never extend 
 quite round the circumference of the bowel : their direction 
 is towards the great intestine : they are so numerous, that 
 each partly covers that below, like tiles upon a roof. The 
 folds of the great intestine appear like sharp circular con- 
 strictions. 
 
 The stomach is a conical sac, the large end or fundus of 
 which is contained in the left hypochondrium near this 
 extremity the oesophagus opens by what is termed the 
 cardiac orifice ; the stomach crosses the epigastrium, and 
 its narrow end, or pyloric portion, lies in the right hypo- 
 chondrium. The stomach is braced to the diaphragm by 
 the oesophagus, and to the liver by the lesser omentum and 
 capsule of Glisson, which adhere to its upper and concave 
 edge or lesser curvature : when the stomach becomes dis- 
 
120 Of the Gastric Secretion. 
 
 tended, it rises by revolving upon its cardiac and pyloric 
 attachments, and presents its unattached convex margin 
 forwards in the epigastrium. 
 
 The glands of the stomach are extremely numerous : 
 they are single : they vary in diameter from .02 to .08 of 
 an inch. The largest are towards the fundus, the smaller 
 towards the pylorus. There are none immediately round 
 the cardia, but I have counted forty at the lower part of the 
 oesophagus, disposed in an irregular circle .3 of an inch 
 above the orifice of the stomach. 
 
 The secretion of the stomach is termed the gastric juice; 
 it has been procured from the human stomach by that 
 spontaneous effort, through which some persons are able 
 without feeling nausea to throw up the contents of the sto- 
 mach, as well as by exciting nausea and vomiting mechani- 
 cally in a person who had previously fasted. M. Thenard 
 analyzed small quantities of gastric secretion obtained by 
 the first of these methods : it was found to consist of a large 
 proportion of water, some mucus, and salts of soda and 
 lime ; on one occasion the liquid was of an acid nature, on 
 another it was not. 
 
 Spallanzani describes liquid, which he procured from his 
 own stomach, as frothy and somewhat glutinous, salt to the 
 taste, and not bitter. In investigating its properties, some 
 of this liquid was put into a glass tube with boiled beef 
 that had been masticated : the tube was then hermetically 
 sealed, and exposed near the fire to a considerable heat, 
 though not perhaps exactly equal to the temperature of the 
 stomach. By the side of this tube was placed another, 
 containing the same quantity of flesh immersed in water : 
 the subsequent appearances in both were the following: in 
 twelve hours, the flesh in the former began to lose its 
 fibrous structure, and in thirty-five hours had lost its con- 
 sistence ; to the naked eye it appeared to be reduced to a 
 pultaceous mass, and to have lost its fibrous texture ; but a 
 microscope rendered fibres visible. After this semifluid 
 mass had continued two days longer in the gastric fluid, 
 the solution did not seem to have made any further pro- 
 gress, and the reduced fibres were still just as apparent. 
 
Of Spontaneous Vomiting. 121 
 
 The flesh did not emit the least bad smell, while that im- 
 mersed in water was putrid in sixteen hours. 
 
 Dr. Fordyce attributes to the gastric secretion, when 
 removed from the body, the same solvent effect which 
 Spallanzani was persuaded it possessed. But others, among 
 whom are M. Montegre and Mr. Thackrah, have asserted 
 the contrary, and the question cannot be considered as 
 finally decided. 
 
 A property universally attributed to the gastric juice is 
 that of coagulating albuminous fluids. What is termed 
 rennet consists of an infusion of the digestive stomach of a 
 calf; by adding this to milk, the albuminous part is con- 
 verted into curd. Dr. Fordyce mentions, that six or seven 
 grains of the inner coat of the stomach infused in water 
 gave a liquor, which coagulated more than a hundred 
 ounces of milk. 
 
 There are three methods by which on different occasions 
 the contents of the stomach are expelled. The first is that 
 which occurs in the ordinary progress of digestion, and con- 
 sists in the peristaltic action of the circular fibres of the sto- 
 mach. The second is the spontaneous rejection of food 
 recently taken into the stomach, unattended with nausea 
 and sickness ; an effort is made, and the fauces become 
 filled with the recently swallowed food : the effort consists 
 in an exertion of the diaphragm and abdominal muscles, 
 which compress the stomach, at the same time that the 
 fibres of the .oesophagus are relaxed, and allow of the retro- 
 grade passage of the food. The third instance is vomiting, 
 with nausea and retching. 
 
 Vomiting has frequently been supposed to result from an 
 inverted peristaltic action. But as early as 1686 an experi- 
 ment was made by M. Chirac, which sufficiently proved 
 the true nature of this phenomenon, The experiment was 
 the following : corrosive sublimate was given to a dog upon 
 bread, which was almost immediately thrown up, but 
 nausea and violent retching continued. Upon exposing the 
 cavity of the abdomen, the stomach exhibited a peristaltic 
 motion so feeble as to persuade the operator that the expul- 
 sion of its contents could not result from this cause. The 
 wound in the abdomen was then closed ; and while the 
 
Of Spasmodic Vomiting. 
 
 animal continued its efforts to vomit, the finger was intro- 
 duced and applied to the stomach, which was found to 
 remain free from contraction, and only to be flattened and 
 compressed by the abdominal muscles and diaphragm, at 
 each effort to expel its contents. 
 
 Subsequently, several physiologists were inclined to re- 
 vert to the supposition that the fibres of the stomach are 
 the principal agents in vomiting. Lieutaud and Haller 
 were of this party. 
 
 But the following experiments by M. Magendie evince 
 the justness of the original theory of Chirac ; they include 
 the mention of an additional fact, which Dr. Haighton had 
 observed, that the division of the par vagum does not 
 prevent vomiting, and present other curious matter for 
 reflection. 
 
 If two grains of tartarized antimony dissolved in an ounce 
 and a half of water be thrown into the crural vein of a dog, 
 nausea is produced almost instantaneously ; if the stomach 
 be then drawn through a wound in the abdomen, the spasm 
 of retching takes place in the diaphragm and abdominal 
 muscles, but the stomach remains without movement, and 
 no vomiting ensues. If the stomach be then replaced in 
 the cavity of the abdomen, it may be felt by the finger in- 
 troduced into the wound to remain relaxed, at the time that 
 its contents are beiiig expelled through the renewed efforts 
 of retching. 
 
 If the nervi vagi be divided, and the emetic substance be 
 introduced as above, nausea and vomiting follow. 
 
 If the abdominal muscles be removed, leaving the linea 
 alba entire, upon the injection of the emetic substance 
 nausea and vomiting take place, the stomach being com- 
 pressed between the diaphragm and linea alba. 
 
 If the phrenic nerves be divided, and the emetic sub- 
 stance injected, nausea occurs, and vomiting, but more 
 feebly than in the preceding experiment. The diaphragm 
 receives a few twigs from the eleventh and twelfth dorsal 
 nerves, which enable it still to act partially in opposition to 
 the abdominal muscles. 
 
 Finally, if the stomach be removed, and a pig's bladder 
 substituted in its place communicating artificially with the 
 
Of the Pylorus. 123 
 
 oesophagus, the injection of tartarized antimony into a vein 
 is followed by nausea, by retching, and the expulsion of the 
 contents of the bladder in the fauces. 
 
 Animals are observed instinctively to swallow a large 
 quantity of air previously to vomiting, which acts like the 
 draughts of liquid prescribed after an emetic by distending 
 the stomach; so that it resists the spasm of the diaphragm 
 and abdominal muscles, and prevents the necessity for their 
 extreme and painful contraction*. 
 
 The stomach is remarkable for its sympathies. A blow 
 upon the head produces nausea and vomiting ; indigestion 
 produces irritation in the lungs, palpitation of the heart, 
 clouded intellect and depression of spirits ; a violent blow 
 on the stomach is instantly fatal. 
 
 The valve of the pylorus consists of muscular fibres, that 
 are four times the thickness of the muscular coat of the sto- 
 mach, and form a strong circular band projecting into the 
 alimentary canal, which is besides externally much narrower 
 at this point than elsewhere. When air is blown into the 
 duodenum in a living animal, it readily finds its way into 
 the stomach : but when blown from the oesophagus into 
 the stomach, the latter yields to a great degree of disten- 
 sion before the pylorus allows the air to pass into the 
 duodenum. 
 
 The small intestine is a tube, the length of which is four 
 times that of the body. A short piece when inflated ap- 
 pears cylindrical, but the bowel is really conical. The 
 small intestine continually but insensibly diminishes from 
 the pylorus to the valvula coli, in capacity, in thickness, in 
 vascularity, in the size of its villi, in the depth and number 
 of its valvulaB conniventes. The first portion of the small 
 intestine, termed the duodenum, is about twelve inches in 
 length, and closely tied down to the back by the perito- 
 neum, which imperfectly covers it : the duodenum extends 
 first to the right side below the liver, then downwards 
 before the right kidney, then obliquely across the spine 
 towards the left. The remaining portion of the small intes- 
 
 * M&noire aur le Vomissement. 
 
124 Of the Small Intestines. 
 
 tine is attached to the spine by a deep fold of doubled 
 peritoneum, called the mesentery, which allows of ample 
 play to the convolutions of the bowels. The root of the 
 mesentery extends from the left side of the second lumbar 
 vertebra to near the right groin : the mesentery conveys the 
 vessels and nerves of the small intestine, the upper two- 
 fifths of which below the duodenum are termed jejunum, 
 the three lower ileum. 
 
 The glands in the small intestine are very numerous ; its 
 whole length is shown by the microscope to contain an 
 infinite number of the minutest follicles, not collected in 
 groups, but equally scattered throughout. Besides there 
 are glands, of a larger dimension, that present different 
 characters at opposite parts. Near the beginning of the 
 small intestine, especially in the duodenum, the glands of 
 Brunner are found, which are small flattened lenticular 
 bodies, at the outside a line in diameter, and opening by 
 large orifices. The glands of Peyer are found in the ileum 
 only, beginning insensibly, and gradually increasing in im- 
 portance towards its termination. They form about thirty 
 groups, for the most part oblong and rounded, rarely 
 triangular, disposed with their long axes parallel to that of 
 the intestine, and situated either upon the unattached 
 margin of the bowel, or at its sides. The length of 
 these groups varies from a few lines to three or four 
 inches. 
 
 The villi of the small intestines are larger than those 
 of the stomach ; there are about four thousand to the 
 surface of a square inch : their length is about one-fourth 
 of a line; at the upper part of the small intestines they 
 are broader, and frequently shorter, than at the lower part ; 
 so that they often form microscopic respresentations of the 
 valvulae conniventes. 
 
 The small intestine opens into the great intestine, as the 
 oesophagus opens into the stomach, leaving a sort of fundus 
 termed the caecum upon the left side. At its opening is 
 found the valvula coli, which consists of a production of 
 the ileum in the form of two crescentic flaps, which join at 
 their horns, and are disposed transversely in the great intes- 
 tine. These flaps contain muscular fibres which are 
 
Of the Great Intestines. 125 
 
 necessary to give effect to the valve. The caecum varies in 
 length from two inches to six ; from its extremity the ap- 
 pendix caeci vermiformis is produced. 
 
 The first five feet of the great intestine are termed the 
 colon, and the caecum is otherwise termed the caput coli. 
 The colon is distinguished by its capacious size, its epi- 
 plo'ical appendages, its longitudinal bands, its sacculated 
 appearance ; and is divided into an ascending portion, a 
 transverse portion or arch, a descending portion, and a 
 sigmoi'dal flexure which terminates in the rectum. 
 
 The smooth inner membrane of the great intestine, when 
 examined with a microscope, appears everywhere indented 
 or honeycombed with extremely small and shallow fossulae. 
 The number of mucous glands, either single, or in pairs, or 
 in larger groups, is very considerable. 
 
 The last circular fibres of the bowel constitute the in- 
 ternal sphincter of the anus. Without this is another 
 set of fibres of a different character, which are called the 
 external sphincter ; they are attached to the bulb of the 
 urethra before, to the os coccygis behind, and are under 
 the control of the will. The anus being a fixed point, 
 when the peristaltic action of the rectum is violent, or 
 the bowel not fixed in its place by a sufficiently firm 
 adhesion to the surrounding parts, it is liable to be thrust 
 in an everted state through the external orifice : when this 
 happens, the longitudinal and circular fibres are everted as 
 well as the mucous and nervous coats. 
 
 Mr. Abernethy met with the following curious malforma- 
 tion of the bowels in the body of a boy, which measured 
 four feet three inches in length, was well formed, and had 
 limbs moderately large, yet flaccid, as if wasted by recent 
 disease. The duodenum, jejunum, and ileum, when de- 
 tached from the body, measured only two feet in length : 
 the great intestines, which were considerably distended, so as 
 to be three inches in diameter, were four feet in length *. 
 
 The fleshy viscera connected with the stomach and small 
 intestines are the spleen, the pancreas, and the liver. 
 
 The spleen is a flattened oval viscus, coloured by the 
 * Phil. Trans, vol. Ixxxiii, p. 64. 
 
 T 
 
126 OftheSpken. 
 
 blood which it contains, and adherent to the fundus of the 
 stomach ; its average weight is eight ounces. The splenic 
 artery is large and tortuous, and divides into branches 
 previously to entering the gland, from which five or six 
 small vessels termed vasa brevia are reflected to the sto- 
 mach. The splenic nerves are derived from the coeliac 
 plexus. It occasionally happens that one or more small 
 glands exactly like the spleen in appearance, are met with 
 in the great omentum below the spleen. 
 
 The texture of the spleen is remarkably brittle, and tears 
 like a congeries of . membranous cells filled with clotted 
 blood. It appears, however, upon the most careful exami- 
 nation, that there are no cells in the spleen interposed 
 between the arteries and veins and containing blood. The 
 minute branches of the splenic artery in the substance of 
 the gland divide into very delicate vessels, disposed like the 
 hairs of a pencil, which do not anastomose together : the 
 veins which encircle them anastomose very freely with each 
 other. Anatomical injections pass readily from the arteries 
 of the spleen into the veins. The spleen contains a great 
 number of soft whitish bodies, of a sixth of a line and up- 
 wards in diameter: whether these are cells containing an 
 opaque fluid or glandular molecules is not determined. 
 
 It is well known that the spleen may be removed without 
 any serious effect being produced on the system. A dog, 
 from which I removed the spleen, became upon recovering 
 from the wound fatter than before : in a year's time it had 
 returned to its former condition, and no difference was 
 observed in its appearance or habits from those of other 
 dogs : it died about three years afterwards of inflammation of 
 the bowels. On examining its abdomen, the following 
 appearances, which were probably accidental, were re- 
 marked. The omentum was loaded with fat, so as to be an 
 inch in thickness at its attachment to the stomach. The 
 left kidney was a trifle larger than the right, and there were 
 two or three large lymphatic glands upon the aorta. 
 
 The use of the spleen may be regarded as wholly un- 
 known : it forms one of a class of parts, that have the 
 texture of glands, and have great vascularity, but want 
 
Of the Pancreas. 127 
 
 excretory ducts : the parts to which I refer are the thyreoid 
 gland, the thymous gland, and the renal capsules. 
 
 The pancreas is an elongated gland which lies obliquely 
 across the ventral aorta and the first lumbar vertebra; 
 it has two ducts, the larger of which opens into the 
 duodenum at the same point with the ductus communis 
 choledochus ; the smaller either opens into the greater, or into 
 the duodenum at an inch distance from it. The pancreas 
 is of the same colour and structure with the parotid and 
 submaxillary glands, and the fluid it secretes accurately 
 resembles the saliva. It weighs from four to six ounces. 
 Its arteries are derived from branches of the cceliac, its 
 nerves from the coeliac plexus. 
 
 The form of the liver, the shallow fissures which separate 
 its surface into lobes and lobules, have reference only to its 
 commodious adaptation to the neighbouring parts, and 
 have no other physiological interest. The laxness of the liga- 
 mentum latum must allow the liver a considerable change 
 of place, as the position of the body varies. The liver weighs 
 about four pounds. The parenchyma of the liver is not ho- 
 mogeneous: it appears to consist of a coherent, honey- 
 combed, or reticular mass of yellow substance, in the inter- 
 stices of which (that are polygonal and about aline in diameter) 
 a substance of a softer nature and of a darker colour is 
 deposited. The liver is brittle, and when torn presents a 
 granular surface : the granules seem composed of both ele- 
 ments blended. The biliary ducts which arise in every part 
 of the gland, but by beginnings so fine as to elude observa- 
 tion, unite together with great irregularity, and gradually 
 form larger tubes ; these coalesce by pairs to form at length 
 a single excretory duct for each lobe. By the junction of 
 these at the transverse fissure of the liver the common 
 hepatic duct is formed. 
 
 From the common hepatic duet at an acute angle is re- 
 flected forwards the cystic duct, which enlarging, becomes 
 tortuous, and expands to form the gall-bladder. The 
 gall-bladder is contained between the peritoneum and the 
 liver ; it consists of a white fibrous coat, which is probably 
 
 i 2 
 
128 Of the Liver. 
 
 contractile, and a thin mucous tunic which lies in fine re- 
 ticular rugae. 
 
 The ductus communis choledochus is the common trunk 
 formed by the union of the cystic and the hepatic duct : it 
 perforates the duodenum obliquely at about three inches 
 from the pylorus. 
 
 The liver receives blood from two sources. The right 
 and left hepatic arteries are branches from the cceliac ; 
 they are small in proportion to the magnitude of the viscus. 
 But the veins which return from the spleen and pancreas, 
 from the stomach and bowels, unite to form a large trunk, 
 termed the vena portae, which likewise enters the liver at its 
 transverse fissure, and is distributed after the manner of an 
 artery throughout the substance of the liver. When fine 
 injection is throw into the hepatic artery, it passes from 
 the capillaries of that vessel into the branches of the vena 
 portae. The veins which return the blood from the liver 
 are termed venae cavae hepaticsa : they consist of three or 
 four large trunks, which open at the back part of the 
 liver into the ascending cava. Fluids injected into the 
 hepatic artery or into the vena portae readily pass into 
 the venae cavae hepaticae and into the hepatic ducts. The 
 connection of the vessels and biliary ducts is unknown. 
 The nerves of the liver are derived from the par vagum, 
 the phrenic nerves, and the semilunar ganglia. The ab- 
 sorbents of the liver in part join the thoracic duct in the 
 abdomen, in part perforate the diaphragm, and ascend in 
 the anterior cavity of the mediastinum. 
 
 The bile is the secretion of the liver ; the gall-bladder 
 appears intended as a reservoir in which the bile may be 
 retained when not needed in the small intestine : the bile 
 is supposed to become inspissated during its stay in 
 the gall-bladder through the absorption of its aqueous 
 parts. 
 
 The bile is sometimes green, sometimes of a yellowish 
 brown, sometimes nearly colourless. Its taste is not very 
 bitter. It is seldom completely liquid, but usually contains 
 some yellow matter suspended in it. When evaporated 
 
 I 
 
Bile formed from Arterial and from Venous Blood. 129 
 
 to dryness, it leaves a brown matter amounting to about 
 one-eleventh of the original weight. 
 
 The bile appears to be the most complex of all the 
 animal fluids. Besides saline ingredients of the inorganic 
 class, it contains mucus, albumen, osmazome, gliadine, 
 casein, picromel, asparagin, acetic acid, oleic acid, margaric 
 acid, cholic acid, resin, and colouring matter. 
 
 It appears that the secretion of bile may take place from 
 arterial blood. Mr. Abernethy mentions having examined 
 the body of a female infant, which measured two feet in 
 length, and seemed about ten months old. The muscles of 
 the child were large and firm, and covered by a considerable 
 quantity of healthy fat ; and the appearance of the body 
 strongly implied that the child had, when living, possessed 
 much vigour of constitution. The liver was of the ordi- 
 nary size, but had not the usual inclination to the right 
 side of the body; it was situated in the middle of the 
 upper part of the abdomen, and nearly an equal portion 
 of the gland extended into either hypochondrium. The 
 gall-bladder lay collapsed in its usual situation : it was 
 of a natural structure, but rather smaller than common. It 
 contained about a tea-spoonful of bile, in colour resembling 
 the bile of children, being of a deep yellow ; it also tasted 
 like bile : it was bitter, but not so acridly or nauseously 
 bitter as common bile. In this infant (and the case is not 
 a solitary one) the vena portae terminated in the inferior 
 cava, and the entire supply of blood to the liver was derived 
 through an hepatic artery larger than common*. 
 
 On the other hand, the recent experiments of M. Simon 
 upon pigeons have shown, that when the hepatic artery is 
 tied, the secretion of bile continues ; but that if the veins 
 of the porta and the hepatic canals be tied, no trace of bile 
 is subsequently found in the liver : several pigeons survived 
 the latter operation for six-and-thirty hours. In these 
 animals it therefore appears that the secretion of bile takes 
 place from venous blood. 
 
 * Phil. Trans, vol. Ixxxiii, p. 61. 
 
130 Experiments of M. Simon. 
 
 M. Simon observed, that when the hepatic ducts alone 
 were tied, the liver became choked up and filled with 
 globules of a green tint ; and that this colour was diffused 
 over the whole surface of the organ, and affected the ad- 
 joining parts : it is extremely remarkable, that in from ten 
 to twenty hours after this experiment, the animals dis- 
 charged by the anus matter absolutely green, and of the 
 colour of the bile, with which the liver was overloaded ; 
 and it seems not unreasonable to suppose that this ap- 
 pearance resulted from a vicarious secretion by the kid- 
 neys*. 
 
 Perhaps we are bound to attribute the secretion of bile 
 in human beings both to the artery and to the vein ; that the 
 venous blood returned from the bowels will serve, we may 
 presume from the experiments narrated ; and to employ it 
 as far as it will go, upon this object, is consistent with the 
 general economy of Nature. 
 
 SECTION III. 
 Of the Function of the Stomach. 
 
 The progress of the food along the oesophagus is slow 
 but uninterrupted, as we learn when what we swallow has a 
 higher temperature than the blood. The descent of the 
 food depends entirely upon muscular action, so that by 
 practice one may swallow with the head downward. The 
 fibres of the upper part of the oasophagus are observed, in 
 experiments upon animals, to become relaxed directly the 
 food has passed ; but those belonging to the lower third of 
 the canal remain firmly contracted for several seconds. 
 M. Halle remarked in a woman afflicted with a malady 
 
 * Edinburgh Medical Journal, No. 90, p. 229. 
 
Of the Valve at the Cardia. 131 
 
 which permitted the interior of the stomach to be seen, 
 that at each entrance of food into that cavity the inner 
 membranes of the oesophagus were partially everted, so as to 
 form a prominent circular fold at the cardia. Nothing, 
 however, like a valve exists in human beings at the 
 entrance of the stomach : to supply the place of one, 
 when the stomach is distended, the lowest fibres of the 
 oesophagus are observed frequently to fall into a state of 
 contraction : their action and relaxation likewise keeps 
 time in some degree with the breathing ; the former generally 
 taking place during inspiration, when the pressure on the 
 stomach is the greatest. The sensations excited in the oeso- 
 phagus by pressure, laceration, and differences of tempera- 
 ture, exactly resemble those of the skin on similar occasions. 
 This mode of sensibility appears to terminate abruptly at 
 the cardia : the stomach seems to possess nothing of the 
 kind, unless we take as evidence the sensation of cold, which 
 is referred to the epigastrium, after swallowing liquids at a 
 low temperature. 
 
 The first portions of the food that enter the stomach 
 easily find room in its cavity ; as more is introduced, that 
 which was a flattened flaccid sac covered by the liver now 
 becomes rounded and prominent; and as the stomach is 
 fixed at the cardia, pylorus, and lesser curvature, it rises 
 during its distension and projects in the epigastrium. As 
 the contents of the abdomen are increased more rapidly 
 than the abdominal parietes are disposed to yield, the 
 different viscera undergo compression ; thence the bladder 
 and the rectum have a tendency to evacuate what they 
 contain ; the descent of the diaphragm likewise has greater 
 resistance offered to it; so that after a hearty meal, the 
 breathing is shorter, and the exertion of continued speak- 
 ing or of singing is attended with more than usual 
 effort. 
 
 The pyloric orifice is closed by the contraction of the 
 strong circular fibres, which form the valve. The food does 
 not, however, appear to be equally diffused throughout the 
 stomach ; it rather accumulates in the great or cardiac ex- 
 
132 Food digested in the Stomach. 
 
 tremity, a third of the length of the stomach towards the 
 pylorus being cut off from the rest by a sort of hour-glass 
 contraction of the circular fibres. Sir Everard Home first 
 described this appearance in the human stomach ; its oc- 
 currence has since been disputed ; but it has happened to 
 me on several occasions to have seen it, in instances where 
 death has occurred suddenly while digestion was going on. 
 The food retained in the great extremity of the stomach is 
 slowly dissolved ; the solution takes place upon the surface, 
 and in proportion as it proceeds, the dissolved part is 
 rolled off the rest by the peristaltic action of the fibres of 
 the stomach, and carried to the pyloric portion. 
 
 All that is swallowed is not digested. By practice one 
 may learn to swallow air, which either soon leaves the sto- 
 mach, or produces pain and nausea. Plain water, or spirits 
 largely diluted with water, and the like, are readily absorbed 
 without undergoing a previous change. M. Magendie men- 
 tions that when a ligature has been tied upon the pylorus 
 in an animal, the disappearance of the aqueous contents of 
 the stomach is not materially retarded by it. Various me- 
 dicinal substances, whether mineral or vegetable, are di- 
 rectly absorbed or imbibed by the vascular surface of the 
 alimentary canal. The food of some tribes of savages again 
 is partly of a mineral nature. The Otomacs swallow daily 
 for a season large quantities of an unctuous earth. It is 
 probable, however, that they derive no nourishment from 
 it ; and that it only serves mechanically to allay the 
 cravings of their hungry stomachs. 
 
 The materials which we digest are furnished by animals 
 and vegetables : the office of the stomach is to convert food 
 of this description into an uniform semifluid mass, which is 
 termed chyme : this change is wrought in human beings, as 
 many experiments have shown, through the exclusive influence 
 of the fluids of the stomach. In proof of the solvent effect 
 of the gastric juice, Spallanzani contrived to throw up, by 
 exciting vomiting mechanically, a tube containing flesh and 
 perforated with holes, which he had swallowed four hours 
 before : the flesh was thoroughly soaked with the fluid of 
 
Formation of Chyme. 133 
 
 the stomach, and its surface was soft and gelatinous : it 
 had moreover wasted from fifty-three to thirty-eight grains*. 
 Dr. Stevens induced a person practised in swallowing pebbles, 
 to swallow a hollow silver sphere, containing raw or cooked 
 flesh or vegetables, and perforated with holes that would 
 admit a crow-quill : the sphere was voided in about forty 
 hours perfectly empty. Mr. Hunter observed that the 
 splenic portion of the human stomach is found occasionally 
 softened, and even partially or wholly dissolved, after death. 
 In the latter case, the edges of the opening appear pulpy, 
 tender, and ragged ; and the parts adjacent to the stomach, 
 the spleen, the diaphragm, and even the lung, are some- 
 times additionally affected f. No one accustomed to dis- 
 section but has verified these observations to a greater or 
 less extent. Dr. W. Philip particularly describes a similar 
 appearance in the stomachs of rabbits, when killed after 
 taking food ; and remarks upon the singularity of this oc- 
 currence in animals habituated to the digestion of vegetable 
 matter only. 
 
 The conversion of the food into chyme is wholly different 
 from the spontaneous resolution which heat and moisture 
 tend to produce in it. The gastric juice is of an antiseptic 
 nature. Spallanzani ascertained that the gastric juice of 
 the cow and the dog will preserve veal and mutton, and 
 that without loss of weight, for thirty-seven days in winter. 
 And Dr. Fordyce found that the most putrid meat, after 
 remaining a short time in the stomach of a dog, became 
 perfectly sweet. 
 
 The action of the juices of the stomach upon its con- 
 tents, resembles that of a chemical reagent capable of dis- 
 solving them. A morsel of white of egg, for example, after 
 remaining in the stomach, has much the same appearance 
 as if it had been macerated in weak vinegar or in a solution 
 of potass. According to the notion ordinarily entertained, 
 chyme is an homogeneous greyish pulp, of a sickly sweetish 
 taste, and slightly acid. But it appears likely that there 
 
 Dissertations, &c., vol. i, p. 231. 
 
 f Hunter on the Animal (Economy, p. 229. 
 
134 Varieties of Chyme. 
 
 are as many species of chyme as there are of aliments, each 
 having some sensible points of difference from the rest, and 
 retaining other points in common. 
 
 In the elaborate experiments of Tiedemann and Gmelin 
 the following differences were observed in the digestion of 
 different principles. The animals chosen for these experi- 
 ments were dogs and horses. Liquid albumen introduced into 
 the stomach forms a homogeneous fluid, in which the albumen 
 remains quite unaltered ; and this sort of chyme passes the 
 pylorus more rapidly than any other. Coagulated albumen is 
 much more slowly dissolved, and the fluid possesses the pro- 
 perties of coagulated alb umen dissolved in acetic acid . Fibrin 
 and vegetable gluten undergo a similar change. Gelatin is 
 converted into a clear brownish fluid, in which neither gelatin 
 nor albumen can be discovered. White cheese forms an 
 opaque, dirty white fluid, containing much animal matter, 
 which however is neither casein, gelatin, nor albumen. 
 Starch is gradually dissolved, and loses its reaction with 
 iodine, being converted into sugar and amidine. The re- 
 sults obtained with compound articles of food, such as 
 milk, beef, bread, and oats, in various states of mixture, 
 were such as the foregoing facts would lead one to antici- 
 pate. Bones gave a liquid, which contained not only ani- 
 mal matter, but likewise a large quantity of lime. The 
 general result of the whole series of experiments is, that 
 all the animal principles, except liquid albumen, undergo a 
 material change during their solution in the gastric juice, 
 and that the change generally consists in their being made 
 to approach nearer in their nature to albumen*. 
 
 The character common to chyme, from whatever kind of 
 food it may have been produced, is its acidulous flavour. 
 Dr. Prout ascertained that the acid generated is the mu- 
 riatic, both free and in combination with alkalis f. The 
 same conclusion was soon after formed by Tiedemann and 
 Gmelin. They assert the clear ropy fluid of the stomach 
 without food to be nearly or entirely destitute of acidity, 
 
 * Ebinburgh Medical Journal, No. xciii, p. 369. 
 f Phil. Trans., 1824, p. 48. 
 
Ordinary period of the Formation of Chyme. 135 
 
 while the presence of food or of the most simple stimulus 
 to the mucous membrane, occasions it to become acid, and 
 more so, according to the greater indigestibility of the food. 
 The acid is very copious. They also assert the presence of 
 acetic acid ; but Dr. Prout believes this neither necessary 
 nor ordinary, and derived from the aliment when it is ob- 
 served. Dr. Prout likewise considers the general change 
 of the aliment in the stomach to consist in its greater or 
 less approach to the nature of albumen, but he has been 
 unable to detect true albumen there, when none has been 
 taken *. 
 
 Very little gas is found in the stomach during chymifica- 
 tion. M. Magendie gives the analysis by M. Chevreuil of 
 a small quantity taken from the stomach of an executed 
 criminal. 
 
 Oxygen 11.00 
 
 Carbonic acid 14.00 
 
 Hydrogen 3.65 
 
 Nitrogen 71.45 
 
 100.00 
 
 About four or five hours may be supposed to be the 
 ordinary time in which the conversion of a meal into chyme 
 is effected. M. Richerand mentions that a woman, who 
 had a fistulous ulcer in the stomach at one-third of its 
 length from the pylorus, habitually discharged chyme 
 through the aperture between three and four hours after a 
 meal. She was irresistibly led to remove the dressing 
 from the part at this time. The chyme issued rapidly 
 with a noise and an expulsion of gas. However, the 
 period that chymification takes depends in a great degree 
 upon the nature of the food. According to the observa- 
 tions of M. Magendie, fat, tendon, cartilage, coagulated 
 albumen, mucilaginous and sugary vegetables, resist the 
 action of the stomach longer than fibrinous and glutinous 
 substances. In experiments made by Sir Astley Cooper, 
 fat was found to be digested in the stomach of a dog 
 
 * Elliotson's translation of Bluinenbach's Physiology, p. 325. 
 
136 Causes which retard Chymification. 
 
 considerably more rapidly than muscular flesh, than cheese, 
 than skin, cartilage, tendon, or bone, each of which had 
 lost less in weight than the preceding in a given time 
 through the influence of the gastric secretion*. 
 
 An imperfect mastication of food renders the process of 
 chymification slower. Violent exercise immediately after a 
 meal suspends the production of chyme, and is liable to 
 cause nausea and vomiting. The recumbent position re- 
 tards the formation of chyme : sleep retards it : gentle 
 exercise with cheerfulness and moderate exertion of the 
 mind promotes it. 
 
 As the conversion of the food into chyme proceeds, the 
 sensation of fulness and the disinclination to exertion 
 which ensue upon a hearty meal gradually wear off; and 
 the system recovers from the general languor and oppres- 
 sion of other faculties, which seem to exist during the com- 
 mencement of digestion. 
 
 In what degree digestion is under the influence of the 
 nervous system is an inquiry that has led to numerous ex- 
 periments. 
 
 It appears sufficiently established, that a meal may be 
 converted into chyme after the nervi vagi have been di- 
 vided in such a manner as to interfere as little as posible 
 with the functions of other organs besides the stomach. 
 
 Mr. Brodie divided the par vagum upon the cardia, and 
 found that the operation did not prevent the conversion of 
 the food into chyme. 
 
 M. Magendie exposed the pneumogastric nerves upon the 
 oesophagus immediately above the diaphragm, after taking 
 out a portion of a rib, and divided them. The animal 
 was then compelled to swallow food, which was converted 
 into chyme, and was found to furnish afterwards an abun- 
 dant quantity of chylef. 
 
 When, however, the nervi vagi are divided in the neck, 
 the production of chyme has been described as very im- 
 perfect in those cases wherein it is not entirely prevented ,* 
 ob.-fl *io ffoaftroJp sfft tu buten'gib s-rf oK !>rrn'.'l* 
 
 * Scudamore on Gout, p. 636. 
 
 f Magendie, EHmens de Physiologic, tome ii, p. 103. 
 
Influence of the Nerves upon Digestion. 137 
 
 but it is probable that these results ensue indirectly, and are 
 to be attributed to the derangement of other functions. 
 The researches of Dr. W. Philip, confirmed by those of 
 MM. Breschet, Edwards, and Vavassour, tend to make it 
 appear that the galvanic influence directed upon the sto- 
 mach after the division of the nervi vagi in the neck 
 restores its digestive properties ; and that the removal of a 
 portion of each nervus vagus interferes with digestion 
 considerably more than the simple division of these nerves. 
 But whatever light has been thrown upon this subject 
 generally by the researches of the physiologists I have 
 mentioned, and by the experiments of Mr. Broughton and 
 of Mr. Cutler, we must admit that it remains involved in 
 great uncertainty. 
 
 MM. Leuret and Lassaigne are among the last who 
 have resumed and varied the experiment of the division of 
 the pneumogastric nerves. They state as the result of their 
 inquiries, that the only obvious and necessary effect of the 
 operation is to paralyze the sphincter muscle of the cardiac 
 orifice of the stomach. They found, that when five or 
 six inches of each nervus vagus were cut away in the neck 
 of a horse, and the gullet was tied after the animal had 
 been fed with oats, digestion went on as rapidly as usual : 
 in eight hours one-half of the oats had passed the pylorus ; 
 what remained in the stomach was all converted into 
 chyme, and the lacteals were everywhere distended with a 
 white fluid possessing the physical and chemical properties 
 of chyle. This experiment was frequently repeated, and 
 invariably with similar results*. 
 
 It appears from experiments by M. Magendie, that 
 when the cerebrum and great part of the cerebellum have 
 been removed in ducks, the instinct of seeking food is^ lost 
 in every instance, and the instinct of deglutition in many ; 
 nevertheless, food that has been introduced into the sto- 
 mach is found to be digested. 
 
 * Edinburgh Medical Journal, No, xciii, page 365. 
 
138 
 
 SECTION IV. 
 Of the Formation of Chyle. 
 
 The chyme no sooner collects in the pyloric extremity 
 of the stomach, than it is carried into the duodenum; 
 so that two or three ounces of chyme are the largest 
 quantity ever found in the part of the stomach adjoining 
 the pylorus. Upon watching the manner in which the chyme 
 is carried into the small intestine, a peristaltic action is first 
 observed to commence upon the duodenum and gradually to 
 extend itself over the stomach. This having ceased, a ver- 
 micular motion begins upon the stomach itself, which is con- 
 tinued in the opposite direction over the pylorus to the 
 duodenum, carrying the chyme before it. These phenomena 
 are repeated at intervals, and are not observed to be sus- 
 pended by the division of the pneumogastric nerves. 
 
 Upon entering the duodenum the chyme becomes mixed 
 with the bile, the pancreatic secretion, and the mucus of 
 the intestine. 
 
 The bile may be seen in living animals to exsude from 
 the ductus choledochus, not continually but at intervals, a 
 drop appearing at the orifice and diffusing itself over the 
 neighbouring surface about twice in a minute. The pan- 
 creatic secretion is yet slower in its elimination*. The 
 bile entering the intestine quickly imparts its sensible 
 qualities to the chyme, its colour and bitterness. In a 
 short time a spontaneous change is observed to take place in 
 the compound. It commonly separates into a whitish tena- 
 cious liquid termed chyle, and a yellow pulp. The former 
 is the recrementitious part of the aliment ; the latter, the 
 excrementitious portion, which after undergoing a further 
 
 * Tiedemann and Gmelin find that the pancreatic secretion contains 
 a very large proportion of highly azotized principles, namely, albu- 
 men, casein, osmazome, and a matter which is turned red by chlo- 
 rine. 
 
Appearance of the Chyle in the small Intestines. 139 
 
 change is to be thrown out of the system. Both together 
 are slowly carried along the small intestines, the viscid 
 chyle adhering to the villi, and being detained in the 
 furrows between the valvula3 conniventes ; the excrementi- 
 tious part finally reaching the colon. The chyle gradually 
 disappears in its passage along the small intestines, being 
 absorbed by vessels, which, with their contents, will be 
 described in the following chapter. 
 
 The appearance of opaque white tenacious flocculi is how- 
 ever only met with in the contents of the duodenum, when 
 they are derived from the digestion of animal or vegetable 
 matter containing fat or oil. Under other circumstances a 
 viscid greyish substance is found, that forms a layer of greater 
 or less thickness, which adheres to the mucous membrane, 
 and which must be considered as chyle. This difference 
 has been the cause of several mistakes in investigating the 
 source of the chyle. 
 
 It is natural to suppose, that the separation of this 
 important substance from the food essentially depends upon 
 its mixture with the peculiar extraneous secretions that are 
 poured into the duodenum. But various facts have been 
 brought forward, which favour a different conclusion. The 
 question is one of the greatest interest ; and it has been re- 
 cently discussed with so much ability in an article in the 93d 
 number of the Edinburgh Medical and Surgical Journal, 
 that I shall not scruple, for the advantage of my readers, 
 to extract at length the observations of the anonymous 
 critic, who appears to me on good grounds to consider some 
 experiments of my own fallacious. 
 
 "A few years ago Mr. Brodie was led to infer, from 
 some experiments on the effects of tying the excretory duct 
 of the liver in animals, that the chief purpose of the bile is 
 to separate the chyle from the chyme. For he remarked, 
 that when the choledochus duct was secured with a liga- 
 ture, and food then given, chymification went on in the 
 stomach as usual, but no chyle could be found in the in- 
 testines, or in the lacteals. The lacteals contained a trans- 
 parent fluid, which he supposed to be lymph, and the 
 
140 Researches of Tiedemdnn and Gmeliti, 
 
 watery part of the chyme*. Mr. Brodie's observations 
 have been confirmed by the subsequent experiments of 
 Mr. Herbert Mayo, who remarks, that when the choledochus 
 duct was tied in the cat or dog, and the animal killed at 
 various intervals after eating, ' there was no trace whatever 
 of chyle in the lacteal vessels f.' 
 
 " These results are at variance with the experiments both 
 of Leuret and Lassaigne, and of Ginelin and Tiedemann. 
 The former tied the common duct in a dog, and cleared out 
 the intestines by giving it a little castor oil. Twelve hours 
 after the operation they gave it bread and milk with sugar 
 thrice at intervals of six hours ; and eight hours after the 
 last meal it was strangled and examined immediately. The 
 stomach contained an acid pulp ; a very soft, whitish, 
 sweet-tasted chyme adhered to the villous coat of the 
 duodenum ; this matter increased in consistence down- 
 wards ; and in the great intestines it was firm, but had the 
 same colour, and was nearly destitute of taste or smell. 
 The thoracic duct was distended with a yellowish red trans- 
 parent fluid, which coagulated on standing exposed to the 
 air, and yielded the usual proportion of fibrin, albumen, and 
 saline matters. 
 
 " The experiments of Tiedemann and Gmelin are much 
 more elaborate and precise. They remarked that the 
 animals were attacked with vomiting soon after the opera- 
 tion, then with thirst and aversion to food ; on the second 
 or third day the conjunctiva of the eyes became yellow ; 
 the stools chalky and very fetid, and the urine yellow and 
 convertible to blue, and then to red, with nitric acid. 
 Some of the animals died ; some were killed. Of the latter 
 some had previously recovered from the jaundice, which 
 was owing to a singular phenomenon also noticed by 
 Mr. Brodie in his experiments, the re-establishment of the 
 duct by the effusion of lymph around the tied part, and the 
 subsequent dropping of the ligature. In those in which 
 
 /* Journal of Science and the Arts, xiv, p. 343. 
 t Medical and Physical Journal for October 1826. 
 
and of Lettref and Lassaigne on Digestion. 141 
 
 the biliary duct continued impervious the colouring matter 
 of the bile was found in the blood, the serous membranes, 
 the cellular tissue, the coats of the arteries and veins, and in 
 the fat. Like Brodie, Mayo, and MM. Leuret and Lassaigne, 
 they observed that chymifi cation went on as perfectly as in 
 a sound animal. In the small intestines they found nearly 
 the same principles as in sound animals, with the excep- 
 tion of those derived from the bile ; and in particular they 
 found in the duodenum, and in contact with its membrane, 
 the soft mucous flakes which some physiologists consider, 
 but as our authors imagine erroneously, to be chyle. The 
 contents of the great intestines were likewise, with the ex- 
 ception of the absence of certain biliary principles, the 
 same as in sound animals, but they had an exceedingly 
 fetid and disagreeable odour. The thoracic duct and the 
 lac teals, in animals fed recently before death, always con- 
 tained an abundant fluid, which was generally of a yellowish 
 colour. It coagulated, like ordinary chyle ; the crassamen- 
 tum acquired the usual red colour ; in short, the only 
 difference between it and the chyle seen in a sound animal 
 was, that after the tying of the choledochus duct it was 
 never white. The reason of the difference appears to be, 
 that the white colour is owing to fatty matter, taken up 
 from the food by means of the bile, which possesses the 
 power of dissolving fat, and probably, therefore, aids in 
 effecting its solution in the chyle at the mouths of the lac- 
 teals. Mr. Brodie appears to have been misled by the ab- 
 sence of the white colour, which the chyle usually pos- 
 sesses, but which it is well known equally to want in 
 ordinary digestion, if the food does not contain fatty matter. 
 Professors Tiedemann and Gmelin confine the agency of the 
 bile in chylification simply to the accomplishing the solu- 
 tion of the fatty matter*. 
 
 " The question, therefore, comes to be, what are really 
 
 * Dr. Blundell has notes of the cases of two infants, four or five 
 months old, in whom the hepatic ducts terminated blindly ; so that no 
 bile entered the intestines, and the stools were white like spermaceti, 
 and the skin jaundiced. But the infants had grown rapidly, and 
 thriven tolerably notwithstanding. Elliotson's Physiology, p. 339. 
 
 K 
 
142 Researches of Tiedemann and Gmelin, 
 
 the purposes served by the bile ? This question has been 
 fully considered by the Heidelberg professors. They con- 
 ceive, in the first place, that by its stimulant properties it 
 excites the flow of the intestinal fluids, which is clearly 
 proved to be the case by the unusual dryness of the feces 
 in jaundiced persons, and in animals whose biliary duct has 
 been tied. In the next place, it probably stimulates the 
 intestinal muscles to action. In the third place, consider- 
 ing the abundance of highly azotized principles it contains, 
 it probably contributes to animalize those articles of food 
 which do not contain azote. Fourthly, they believe it tends 
 to prevent the putrefaction of the food during its course 
 through the intestines, because when it is prevented from 
 flowing into them their contents appear much farther 
 advanced in decay than in the healthy state. Fifthly, 
 as already mentioned, it probably tends to liquefy and 
 render soluble the fatty part of the food. But, lastly, 
 they are disposed to consider it also as an important ex- 
 cretion. 
 
 "The arguments by which they endeavour to support 
 this opinion, and more particularly to prove that the secre- 
 tion of bile is supplementary to the function of the lungs, 
 are ingenious, if not conclusive. They first show, from the 
 relative size of the vena porta and hepatic ducts, from the 
 more intimate connection of the biliary capillaries with 
 those of the vena porttz, than with those of the hepatic 
 artery; and, finally, from the experiments of Malpighi, 
 recently confirmed by those of Simon, that the bile is a 
 secretion from venous, not from arterial blood. They next 
 prove that a great number of the principles of the bile, 
 such as its resin, colouring matter, fatty matter, mucus, 
 and salts, are thrown out of the body with the feces, in the 
 natural state of the biliary system, or by the urine, and into 
 the cellular tissue, when the excretory duct of the liver is 
 obstructed. These principles all contain a large proportion 
 of carbon, and would appear, therefore, to be intended to 
 carry off the excess of that element which is introduced into 
 the system with the vegetable part of the food, and which 
 is not thrown off by the lungs. In the lungs it is thrown 
 
and of Leuret and Lassaigne on Digestion. 143 
 
 off in a state of oxidation ; in the liver it is thrown oft' 
 chiefly in union with hydrogen, as in the form of resin and 
 fatty matter. That the bile is thus intended to assist the 
 lungs in decarbonizing the blood appears, they conceive, 
 from the following facts. The resin of the bile abounds 
 most in herbivorous animals, whose food contains a great 
 disproportion of carbon and hydrogen. But, what is of 
 more importance, the pulmonary and biliary organs are in 
 different tribes of animals, nay, even in different individuals 
 of the same species, in a state of antagonism to one another. 
 The size of the liver and the quantity of the bile are not 
 proportionate to the quantity of food and frequency of 
 eating; but inversely proportional to the size and perfec- 
 tion of the lungs. Thus, in those warm-blooded animals, 
 which have large lungs, and live always in the air, the liver, 
 compared with the body, is proportionally less than in those 
 which live partly in water. The liver is proportionally still 
 larger in reptiles which have lungs with large cells incapa- 
 ble of rapidly decarbonizing the blood, and in fishes, 
 which decarbonize the blood but slowly by the gills, and 
 above all, in molluscous animals, which effect the same 
 change very slowly either by gills or by small imperfectly 
 developed lungs. It is also worthy of remark, that the 
 quantity of venous blood sent through the liver increases 
 as the pulmonary system becomes less perfect. In the 
 mammalia and in birds the vena porta is formed by the 
 veins of the stomach, intestines, spleen, and pancreas ; in 
 the tortoise it receives also the veins of the hind legs, pelvis, 
 tail, and the vena azygos ; in serpents it receives the right 
 renal, and all the intercostal veins ; in fishes it receives the 
 renal veins, and those of the tail and genital organs. Far- 
 ther, during the hibernation of certain animals of the class 
 mammalia, when the respiration is suspended, and no food 
 is taken, the secretion of bile goes on. Another argument 
 is drawn from the physiology of the foetus, in which the 
 liver is proportionally a great deal larger than in the adult, 
 and in which the bile is secreted abundantly, as appears 
 from the great increase of the meconium during the latter 
 months of utero-gestation. The last argument is drawn 
 
 K 2 
 
144 Researches of Tiedemann and Gmelin, 
 
 from pathological facts. In pneumonia and phthisis the 
 secretion of the bile, according to the observations of our 
 authors, is increased ; in diseases of the heart the liver is 
 enlarged ; and in the morbus coeruleus the liver retains its 
 fetal state of disproportion. In hot climates, too, where, 
 in consequence of the greater rarefaction of the air, respira- 
 tion is less perfectly carried on than in colder climates, a 
 vicarious decarbonization is established by an increased 
 flow of the bile. 
 
 " Besides the bile and pancreatic juice, the chyme re- 
 ceives in the intestines an additional admixture of mucous, 
 or other secretions from the intestinal villous membrane. 
 Tiedemann and Gmelin remarked, that in animals which had 
 fasted long, the inner surface of the small intestines was 
 covered with a thin layer of firm mucus, tinged faintly 
 yellow with bile, and that if pebbles or pepper had been 
 swallowed recently before death, a considerable quantity of 
 thinner ropy mucus, and an increased quantity of bile, had 
 been poured out; and Leuret and Lassaigne farther ob- 
 served, that, when the villous coat of the duodenum was 
 exposed and cleaned, and then touched with diluted 
 vinegar, the membrane immediately exhaled a clear fluid, 
 and the choledochus duct discharged much bile and pan- 
 creatic juice. It must, however, be evidently almost impos- 
 sible to acquire a correct idea of the composition and pro- 
 perties of the intestinal secretion, as it cannot be procured 
 free from bile and pancreatic juice. Tiedemann and Gmelin 
 found, that, in animals which had swallowed pebbles while 
 fasting, there was in the intestinal contents more albumen 
 than the pancreatic juice could account for; and Leuret 
 and Lassaigne also found, that the matter adhering to the 
 intestines is in similar circumstances faintly acid. Both 
 believe that it possesses the power of dissolving the food, 
 and Leuret and Lassaigne even give experiments from 
 which they wish it to be inferred, that the intestinal secre- 
 tions, when mixed with the bile, form a solvent for the food 
 quite as active as the gastric juice, if not even more 
 energetic. But their experiments are unsatisfactory, be- 
 cause in the way in which the intestinal contents were 
 
and of Leuret and Lassaigne on Digestion. 145 
 
 collected they could not fail to be mingled with gastric 
 juice*. 
 
 ^ " But whatever may be the agent or agents in the pro- 
 cess, it is well known that in their course through the 
 intestines the portions of food which escape chymification 
 in the stomach are gradually altered in nature. The more 
 nutritive articles, such as coagulated albumen, fibrin, 
 casein, gelatin, disappear entirely, according to Tiedemann 
 and Gmelin, before they reach the lower end of the ileum, 
 and when any fecula passes the pylorus unaltered, it is 
 converted as in the stomach into sugar and amidine. There 
 is therefore a close analogy between the process of chymifi- 
 cation as carried on in the stomach, and the changes which 
 are effected in the small intestines. 
 
 " On account of the great number and the complexity of 
 the fluids which are added to the chyme after it reaches 
 the intestines, it is very difficult to determine what precise 
 changes are effected on the food after chymification. The 
 chief facts determined are, that the acidity of the chyme 
 decreases as it passes downwards, and at length disappears 
 long before it reaches the csecum ; that albumen exists abun- 
 dantly in the duodenum, and decreases rapidly downwards ; 
 and that the casein and other highly azotized principles 
 contained in the pancreatic juice also gradually disappear. 
 The disappearance of the acidity of the chyme is partly ex- 
 plained by the admixture of the alkali contained in the bile; 
 the albumen is lost, because it forms an important element 
 of the chyle ; and Tiedemann and Gmelin suppose that the 
 other more highly azotized principles go to convert into 
 albumen the unazotized principles in vegetable food, an 
 idea which derives some support from the fact, that herbi- 
 vorous animals have a larger pancreas than carnivorous 
 
 * M. Magendie found on introducing a piece of raw flesh into the 
 duodenum of a healthy dog, that in an hour it had been carried to the 
 rectum with no farther change than a discoloration of its surface. 
 Upon fixing a morsel of flesh in the small intestine with a thread, 
 after the lapse of three hours it appeared to have lost about half its 
 weight : the fibrin had been principally removed ; what was left was 
 entirely cellular and remarkably foetid. 
 
146 Researches of Tiedemann and Gmelin. 
 
 animals, and that a corresponding difference exists between 
 the wild and domestic cat, the former of which lives entirely 
 on animal food, and has the least pancreas. 
 
 " The changes wrought on the food in the intestines take 
 place chiefly in the duodenum and upper part of the jeju- 
 num. This is shown by the visible properties of the con- 
 tents of the intestines, and by chemical analysis, and it is 
 farther proved by the gases evolved in the small intestines 
 being produced, according to Leuret and Lassaigne, chiefly, 
 if not solely, in the upper part of their course. These 
 gases, according to 'the same experimentalists, consist of 
 carbonic acid, azote, and carburetted hydrogen, and are the 
 result, not as some think of putrefaction, but of the chemical 
 changes caused by the digestive process. 
 
 " Tiedemann and Gmelin maintain that it is an error to 
 suppose, as some physiologists, and very recently Magendie, 
 have done, that chyle is formed, and may be seen in the in- 
 testines. White flakes may be remarked floating in their 
 contents, and adhering to their inner surface, and these 
 have been believed to be the chyle on the point of being 
 absorbed. They are certainly not formed, as has been 
 imagined, by the action of the bile on the chyme, for no 
 such effect is caused by the bile on the chyme out of the 
 body ; and on the whole, it appears that they are really 
 nothing else than flakes of thickened mucus. Leuret and 
 Lassaigne, however, affirm, that all the essential principles 
 of the chyle exist ready formed in the chyme. The serous 
 part of the chyle is well known to be present. The fibri- 
 nous particles, they say, may also be detected. It is in 
 vain, indeed, to attempt to discover them by chemical 
 analysis ; this cannot be done even when chyle is purposely 
 mixed with chyme, the proportion of other principles 
 mixed with them being too great. But if the chyme be 
 attentively examined with the microscope, globules will be 
 found even in the stomach, but much more numerously in 
 the duodenum, which resemble exactly the fibrinous glo- 
 bules of the chyle. That they are in fact nothing else, 
 appears, they think, from their being seen before the 
 microscope to run together and form fine fibrils, and from 
 
Function of the Colon. 147 
 
 the absence of such globules in the gastric juice, bile, pan- 
 creatic fluid, and intestinal mucus, so that nothing but the 
 food can yield them. If these remarks shall be confirmed, 
 the Parisian physiologists have certainly added an impor- 
 tant fact to our knowledge of the process of chylification." 
 
 Gas obtained from the small intestines of criminals ex- 
 ecuted shortly after a repast was found by M. Chevreuil 
 to contain no oxygen. In the two first cases in the follow- 
 ing table, the repast had preceded execution two hours : 
 in the third, it had preceded death four hours. 
 
 Carbonic Acid. Hydrogen. Nitrogen. 
 
 Jst 24.39 -f- 55.63 + 20.08 = 100 
 
 2d 40.00 -h 51.15 + 8.86 = 100 
 
 3d 25.00 + 8.40 + 66.60 = 100 
 
 SECTION V. 
 Office of the Great Intestines. 
 
 The changes which take place upon the matter introduced 
 into the colon are a farther absorption of its fluid parts and 
 an admixture with the secretion of the bowel, from which 
 the excrementitious substance derives its fecal odour, which 
 till then is wanting. 
 
 Tiedemann and Gmelin observe, that the contents of the 
 alimentary canal, though no longer acid in the lower part 
 of the small intestines, again become acid in the commence- 
 ment of the great intestine, and are more acid in proportion 
 as the aliment is less digestible. These remarks evidently 
 strengthen the analogy already adverted to, between the 
 stomach and the caput coli. Albumen likewise often re- 
 appears in the great intestine. Dr. Prout found the fluids 
 of the large intestines coagulate lymph even as low as the 
 rectum. 
 
 By whatever means absorption takes place from the great 
 intestine, it appears probable that nourishment may be 
 received through this channel. Injections of strong broth 
 
148 
 
 Analysis of the Contents of the Cacum. 
 
 into the rectum are known to have proved nutritious. It 
 would be important to ascertain the height to which fluids 
 pass, that are thrown for this purpose into the lower bowels. 
 
 The difference of the gaseous contents of the great and 
 small intestines consists in the absence of pure hydrogen 
 from the former : in its place a somewhat smaller proportion 
 of carburetted and sulphuretted hydrogen is found. 
 
 I extract from Dr. Prout's inquiries part of a tabular 
 view of the contents of the alimentary canal in dogs fed 
 upon vegetable and animal food, which will serve additionally 
 to illustrate the changes produced in different parts of the 
 
 great intestine. 
 
 VEGETABLE FOOD. 
 
 From the C&cum. 
 Of a yellow brownish colour, and 
 of a thick and somewhat slimy 
 consistence. Did not coagulate 
 milk. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination of mucous prin- 
 ciple with altered alimentary mat- 
 ters insoluble in acetic acid, and 
 constituting the chief bulk of the 
 substance. 
 
 C. Albuminous matter, none. 
 
 D. Biliary principle, somewhat 
 altered in quantity, nearly as be- 
 fore. 
 
 E. Vegetable gluten ? none ; but 
 contained a principle soluble in 
 acetic acid, and precipitable very 
 copiously by oxalate of ammonia. 
 
 F. Saline matters, nearly as be- 
 fore. 
 
 G. Insoluble residuum, in small 
 quantity. 
 
 VEGETABLE FOOD. 
 
 From the Colon. 
 
 Of a brownish yellow colour of 
 the consistence of thin mustard, 
 
 ANIMAL FOOD. 
 From the Ctecum. 
 Of a brown colour, and very 
 slimy consistence: smell very of- 
 fensive and peculiar. Coagulated 
 milk. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination of mucous prin- 
 ciple with altered alimentary mat- 
 ters insoluble in acetic acid, and 
 constituting the chief bulk of the 
 substance. 
 
 C. Albuminous matter, a dis- 
 tinct trace. 
 
 D. Biliary principle, somewhat 
 altered in quantity, nearly as be- 
 fore. 
 
 E. Vegetable gluten ? none; but 
 contained a principle soluble in 
 acetic acid, and precipitable very 
 copiously by oxalate of ammonia. 
 
 F. Saline matters, nearly as be- 
 fore. 
 
 G. Insoluble residuum in small 
 quantity. 
 
 ANIMAL FOOD. 
 
 From the Colon. 
 
 Consisted of a brownish tremu- 
 lous and mucus-like fluid, part 
 
Analysis of the Contents of the Colon. 
 
 149 
 
 VEGETABLE FOOD. 
 
 From the Colon. 
 
 and full of air bubbles. Smell 
 faintish and peculiar, somewhat 
 like raw dough. Did not coagu- 
 late milk. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination of mucous prin- 
 ciple with altered alimentary mat- 
 ters, the latter in excess, insoluble 
 in acetic acid, and constituting the 
 chief bulk of the substance. 
 
 C. Albuminous matter, none. 
 
 D. Biliary principle, nearly as 
 before in all respects. 
 
 E. Same as in the caecum. 
 
 F. Salts nearly as above. 
 
 G. Insoluble residuum, less than 
 in the caecum. 
 
 VEGETABLE FOOD. 
 
 From the Rectum. 
 Of a firm consistence, and of an 
 olive-brown colour inclining to 
 yellow. Smell foetid and offen- 
 sive. Did not coagulate milk. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination or mixture of 
 altered alimentary matters in much 
 greater excess than in the colon, 
 with some mucus ; insoluble in 
 acetic acid, and constituting the 
 chief bulk of the feces. 
 
 C. Albuminous matter, none. 
 
 D. Biliary principle, partly 
 changed to a perfect resin. 
 
 E. Vegetable gluten? none; but 
 
 ANIMAL FOOD. 
 
 From the Colon. 
 
 with some whitish flakes, some- 
 what like coagulated albumen, 
 suspended in it. Smell faintish, 
 and not peculiarly frjetid, like bile. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination of alimentary 
 matter in excess with mucous 
 principle, insoluble in acetic acid, 
 and constituting the chief bulk of 
 the substance. 
 
 C. Albuminous matter, none. 
 
 D. Biliary principle, nearly as 
 before in all respects. 
 
 E. Same as in the caecum. 
 
 F. Salts nearly as above. Only 
 some traces of an alkaline phos- 
 phate are observed. 
 
 G. Insoluble residuum, a flaky 
 matter in very minute quantity. 
 
 ANIMAL FOOD. 
 
 From the Rectum. 
 Consisted of firm scybala, of a 
 dark brown colour inclining to 
 chocolate. Smell very foetid. Milk 
 was coagulated by the water in 
 which it had been diffused. 
 
 A. Water, quantity not ascer- 
 tained. 
 
 B. Combination or mixture of 
 altered alimentary matters in much 
 greater excess than in either of 
 the other specimens, with some 
 mucus; insoluble in acetic acid 
 and constituting the chief bulk of 
 the feces. 
 
 C. Albuminous matter, none. 
 
 D. Biliary principle, more con- 
 siderable than in the vegetable 
 feces, and almost entirely changed 
 to a perfectly resinous-like sub- 
 stance. 
 
 E. Vegetable gluten ? none ; but 
 
150 Analyst* of the Contents of the Rectum. 
 
 VEGETABLE FOOD. ANIMAL FOOD. 
 
 From the Rectum. From the Rectum. 
 
 contained a principle similar to contained a principle similar to 
 
 that in the caecum and colon. that in the caecum and colon. 
 
 F. Salts nearly as before. F. Salts nearly as before. 
 
 O. Insoluble residuum, consist- G. Insoluble residuum, consist- 
 ing chiefly of vegetable fibres ing chiefly of hairs, 
 mixed with hairs. 
 
 The analysis of human feces, according to Berzelius, 
 yields 
 
 Water 73.3 
 
 Vegetable and animal remains 7-0 
 
 . Bile 0.9 
 
 Albumen 0.9 
 
 Peculiar and extractive matter 2.7 
 
 Slimy matter, consisting of picromel, peculiar animal 
 
 matter, and insoluble residue 14.0 
 
 Salts 1.2 
 
 100.0* 
 
 As the excrementitious mass descends, it gradually parts 
 with its fluids, becoming towards the rectum particularly 
 dry : it here produces a sensation leading to the desire to 
 expel it, accompanied by an involuntary contraction of 
 the fibres of the bowel. It commonly happens that the 
 peristaltic action of the fibres of the rectum when first dis- 
 tended with fecal matter is opposed by the contraction of 
 the sphincter externus ani ; and for the subsequent expul- 
 sion of the feces the bowel has again to be thrown into ac- 
 tion by an effort of the will. 
 
 But we have not grounds for believing that the muscular 
 coat of the bowel is a part that can act voluntarily : all that 
 we know to take place is, that when pressure is made upon the 
 bowel by the diaphragm, abdominal muscles, and levator ani, 
 its peristaltic action recommences. The longitudinal fibres of 
 the rectum tend to prevent a protrusion of the lower part of 
 the bowel, and assist in retracting it from the matter in 
 progress of expulsion. 
 
 The frequency with which the lower bowels are emptied 
 
 * Thompson's Chemistry, vol. iv, page 555. 
 
Of the various Articles of Food. 151 
 
 depends partly upon habit, partly upon peculiarity of con- 
 stitution. Herberden mentions a person who naturally had 
 a motion once a month only, and another who had twelve 
 motions every day during thirty years, and then seven 
 every day for seven years, and rather grew fat than other- 
 wise. In general the accumulation of fecal matter takes 
 place in the rectum daily at the same hour : if the usual 
 time for its evacuation is allowed to pass by, the contents 
 of the rectum appear to be thrown back upon the colon : 
 or at any rate the attempt to evacuate the bowels is fruit- 
 less. 
 
 SECTION VI. 
 
 Of the various Substances employed as Food. 
 
 Vegetation seems interposed between the soil and animal 
 life as a chemical apparatus for combining the elements of 
 inert matter into forms, in which they become capable of 
 being assimilated by the animal body to its own nature. 
 Animals again differ among themselves in the original fitness 
 of their organs for digesting vegetable matter; so that some 
 appear to form an intermediate class in reference to the 
 function of digestion, being intended to animalize vegetable 
 matter, while they are themselves prepared by Nature to be 
 the prey of animals exclusively carnivorous. Those which 
 are herbivorous have the alimentary canal considerably more 
 complicated than those which live on animal food ; either 
 the stomach is divided into distinct chambers, or the colon 
 and csecum are remarkably developed to fit them for a more 
 elaborate concoction of the food. 
 
 The common food of human beings consists either of 
 muscular flesh and fat, of milk and eggs, or of the seeds 
 of certain grasses, of the roots, the leaves, and stalks of 
 different vegetables, and of various kinds of fruit. But the 
 former substances are found to be more nutritious than the 
 latter ; and the greatest bodily strength is attained by com- 
 
152 Of the various Articles of Food. 
 
 bining a diet composed chiefly of animal substance with 
 habits of strong and regular exercise. 
 
 The proximate principles of animal matter which serve 
 for nutriment are fibrin, albumen, jelly, oil, casein, and 
 osmazome or the extractive matter of meat, which seems to 
 give the specific flavour to the flesh of different animals, 
 but may possibly consist of fibrin only, slightly altered by 
 heat*, 
 
 Gluten, farina, mucilage, oil, and sugar, are the nutritive 
 proximate principles of vegetable matter ; at the head of 
 which gluten is placed, as a substance containing nitrogen, 
 and more resembling animal matter than any other proxi- 
 mate principle in plants. 
 
 Dr. Prout reduces all the articles of nourishment among 
 the higher animals to three classes, the saccharine, the oily, 
 and the albuminous. The first comprehends sugars, 
 starches, gums, acetic acid, and some other analogous prin- 
 ples ; the second, oils and fats, alkohol, &c. ; the third, 
 other animal matters and vegetable gluten. The following 
 passage is quoted by Dr. Elliotson in his translation of 
 
 Tl J 
 
 Blumenbach's Physiology from an unpublished work by 
 Dr. Prout on the subject of digestion. 
 
 " Observing that milk, the only article actually furnished 
 and intended by nature as food, was essentially composed 
 of three ingredients, viz. saccharine, oily, and curdy or 
 albuminous matter, I was by degrees led to the conclusion 
 that all the alimentary matters employed by man and the 
 more perfect animals, might, in fact, be reduced to the 
 same three general heads ; hence I determined to submit 
 them to a rigorous examination in the first place, and 
 ascertain, if possible, their general relations and analogies. 
 An account of the first of these classes, viz. the saccharine 
 matters, has been just published in the Philosophical Trans- 
 actions, and the others are in progress. The characteristic 
 property of saccharine bodies is that they are composed 
 simply of carbon united to oxygen and hydrogen in the 
 
 * Thompson's Chemistry, vol. iv, p. 424. 
 
Of the various Articles of Food. 153 
 
 proportions in which they form water ; the proportions of 
 carbon varying in different instances from about 30 to 50 
 per cent. The other two families consist of compound 
 bases (of which carbon constitutes the chief element) like- 
 wise mixed with and modified by water, and the proportion 
 of carbon in oily bodies, which stand at the extreme of the 
 scale in this respect, varies from about 60 to 80 per cent. ; 
 hence, considering carbon as indicating the degree of nutri- 
 tion, which in some respects may be fairly done, the oils may 
 be regarded in general as the most nutritious class of bodies; 
 and the general conclusion from the whole is, that sub- 
 stances naturally containing less than 30 or more than 80 
 per cent, of carbon are not well, if at all, adapted for 
 aliment. 
 
 "It remains to be proved whether animals can live on 
 one of these families exclusively, but at present experiments 
 are decidedly against this assumption, and the most pro- 
 bable view is, that a mixture of two at least, if not of all 
 three of the classes of nutriment is necessary. Thus, as has 
 been stated, milk is a compound of this description, and 
 almost all the gramineous and herbaceous matters employed 
 as food by animals, contain at least two of the three. The 
 same is true of animal aliments, which consist, at least, of 
 albumen and oil ; in short, it is, perhaps, impossible to 
 name a substance employed by the more perfect animals as 
 food, which does not essentially constitute a natural com- 
 pound of at least two, if not of all three of the above three 
 great classes of alimentary matters. 
 
 " But it is in the artificial food of man that we see this 
 great principle of mixture most strongly exemplified. He, 
 dissatisfied with the productions spontaneously furnished 
 by nature, culls from every source, and, by the power of 
 his reason, or rather his instinct, forms in every possible 
 manner, and under every disguise, the same great alimentary 
 compound. This, after all his cooking and art, how much 
 soever he may be inclined to disbelieve it, is the sole object 
 of his labour, and the more nearly his results approach to 
 this, the more nearly they approach perfection. Thus, 
 from the earliest times, instinct has taught him to add oil 
 
154 Of the various Articles of Food. 
 
 or butter to farinaceous substances, such as bread, and 
 which are naturally defective in this principle. The same 
 instinct has taught him to fatten animals, with the view of 
 procuring the oleaginous in conjunction with the albumi- 
 nous principle, which compound he finally consumes, for 
 the most part in conjunction with saccharine matter, in the 
 form of bread or vegetables. Even in the utmost refine- 
 ments of his luxury and in his choicest delicacies, the same 
 great principle is attended to, and his sugar and flour, his 
 eggs and butter, in all their various forms and combinations, 
 are nothing more nor. less than disguised imitations of the 
 great alimentary prototype, milk, as presented to him by 
 nature." 
 
 The following remarkable experiments by M. Magen- 
 die, tend to support the views contained in the preceding 
 extract. 
 
 A dog fed upon white sugar and water exclusively ap- 
 peared for seven or eight days to thrive upon this suste- 
 nance. He was lively, and ate and drank with avidity. 
 Towards the second week, however, he began to lose flesh, 
 though his appetite continued good. In the third week he 
 lost his liveliness and appetite ; and an ulcer formed on the 
 middle of each cornea, which perforated it, and the humours 
 of the eye escaped : the animal became more and more 
 feeble, and died the thirty-second day of the experiment. 
 Results nearly similar ensued with dogs fed upon olive oil 
 and distilled water ; but no ulceration of the cornea took 
 place, and in dogs fed with gum, and with butter. 
 
 A dog fed with white bread made from pure wheat and 
 with water died at the expiration of fifty days. Another 
 fed exclusively on military biscuit, suffered no alteration in 
 its health. 
 
 Rabbits or Guinea pigs fed upon one substance only, as 
 corn, hay, barley, carrots, cabbage, See., die with all the 
 marks of inanition, generally in the first fortnight, and some- 
 times sooner. 
 
 An ass fed upon boiled rice died in fifteen days, having 
 latterly refused its nourishment. A cock lived for many 
 months upon this substance, and preserved its health. 
 
Of the various Articles of Food. 155 
 
 Dogs fed exclusively with cheese, or with hard eggs, are 
 found to live for a considerable period, but become feeble, 
 meagre, and lose their hair. 
 
 The substance from which rabbits and Guinea pigs can 
 derive subsistence for the longest period appears to be mus- 
 cular flesh. 
 
 When a certain degree of emaciation has been produced 
 by feeding an animal for some time upon one substance, as 
 for instance upon white bread during forty days, the animal 
 has appetite left to eat with avidity different kinds of food, 
 but the change in diet comes too late ; the animal does not 
 regain its strength ; it continues to waste, and dies about 
 the same time at which its death would have happened had 
 the exclusive diet been continued. 
 
 Or we know empirically respecting our food : that to 
 be nutritious, it must be mixed and varied ; that when we 
 are in health, the flesh of adult animals simply roasted, 
 or broiled, is the most wholesome and nourishing element 
 in our meals; that condiments and fermented drinks are 
 in moderation salutary, by stimulating the stomach ; that 
 the quantity of liquid at a meal within certain limits is 
 indifferent and a matter of habit ; that it is dangerous 
 suddenly to deviate to any great extent from our established 
 habits in diet; that two or at most three meals are all 
 that the stomach of an adult can well digest in the twenty- 
 four hours. 
 
 In sickness every thing is changed ; the lightest food, 
 which would produce disorder and acidity in a strong 
 stomach, and its frequent repetition, often become a 
 principal means towards recovery : just as absolute rest 
 restores a broken bone, which in health it would have 
 weakened. 
 
 
 
CHAPTER VIII. 
 OF THE LACTEAL AND LYMPHATIC VESSELS. 
 
 WE have next to follow the route of the chyle from the 
 small intestines into the venous system. 
 
 In the year 1622 Aselli accidentally observed upon the 
 mesentery of a dog a number of white lines extending from 
 the bowel towards the liver : on puncturing them a milk-like 
 fluid escaped, and left them transparent vessels. They were 
 termed lacteals, and were justly supposed by their discoverer 
 to absorb the chyle and to convey it into the blood. Succes- 
 sive inquiries have shown not merely the origin and termina- 
 tion of these vessels, but that they form part of a system as 
 minutely distributed through the frame as the blood-vessels, 
 and theoretically termed the absorbent system. 
 
 At the angle formed by the meeting of the subclavian 
 with the internal jugular vein upon either side of the neck, 
 two or more of these pellucid vessels open, so as to pour 
 their contents into the current of blood passing towards the 
 right auricle. These are the main trunks of the absorbent 
 system, which ramifies from the veins of the neck and of 
 the trunk to every region and organ of the body. 
 
 The thoracic duct, the largest absorbent vessel in the 
 body, is about three lines in diameter when distended, has 
 a thin but strong texture, and appears when collapsed semi- 
 transparent and of a reddish grey colour. The thoracic 
 duct of a horse, inverted upon the thickest rod it will admit, 
 is shown by the rupture of its lining membrane to consist of 
 a serous inner tunic and an outer fibrous one. It is pre- 
 
 
Of the Conglobate Glands. 157 
 
 sumed that a similar distinction of parts exists in human 
 absorbents*. 
 
 Each absorbent vessel contains many valves, consisting 
 of pairs of semilunar folds of membrane attached by their 
 convex edges, as in the veins, and capable of being thrown 
 down by the reflux of its contents, so as to prevent their 
 passage in a retrograde direction towards the extremities. 
 Upon the fleshy viscera the resistance of the valves may be 
 overcome by continued pressure, so that mercury will pass 
 from a trunk into the branches, which are there found to be 
 distributed arborescently, with a minuteness so surprising, 
 that the surface of the viscus is entirely covered as with a 
 reticular sheet of quicksilver. These vessels anastomose 
 with other vessels distributed through the substance of the 
 organ. 
 
 In the limbs the absorbent trunks are distributed in two 
 sets ; one that accompanies the arteries, another which ac- 
 companies the subcutaneous veins : to each artery from three 
 to seven absorbent vessels are attached ; with the subcuta- 
 neous veins from thirty to fifty are associated, which are 
 spread over the most protected surfaces of the limbs. 
 
 At particular parts of the body small flattened bodies 
 circular or oval, from three to ten lines in diameter, are 
 found connected with absorbent vessels. These bodies are 
 termed conglobate or absorbent glands. They are very vas- 
 cular, and have filaments of nerves distributed to them : 
 each appears to consist of a soft fleshy porous substance 
 contained in a membranous capsule : the central part is 
 whiter and firmer than the rest. Generally many absor- 
 bent vessels, termed vasa inferentia, enter a conglobate 
 gland upon the side remote from the heart, and a smaller 
 number, termed vasa efferentia, leave it upon the near 
 side. 
 
 Mercury injected into the vasa inferentia is seen to fill 
 a series of cells in the corresponding absorbent gland ; it then 
 escapes by means of the vasa efferentia. After an injection 
 with wax, the whole substance of the gland appears to consist 
 
 * Cruikshank, Anatomy of the Absorbing Vessels, p. 1. 
 
 L 
 
158 Of the Conglobate Glands. 
 
 of convoluted absorbents irregularly dilated, and which reci- 
 procally communicate. 
 
 The situation of the absorbent glands and their connec- 
 tion with the different sets of absorbent vessels is as follows. 
 
 Two or three small absorbent glands are found at the 
 inner ancle, four or five in the ham, eight or ten at the 
 groin. To the subcutaneous glands at the groin absorbents 
 tend from the leg and thigh, from the pudenda, the ab- 
 dominal parietes, the nates, and the loins. 
 
 A chain of absorbent glands and a plexus of absorbent 
 vessels ascends around the iliac arteries to the aorta, con- 
 tinually receiving trunks derived from the neighbouring 
 parts. Opposite to the second lumbar vertebra the absor- 
 bents of the mesentery, having passed through a cluster of 
 glands, collect into an oval sac termed the receptaculum 
 chyli ; the trunk continued from the receptaculum chyli 
 and from the absorbents of the lower extremities is termed 
 the thoracic duct : it ascends between the aorta and right 
 crus of the diaphragm into the posterior mediastinal cavity, 
 which it obliquely traverses from right to left in its course 
 to the neck : having perforated the fascia cervicalis pro- 
 funda, the thoracic duct ascends behind the subclavian 
 artery of the left side, and then arches downwards to open 
 into the angle at which the subclavian vein joins the in- 
 ternal jugular. In this course the thoracic duct is joined 
 by absorbents from the viscera and neighbouring parts. 
 Absorbent glands accompany these vessels, which are 
 most numerous around the bronchi, where they are of a 
 black colour. 
 
 Two or three absorbent glands are found at the bend of 
 the elbow joint, and clusters of them surround the axillary, 
 subclavian, and carotid arteries. The absorbent vessels of 
 the left side of the head and of the left upper extremity 
 mostly join the thoracic duct, but in part open by two 
 or three separate orifices into the subclavian vein. The cor- 
 responding absorbent vessels of the right side open by three 
 or four trunks into the angle at the right subclavian vein 
 and internal jugular : these are sometimes joined by a large 
 branch given off from the thoracic duct in the chest; an 
 
Absorbent Vessels either Lacteals or Lymphatics. 159 
 
 anomaly, a specimen of which, that I injected, is preserved 
 in the Museum in King's College. 
 
 During the completion of digestion in the small intes- 
 tines, the absorbent vessels of the mesentery, the recepta- 
 culum chyli, and the thoracic duct, are found full of chyle : 
 at other times these vessels contain more or less of a transpa- 
 rent fluid termed lymph, which forms the habitual contents 
 of the remaining larger part of the system. 
 
 The absorbent vessels of the small intestines and of the 
 mesentery are termed Lacteals, those in every other part of 
 the body Lymphatics. 
 
 Till within these few years, it was the commonly received 
 opinion among anatomists, that the veins and absorbents 
 communicated at the points alone which have been already 
 mentioned. To several, indeed, it had happened, when 
 injecting absorbents, to find the mercury run into veins 
 elsewhere ; but the circumstance had been considered 
 either as a deviation from ordinary structure, or as the 
 result of some error in the process of injecting. Aselli 
 likewise, the original discoverer of the absorbent system, 
 was persuaded that the lacteals terminated in the vena 
 portae of the liver : but afterwards, when the direct com- 
 munication of these vessels with the thoracic duct through 
 the receptaculum chyli had been demonstrated, the supposi- 
 tion of Aselli was considered to be erroneous, and was aban- 
 doned. Recently, however, the observations of Fohman have 
 shown that it was partially correct, and that many of the 
 lacteal vessels open into branches of the visceral veins. 
 
 The researches of Lippi* go to prove connections between 
 the venous and absorbent system, yet more numerous and 
 general. He has shown that the absorbent vessels in the 
 abdomen open freely into the iliac, the spermatic, the emul- 
 gent, the lumbar veins, and the vena cava, as well as into 
 the branches of the portal system : that they communicate 
 both by plunging into the great venous trunks, and by 
 opening into the small veins that issue from the conglobate 
 glands, and by direct continuity with the capillary veins ; 
 
 * Illustrazioni fisiologichee patologiche del sistema linfatico-chilifero, 
 del professore Regolo Lippi. Fireuze, 1825. 
 
 L 2 
 
160 Researches of Lippi, 
 
 and, finally, that several absorbent trunks in the belly ter- 
 minate directly in the pelvis of the kidney ; a fact, which 
 curiously confirms the supposition of Sir Everard Home, 
 that there exists a short route from the stomach to the 
 urinary organs. 
 
 Lippi is of opinion, that no communications between 
 the absorbents and the veins take place in the limbs. He 
 observes, t ho poi imprese le injezione piil volte dalle estre- 
 mita inferiori per osservare se mi riusciva riscontrare qualche 
 communicazione di linfatici colle vene degli articoli; ma 
 giammai non sono in questo riuscito." For my own part, 
 I think it not unlikely that such communications do exist. 
 At all events, I have sometimes seen the mercury thrown 
 into absorbents of the limbs unaccountably make its way 
 into the veins. 
 
 Mascagni remarked, that on successfully injecting the 
 arteries of a part with size and vermilion, the lymphatics 
 became filled with strained size. On injecting the arteries 
 of the mesentery of a dog with ink, I observed the veins 
 next to become filled with a black fluid, and then the lac- 
 teals ; and I have certainly seen, in one instance, absorbents 
 of the liver filled with coloured injection from the hepatic 
 artery. 
 
 Chyle extracted from the thoracic duct of a dog or cat 
 killed during digestion and opened immediately after death, 
 varies in appearance as the food has or has not contained 
 oil or fat : in the former case its colour is milk-white, in the 
 latter it is nearly transparent. Coloured substances mixed 
 with the food are rarely found to impart the least tinge 
 of colour to the chyle. 
 
 Chyle is something heavier than distilled water ; it is of 
 a salt taste, and sensibly alkaline. Soon after being drawn 
 it coagulates, and afterward separates into three parts ; one 
 solid, which rests at the bottom of the vessel ; another 
 liquid ; and a third substance forming a thin layer on the 
 surface of the latter, and less observable in the semi-trans- 
 parent than in the opaque chyle. At the same time the 
 chyle assumes a reddish tint. The solid substance appears 
 to resemble fibrin ; the liquid, serum ; the third element is 
 
Of Lymph. 161 
 
 of an oily nature. The chyle contains minute globules of 
 various sizes, but the largest are smaller than the particles 
 of the blood. 
 
 Chyle formed from the digestion of sugar contains but 
 little fibrin. Dr. Marcet found that chyle derived from 
 vegetable matter contains three times as much carbon as 
 that from animal matter. 
 
 Lymph extracted from the thoracic duct of an animal 
 killed after fasting for three or four days is a fluid nearly 
 transparent, slightly opaline, and tinged with red, but 
 sometimes of a yellow tint : of a saline taste, of the specific 
 gravity compared with water of 1022.28 to 1000. From a 
 large dog it may be collected in the quantity of an ounce 
 and a half. 
 
 Lymph spontaneously coagulates, and then appears com- 
 posed of a fibrous clot, in the irregular cells of which a 
 fluid is contained, which on compression again coagulates. 
 The red tint of the lymph is deepened on its coagulation. 
 If the clot be exposed to oxygen it becomes scarlet ; if to 
 carbonic acid, purple. Lymph contains globules resem- 
 bling, but less in size than, those of the blood. According to 
 M. Chevreuil, the composition of lymph is the following : 
 
 Water 926.4 
 
 Fibrin 4.2 
 
 Albumen 61.0 
 
 Muriate of soda 6.1 
 
 Carbonate of soda 1.8 
 
 Phosphate of lime ^ 
 
 Phosphate of magnesia > .5 
 
 Carbonate of lime J 
 
 1000.0 
 
 Prolonged fasting in a dog is found to produce a 
 redder colour in the lymph, nearly approaching that of 
 the blood. 
 
 The following is an analysis of the researches of Tiede- 
 mann and Gmelin on the nature of the chyle. The firmness 
 of the coagulum of chyle seems to depend chiefly on the 
 quantity of fibrin. Chyle hardly coagulates at all before it 
 
162 Researches of Tiedemann and Gmelln. 
 
 has passed through the mesenteric glands. After passing 
 through them, the fibrin begins to appear, and it is much 
 more abundant after the addition of the lymph from the 
 spleen, which contains a very large quantity of fibrin. The 
 quantity is considerably lessened in the chyle of digestion : 
 it is increased in the chyle formed after the ligature of the 
 ductus choledochus. It abounds in the lymph from the 
 lower extremities. In like manner the chyle before passing 
 the mesenteric glands contains no red particles : but it does 
 immediately afterwards, and more particularly after it is 
 mixed with the lymph from the spleen, which abounds with 
 them as with fibrin. These particles are also, like the 
 fibrin, very much diminished in the chyle of digestion, and 
 proportionally to the nutritiveness and digestibility of the 
 food. They are increased by tying the choledochus duct. 
 They abound in the lymph of the lower extremities. The 
 chyle frequently contains fatty matter, very little or none, 
 however, if the animal is fasting, or has fed on food which 
 does not contain fat, and most, when the food is very 
 fatty, when, for example, butter is mixed with it, The 
 fatty matter is not dissolved, but exists merely in a state of 
 minute division and suspension, giving to the chyle its 
 peculiar white colour; for the colour is removed, and the 
 chyle rendered limpid by ether, which carries away the 
 fatty particles. There is no fatty matter in the lymph of 
 the lower extremities; it is much less abundant in the 
 thoracic duct than in the chyle before it passes through the 
 mesenteric glands, and it hardly exists in the chyle at all 
 when the ductus choledochus is tied. The serum of the 
 chyle is very generally alkaline ; in two instances only was 
 it found neutral, namely in a dog fed on fibrin, and in a 
 sheep fed on oats. Its solid contents differ in the chyle of 
 fasting animals and in that of digestion. In the horse while 
 fasting the solid part of the serum consists on an average of 
 76.2 per cent, of albumen, 6.7 animal matter soluble in 
 water, and 16 animal matter soluble in alcohol; but after 
 digestion, of 61 albumen, 3 animal matter soluble in water, 
 34 animal matter soluble in alcohol, of which twenty parts 
 were fat. Our authors were not able to decide whether the 
 
Nature of Chyle and Lymph. 163 
 
 total amount of solid matter in the serum is increased or 
 diminished during digestion. 
 
 The inference drawn by Tiedemann and Gmelin from 
 the foregoing facts is, that the fibrin, colouring particles, 
 and albumen of the chyle, are supplied either not at all by 
 the intestinal lacteals, or at least in much less quantity 
 than by the lymph, which is formed by the blood, and that 
 the food supplies chiefly fatty matter, and other principles 
 soluble in alcohol, particularly osmazome. Before they are 
 entitled, however, to form these conclusions unreservedly, it 
 is necessary to establish a preliminary condition, which 
 they have entirely neglected, namely, that the flow of the 
 lymph increases along with the flow of the intestinal chyle 
 during digestion ; for if it does not, then the proportional 
 deficiency of albumen and fibrin in the chyle of digestion, 
 when compared with the lymph, is no proof whatever that 
 the former does not supply even more of these principles 
 than the latter to the blood. The inferior proportion may 
 be more than compensated by the great increase in the 
 quantity of fluid *. 
 
 We may next inquire what has been ascertained respect- 
 ing the commencements of the absorbent vessels. Our 
 knowledge in this instance is of the dubious character 
 which belongs to microscopical evidence, and applies but to 
 the smallest part of the absorbent system : yet it is difficult 
 to distrust the exactness of Cruickshank and William Hunter, 
 and what can be demonstrated of a part, we may infer ana- 
 logically to be true of the whole. 
 
 " A woman," says Mr. Cruickshank, te died in conse- 
 quence of convulsions after lying-in, about five in the morn- 
 ing. She had been in perfect health the preceding evening, 
 and ate heartily at supper. The lacteals (upon the mesen- 
 tery) were distended with chyle, which here formed a firm 
 coagulum. Many of the villi were so full of chyle that I 
 saw nothing of the ramifications of the arteries or veins ; the 
 whole appeared as one white vesicle, without any red lines, 
 pores, or orifices whatever. Others of the villi contained 
 
 * Edinburgh Medical Journal, 1. c. 
 
164 Origin of the Lacteals. 
 
 chyle, but in a small proportion ; and the ramifications of 
 the veins were numerous, and prevailed by their redness 
 over the whiteness of the villi. In some hundred villi I saw 
 the trunk of a lacteal forming or beginning by radiated 
 branches. The orifices of these radii were very distinct on 
 the surface of the villus, as well as the radii themselves, 
 seen through the external surface, passing into the trunk 
 of the lacteal : they were full of a white fluid. There was 
 but one of these trunks in each villus. The orifices on 
 the villi of the jejunum, as Dr. Hunter himself said (when 
 I asked him as he 'viewed them in the microscope, how 
 many he thought there might be), were about fifteen or 
 twenty on each villus ; and in some I saw them still more 
 numerous*/' 
 
 Thus it appears that the lacteal system originates by 
 numerous capillary orifices upon the villi of the small 
 intestines ; and it is natural to presume that the absorption 
 of chyle commences upon physical principles. Accord- 
 ingly, if the mesentery be exposed immediately after the 
 death of an animal killed during digestion, and the con- 
 tents of a lacteal be pressed forwards towards the thoracic 
 duct, and a ligature be tied upon the empty vessel, the 
 lacteal is found to become filled again with chyle by the 
 continuance of intestinal absorption. The valves in the 
 larger lacteal vessels are exceedingly numerous. It is 
 reasonable to believe them equally numerous in the minute 
 branches in which the system originates. Let us suppose 
 that through capillary attraction, the fluid with which 
 it is bathed would ascend in the capillary orifice of a 
 lacteal; if it rise beyond a single pair of valves, the 
 contraction of the vessel itself will be sufficient to urge 
 it onward to the venous system. 
 
 But this simple explanation of the mechanism of lacteal 
 absorption requires to be somewhat modified. Of the 
 numerous liquid substances which reach the small intestine, 
 the lacteals appear to absorb chyle only. 
 
 The experiments of Hunter went indeed to prove the 
 
 * Cruicfcshank, Anatomy of the Absorbing Vessels, p. 59. 
 
Hunterian Experiment upon Lacteal Absorption. 165 
 
 reverse. When a solution of starch and indigo, or milk 
 and water, were injected by Mr. Hunter into the small 
 intestines of sheep and asses, a blueish or whitish liquid 
 appeared to rise in the lacteals. But there is reason to 
 believe that these observations were not made with sufficient 
 exactness. They have been repeated by M. Flandrin, and 
 various physiologists of the present day, and no sub- 
 stance, thrown into the bowel, distinguishable by its odour, 
 colour, or poisonous effects, appeared to enter the lacteals. 
 When Mr. Hunter saw a white fluid rise in the lacteals 
 after pouring milk into the bowel, we must suppose that 
 some remains of chyle in the small intestine continued to 
 be absorbed ; and where the blue liquid was used, the 
 deception probably resulted from the following circum- 
 stance. When the lacteals are empty, and are seen against 
 a dusky medium, they appear as blue lines upon the 
 mesentery. I observed this circumstance when repeating 
 the Hunterian experiment upon different animals. The lac- 
 teals, which when a solution of starch and indigo was first 
 placed in the cavity of the bowel were full of chyle, on being 
 examined half an hour afterwards appeared of a clear blue 
 colour, and those present were for an instant satisfied that 
 the indigo had been absorbed : but upon placing a sheet 
 of white paper behind the mesentery, the blue tinge 
 disappeared, the vessels were seen to be transparent and 
 empty. On removing the white paper, they reassumed 
 their blue colour. 
 
 Thus the repetition of the Hunterian experiment has esta- 
 blished a different conclusion to that which its author drew 
 from it, and goes to prove the function of the lacteals to 
 be limited to the absorption of chyle. We are at liberty to 
 conjecture that the orifices of the lacteals are of such a nature 
 as to close on the contact of every other substance. It is a 
 singular circumstance, that the veins of the mesentery 
 are sometimes found to contain a white fluid, which seems 
 to be chyle : it has not been proved through what channel 
 this fluid arrives there. 
 
 If the thoracic duct at a proper interval after a meal be 
 exposed in the neck of a dog where it enters the subclavian 
 
166 Evidence that Lymphatics absorb. 
 
 vein, upon opening the duct chyle escapes with great 
 rapidity. Its velocity is observed to be increased every 
 time that the animal contracts the abdominal muscles, or 
 when the abdomen is compressed by the hand, and to 
 bear a proportion to the quantity of chyme under decomposi- 
 tion in the small intestine. During the first five minutes 
 after opening the thoracic duct in a middle-sized dog, 
 half an ounce of liquid escaped ; subsequently the flow of 
 chyle was much slower*. 
 
 The use of the conglobate glands is unknown, but they 
 are observed to be disproportionately large, and to contain 
 more fluid in early life than at a later period. 
 
 Of the lymphatic system, beyond the anatomical dis- 
 tribution of its branches, nothing is known with certainty. 
 But we are at liberty to conjecture upon analogy, that 
 lymphatics begin upon the mucous surface of the stomach 
 and great intestines, and that they take up a liquid elabo- 
 rated in those parts from the food. When indeed a dog 
 is forced to drink diluted alcohol during digestion, the 
 blood has the odour of alcohol, the chyle has not. The 
 blood in the veins of the small and great intestines of the 
 horse is found to have the odour of their contents, which the 
 chyle wholly wants. But on the other hand, MM. Leuret 
 and Lassaigne assert, that chyle is taken up from the stomach , 
 and may be found in the lymphatic vessels of that 
 viscus, if an animal be examined soon after digestion has 
 begun. 
 
 And we may farther conjecture with the Hunters, from the 
 universality of their distribution, and their fabric every- 
 where similar to that of the lacteals, that lymphatics com- 
 mence at every part of the body; and that their office 
 is to take up and carry back to the blood those elements 
 of the body which disappear, either to make place for 
 newly secreted matter, or without substitution. This con- 
 jecture, at any rate, is the most rational which has been 
 proposed as to the use of the lymphatic system, and is 
 remarkably borne out by various circumstances noticed in 
 
 * Magendie, Ellmens de Physiologic, vol. ii, p. 182, 
 
Of the Lymphatics. 167 
 
 disease, of which I shall content myself with citing the 
 most conclusive. 
 
 Whenever the flesh becomes impregnated with, or im- 
 bibes, an acrid substance, as for instance the venereal virus, 
 and ulceration follows, the lymphatic system alone appears 
 to suffer sympathetic irritation. The lymphatic vessels in 
 such cases commonly become tender and hardened, or their 
 inflamed state shows itself by red lines upon the skin, or 
 the lymphatic glands inflame, and matter forms around 
 them. But if, during the absorption of a poisoned part, 
 one particular set of vessels exclusively becomes irritated, 
 can we doubt that those vessels are the absorbents ? 
 
 It must after all be admitted that we are very far from 
 having attained a satisfactory knowledge of this function. 
 Nevertheless, in the data which have been adduced in the 
 present and a preceding chapter, there appear to be good 
 grounds for arranging under three different heads the varied 
 phenomena of absorption, which used to be viewed as all 
 of one nature. 
 
 1. When poisonous substances are applied to an internal 
 and vascular membranous surface, or are introduced into a 
 wound, or by friction upon the surface of the body are 
 forced through the epidermis, they ate imbibed by the po- 
 rous and vascular flesh, and find their way directly into the 
 bhod t through the coats of the blood-vessels*. 
 
 2. The chyle formed during the digestion of the food 
 is taken up from the mucous surface of the intestines by 
 the lacteahj which are specially organized for this purpose. 
 
 3. When the molecular structure of the body is absorbed, 
 either in the ordinary growth and renovation of the frame, 
 or in the removal of parts which are not at the same time 
 replaced, as in ulceration, it is reasonable to suppose that 
 the lymphatics are the agents employed. 
 
 * Let me refer the reader to the conclusive experiment by M. Se*galas, 
 mentioned already in connection with the subject of venom absorption. 
 
CHAPTER IX. 
 OF THE URINARY ORGANS, 
 
 THE function of the urinary organs may serve better than 
 any other to illustrate a position assumed by physiologists, 
 that certain principles constantly accumulating in the 
 blood during nutrition require to be continually separated 
 from it in order that it may retain its salutary qualities. In 
 other instances where excretion manifestly takes place, as 
 upon the skin, from the lungs, or from the mucous membrane 
 and glands of the bowels, it may remain a question whether a 
 second object of equal or greater importance be not cqntem- 
 plated : but in the present instance the exclusive use of a 
 very elaborate contrivance appears to consist in getting rid 
 of a superfluous element. As nitrogen exists in a large pro- 
 portion in the characteristic ingredient of urine, the kidneys 
 are supposed to be the vent at which the excess of this 
 principle is discharged. 
 
 The kidneys are placed at the sides of the lumbar ver- 
 tebrae, before the psose and quadrati lumborum, and im- 
 bedded in fat. The kidneys vary in size : they have been 
 found united by an isthmus extending across the aorta. 
 One kidney is sometimes wanting. 
 
 The kidney is a conglomerate gland, and in the foetus, 
 and occasionally in the adult, is marked by furrows upon 
 its surface which show its internal division into separate 
 lobes. The kidney is covered by peritoneum on the fore 
 part only, and its proper membranous tunic is proportion- 
 ately denser than that of the liver or spleen. Its artery, 
 termed the renal or emulgent, is, relatively to the size of 
 the gland, the largest in the body : it readily transmits 
 
Structure of the Kidney. 169 
 
 injected fluids into the emulgent veins and excretory tubes. 
 The renal nerves are derived from the semilunar ganglia 
 or solar plexus; several small ganglia are formed upon 
 them : when the renal nerves are divided in a dog, the 
 animal suffers pain. 
 
 On making a section from the external convex edge of 
 the kidney through to the internal concave edge or hilum, 
 the different substances of which the gland is composed 
 become apparent. The outer or cortical part is of a granu- 
 lated texture, but seems after a successful injection to 
 consist of tortuous vessels alone ; processes of the same 
 substance extend towards the hilum of the kidney, between 
 which are contained cones of what seem white convergent 
 fibres. The rounded ends of these cones project towards the 
 notch of the kidney, and are termed mammillary processes : 
 their surface is perforated with small apertures, through 
 which the urine may be seen to exude in living animals, 
 and the white fibres appear to be excretory tubes, which 
 have their origin in the cortical substance ; the mode of 
 their connection with the blood-vessels has not been ascer- 
 tained. 
 
 Each mammillary process is inclosed in a loose conical 
 sac termed an infundibulum : each infundibulum opens into 
 a common channel, of which there are generally two ; one 
 leading from the upper, the other from the lower part of 
 the kidney : these two channels unite to form a capacious 
 conical sac termed the pelvis of the kidney, which gradually 
 narrows, and is continuous with a tube termed the ureter, 
 which is cylindrical, being from three to four lines in 
 diameter when inflated, and leads to the bladder. The 
 infundibulum, pelvis, and ureter, are lined with a fine 
 mucous membrane : their texture is white, fibrous, and 
 of great strength. 
 
 The bladder is oviform, the great end looks towards the 
 sacrum and lower opening of the pelvis, and rests upon the 
 levator ani ; the narrow end or fundus looks forward and 
 upward ; the anterior and inferior surface rests upon the pubes ; 
 the posterior and upper surface is covered by peritoneum, and 
 the bowels rest upon it. Ligamentous bands, which show 
 
170 Of the Urethra. 
 
 the former course of the urachus and hypogastric arteries, 
 attach the sides and fundus of the bladder to the navel : 
 the opening of the bladder into the urethra is at its most 
 dependent part, that is to say, at the lowest part of the 
 greatest breadth of the bladder; the part at which the 
 urethra commences is termed the neck of the bladder ; a 
 ligament attaches it to the pubes. 
 
 The bladder consists of an internal mucous membrane 
 continuous with that of the ureter, but thicker, and of 
 muscular fibres, termed the detrusor urinae, the inner layer 
 of which is for the most part disposed reticularly ; the 
 fibres of the outer layer extend longitudinally from the 
 neck of the bladder to the fundus. The nerves of the 
 bladder are derived from the hypogastric plexus. 
 
 The canal of the male urethra first passes through the 
 prostate gland, and from thence forwards to the ligament 
 of Camper is surrounded by a plexus of vessels and braced 
 to the arch of the pubes by fibres discovered by Mr. Wilson, 
 and named by him the compressor urethrae : the glands 
 of Cowper are placed on either side of the urethra at this 
 part. Beyond the ligament of Camper and from thence 
 to the orifice of the penis, the male urethra is contained in 
 the corpus spongiosum. 
 
 The mucous membrane of the urethra does not appear 
 to be an irritable substance ; but it seems not improbable 
 that the tissue which surrounds it is capable of contracting, 
 much in the same manner as the skin. The canal is most 
 capacious at the commencement of the spongy body, where 
 it is termed the bulb of the urethra, and is two parts sur- 
 rounded for three or four inches by the fibres of the 
 accelerator urinae, which are capable of compressing and 
 emptying this chamber of the urethra. 
 
 The female urethra is short and nearly straight; has 
 no glandular bodies attached to it, but is supported by a 
 compressor urethras, and is readily dilatable. 
 
 The urine during health alone continually varies in 
 quantity and in composition ; during cold weather, or when 
 a large quantity of liquid has been received into the 
 stomach, the urine is increased in quantity, and is nearly 
 
Nature of the Urine. 171 
 
 colourless ; during warm weather, when the cutaneous 
 transpiration is greater, less urine is secreted : it is then high 
 coloured, and contains a less proportion of water. Various 
 kinds of food increase the flow of urine, or modify the 
 nature of its constituent parts. The average quantity 
 secreted daily amounts to about four pints. 
 
 According to Berzelius, the following is the composition 
 of urine : 
 
 Water 93300 
 
 Urea 30.10 
 
 Sulphate of potash 3.71 
 
 Sulphate of soda 3.16 
 
 Phosphate of soda 2.94 
 
 Muriate of soda 4.45 
 
 Phosphate of ammonia 1.65 
 
 Muriate of ammonia 1.50 
 
 Free lactic acid -v 
 
 Lactate of ammonia I 1714 
 
 Animal matter soluble in alcohol j 
 
 Urea not separable from the preceding J 
 
 Earthy phosphates with a trace of fluate of lime 1.00 
 
 Lithic acid 0.32 
 
 Silex 0.03 
 
 1000.00 
 
 The ultimate elements of urea, according to Dr. Prout, 
 exist in the following proportion : 
 
 Nitrogen 46.66 
 
 Carbon 19.99 
 
 Hydrogen 6.66 
 
 Oxygen 26.66 
 
 29.97 
 
 The urine continually exuding into the infundibula of 
 the kidney, urges forward that previously secreted, into the 
 bladder. The ureters open obliquely into the bladder, so 
 that the pressure of the urine accumulating in that viscus, 
 tends to close the aperture of the ureters, and to prevent 
 any reflux towards the pelvis of the kidney. 
 
 Mr. Bell has remarked that the thick fasciculi of 
 
172 Absorbed Substances easily detected in the Urine. 
 
 muscular fibres, through which the ureters enter the bladder, 
 must contribute during the expulsion of the urine to pre- 
 serve the obliquity of the entrance by their disproportionate 
 action. 
 
 When a certain quantity of urine is contained in the 
 bladder, a peculiar sensation arises, with a desire to 
 evacuate it. By a voluntary effort the levator ani, the 
 abdominal muscles, and the diaphragm contract ; and in 
 a few seconds the bladder acts, and the urine flows. There 
 appears to be no necessity for supposing the bladder to be 
 directly influenced by the will. The conscious effort 
 during the expulsion of the urine is not referred to the 
 bladder itself, but to the muscles of the pelvis and abdo- 
 men. The fibres of the bladder resemble those of the 
 alimentary canal ; when they are pinched immediately after 
 death, a slow contraction of the bladder is observed to 
 begin, which continues for several seconds. When the 
 bladder is laid open by an incision, the contraction which 
 follows the escape of its contents takes place very gradually. 
 
 The compressor urethras we may suppose to act as the 
 sphincter muscle of the bladder. 
 
 One of the most remarkable phenomena in the secretion 
 of urine, is the facility with which substances taken into 
 the stomach find their way to the bladder. Sir Everard 
 Home observed, that rhubarb could be detected in the 
 urine in seventeen minutes after it had been swallowed. 
 The dose consisted of half an ounce of tincture of rhubarb 
 diluted with an ounce and a half of water, and was taken 
 immediately before a breakfast consisting of tea. The test 
 employed was a solution of caustic potash. Upon an ex- 
 amination of animals to which rhubarb had been given in 
 successive doses for several hours before death, the urine 
 was found deeply tinged, and the serum of the blood in 
 the splenic vein, in the inferior cava, and in the right 
 auricle of the heart, showed evidence of containing rhu- 
 barb*. At this time Sir Everard Home was led to believe 
 
 * Phil. Trans, vol. xcviii, p. 5J. 
 
Eject of removing the Kidneys. 173 
 
 that the spleen and the lymphatic system were the route 
 through which the rhubarb in the instance cited passed into 
 the blood. But upon renewing these researches at a sub- 
 sequent period he found, that after removing the spleen and 
 tying the thoracic duct, rhubarb injected into the stomach 
 may be still detected in the urine and in the bile, the con- 
 tents of the lacteals showing at the same time no trace of 
 rhubarb*. 
 
 The facts which have been mentioned contain, it is obvi- 
 ous, the rudiments of the discovery of the imbibition ex- 
 ercised by the blood-vessels. What appears to have thrown 
 into shade the true explanation of the phenomena described, 
 is the difficulty of detecting the element in the blood, which 
 so freely passes from the stomach into the urine. This 
 anomaly is elucidated in the following observations by 
 M. Magendie. 
 
 If a small quantity of prussiate of potash be injected into 
 the veins, or absorbed from a mucous or serous surface, it 
 becomes readily distinguishable in the urine, but cannot be 
 detected in the blood. If, however, the experiment be 
 made with a larger quantity, the presence of prussiate of 
 potash in the blood becomes evident. The same difference 
 M. Magendie observed to exist in the facility of detecting 
 prussiate of potash when mixed with urine and with blood 
 out of the body. In the former case the smallest quantity 
 is discoverable by chemical tests, the action of which is by 
 some means obscured in the latter. 
 
 The effect of the excision of the kidneys has been already 
 alluded to. MM. Prevost and Dumas found, that little 
 effect is produced upon the health of a cat or dog by the 
 removal of a single kidney; but that within three days after 
 the removal of the second, copious liquid brown evacua- 
 tions take place, with vomiting of the same matter, rapid 
 small pulse, great constitutional irritation, and laboured 
 breathing : the animal dies between the fifth and ninth day. 
 MM. Prevost and Dumas calculate that a healthy dog 
 habitually produces about a drachm of urea in twenty-four 
 
 * Phil. Trans, vol. ci, p. 163. 
 M 
 
J74 Effect of removing the Kidneys. 
 
 hours. After the preceding operations had been performed, 
 five ounces of blood were found to contain a scruple of 
 urea*. 
 
 M. Magendie observed, that after the removal of the 
 kidneys, the secretion of bile is. extraordinarily increased, so 
 that the stomach and intestines are found to contain bile in 
 large quantities. 
 
 M. Segalas found that the introduction of urea into the 
 blood of animals operates as a diuretic. 
 
 * Anderson's Quarterly Journal, vol. i, p. 294, 
 
CHAPTER X. 
 OF THE SKIN. 
 
 THE general integument of the body varies in thickness 
 from about a sixth to a twentieth of an inch. At the com- 
 mencement of putrefaction the epidermis spontaneously 
 separates, as a thin dry elastic unorganized membrane, 
 from the tough and vascular cutis. Between the epidermis 
 and the true skin, a tenacious moisture is at the same time 
 found, which seems to result from the decomposition of an 
 intermediate substance. This substance, found in small 
 quantity in Europeans, is that which, under the name of 
 rete mucosum, gives the characteristic hue to the skin in 
 the coloured families of mankind. 
 
 In the Negro, the cutis has the same appearance as in 
 the European ; and the cuticle is scarcely a shade darker ; 
 while the rete mucosum presents a shade yet deeper than 
 the colour of the skin before the removal of the epidermis. 
 
 The usual appearance of the rete mucosum is that of a 
 black mucus, resembling the pigmentum nigrum in the eye : 
 it diffuses itself in water, and communicates a turbid cloud 
 to the fluid ; then subsides as an impalpable powder to the 
 bottom. Sometimes the rete mucosum admits of being 
 detached as a coherent membrane ; the side adjoining the 
 cutis then appears of the deepest colour : sometimes it 
 remains incorporated with the cutis, after the cuticle has 
 become detached. 
 
 The cutis appears to be a peculiar modification of gelatin. 
 The cuticle seems to be a form of coagulated albumen *. 
 In the living body the cuticle may be removed by abrasion, 
 
 * Thomson's Chemistry, vol. ii, p. 470 & 472. 
 
 M2 
 
176 Of the Cutis. 
 
 or raised from the cutis by the action of a vesicatory. The 
 colour of the rete mucosum in a Negro may be temporarily 
 removed by immersing a part in water impregnated with 
 chlorine : after a few days the black colour returns with its 
 former intensity. 
 
 The skin is marked by furrows of different sizes, of which 
 the largest are upon the palms of the hands or at the joints 
 of the fingers. Specimens of almost all the lesser kinds 
 may be perceived upon the back of the hand. Upon the 
 ridges between the furrows, upon the palms of the hands, and 
 upon the fingers, numerous little pits are seen, which have 
 the appearance of pores, but are found to be shallow 
 depressions only, which, like the preceding, are made 
 shallower, or disappear when the skin is distended. 
 
 The inner surface of the cutis is hollowed into innumera- 
 ble shallow fossulse placed close to each other, and varying 
 in diameter from a twelfth to an eighth of an inch. They 
 receive the subcutaneous layer of fat, upon the quantity of 
 which the sleek or wrinkled appearance of the skin depends. 
 
 The skin at certain parts is perforated by two sorts of 
 cylindrical pores, each of which is lined by a fine prolonga- 
 tion of the cuticle. At the bottom of a pore of either sort a 
 small gland exists, which is lodged at the posterior surface 
 of the skin. The substance secreted from the one kind is 
 an oily sebaceous matter, which continually exudes upon 
 the surface of the skin ; from glands of the second kind 
 the hair grows. Each hair is conical : at its root is a 
 conical cavity, in which the bulb is lodged which forms it. 
 The chemical composition of a hair resembles that of the 
 epidermis ; it consists of a dense external crust, and an 
 interior substance of a slighter texture. The pore which 
 transmits each hair is oblique. 
 
 The cuticle is so elastic, that when it has been perforated 
 with a needle the apertures are not distinguishable with a 
 magnifying- glass : it is not therefore surprising, that when 
 it is separated from the cutis, we are unable to discern any 
 thing like a series of pores through which the perspiration 
 may be supposed to exude. Whether there are special 
 apertures for this object, or whether the perspiration 
 transude through the whole membrane, is unknown. The 
 
Of the Nerves and of the Absorbents of the Skin. 177 
 
 cuticle is laid over the cutis like a thin varnish of elastic 
 gum ; its main purpose appears to be the prevention of 
 evaporation. How well it serves this end, is shown by the 
 preservation of the moisture of the skin for many days after 
 death where the cuticle has remained entire, contrasted 
 with its rapid desiccation at those parts where the cuticle 
 may happen to have been removed. The object next in im- 
 portance we may suppose to be the prevention of indiscrimi- 
 nate imbibition or absorption by the vascular surface of the 
 cutis ; and finally, we may view the cuticle as interposed 
 to modify the sensation of touch, the acuteness of which 
 else amounts to pain. 
 
 The nerves distributed to the skin are derived from the 
 spinal nerves, from the fifth, and from the portio dura of 
 the seventh. 
 
 The absorbent vessels of the cutis are so numerous, ac- 
 cording to Dr. Gordon, that after a successful injection of 
 them with mercury, the whole surface looks like a sheet of 
 silver : their distribution resembles network more than 
 regular ramification*. 
 
 The cutis is exceedingly vascular upon its outer surface, 
 which shows all the furrows and markings that are to be 
 seen upon the integument before the removal of the epi- 
 dermis, and is not plain, but raised into innumerable 
 delicate processes or papillae, that are best developed where 
 the sense of touch is most exquisite. 
 
 There is a remarkable analogy between the skin and the 
 mucous membranes. The latter may be viewed as prolon- 
 gations of the skin over internal surfaces, modified only to 
 suit the difference of place ; or the skin may be said to 
 contain the elements of the mucous tubes, but more firmly 
 and closely wrought, and protected by the cuticle, as the 
 latter are protected by the mucus they secrete. 
 
 The skin consists of a dense white elastic substratum, 
 analogous to the submucous tunic in the alimentary canal, and 
 of a vascular surface analogous to the mucous or villons 
 membrane. But in the skin the vascular superficies is not 
 
 * Gordon's Anatomy, p. 234. 
 
178 Analogy between the Skin and Mucous Membranes. 
 
 separable by any artifice from the thick substratum which 
 supports it. 
 
 Let us consider the skin at present in reference to its- 
 functions of absorption and transpiration. 
 
 Dr. Edwards contrived that a lizard, which had suffered 
 a considerable diminution of weight by exposure to a free 
 current of air for several days, should remain partially 
 immersed in water, which covered its tail, its hind legs, and 
 the hinder part of its body. Under these circumstances 
 the animal re-acquired the weight which it had before lost, 
 and its limbs and body regained their plumpness and 
 former volume*. 
 
 Dr. Edwards confined a snake in air saturated with 
 moisture, removing it and weighing it at intervals : at first 
 it was found to lose in weight ; after a time it ceased to 
 become lighter, and was observed to gain in weight. 
 
 M. Seguin observed that when the human body is im- 
 mersed in water at a temperature between 12.5 and 22. 5 
 cent, no loss of weight takes place beyond the usual loss 
 by pulmonary transpiration. Immersion therefore in water 
 at the above temperature, should either prevent cutaneous 
 transpiration, or allow an absorption to take place equal to 
 the loss it occasions. The preceding analogies are in 
 favour of the latter solution. But subsequent researches 
 by the same author seem to show, that water in contact 
 with the cuticle of the human body is not absorbed. If the 
 water hold a salt of mercury in solution, it very rarely hap- 
 pens that any evidence of the absorption of the mineral 
 manifests itself even after long and repeated immersion. 
 
 The cuticle appears to be the main impediment to cuta- 
 neous absorption : if this membrane be removed, absorption 
 takes place rapidly from the surface of the cutis ; or if by 
 continued pressure, as during mercurial friction, a sub- 
 stance be mechanically forced through it, absorption does 
 not fail to take place ; or if a substance which is of an acrid 
 nature, and calculated chemically to combine with it, be 
 placed in contact with the epidermis, the same result is 
 found to ensue. 
 
 * De 1'Influence, &c. p. 347. 
 
Of Cutaneous Transpiration. 179 
 
 With respect to the vessels which minister to this func- 
 tion, we have not greater reason for supposing, that the 
 lymphatics absorb poisons or medicines applied to the skin, 
 than that the lacteals perform this office in the small intes- 
 tines. There is little doubt, that when the impediment 
 which the cuticle offers is removed or overcome, foreign 
 matter in contact with the skin finds its way into the blood- 
 vessels by imbibition. 
 
 The action of the skin upon the air is obscurely under- 
 stood : analogy perhaps would lead us to suppose that an 
 absorption of oxygen takes place at the surface of the body ; 
 for the experiments of Mr. Cruickshank and of Mr. Aber- 
 nethy have shown that carbonic acid is produced when the 
 hand or the foot is confined in atmospheric air. But this 
 subject requires to be further investigated. 
 
 A certain quantity of fluid continually transudes through 
 the skin ; sometimes this wholly disappears by evaporation : 
 at other times it collects as a liquid upon the surface of the 
 body. In the former case it is termed the Insensible Per- 
 spiration ; in the latter the Sensible Perspiration. 
 
 When collected, the perspiration is found to consist of 
 water containing a small proportion of acetic or lactic acid, 
 of muriates of potash and soda, with a trace of animal 
 matter, apparently gelatin. 
 
 The most unexceptionable experiments perhaps relating 
 to the quantity of the insensible perspiration are those of 
 Lavoisier and Seguin. Upon their testimony the average 
 quantity amounts to eleven grains per minute. During 
 digestion the quantity of cutaneous transpiration appears to 
 be at its minimum, According to Dr. Edwards, during the 
 six hours before noon the insensible transpiration, c&terts 
 paribus, attains its maximum. Sleep would seem to pro- 
 mote it remarkably : a dry state of the atmosphere, exposure 
 to a current of air, diminished barometrical pressure, have 
 a similar tendency. 
 
 The influences last named are such as would affect the 
 rate of evaporation from a dead body. Dr. Edwards has 
 founded upon these and similar observations, an apparently 
 just division of the elements of the insensible perspiration 
 
180 Of the Standard Heat of the Body. 
 
 into such as are derived from secretion, and such as result 
 physically from the evaporation of the moisture of the skin 
 itself. Upon estimating the comparative loss of weight 
 which frogs suffer when placed at a lower temperature in 
 dry air and in air laden with moisture, the proportion of 
 fluid lost by secretion to that lost by transudation appeared 
 to be as 1 : 6*. But it is possible that in dry air the 
 quantity of secretion may be greater than in air laden with 
 moisture j the increase of the demand may increase the 
 quantity of the supply, agreeably with a fact respecting the 
 secretion of milk, to which I have already adverted. 
 
 At an elevated temperature and during violent exercise 
 the perspiration becomes sensible. No estimate appears to 
 have been made of the actual quantity of liquid produced 
 under these circumstances, or of the ratio in which the 
 different causes alluded to influence the secretion of the 
 sweat. Sir C. Blagden remarked, that on staying for 
 twenty minutes in a chamber heated to 198 the perspira- 
 tion was so little increased that his shirt was only damp at 
 the end of the experiment f. A few minutes of violent 
 exercise at a much lower temperature would have produced 
 a copious flow from the skin. 
 
 The principal object of the sensible perspiration appears 
 to be the reduction of the temperature of the body. The 
 present occasion, therefore, leads us again to consider the 
 subject of vital heat. Heat, it seems, can be produced in 
 all living beings ; but while in plants and cold-blooded 
 animals the temperature closely follows that of the media in 
 which they are immersed, in mammiferous animals and in 
 birds a given temperature is sustained, which is termed 
 their standard heat. In human beings the standard heat is 
 about 97, in viviparous quadrupeds 100 or 101 : the tem- 
 perature of birds is yet higher, and rises to 107 or 108*. 
 
 Extremes of heat or cold appear temporarily to raise or 
 lower the temperature of the body. After staying sixteen 
 minutes in a dry air at 64 cent, M. Delaroche observed 
 the temperature of the skin to be raised 4. 
 
 * De rinfluence, &c. p. 334. f Phil. Trans, vol. Ixv, p. 119, 
 
Difference observed in very young Animals. 181 
 
 During various disorders the temperature of human 
 beings is liable to be raised to a higher standard. In fever 
 the heat has been observed at 104*. M. Prevost wit- 
 nessed a case of tetanus in which the temperature was 
 elevated 7 cent above the natural standard. Mr. Caesar 
 Hawkins mentioned to me having remarked, that in a 
 person who died within twenty-four hours after an injury of 
 the spinal chord at the lower part of the neck, which crushed 
 it, and produced paraplegia, the thermometer applied to the 
 groin ten minutes before death rose to 111. 
 
 The young of warm-blooded animals have a temperature 
 lower than that of adults. The same difference has been 
 noticed in the human species. M. Breschet ascertained, 
 upon an examination of ten infants within forty-eight 
 hours after birth, that their temperature varied from 34 to 
 35.5 cent. 
 
 There appears to be a remarkable difference in the young 
 of warm-blooded animals as to their power of producing 
 heat. A Guinea pig soon after birth is able to resist a low 
 temperature nearly as well as an adult; but kittens and 
 puppies newly -born lose their temperature rapidly when the 
 external heat is artificially lowered ; in a fortnight, however, 
 they acquire the power of evolving heat. This difference 
 bears a relation to the general forwardness of animals. 
 Those which are bom with their eyes open, can sustain 
 themselves at a standard temperature : the opposite class re- 
 semble at first cold-blooded animals, and their temperature 
 falls with that of the surrounding media. A parallel dif- 
 ference is observed in birds, some of which quickly walk 
 and run upon breaking the egg : but others, as for instance 
 the jay, appear hatched before their time, and three or 
 four weeks elapse before they can sustain a standard tem- 
 perature. 
 
 Dr. Edwards, from whose valuable work on the influence 
 of physical agents upon the animal ceconomy I have largely 
 borrowed, gives in connexion with the preceding remarks 
 an interesting account of the temperature of a child born 
 
 * Currie's Reports, p. 21 et seq. 
 
182 Effects of extreme Cold. 
 
 at seven months. At this period the existence of the 
 membrana pupillaris ranks the infant with those animals 
 born with closed eyelids ; and the temperature of the infant 
 in the case alluded to did not exceed 32 cent, although 
 the child was well wrapped up and placed before a fire. 
 
 The power of producing heat seems to be different at 
 different seasons. Dr. Edwards artificially exposed five 
 sparrows to the influence of a low degree of temperature 
 during three hours at different periods of the year. In 
 February the heat lost averaged at 0.4 cent, in July at 
 3*. 62 cent, in August 4. 87 cent. The constitution thus 
 adapts itself to the temperature in which it is placed : 
 when less heat is called for, less heat is habitually produced ; 
 and the power of producing it in large quantity is tem- 
 porarily lost. 
 
 Animals that hibernate remain during life unable to 
 sustain a standard temperature against any considerable 
 external cold. In the month of April, the air being at 
 16 cent, Dr. Edwards exposed a bat to the temperature 
 of 1 for an hour : in this time its temperature fell from 34 
 to 14. Adult sparrows and Guinea pigs under correspond- 
 ing circumstances lost from 2 to 3 only. 
 
 Animals of this description on the approach of winter 
 seek to envelope themselves in substances which contribute 
 to prevent the abstraction of heat and the access of fresh 
 air, and then fall into a torpid state, during which they 
 take no nutriment; and their breathing and the circulation 
 of the blood are so languid, that the performance of these 
 functions has been doubted. 
 
 During the torpid state the temperature of the body falls 
 nearly to that of the surrounding media : if the animal be 
 roused, its temperature becomes elevated. 
 
 The air of the apartment being 1.5 cent, the tempera- 
 ture of a torpid bat was 4. M. de Saissy roused it by 
 mechanically disturbing it. The animal took an hour to 
 wake : at the expiration of thirty minutes its temperature 
 had risen to 15% when fully roused, to 27. The tempera- 
 ture of a dormouse under similar circumstances rose to 36% 
 its standard heat. 
 
E/ects of extreme Cold. 183 
 
 It is remarkable that cold serves as a means of waking 
 hibernating animals, as well as mechanical excitement or 
 a high temperature. M. de Saissy carefully exposed a 
 torpid dormouse at a window looking to the north, when 
 the centigrade thermometer stood at 4. After a period 
 somewhat longer than in the preceding experiment, the 
 animal was roused, and its temperature rose to 36. But 
 in this instance the cold which wakes the animal from its 
 torpid state becomes quickly fatal; the temperature falls 
 again, and the animal sinks into a lethargy which is mortal. 
 
 The hibernating animal thus perishes of cold like other 
 animals. 
 
 In human beings, when sufficient heat cannot be pro- 
 duced to meet the demand from without, the temperature 
 of the body falls, excessive drowsiness and inclination to 
 sleep is felt, which, when indulged in, proves fatal. The 
 frame is then in a condition the least calculated to resist 
 the effects of cold; as heat is habitually produced in 
 greater quantity during the waking state than in sleep, 
 during exercise than during repose. Dr. Edwards made 
 the curious remark, that the power of enduring and re- 
 covering from the effects of cold in young animals, is 
 inversely as their power of producing heat ; so that kittens 
 or puppies newly-born can live for two or three days at 
 a temperature of 20 cent, or even two or three degrees 
 below it*. 
 
 The accumulation of heat in the system is not less fatal 
 than its rapid abstraction. Copious perspiration and in- 
 tense thirst, difficulty of breathing, violent pain in the 
 breast, and palpitation of the heart, followed by insensi- 
 bility, were the symptoms remembered by one who survived 
 the imprisonment in the black hole at Calcutta. Of one 
 hundred and forty-six who shared these sufferings, twenty- 
 three only outlived one night's confinement in a crowded 
 dungeon during a tropical night f. This great mortality 
 appears to have ensued in consequence of the hot and con- 
 fined air becoming saturated with moisture, which prevented 
 
 * De 1'lnfluence, &c. p. 474. t Dodsley's Ann. Re#. 1758. 
 
184 Effect of great Heat on the System. 
 
 further evaporation from the skin, and kept the heat of 
 the body permanently raised above the usual standard. 
 M. Delaroche has ascertained by experiment, that animals 
 placed in an atmosphere charged with moisture cannot 
 support a degree of heat slightly raised above their natural 
 standard. 
 
 Sir C. Blagden, upon exposing himself for a few minutes 
 with his clothes on and after a hearty repast to a tempe- 
 rature of 240, experienced an oppression upon the chest, 
 attended with a sense of anxiety. He found that his pulse 
 beat 144 pulsations immediately upon leaving the heated 
 room. Upon exposing himself in the forenoon after a 
 moderate breakfast to the temperature of 220 without his 
 shirt, the impression of the heated air was at first painfully 
 disagreeable; but in five or six minutes a profuse sweat 
 broke out, which gave instant relief, and took off all the 
 extraordinary uneasiness : at the end of twelve minutes 
 he left the room very much fatigued, but not otherwise dis- 
 ordered; his pulse had risen to 136*. 
 
 * Phil. Trans, vol. Ixv, p. 489. 
 
CHAPTER XL 
 ON THE FUNCTIONS OF THE NERVOUS SYSTEM. 
 
 THE offices of the nervous system are of two kinds: the 
 brain and nerves on the one hand exert a control over the 
 automatic functions of the body ; on the other, they form 
 the immediate organs of consciousness. 
 
 Viewed in the latter relation, the physiology of the 
 nervous system embraces the two following inquiries : What 
 is the nature of mind in man and animals ? Upon what 
 conditions of the bodily organs does the manifestation of 
 consciousness depend ? 
 
 SECTION I. 
 Of the Mental Phenomena in Man and Animals. 
 
 I propose in the present section briefly to describe the 
 different affections of the human mind, and to compare them 
 with the mental endowments which animals display. It is 
 difficult to disbelieve that a common principle of conscious- 
 ness exists in both ; in the one expanded into a reasonable 
 nature, in the other narrowed and subjected to blind impulse 
 and necessity. 
 
 Of Sensation and Perception. When adequate impres- 
 sions are made upon our organs we are conscious of sensa- 
 tion. When, for example, coloured rays impinge upon the 
 retina, sensations of light are produced in us. Perception 
 is a term which in common discourse is used synonymously 
 with sensation : we employ, for instance, indifferently the 
 
186 Of Sensation and Perception. 
 
 expressions, to experience sensations of colour, and to per- 
 ceive colours. But metaphysicians attach different mean- 
 ings to the words sensation and perception, and use the 
 latter to express the knowledge of the presence and qualities 
 of external objects which follows upon sensation. In order 
 thoroughly to sift this distinction, let us analyse the very 
 complicated impression which is conveyed to the mind 
 through momentary exercise of an organ of sense. I look, 
 for instance, at an object of such dimensions, that a glance 
 serves to satisfy me respecting its nature: the impression 
 which I receive through this experiment is threefold : com- 
 prising, 1. Present sensations of colour: 2. A conviction 
 that those sensations are excited by something external : 
 3. A knowledge of the real size and form and distance 
 of the object which I have seen. The second of these im- 
 pressions, or the notion which we form of a something 
 external as the cause of sensation, constitutes perception. 
 The third class of impressions that I have described, and 
 which we have learned to associate with the preceding, are 
 our acquired perceptions. 
 
 Upon comparing sensation and perception in animals with 
 the like affections in man, it is evident that the former 
 have a partial superiority as to both. The vision of many 
 birds, the sense of smell in birds, and in a still higher de- 
 gree in many quadrupeds, is more acute than our own. The 
 sense of smell in animals is closely connected with their 
 most powerful instincts. Its existence and its force may be 
 traced even in creatures of a different caste of organization 
 from ourselves. The aversion, for instance, which bees are said 
 to show to particular individuals is probably excited through 
 this sense. How far in man as in animals this sense might 
 come to suggest motives of conduct, is curiously shown in 
 the account by Dugald Stewart of James Mitchell, who had 
 the misfortune to be bom deaf and blind, and was thus de- 
 prived of the two most important channels through which 
 knowledge is ordinarily received. I may quote the follow- 
 ing statement, given upon the authority of Mr. Wardrop 
 
 " When a stranger approached Mitchell, he eagerly began 
 to touch some part of his body, commonly taking hold of 
 
Of Sensation and Perception. 187 
 
 his arm, which he held near his nose ; and after two or three 
 strong inspirations through his nostrils, appeared decided in 
 his opinion. If it happened to be unfavourable, he sud- 
 denly went to a distance with the appearance of disgust ; if 
 favourable, he showed a disposition to become more inti- 
 mate, and expressed by his countenance more or less 
 satisfaction." 
 
 With human beings the faculty of perception is of slow 
 growth. Several weeks elapse before we discern intelligence 
 in an infant's gaze, or read in its vacant eye that sensation 
 produces in it a notion of something external. Nor in this 
 case are we wholly to attribute the backwardness of percep- 
 tion to the general imperfection of the infant's mind. In 
 the well-known case recorded by Cheselden, in which by 
 the operation of couching a new class of sensations was sud- 
 denly excited in one already grown up and of more than 
 common parts and quickness, correct perception did not 
 immediately follow upon visual impressions, although every 
 other sense was already thoroughly educated, and the under- 
 standing ready and bent upon perceiving a familiar world 
 through a new sense. " When this young gentleman/' ob- 
 serves Cheselden, " first saw, he was so far from making 
 any judgment about distances, that he thought all objects 
 whatever touched his eye (as he expressed it), as what he 
 felt touched his skin. He knew not one thing from another, 
 however different in shape and magnitude ; but upon being 
 told what things were, whose form he before knew from 
 feeling, he would carefully observe that he might know 
 them again." 
 
 In animals, the faculty of perception is wonderfully per- 
 fect at first and at once. 
 
 "As soon as her chickens are hatched," observes Dr. Smith, 
 " the hen carries them to the field to feed, where they walk 
 about at their ease it would seem, and appear to have the 
 most distinct perception of all the tangible objects which 
 surround them. We may often see them accordingly by the 
 straightest road run to pick up any little grains which she 
 shows them, even at the distance of several yards; and they 
 no sooner come to the light than they seem to understand 
 
188 Of Volition. 
 
 the language of vision as well as they ever do afterwards. 
 The young of the partridge and of the grouse seem to have 
 at the same early period the most distinct perceptions of the 
 same kind. The young partridge, almost as soon as it 
 comes from the shell, runs about among long grass and com ; 
 the young grouse among long heath ; and both would most 
 essentially hurt themselves, if they had not the most acute, 
 as well as distinct perception of the tangible objects, which 
 not only surround them, but press upon them on all sides. 
 The young of several sorts of quadrupeds seem, like those 
 of the greater part of birds which make their nests upon 
 the ground, to enjoy as soon as they come into the world 
 the faculty of seeing, as completely as they ever do after- 
 wards. The day, or the day after they are dropt, the calf 
 follows the cow, and the foal the mare to the field ; and 
 though from timidity they seldom remove far from the 
 mother, they yet seem to walk about at their ease, which 
 they could not do unless they could distinguish, with some 
 degree of precision, the shape and proportion of the tangi- 
 ble objects which each visible one suggests." 
 
 Of Volition. It is easy to imagine a being capable of 
 sensation but wanting every other mental endowment. 
 We may suppose, for example, that plants have sensibility. 
 But it is impossible to prove the conjecture true. Move- 
 ments in other beings, resembling those which in ourselves 
 are voluntary, constitute our only evidence that they feel. 
 
 By volition I mean the mental attempt to produce mus- 
 cular action. Under ordinary circumstances its exertion is 
 followed by two effects : certain muscles act, and their 
 action is attended with some degree of sensation. The 
 mental effort may, however, be complete, yet neither of 
 these consequences follow. There is a disease termed 
 anaesthesia, which affects the extremities, and consists in the 
 loss of sensation only. A patient afflicted with this disorder 
 can move the muscles of his limbs at pleasure ; but the 
 voluntary act is unattended with feeling in the part. When 
 the spinal chord is torn across, paraplegia, or loss both of 
 sense and motion in the lower part of the frame, ensues ; the 
 sufferer in such a case looks at his palsied limbs, and tries in 
 
Of Instinct. 189 
 
 vain to move them. He is conscious of the perfect mental 
 effort, but neither motion nor sensation follow. 
 
 Of Instinct. Besides sensation, perception, and volition, 
 one other element at least is wanted to compose a scheme 
 of consciousness analogous to our own. Some cause must 
 be found, why voluntary action should occur at one time 
 and not at another, in one class of muscles and not in all at 
 the same moment, and so on. Motives must exist to actuate 
 the will. 
 
 Upon referring to the ordinary operations of our own 
 minds, volition appears to take place whenever we antici- 
 pate a greater degree of gratification or advantage from 
 exerting than from repressing it. We know by experience 
 the prompt influence of the will over our muscular frame : 
 we are able to conjecture with more or less certainty the 
 consequences of different voluntary actions : and we will, 
 with a general or precise anticipation of what the result 
 will be, and in order to obtain it. A hungry person knows 
 that the food he prepares to eat will gratify his appetite : a 
 drowning person hopes that his cries will bring people to 
 his assistance. But there are instances in human beings in 
 which intelligent motives cannot be assigned for voluntary 
 actions. The infant at the breast, or struggling when first 
 plunged into water, employs muscular efforts for its susten- 
 ance or preservation, no less voluntary than those which the 
 schoolboy makes when draining his orange, or the exhausted 
 swimmer when he calls for help. But in the infant, the motive 
 which leads to the voluntary effort, is not the anticipation 
 of pleasure or advantage, but a spontaneous tendency, a 
 blind inclination, an instinct. 
 
 Instinct then appears to consist in a natural tendency to 
 execute certain voluntary movements, without any previous 
 conception of the object they are calculated to attain, upon 
 the occurrence of particular sensations or states of inward 
 feeling. This account of instinct corresponds very nearly 
 with the popular meaning of the term. The modifications 
 of this property, as I have described it, are especially 
 characteristic of human and brute intelligence : in man 
 they are subdued and subservient to reason : in animals 
 
 N 
 
190 Of Instinct. 
 
 they greatly surpass in vigour and influence the faint 
 glimmerings of reason which they exhibit, and in some 
 instances curiously rival in their effects the most elaborate 
 results of human thought. 
 
 But perhaps it will not be generally granted that instinc- 
 tive actions are voluntary : let us proceed therefore to exa- 
 mine this question at greater length. 
 
 The principal reason for a contrary supposition, consists 
 in our retaining no consciousness of having exerted the will 
 at the time of their performance. But there are many 
 voluntary actions, which leave no recollection the instant 
 afterwards of an effort of the will having preceded them. 
 I allude to those, which from frequent repetition have become 
 habits. Philosophers are generally agreed, that such actions 
 continue to be voluntary, even when the influence of the will 
 in their production eludes observation. We are therefore not 
 authorized to conclude, that instinctive actions are involun- 
 tary, merely because we have no recollection of having willed 
 their performance. 
 
 Sir Charles Bell attempted to prove that there are dif- 
 ferent nerves for the transmission of the instinctive and of 
 the voluntary impulse to muscles. But the experimental 
 evidence which he advanced in support of his theory was 
 fallacious. His experiments were made upon the branches 
 of the fifth and seventh nerves, which supply the flesh and 
 integuments of the nostrils and of the lips in the ass. They 
 appear to have been suggested by the following views. The 
 muscles of the face are remarkable for exhibiting at one 
 time instinctive action, as in the play of the features in 
 expression, while at another they are certainly moved by a 
 deliberate effort of the will, as when food is seized with the 
 lips. But the muscles of the face have been thought to be 
 further distinguished from the muscles of most other parts 
 by having two nerves distributed to them, one a portion of the 
 fifth, the other a portion of the seventh nerve. Is it not 
 likely then, reasoned Sir Charles, that one of these nerves 
 (and he chose the seventh) is a nerve superadded to minister 
 to that instinctive action so conspicuous in the facial 
 muscles, while the other (the fifth) is the nerve of ordinary 
 
Of Instinct. 191 
 
 qualities, intended to minister in the same parts to sensation 
 and voluntary motion. The error in the experiments which 
 he instituted to establish his theory essentially lay in this : 
 he overlooked the fact, that, while an animal has two nostrils, 
 it has but one mouth : in other words, while he observed 
 that the muscle which expands the right nostril, is supplied 
 with nerves from the fifth and seventh of the right side alone, 
 he overlooked the fact that the muscle which closes the 
 lips, being disposed with one of its halves on each side of 
 the face, is supplied both by the right and left nerves 
 jointly. Neglecting this difference, Sir C. Bell supposed 
 that he had ascertained the influence of the seventh nerve 
 over the orbicular muscle of the lips no less than over the 
 muscles of the nostril, when he had divided that nerve on one 
 side only. And as he saw that after the division of one 
 seventh nerve, the nostril on that side ceased to move in 
 breathing (an instinctive action), although the lips conti- 
 nued to be employed in seizing food (a voluntary action), 
 Sir C. Bell concluded that he had obtained by this experi- 
 ment a proof, that the portio dura controls the instinctive ac- 
 tions, but not the voluntary actions of the muscles of the face. 
 Observing the source of error which I have pointed out, I 
 performed the experiment of dividing the seventh nerve on 
 both sides, and obtained a new result. I discovered by this 
 experiment, that the portio dura of the seventh nerve is the 
 common and exclusive motor nerve of the face ; inasmuch 
 as upon its division on both cheeks (the other nerves being 
 untouched) the muscles of the lips as well as of the nostrils 
 are totally paralyzed. They retain indeed under these cir- 
 cumstances sensibility, with which they are endowed by the 
 fifth. Branches of the latter nerve, which emerge from the 
 infra-orbital and mental foramina, to supply the muscles 
 and integuments of the face, Sir C. Bell had supposed to be 
 nerves both of sensation and voluntary motion. I discovered 
 that they are exclusively nerves of sensation *. 
 
 * Mayo's Anatomical and Physiological Commentaries, London, 1822. 
 The reader, who may take a critical interest in this inquiry, should not 
 omit to. read Sir C. Bell's first essay, printed in the Philosophical Trans- 
 actions for 1821, in which his opinions are distinctly stated to be such 
 
 N 2 
 
192 Of Instinct. 
 
 Thus it appears that upon the face, a part in which the 
 occurrence both of instinctive and of premeditated actions 
 is eminently conspicuous, one nerve is proved to minister to 
 this double function. We are authorized in concluding from 
 this fact, that the immediate cause of muscular action is 
 the same in both cases. 
 
 There are some occasions upon which actions decidedly 
 voluntary are substituted for instinctive actions, and the re- 
 verse. As an experiment, a physiologist will temporarily 
 alter his rate of breathing, drawing for a period deeper and 
 fewer inspirations than usual, and afterwards reverting to 
 the natural rate. An actor again will at pleasure in an in- 
 stant throw into his countenance the full expression of mimic 
 passion; directly afterwards perhaps the features subside 
 into their ordinary expression. In these instances there is 
 no effort observed when the change takes place from the 
 one kind of action to another, such as might be expected if 
 different principles were in operation in the two cases. 
 
 The instinctive actions, to which I have last adverted, 
 have the following remarkable character in common with 
 those which are consciously voluntary. By an exertion of 
 attention and resolution we can refrain from them ; and the 
 constraint which we put upon ourselves, as the effort is more 
 or less successful, closely resembles that comrnonly expe- 
 rienced upon refraining from the indulgence of those move- 
 ments which are called habits. 
 
 The conclusion towards which the preceding arguments 
 tend has the additional advantage of being intrinsically 
 more philosophical than that to which it is opposed : the 
 first, which classes instinct as a motive to the will, is sup- 
 as 1 have here represented them. In all his subsequent writings on this 
 subject (writings published after the first part of my anatomical and phy- 
 siological commentaries had in the mean time appeared) Sir C. Bell, re- 
 taining the terms which he had employed to explain his theory, such as 
 superadded, respiratory, &c., has [substituted for his original opinions 
 my conclusions, 1 regret to say without acknowledging the source from 
 whence he derived them. It is very painful to me for many reasons to 
 speak in terms of censure of Sir C. Bell ; but in justice to myself I am 
 compelled to make the foregoing statement. 
 
Of modified Instincts. 1 93 
 
 ported by analogy : the second, which represents instinct 
 as a principle equivalent at once both to motives and 
 volition, disregards all analogy. 
 
 I shall now quote one or two examples of the instincts of 
 animals, which may contribute to persuade the reader that 
 instinctive actions are voluntary, and which will at the same 
 time bring us to another disputable question, as to where in- 
 stinct ends and reason begins. " On dissecting," says Galen, 
 " a goat great with young, I found a brisk embryon, and 
 having detached it from the matrix, and snatched it away 
 before it saw its dam, I brought it into a room, where there 
 were many vessels, some filled with wine, others with oil, 
 some with honey, others with milk or some other liquor, and 
 in others there were grains and fruits. We first observed the 
 young animal get upon its feet and walk; then it shook 
 itself, and afterwards scratched its side with one of its feet ; 
 then we saw it smelling to every one of these things that 
 were set in the room, and when it had smelt to them all, 
 it drank up the milk." What is this but an instance of 
 sensation occasioning a blind impulse to a determinate 
 course of voluntary action ? 
 
 The next example which I shall adduce, is one of many 
 in which the guiding principle of animals seems at first 
 sight not to be blind, but intelligently to accommodate 
 itself to circumstances, when the ordinary train of action 
 would be unsuitable. " If a hive of bees be this year in 
 possession of a queen duly fertilized, and consequently sure 
 the next season of a succession of males, all the drones, 
 towards the approach of winter, are massacred by the 
 workers with the most unrelenting ferocity. To this seem- 
 ingly cruel course, they are doubtless impelled by an im- 
 perious instinct : and as it is regularly followed in every 
 hive thus circumstanced, it would seem at the first view 
 to be an impulse as intimately connected with the organiza- 
 tion and very existence of the workers, and as incapable of 
 change as that whick leads them to build cells or to store 
 up honey. But this is far from being the case. However 
 certain the doom of the drones this autumn if the hive be 
 furnished with a duly fertilized queen, their undisturbed 
 
194 Of Conception and Memory in Animals. 
 
 existence over the winter is equally sure if the hive have 
 lost its sovereign, or her impregnation have been so re- 
 tarded as to make a succession of males in the spring 
 doubtful. In such a hive the workers do not destroy a 
 single drone, though the hottest persecution rages in all 
 the hives around them*." 
 
 Now how are we to> explain this difference of conduct ? 
 Are we to suppose that the bees know and reason upon this 
 alteration in the circumstances of their community that 
 they infer the possibility of their entire extinction if the 
 whole male stock were destroyed when without a queen 
 and that thus influenced by a wise policy they restrain the 
 fury they would otherwise have exercised ? This would be 
 at once to make them not only gifted with reason, but en- 
 dowed with a power of looking before and after, and a 
 command over the strongest natural propensities, superior 
 to what is expected in a similar case even from a society of 
 men ; and it is obviously unwarrantable. The more proba- 
 ble supposition is, that here again the conduct of the ani- 
 mal blindly follows an impulse originating from impressions 
 on the senses : in other words, that a new instinct is de- 
 veloped, suited to the extraordinary situation in which the 
 community stands, leading the workers now to regard with 
 kindness the drones, for whom otherwise they would have 
 felt the most violent aversion. 
 
 But doubtless we may arrive at a point in studying the 
 habits of animals, where instinct yields to other principles. 
 Let us, there fore, proceed to inquire what mental affec- 
 tions are discernible in animals, besides sensation, percep- 
 tion, volition, and instinct, and what effect they have in 
 modifying or superseding the latter. 
 
 It is evident that in animals, as in human beings, im- 
 pressions once traced upon the mind may recur to it. Who- 
 ever has observed a dog during its sleep prick its ears and 
 whine, must be persuaded that the animal dreams : in 
 other words, it has the faculty of correeiving former objects 
 of sense. 
 
 It is not less certain that animals have memory : this is 
 * Kirby and Spcncc's Entomology, vol. ii, p. 504. 
 
Of Imitation ami Attention. 195 
 
 shown in the power of personal recognition which they 
 evince. 
 
 The principle of imitation again exists in various degrees 
 in animals. This principle is one that modifies instinct. 
 A bird untaught will practise from instinct the song of its 
 kind ; but placed under circumstances where it hears 
 another song exclusively, the young bird learns the notes 
 in place of its proper song. 
 
 Animals display a principle analogous to the association 
 of ideas, and that no less in a wild state than when tamed. 
 The wariness which wild animals acquire with age is evi- 
 dently attributable to this principle, and the education of 
 domesticated animals is founded entirely upon it. 
 
 Animals certainly possess a power of attentive observa- 
 tion. When you have thrown a ball two or three times in 
 succession for a dog to fetch, if you repeat the gesture 
 of throwing, but retain the ball in your hand, the animal 
 starts headlong after the object you have feigned to throw ; 
 but it quickly discovers the deceit : and now, when you 
 would repeat the deception, the animal carefully watches 
 whether the gesture of throwing be real or a feint, before it 
 starts upon its course. 
 
 But the most remarkable illustrations of this faculty in 
 animals, or rather perhaps of correct observation combined 
 with surprising accuracy of recollection, are to be found 
 in those cases in which animals have made their way 
 home by a route they had never before pursued. That a 
 dog should retrace its exact path for a Imndred miles by 
 the sense of smell, or that a carrier pigeon, even with the 
 acute vision of a bird, should see its way towards home, 
 are things sufficiently wonderful; but that an animal should 
 discover its path home without any conceivable guide but 
 the remembrance of the direction in which it has been 
 brought, can scarcely be believed, even where its occurrence 
 is perfectly attested. The following, which 1 extract from 
 Messrs. Kirby and Spence's Entomology, is the most mar- 
 vellous instance of the kind which I have read of. 
 
 " In March, 1816, an ass, the property of Capt. Dunclas, 
 then at Malta, was shipped on board the Ister frigate, 
 
196 Of the observation of direction shown in animals. 
 
 Capt. Forrest, bound from Gibraltar for that island. The 
 vessel having struck on some sands at Point de Gat, at some 
 distance from the shore, the ass was thrown overboard to 
 give it a chance of swimming to land a poor one, for the 
 sea was running so high, that a boat which left the ship was 
 lost. A few days afterwards, when the gates of Gibraltar 
 were opened in the morning, the ass presented itself for 
 admittance, and proceeded to the stable of Mr. Weeks, a 
 merchant, which he had formerly occupied, to the no small 
 surprise of this gentleman, who imagined that from some 
 accident the animal -had never been shipped on board the 
 Ister. On the return of this vessel to repair, the mystery 
 was explained ; and it turned out, that Valiante (as the ass 
 was called) had not only swam safely to shore, but without 
 guide, compass, or travelling map, had found its way from 
 the Point de Gat to Gibraltar, a distance of more than two 
 hundred miles, through a mountainous and intricate coun- 
 try, intersected by streams, which he had never traversed 
 before, and in so short a period that he could not have 
 made one false turn*." 
 
 It is in instances however in themselves much less sur- 
 prising than the preceding, that animals show the nearest 
 approach to human reason. It has been observed, that 
 animals acquire a degree of sagacity with age; that an 
 experienced greyhound, for example, will in coursing the 
 hare deviate from the direct pursuit of its game, and make 
 straight towards a wood, to turn the hare from gaining its 
 cover. The following singular circumstance, which is 
 nearly to the same purpose, is narrated by Dr. Fleming. 
 
 " The hooded crow of Zetland, when feeding on the tes- 
 taceous mollusca, is able to break some of the tenderer kinds 
 by means of its bill, aided in some cases by beating them 
 against a stone ; but as some of the larger shells, such as 
 the buckie and the whelk, cannot be broken by such means, 
 it employs another method, by which, in consequence of 
 applying foreign power, it accomplishes its object: seizing 
 the shell with its claws, it mounts up into the air, and then 
 
 * Kirby and Spence's Entomology. 
 
What we term in animals rational. 197 
 
 loosing its hold, causes the shell to fall among stones (in 
 preference to the sand, the water, or the soil on the ground) 
 that it may be broken, and give easier access to the con- 
 tained animal. Should the first attempt fail, a second or a 
 third are tried, with this difference, that the crow rises 
 higher in the air, in order to increase the power of the fall, 
 and more effectually remove the barrier to the contained 
 morsel." 
 
 In both the cases which I have just described, it is not to 
 be doubted that the animal understands that the indirect 
 means which it adopts will lead to the attainment of a de- 
 sired end; it is hardly possible therefore to call these ac- 
 tions any other than rational. At the same time, if the 
 guiding principle in these instances be reason, it must be ad- 
 mitted that its light extends no further than to guide the 
 creature one step in supplying an urgent appetite, and that 
 the general nature of the animal remains irrational still. It 
 is possible that there are beings above us, who look at our 
 prodigies in arithmetical talent in the light in which we 
 view these instances, as partial glimpses in an inferior race 
 of a higher caste of mental faculties. 
 
 The strongest contrast that can be drawn between the 
 mental nature of animals and man, consists in comparing 
 together the condition of the most sagacious animals under 
 circumstances the most favourable for the improvement of 
 their sagacity, and the mental attainments of human beings 
 when most excluded from the ordinary channels of acquiring 
 knowledge. 
 
 The dog, the horse, the elephant, and the monkey, asso- 
 ciating frequently with man, and exhibiting almost human 
 sympathies with him, reading his eye, his gestures, yet 
 make no step through their intercourse with him towards 
 a rational nature. Compare all that is most surprising in 
 their acquired character and habits with the following ac- 
 count by Professor Glennie of the poor lad born blind 
 and deaf, to whose case I have before adverted. 
 
 " His countenance," as Professor Glennie writes at the 
 time, " notwithstanding his unfortunate defects, does by 
 no means indicate fatuity ; nay the lineaments of thought 
 
198 Professor G Jennie's account 
 
 are very observable upon it. His features at times are per- 
 fectly composed and sedate. When sensible of the presence 
 of a stranger, or of any object which awakens his curiosity, 
 his face appears animated ; and when offended or enraged, 
 he has a very marked ferocity of look. He behaves himself 
 in company with much more propriety than could be ex- 
 pected ; a circumstance owing undoubtedly to the great 
 care of his parents, and of his elder sister. He feeds him- 
 self. When a stranger arrives, his smell immediately and 
 invariably informs him of the circumstance, and directs him 
 to the place where the stranger is, whom he proceeds to 
 survey by the sense of touch. In the remote situation 
 where he resides, male visitors are frequent, and therefore 
 the first thing he generally does is to examine whether or 
 not the stranger wears boots : if this be the case, he imme- 
 diately quits the stranger, goes to the lobby, feels for and 
 accurately examines his whip : then proceeds to the stable, 
 and handles his horse with great care, and with the utmost 
 seeming attention. It has occasionally happened that 
 visitors have arrived in a carriage, and on such occasions he 
 has never failed to go to the place where the carriage stood, 
 examined the whole of it with much anxiety, and tried 
 innumerable times the elasticity of the springs. The feeling 
 by which he appears to be most powerfully actuated is 
 curiosity, or an anxious desire to make himself acquainted 
 with every thing that is new to him. He appears to feel 
 affection for those of his family very strongly ; discovered 
 extreme sorrow on account of his father's death ; laid him- 
 self upon the coffin, after his father's corpse was put into it, 
 apparently in much grief; went frequently to his grave, and 
 threw himself upon it, whilst he gently patted the turf, and 
 bemoaned himself greatly. He is likewise capable of feeling 
 mirth, and frequently laughs heartily. He is highly grati- 
 fied by getting new clothes ; and as tearing his clothes is 
 the most usual expression of his anger, so the punishment 
 he feels most is being obliged to wear them after he has 
 torn them. 
 
 46 Respecting the manner in which he conveys his feelings, 
 I am at a loss to give the information that might be ex- 
 
of James Mitchell . 199 
 
 pected. It is certain that those of his family know perfectly 
 in what temper he is, and what he wants to have ; and these 
 intimations he conveys to them in the presence of strangers, 
 without these last being sensible of his doing so. When he 
 is hungry, he approaches his mother or sisters, touches them 
 in an expressive manner, and points towards the apartment 
 where the victuals are usually kept. If he wants dry stock- 
 ings, he points to his legs ; and in a similar way intimates 
 his wishes on other occasions. A pair of shoes were lately 
 brought to him, which he found to be too small : his mother 
 then took them, and put them into a small closet. Soon 
 after a thought seemed to strike him, and he contrived to 
 obtain the key of the closet, opened the door, took the 
 shoes, and put them upon the feet of a young lad who 
 attends him, whom they suited exactly. 
 
 " His father, when alive, was at much pains in directing 
 him, as his mother still is ; but his eldest sister has a much 
 greater power of managing him than any other person. 
 Touching his head with her hand seems to be the principal 
 method which she employs in signifying her wishes to him 
 respecting his conduct : this she does with various degrees 
 of force, and in different manners ; and he seems readily to 
 understand the intimation intended to be conveyed. In 
 short, by gratifying him when he acts properly, and with- 
 holding from him the objects of his complacency when he 
 has done amiss, he has been taught a sense of what is be- 
 coming in manners and proper in conduct, much stronger 
 than it could otherwise be believed that any person in his 
 singularly unfortunate situation could acquire." 
 
 But to return from this attempt to compare the mental 
 endowments of animals with our own, to the brief enumera- 
 tion of the elements of the human mind, which I proposed 
 to give. 
 
 The newly-born infant displays sensation and instinct. 
 The same being grown to childhood, perceives through sen- 
 sation the world around him, and exerts deliberate volition. 
 
 Let us examine the various changes which his mind when 
 matured can ring upon the impressions which follow one 
 rapid exercise of sensation. Let us suppose, for instance, 
 
200 Of Conception, Memory, Attention, Comparison. 
 
 that he has had a rapid but distinct view of the fagade of 
 King's College. The perception of the scene is passed, but 
 he is able at pleasure to conceive what he saw. Suppose 
 that the conception of the scene has returned unsought, he 
 recognizes its identity with a former subject of consciousness. 
 An accident appears to have brought the scene again to his 
 mind : yet it was not accident ; the recurrence of his mind 
 to the scene was determined by a wonderful law, that of the 
 association of ideas. 
 
 The whole conception before his mind he can fix and 
 detain at pleasure by an effort of attention. Or he may, by 
 directing his attention to one or more points or relations of 
 the object, detain and contemplate these abstractedly from 
 the rest; the height of the building may thus occupy his 
 mind, without reference to its depth. Or he may, retaining 
 the idea of colour and material, abstract from the height, 
 and number of windows, add to the flight of steps, suppose 
 a cupola superimposed upon the centre, and imagine thus a 
 long building with a dome and a portico, but without wings. 
 
 Or he may compare the conception which he has formed 
 of King's College with that of any other noble architectural 
 building, in one or all of its relations, and judge of the 
 superiority of either. 
 
 Thus will have been successively exerted perception, con- 
 ception, memory, abstraction, imagination, comparison, judg- 
 ment ; besides volition originally called into play, in fixing 
 the sight upon the object perceived, and attention in detain- 
 ing the conception of the scene before the mind, and the law 
 of association which determined its recurrence. 
 
 Or the mind of our supposed observer might run into 
 analytical trains of thought ; and in this vein he might ask 
 himself, Is it true that Sir Robert Smirke designed this 
 building ? Has it been raised for a good purpose ? Is it 
 really beautiful, or am I misled to think it so by the excel- 
 lence of the object for which it is intended, or by the repu- 
 tation of the architect ? Let us suppose an inquirer to stop 
 at the first question, and to investigate the doubts to 
 which it might give rise. He did not see the architect 
 engaged in making the design : what ground has he 'for 
 
Analysis of Belief. 201 
 
 attributing its production to him? What ground has he 
 for believing that the building was planned at all ? What 
 ground has he for believing that it exists ? He is led to 
 examine the nature of belief. 
 
 Truth he makes out to be that which he believes *. But he 
 is aware that his belief is liable to be misled ; and he forms 
 a notion of positive or absolute truth, considering those pro- 
 positions to be absolute truths, which would command his 
 assent if all the evidence relating to them were laid before 
 him and understood by him. Practically, he finds the truths 
 which he admits, or the kinds of evidence which determine 
 his belief, to belong to four classes, which are the following. 
 
 A. Certain truths may be called intuitive, which whether 
 shaped or not as distinct propositions, spontaneously arise 
 in our minds, or are involved in all our reflections ; and are 
 of such a nature that to doubt them for an instant is impos- 
 sible. Of this description are the following. 
 
 1. The belief which we entertain of the reality of those 
 mental affections, of which we are conscious. 
 
 2. Our belief in the evidence of memory : in other words, 
 our belief, when we remember to have experienced an 
 emotion or impression before, that we really have expe- 
 rienced something similar on a former occasion. The 
 strongest illustration, which I can select of the conviction 
 attending the evidence of memory, is our belief in our 
 moral or personal identity ; every man remembers feelings 
 excited in him at a very early age by one incident or another ; 
 and recognizing on the evidence of memory their affinity to his 
 present character, is sure that he who went through such 
 an adventure is the same person who reflects upon it now. 
 
 3. The belief, that every change must have an efficient 
 cause. 
 
 4. The belief that duration and space are without limits. 
 
 5. To many persons the evidence of perception appears 
 of this description. The belief in the existence of an external 
 material world bears indeed a close affinity to intuitive 
 truth, inasmuch as it arises spontaneously in our minds, 
 
 * " Quid est veritas ? " Pilate asked ; " Est vir qui adest," is the sin- 
 gular anagram of these words. 
 
202 Analysis of Belief. 
 
 and cannot be seriously questioned by a rational under- 
 standing. Yet it must be admitted, that such is the con- 
 stitution of our nature, that we can conceive it possible, 
 that matter has no existence, and that our waking sensa- 
 tions, like those which we seem to experience in a dream, 
 flow from some other cause than external material impressions. 
 
 B. Another class of truths comprises those which rest 
 upon experience and analogy. When we have observed 
 that certain consequences have uniformly followed certain 
 antecedents, we are led by the constitution of our nature to 
 expect the recurrence of those consequences, whenever we 
 see their usual forerunners : thus when we see the sun go 
 down, we entertain no doubt that it will rise on the follow- 
 ing morning ; and so on in regard to the general order of 
 nature ; although it is evidently possible that that order 
 may be interrupted to-morrow. 
 
 But the most remarkable illustration of the force which may 
 belong to this kind of evidence, is to be found in the argu- 
 ment which the study of nature affords in proof of the ex- 
 istence of a God. All bodies, of which we can trace the his- 
 tory, that have a structure adapted to determinate purposes, 
 have been contrived by intelligent beings. We therefore con- 
 clude analogically, when we meet with bodies of the origin of 
 which we are ignorant, yet which have a structure and dis- 
 position adapted to determinate ends, that such instances like- 
 wise are the result of design, and have been produced by an 
 intelligent cause. But Nature through all her reign exhibits 
 to the most superficial as well as to the profoundest observer, 
 the most refined and sagacious adaptation of means to im- 
 portant ends. Nature then we are compelled to believe is 
 but Art the work of immeasurable wisdom and power. 
 
 A third instance of the conviction which flows from 
 experience and analogy, is our reliance on testimony. The 
 present instance serves remarkably to show the various 
 shades of belief, which may attach to the kind of evidence 
 which we are now considering. Who doubts that Socrates 
 and our Saviour lived and died? and who believes the 
 rumour of the day during a season of popular agitation ? 
 A child that has never been deceived, believes implicitly 
 
Analysis of Belief* 203 
 
 every assertion made to it. A statesman professes a distrust 
 of history, upon his personal knowledge that it is sometimes 
 falsified. 
 
 C. Mathematical truths are acknowledged to rest upon 
 evidence so convincing, as to claim exclusively the title of 
 demonstration, On what does the conclusiveness of demon- 
 stration depend ? Or what is the nature of each step in 
 mathematical reasoning 1 The proof in each instance 
 amounts to this only : that the point in question is shown 
 to be identical with one already admitted. 
 
 The certainty which belongs to syllogistic reasoning is of 
 the same description. Syllogistic proof consists in showing 
 that the circumstance you would predicate of an individual 
 has been already granted to belong to the genus. 
 
 Induction is the method employed in the discovery of 
 physical causes. By means of an induction of well- 
 chosen or well-contrived instances, the common and essen- 
 tial conditions in an entire class of phenomena are rendered 
 apparent. Our belief in a law established by induction, 
 arises from that law being but another and more general 
 expression for what has been already shown to occur in 
 every conceivable case that has admitted of investigation. 
 
 D. Theoretical or circumstantial evidence, is that which 
 wins our belief by the concurrence of many probabilities 
 towards one conclusion. The mind appears capable of 
 receiving a collective impression from many single im- 
 pressions. Every one knows how, in a fictitious tale, the 
 feeling of horror excited by some harrowing scene is 
 gradually heightened and wrought up by the skilful ac- 
 cumulation of incident upon incident. Thus in circum- 
 stantial evidence, each fresh probability augments the sum 
 of our belief. There are many instances in which the 
 degree of probability of an event admits of being stated 
 numerically : in these the force of cumulative proof 
 may be said to admit of mathematical demonstration. 
 
 In the preceding analysis, the supposed questioner 
 would have ascertained the principles upon which the 
 first of his doubts might be solved. Let us take the next. 
 
204 Of the Moral Sense. 
 
 Is the object contemplated by the founders of King's 
 College a good and meritorious one ? 
 
 Our questioner would divide this inquiry into two 
 parts. As far as goodness means the promoting all that 
 conduces to public order and private happiness, that 
 institution must be good, which unostentatiously combines 
 religious and moral discipline with scientific and profes- 
 sional education. As far therefore as what is eminently 
 useful publicly and privately deserves to be called good, the 
 object of the founders of King's College is good. But in any 
 other sense is it good 1. or is there such a thing as goodness 
 independent of expediency ? Have we in our nature a prin- 
 ciple for discerning good, as we have for discerning truth ? 
 
 Our notions of virtue and vice appear at first sight of 
 so artificial a nature, as to render it doubtful whether we 
 possess any inherent or special faculty for the appreciation 
 of moral excellence. The force of early impressions, the 
 respect entertained for the opinion of society, and the 
 influence of Religion, appear sufficiently to account for 
 the different feelings with which men regard good and 
 evil. We are further confirmed in this view when we 
 consider, that in different countries, and at different periods, 
 the principles of virtue and vice appear to have essentially 
 varied, and the landmarks of morality to have been arbi- 
 trarily displaced and shifted. Yet the latter argument may 
 be sufficiently answered in the following manner. In pro- 
 portion as the moral and intellectual condition of mankind 
 is improved, the opinions of men are observed to concur 
 more nearly as to the standard of virtue. Such a gradual 
 approximation to a common sentiment upon any subject, 
 is the strongest proof of an inherent sense or faculty that 
 it is consistent with analogy to expect. Our questioner 
 therefore concludes, that there is within us a moral sense, 
 a faculty (requiring cultivation, like that of belief, to give it 
 justness) which enables us to derive pleasure from, or to feel 
 strong delight in and approbation of acts of good faith, dis- 
 interestedness, beneficence, piety. As a striking illustration 
 of the force of this principle, it may be mentioned, that 
 
Of Taste. 205 
 
 with many the moral evidence of Christianity is far from 
 being the least persuasive in proof of its divine origin. 
 To this sense Lord Shaftesbury refers in the beautiful 
 expression, that " true wisdom is more of the heart than of 
 the head." 
 
 The third question which I have supposed might in- 
 terest our inquirer would lead him to a parallel train of 
 reasoning to the last, and to a parallel conclusion. 
 
 As the words good and bad exist in the languages of 
 all civilized nations, so likewise we find expressions cor- 
 responding with the following beautiful, sublime, de- 
 corous, ludicrous. These expressions bear an application 
 to human conduct or to incidents in human life, without 
 reference to morality. Emotions similar to most of these 
 may be excited in us by the fine arts, or by natural objects. 
 Scenery may be sublime or beautiful : sculpture, painting, 
 acting, and poetry, delight in a similar manner, inde- 
 pendently of the imitative pleasure belonging to the three 
 first, and the rarity of the talent displayed in all. As we 
 call the cultivated moral sense Conscience, we term the 
 capacity of receiving delight from the sources I have last 
 described, Taste. 
 
 The sketch which I have thus endeavoured to give of 
 the constituent elements of mind would be incomplete 
 without a notion of what is meant by diversities of talent, 
 and of temper and disposition, as well as an enumera- 
 tion of those affections, which form the active principles 
 of our nature. We are perhaps in some degree indebted 
 to Messrs. Gall and Spurzheim, for having thrown into 
 their true prominence in the philosophy of mind, diver- 
 sities of talent and of disposition, as contrasted with those 
 operations of the understanding which are involved in the 
 exercise of the first. 
 
 All exercise of talent implies invention ; from wit, which 
 consists in presenting certain classes of ideas in novel and 
 unexpected relations, to poetry or design, in which new and 
 just combinations of thought or conception are produced, 
 to philosophical genius, which is shown in creating or bring- 
 ing together instances through which inductive truth may 
 
206 Of Talent and Disposition. 
 
 be elicited. Talent therefore of every kind works by the 
 same processes ; and thence it has been said, that difference 
 of talent depends only upon the difference in the classes of 
 associations upon which it operates, and thus that its par- 
 ticular direction in individual instances may possibly be ac- 
 cidental. 
 
 It is probably more just, however, to look at the subject 
 of, or the direction of talent, as distinguishing, and its 
 operations as subordinate, than to view the operations of 
 the mind as the principal element, and the subject as an 
 accident. tt'psM 
 
 The justness of this manner of viewing the subject 
 appears to me borne out by what we know of prodigies 
 of partial talent. The most remarkable instances perhaps 
 are to be found in the faculty of arithmetical calculation 
 which some are endowed with, and in which the most 
 wonderful powers of analysis and combination are shown, 
 but in reference to numerical relations alone. In these we 
 learn, that the gifted individual has enjoyed from early 
 childhood an intuitive perception of the properties of 
 quantities themselves ; that rules for facilitating com- 
 plex arithmetical calculations spontaneously present them- 
 selves to his mind ; that he has an instantaneous per- 
 ception of the best among several modes of perform- 
 ing the same operation. One, who gave to a friend 
 of mine this account of his own powers, stated at the 
 same time that his mental multiplication table reached to 
 1000, a remark which seems to me to throw light upon the 
 nature of this extraordinary talent, or to show it to be the 
 same in kind, though incomparably superior in rapidity, to 
 that which common persons may command by practice. 
 It is but in its extent, facility, and rapidity of combination, 
 that genius differs from ordinary ability. 
 
 To conclude this enumeration of the principles of our 
 nature, I have to mention those shades of character, which 
 constitute diversities of temper and disposition : for this 
 purpose I shall content myself with setting down the 
 different epithets by which these are known. They are 
 the following: one may be irascible or cool, hasty or 
 
Of the Active Principles of our Nature. 207 
 
 deliberate, cheerful or morose, steady or volatile, even or 
 uneven, sanguine or gloomy, irritable or phlegmatic, en- 
 thusiastic or saturnine, vindictive or placable, active or 
 indolent, bold or timid, ingenuous or artful, compassionate 
 or unfeeling. 
 
 Finally, the active principles of our nature, are, 1. Our 
 instincts, the desire of gratifying the appetites, the desire 
 of self-preservation, curiosity) and the principle of self- 
 esteem. 2. Regard for the opinion of the world, emulation 
 and envy, the love of power, personal liking and aversion, 
 fear, anger, sympathy, imitation. 
 
 These are termed active principles, because they produce 
 in us an inclination to action; it is evident that others 
 remain to be enumerated : whatever is pleasing or displeas- 
 ing strikes upon an active principle of our nature. We 
 court change, we are pleased with what is new, and yet 
 we are pleased with what has become habitual : we seek 
 to gratify our taste, and our moral feelings ; and the exer- 
 tion of talent, like the indulgence of our humour, is a 
 source of direct pleasure. 
 
 But what then is the inind, the possessor of these 
 powers, the subject of these numerous affections and 
 shades of humour ? All that we know of it, is contained 
 in the brief history of its affections, and the laws of their 
 recurrence. 
 
 But is it, as the materialist imagines, the result of a par- 
 ticular combination of material atoms? Do thought and 
 feeling flow from a change in organized structure, as music 
 from the vibration of a string? Or is their subject some- 
 thing, which is essentially independent of, and may survive 
 the dissolution of the corporeal frame ? 
 
 Our knowledge upon this matter is contained in a small 
 compass. In the first place, we can imagine that mind 
 may exist without matter ; there is no contradiction involved 
 in supposing each material element of our frame destroyed, 
 yet the distinct recollection of all we have done and 
 suffered and enjoyed remaining. 2. It is utterly impossi- 
 ble for us to conceive how matter can produce mental 
 
 o 2 
 
208 The Mind not the Result of Organization. 
 
 phenomena. 3. We are in possession of the fact, that 
 while our body changes, our mental identity remains. 
 It is difficult to avoid concluding from these premises, 
 that the human mind is something superadded upon and 
 temporarily united to our living bodies, not a series of 
 affections resulting from their material structure. 
 
 I shall conclude this chapter with describing what is 
 known of the condition of the mind during sleep, when 
 the succession of the phenomena of consciousness often 
 appears to be completely interrupted, and with a notice of 
 a few of the more - remarkable instances in which the 
 ordinary course of the mental affections is disturbed. 
 
 The period of a diurnal revolution is shared between 
 sleeping and waking: during six or eight hours of the 
 twenty-four, consciousness appears suspended. After a day 
 spent in active exercise, the limbs feel fatigued, the mind is 
 less lively and less capable of continued attention, the 
 senses become duller, we seek to dispose the body in a pos- 
 ture requiring the least muscular effort to sustain it, we 
 withdraw the mind from reflections calculated to excite 
 its powers, we seek to close the avenues of sensation, the 
 images before the mind become more and more faint, and by 
 
 insensible gradations we become unconscious. 
 
 j I*- 
 
 During sleep the circulation is more gentle, the respira- 
 tions are less frequent and are deeper, the temperature is 
 lowered, the cutaneous transpiration is increased. The 
 sleeper perhaps remains for several hours without motion, 
 undisturbed by the loudest sounds or the brightest light. 
 
 If a sleeping person be awakened by opening the eyelids 
 under a strong light, the pupil for the first second or two is 
 seen to be extraordinarily contracted, which we may pre- 
 sume to be its usual state during sleep : the pupil then 
 becomes widely dilated, but again contracts and dilates 
 before it becomes steady: at the same time the person 
 moves himself, articulates unconnectedly, and seems en- 
 deavouring to collect his scattered thoughts. The mind 
 quickly recovers its wonted character, the memory of the 
 events of the preceding day returns, but with it in most 
 
Of Sleep. 209 
 
 cases no recollection presents itself of a state of conscious- 
 ness between the period of falling asleep and that of 
 waking. 
 
 Among the instances in which the memory affords no 
 evidence of the existence of consciousness during sleep, 
 some are nevertheless attended with phenomena, which 
 distinctly show that consciousness has not been entirely 
 suspended : for, that I may not mention breathing as an 
 evidence of voluntary motion (it being no doubt disputable 
 whether each act of inspiration be voluntary or proceed 
 from an automatic influence), a person asleep will some- 
 times turn his head from the light, or shift the position of a 
 limb or of the body when it is reasonable to suppose that 
 it has become inconvenient : many animals likewise sleep 
 in postures in which they cannot be sustained without the 
 measured employment of voluntary muscles. Among many 
 other facts of common observation, none perhaps is more 
 conclusive than the estimate which seems to be made of 
 the flight of time during sleep, so that a person anxiously 
 bent upon awaking for an important object at a definite 
 hour, will be sure, against his usual habits, and in defiance 
 even of accidental fatigue, to wake before the hour re- 
 quired. 
 
 There are other instances in which the memory retains 
 the clearest impression of various affections of conscious- 
 ness having taken place during sleep. In dreams, the 
 images presented to the mind are sometimes incoherent and 
 disjointed fragments of events : at other times the train of 
 imaginary circumstances is connected, and capable of pro- 
 ducing an interest as intense as reality. Sometimes the 
 mind is in its finest mood of invention. The musician and 
 the poet have been known to regret, upon waking, their 
 imperfect remembrance of what seemed the brightest gems 
 of their fancy. Sometimes a dream is but the imaginary 
 continuation of trifling or important engagements of the 
 preceding day ; at other times it shapes itself to the present 
 impressions upon the senses, and a sound imperfectly heard, 
 a light flashing upon the closed eyelids, suggests to the 
 
210 Influence of the Will over the Voluntary Muscles 
 
 imagination a rapid train of correspondent images, of which 
 it forms a part. At the moment of waking, dreams are 
 often freshly remembered, which quickly fade from the 
 recollection : at other times some accidental association 
 brings distinctly before us the events of a dream, which till 
 that moment had never been recollected ; leaving it uncer- 
 tain how frequently the mind may thus energize, though 
 its impressions associated with, no object of sense may 
 often fail of being brought back to the mind in its waking 
 state. 
 
 The train of thought in ordinary dreaming is the spon- 
 taneous produce of our imagination, freed from the restraint 
 which the perception of surrounding objects imposes upon 
 us when awake. The character of an individual might 
 therefore be elucidated by a history of his dreams ; nor is 
 it more wonderful that their suggestions should sometimes 
 be prophetic, than that a rational judgment should fre- 
 quently be able to foresee the probable occurrence of events, 
 or that in the varied combinations of hazard a wild sug- 
 gestion of the waking fancy should sometimes be realized. 
 It is singular that a dream seldom refers to recent events, 
 unless they have very strongly interested the mind. 
 
 But the phenomena of dreaming are not always confined 
 to the spontaneous suggestions of the fancy ; occasionally 
 the mind seems to bend itself during sleep to an examina- 
 tion of the impressions which occupy it. It must have 
 happened to every one during a dream to have suspected 
 that he was dreaming, and after a process of deliberate 
 reflection to have become satisfied that he was awake. 
 
 It was the opinion of Dugald Stewart, that in sleep " the 
 will loses its influence over those faculties of the mind, 
 and those members of the body, which during our waking- 
 hours are subjected to its authority*/' In the remarks 
 which I have made upon the phenomena of consciousness, 
 I have employed the term will to signify exclusively that 
 affection of the mind, which is the immediate cause of 
 
 '* Stewart's Philosophy of the Human Mind, vol. i, p. 330. 
 
not suspended during Sleep. 211 
 
 muscular action: that this influence is not in every case 
 suspended during sleep, appears evident upon the fact 
 already adverted to, that many animals sleep in postures 
 which require a sustained muscular effort. But we seem to 
 exercise a voluntary power likewise over the affections of 
 the mind : let us examine, before resuming the preceding 
 inquiry, whether the latter influence be suspended during 
 sleep. The faculty by which we direct the mind at plea- 
 sure to one train or mode of thought or to another, is essen- 
 tially unlike that by which we produce a series of voluntary 
 movements. Under ordinary circumstances we are indeed 
 equally led to either, to analyse for instance an affection 
 of consciousness, or to strip the shell from a filbert, by 
 the gratification it promises : but while in the one case the 
 effect we desire is attained directly and instantaneously, 
 we will and the muscles act, in the former the effort 
 consists in fixing the attention upon a subject of inquiry, 
 and patiently observing the bearing of every thought, which 
 presents itself, upon the point before us. In producing a 
 muscular effort, we will a physical change, and it instantly 
 ensues ; in an effort of thought, we but confine the mind to 
 a definite track, expecting that our established habits of 
 association will bring us to the conclusion we wish. 
 
 Now it appears from an instance of dreaming already 
 mentioned, that the mind can during sleep set on foot an 
 analytical inquiry, and may compare its different impres- 
 sions in order to arrive at a conclusion respecting their 
 nature, an operation as voluntary, if the expression be 
 applicable, as any which the mind exhibits in its waking 
 state. 
 
 Mr. Stewart supposes that the phenomena of nightmare 
 or incubus illustrate the suspension of the influence of the 
 will during sleep. The patient appears to himself to ex- 
 perience uneasy sensations, produced perhaps in part by the 
 accidental posture of his body, which he finds it impossible 
 to remove by his own efforts, and he feels distinctly con- 
 scious of an incapacity to move : or in a case perfectly 
 .analogous he imagines himself pursued during a painful 
 
212 Of Somnambulism. 
 
 dream, and attempts to fly, and his legs seem to refuse to 
 perform their office. But it appears questionable whether 
 in these instances the supposed effort of the will really 
 takes place. The person is not conscious of his real position 
 (if he were he would be awake), and makes no effort to 
 change that. He may possibly be suffering an uneasy 
 sensation, but it is not presented in its true form to the 
 mind ; it is wrought up in all the horrors of a dream, and 
 the attempts to escape from the load are in their nature 
 fictions as well as the sufferings which suggest them. A 
 person wide-awake will occasionally give the reins to his 
 fancy, and frame before his mind scenes of the most excit- 
 ing description, in which he supposes himself to play a 
 busy part, interfering to save by a vast display of strength 
 and activity, or indulging perhaps in the happiest flow of 
 eloquence, in keen and pointed reply to imaginary invective, 
 the very tone of which is supposed to add to its poignancy ; 
 but not a muscle does he move, although the scene in which 
 he is engaged has an interest almost equal with reality. 
 In a troublesome dream the case is similar ; but the patient 
 is essentially lost to every thing external, and having no 
 means of detecting their unreal nature, is wholly absorbed in 
 the creations of his fancy, to which alone his anxiety and his 
 fears have reference. He wishes not to jump out of bed, 
 but to escape the grinning jaws of the monster that threatens 
 him. He is uneasy and oppressed, but there is no real 
 load to be thrown off. 
 
 Perhaps it would be more just to say that the influence 
 of the will over the voluntary muscles during sleep, instead 
 of being suspended, appears not to be habitually exerted ; 
 unless indeed breathing be voluntary. But there are some 
 persons who talk during their sleep, as absent persons 
 sometimes indulge themselves in making remarks aloud, or 
 in gestures, which have reference to the reverie in which 
 they are engaged. The phenomena of somnambulism like- 
 wise, although very imperfectly understood, concur with 
 the preceding instance in distinctly proving the exertion 
 and influence of the will during a modification of sleep. 
 
Of false Perception. 213 
 
 In many cases of this affection it appears that the main 
 action conducted has reference to a dream, while the 
 somnambulist, though little conscious of surrounding ob- 
 jects, yet appears in part to be guided by sensation in his 
 voluntary efforts. 
 
 A fit of somnambulism, observes Dr. Pritchard, is in 
 fact a dream so modified that the dreamer gains the power 
 of pursuing, by voluntary motion, the objects which he is 
 desirous of seeking or avoiding in his reverie. This near 
 relation of the state of somnambulism to that of ordinary 
 dreaming is proved by the fact, that sleepwalkers, after 
 they have awakened from the slumbers, which ushered in 
 the fit of somnambulism, have sometimes remembered their 
 adventures and have correctly related them : not however 
 as transactions in which they had been actually en- 
 gaged, but merely as their impressions of their dreams*. 
 
 In perfect health, the impressions of a dream or reverie 
 are instantly dispelled, when compared with actual sensa- 
 tion. But when the nervous system is disordered, the 
 creations of the fancy sometimes appear mingled among 
 real objects, and assume an illusive existence in the ex- 
 ternal world of persons thus affected. To illustrate at 
 once and to exhaust this subject, I extract from Dr. Hib- 
 bert's interesting work upon the philosophy of appari- 
 tions the account given by Nicolai of his own remarkable 
 case. 
 
 " During the ten latter months of the year 1790, I had 
 experienced several melancholy incidents, which deeply 
 affected me, particularly in September, from which time I 
 suffered an almost uninterrupted series of misfortunes, that 
 afflicted me with the most poignant grief. I was accus- 
 tomed to be bled twice a year, and this had been done 
 once on the 9th of July, but was omitted to be repeated at 
 the end of the year 1790. I had in 1783 been suddenly 
 taken with a violent vertigo, which my physicians imputed 
 to obstructions in the fixed vessels of the abdomen, brought 
 
 * Pritchard on Diseases of the Nervous System, p. 400. 
 
214 Case of Nicolai. 
 
 on by a sedentary life, and a continual exertion of the 
 mind. This indisposition was succesfully removed by 
 means of a more strict diet. In the beginning I had found 
 the use of leeches applied te the arms particularly effica- 
 cious, and they were afterwards repeated two or three times 
 annually, when I felt congestions in the head. The last 
 leeches which had been put on previous to the appearance 
 of the phantasms of which I am about to speak, had been 
 applied on the 1st of March, 1790 ; less blood had con- 
 sequently been evacuated in 1790 than was usual with me, 
 and from September I was constantly occupied in business 
 that required the most unremitted exertions, and which 
 was rendered still more perplexing by frequent interrup- 
 tions. 
 
 " I had in January and February of the year 1791 the 
 additional misfortune to experience several extremely un- 
 pleasant circumstances, which was followed on the 24th of 
 February by a most violent altercation. My wife and 
 another person came into my apartment in the morning in 
 order to console me ; but I was too much agitated by a 
 series of incidents, which had most powerfully affected my 
 moral feeling, to be capable of attending to them. On a 
 sudden I perceived, at about the distance of ten steps, a 
 form like that of a deceased person. I pointed at it, 
 asking my wife if she did not see it ? It was but natural 
 that she should not see any thing ; my question therefore 
 alarmed her very much, and she sent immediately for a 
 physician. The phantasm continued about eight minutes. 
 I grew at length more calm, and being extremely exhausted, 
 fell into a restless sleep, which lasted about half-an-hour. 
 The physician ascribed the apparition to violent mental 
 emotion, and hoped there would be no return ; but the 
 violent agitation of my mind had in some way disordered 
 my nerves, and produced further consequences, which 
 deserve a more minute description. 
 
 " At four in the afternoon the form which I had seen 
 in the morning re-appeared. I was by myself when this 
 happened, and being rather uneasy at the incident, went to 
 
Case ofNicolai. 215 
 
 my wife's apartment, but there likewise I was prevented 
 by the apparition, which, however, at intervals disappeared, 
 and always presented itself in a standing posture. About 
 six o'clock there appeared also several walking figures, 
 which had no connection with the first. 
 
 " After the first day the form of the deceased person no 
 more appeared, but its place was supplied with many other 
 phantasms, sometimes representing acquaintances, but 
 mostly strangers : those whom I knew were composed of 
 living and deceased persons, but the number of the latter 
 was comparatively small. I observed the persons with 
 whom I daily conversed did not appear as phantasms, these 
 representing chiefly persons who lived at some distance 
 from me. 
 
 " These phantasms seemed equally clear and distinct at 
 all times, and under all circumstances, both when I was by 
 myself and when I was in company, and as well in the day 
 as at night, and in my own house as well as abroad ; they 
 were however less frequent when I was in the house of a 
 friend, and rarely appeared to me in the street. When I 
 shut my eyes those phantasms would sometimes vanish 
 entirely, though there were instances when I beheld them 
 with my eyes closed ; yet when they disappeared on such 
 occasions, they generally returned when I opened my eyes. 
 I conversed sometimes with my physician and my wife of 
 the phantasms which at the moment surrounded me ; they 
 appeared more frequently walking than at rest, nor were 
 they constantly present. They frequently did not come for 
 some time, but always re- appeared for a longer or shorter 
 period, either singly or in company, the latter, however, 
 being most frequently the case. I generally saw human 
 forms of both sexes, but they usually seemed not to take 
 the smallest notice of each other, moving as in a market- 
 place, where all are eager to pass through the crowd ; at 
 times, however, they seemed to be transacting business with 
 each other. I saw also several times people on horseback, 
 dogs, and birds. All these phantasms appeared to me in 
 their natural size, and as distinct as if alive, exhibiting 
 
216 Case of Nicolai. 
 
 different shades of carnation in the uncovered parts, as well 
 as different colours and fashions in their dresses, though the 
 colours seemed somewhat paler than in real nature; none 
 of the figures appeared particularly terrible, comical, or dis- 
 gusting, most of them being of an indifferent shape, and 
 some presenting a pleasing aspect. The longer these 
 phantoms continued to visit me, the more frequently did 
 they return, while at the same time they increased in number 
 about four weeks after they had first appeared. I also 
 began to hear them talk ; the phantoms sometimes con- 
 versed among themselves, but more frequently addressed 
 their discourse to me ; their speeches were commonly short, 
 and never of an unpleasant turn. At different times there 
 appeared to me both dear and sensible friends of both sexes, 
 whose addresses tended to appease my grief, which had 
 not yet wholly subsided ; their consolatory speeches were 
 in general addressed to me when I was alone. Sometimes, 
 however, I was accosted by these consoling friends while I 
 was engaged in company, and not unfrequently while real 
 persons were speaking to me. These consolatory addresses 
 consisted sometimes of abrupt phrases, and at other times 
 they were regularly executed. 
 
 " Though my mind and body were in a tolerable state 
 of sanity all this time, and these phantasms became so 
 familiar to me that they did not cause me the slightest 
 uneasiness, and though I even sometimes amused myself 
 with surveying them, and spoke jocularly of them to my 
 physician and my wife, I yet did not neglect to use proper 
 medicines, especially when they began to haunt me the 
 whole day, and even at night as soon as I waked. 
 
 "At last it was agreed that leeches should be again 
 applied to me as formerly, which was actually done April 
 20th, 1791, at eleven o'clock in the morning. No person 
 was with me besides the surgeon ; but during the opera- 
 tion my chamber was crowded with human phantasms of 
 all descriptions. This continued uninterruptedly till about 
 half-an-hour after four o'clock, just when my digestion 
 commenced. I then perceived that they began to move 
 
Distinction between Delirium and Madness. 217 
 
 more slowly. Soon after their colour began to fade, and 
 at seven o'clock they were entirely white. But they 
 moved very little, though the forms were as distinct as 
 before; growing, however, by degrees more obscure, yet 
 not fewer in number, as had generally been the case. The 
 phantoms did not withdraw, nor did they vanish, a circum- 
 stance which previous to that time had frequently happened. 
 They now seemed to dissolve in the air, while fragments 
 of some of them continued visible for a considerable time. 
 About eight o'clock the room was entirely cleared of my 
 fantastic visitors. 
 
 "Since that lime I have felt twice or three times a 
 sensation as if these phantasms were going to reappear, 
 without, however, actually seeing any thing. The same 
 sensation surprised me just before I drew up this account, 
 while I was examining some papers relative to these appari- 
 tions, which I had drawn up in the year 1791." 
 
 As during disease creations of the fancy may thus 
 emulate perception, in like manner may any fiction of 
 opinion or feeling when the brain is disturbed appear 
 reasonable, and mix among the sound conclusions and 
 principles of the mind, and produce inconsistency of con- 
 duct and insanity. 
 
 Pure delirium, which results either from concussion or 
 from inflammatory excitement of the brain, is remarkably 
 contrasted in its moral features with insanity: in both 
 the mind attaches reality to fictions ; but in delirium the 
 mind is wholly absorbed as in a dream with its own crea- 
 tions, preserving nevertheless the power, when strongly 
 roused to momentary recollection, of directing itself justly 
 to its situation ; while in insanity truth and error are 
 blended together, and when seen side by side are not 
 distinguishable by the patient. 
 
 It has been remarked, that of the powers of the mind, the 
 memory is the first to decay. Old age, which impairs the 
 mind, makes its first inroad on the memory. Wine, while 
 it raises the animal spirits and stimulates the fancy, at the 
 same time disturbs the memory. After injuries of the head, 
 that have eventually been followed by idiotcy, the failure 
 
218 Of the Decay of the Mind. 
 
 of the memory has been the first mental symptom ob- 
 served. 
 
 The failure of memory is perhaps sometimes considered 
 the only impairment of the mind, when in fact its other 
 powers are likewise injured, inasmuch as an alteration is 
 much more readily detected in the memory than in any 
 other faculty. It is possible likewise, that in many in- 
 stances it is more properly the recollection than the memory 
 which suffers ; the remembrance is not lost, but the facility 
 of finding it in the mind : so that the change would be more 
 justly stated to be in an impairment of the liveliness and 
 rapidity of association. I have heard it observed of old 
 men, that their memory has become impaired, but that their 
 understanding has remained as strong as formerly, only 
 slower in its operations. A supervening slowness of asso- 
 ciation would account in these instances for all the pheno- 
 mena observed. 
 
 How much we may remember, which we cannot recollect, 
 is shown by a curious class of cases, several of which have 
 been collected by Dr. Prichard, in his work upon the nervous 
 system, from which I shall extract the following. 
 
 " A man was brought into St. Thomas's Hospital, who had 
 received a considerable injury of the head, but from which 
 he ultimately recovered. When he became convalescent, he 
 spoke a language which no one about him could compre- 
 hend. However, a Welsh milkwoman came one day into 
 the ward, and immediately understood what he said. It 
 appeared that the patient was a Welshman, and had been 
 absent from his native country about thirty years. In the 
 course of that period he had entirely forgotten his native 
 tongue, and acquired the English language. But when he 
 recovered from his accident, he forgot the language he had 
 been so recently in the habit of speaking, and regained the 
 knowledge of that which he had originally acquired and 
 lost*." 
 
 " A student at an university in the United States, who is 
 
 * Dr. Tapper's Inquiry into Gall's System of Craniology. 
 f &>>/oi1oY ri^od 
 
Of Failure of Recollection. 219 
 
 now one of the most respectable clergymen in that country, 
 possessed a tolerable share of classical knowledge, when the 
 consequences of a fever, which affected his brain, deprived 
 him entirely of his former acquisitions. In fact, he had now 
 become so ignorant, that he was not only unable to read a 
 Latin book, but even knew nothing of the grammar. When 
 he had regained his bodily health, being of a persevering 
 disposition, he began again the first rudiments : every thing 
 was quite new to him : he passed through the accidence and 
 syntax in his grammar, and was learning to construe, when 
 one day, as he was making a strong effort to recollect a part 
 of his daily lesson, the whole assemblage of the ideas 
 which he had formerly acquired and lost, suddenly reap- 
 peared to his mind, and he found himself able to read and 
 understand the Latin authors as he had done before his 
 illness." 
 
 SECTION II. 
 Of the Elements of a Nervous System. 
 
 The hydra viridis, upon which the first experiments of 
 Trembley were made, that showed the divisibility of the 
 lower animals, is a thin gelatinous tube about an inch in 
 length, closed at its narrower end. From the margin of its 
 open extremity a fringe of long and slender filaments or ten- 
 tacula is produced. By means of these it distinguishes and 
 seizes its prey, and conveys it into its digestive cavity. It 
 moves from place to place by alternately attaching either 
 extremity to intermediate points. Its structure seems a 
 jelly containing innumerable granules. When turned inside 
 out, the new internal surface is capable of digesting : when 
 divided, each half becomes a perfect polype. 
 
 Thus in the lowest animals the properties of life seem 
 equally diffused through their substance : each half of a 
 
220 Of the Elements of a Nervous System. 
 
 polype may form a portion of a sentient being, or become 
 upon mechanical division individualized. 
 
 Cuvier has arranged the diversified species of animals 
 under four classes, which consist, 1, of radiated, 2, of 
 articulated animals ; 3, of mollusca ; 4, of vertebral ani- 
 mals. The polype is nearly at the commencement of this 
 series; but in the same division other animals are found, 
 which have a distinction of organs, and a nervous system. 
 
 The material of which a nervous system is formed, is a 
 soft tenacious substance, varying in colour from an orange 
 white to brown, from, a bright yellow to grey or black. 
 When a thin slice of nervous matter is spread upon glass, and 
 viewed in a microscope under a drop of water, it appears to 
 consist of an aggregation of minute molecules of different 
 sizes, the largest considerably smaller than a particle of the 
 blood. 
 
 Nervous matter is commonly met with wrought either into 
 rounded masses or into flattened chords, to which greater or 
 less firmness is given by sheaths of a delicate membrane. 
 This membrane is distributed in fine layers and processes 
 upon the surface and throughout the substance of the ner- 
 vous matter. 
 
 A nervous system appears essentially composed of two 
 parts ; of a central organ consisting of two chords, united 
 at their extremities, one corresponding with either half of 
 the body, upon which nodular masses are generally placed ; 
 and secondly, of other chords called nerves, derived from the 
 central organ to the sentient surfaces or contractile parts of 
 the animal. 
 
 The two chords which form the central organ of the 
 nervous system may be disposed indifferently in parallel 
 lines, and touch each other and cohere at several points ; or 
 each may describe an irregular line, and the two may en- 
 close a space. 
 
 There are three types in the animal kingdom after which 
 the nervous system is framed. 
 
 The first is adapted to classes of animals, some of the indivi- 
 duals of which can live after mechanical division, and from one 
 
Nervous System of Radiated Animals. 
 
 221 
 
 become two sentient beings. This type is followed in the 
 nervous systems both of radiated and of articulated animals. 
 Individuals of the lowest species, in both of these classes, 
 consist of several segments arranged either around a centre, 
 whence the term radiated, or in a successive jointed series, 
 whence the term articulated is taken. There are many of 
 the lowest species in either class, the star-fish for example, 
 and the nais, which admit of being divided without perish- 
 ing, when each half becomes a perfect animal. 
 
 The adjoined figure from Tiedemann represents the nervous 
 system of a star-fish. The central organ is a chord disposed 
 around the orifice of the alimentary cavity, from the part 
 of which chord, that is, opposite to each ray, nerves are 
 given off to be distributed to it. 
 
222 
 
 Nervous System of Articulated Animals. 
 
 The next figure represents the ner- 
 vous system of a centipede from a 
 preparation in the museum of King's 
 College. The central organ in the cen- 
 tipede consists of a double chord dis- 
 posed in two parallel lines, with a no- 
 dule upon each in each segment of 
 the animal, from which the nerves 
 arise. 
 
 The distinguishing character ol 
 the double chord in the centipede, as 
 an articulated animal, is not, how- 
 ever, its disposition in two parallel 
 lines. This circumstance has refer- 
 ence to the external figure alone of 
 the animal, as is proved by compar- 
 ing the anatomy of the lobster with 
 that of the crab. In the former, the 
 central organ of the nervous system 
 resembles that of the centipede, in 
 the latter it is thrown into a circle. 
 The essential distinction between the 
 central organ in the centipede and 
 that in the star-fish, is the nodular 
 enlargements in the former at the 
 points where nerves originate. 
 
 The common point between the 
 two, which brings them to the low- 
 est or composite type of organization, 
 is the equal development of the ner- 
 vous chord at every part of the ani- 
 mal, no segment showing a remark- 
 able superiority of volume over the 
 rest. 
 
 To this peculiarity of structure is 
 doubtless attributable the fact, that 
 sensibility is not destroyed in the tail 
 of some animals of this construction, 
 when the hinder part of the body is 
 
Nervous System of Mollusca. 
 
 223 
 
 cut off, any more than in a segment of a radiated animal 
 separated from the rest. 
 
 The second type is that which is met with in mollusca. 
 The figure which I have given is from a preparation of the 
 nervous system of a fresh-water muscle, made by Mr. Haw- 
 kins. 
 
 Mollusca differ from animals of the two preceding classes 
 in being essentially individualized. They each consist of 
 a single series of organs, the co-operation of which is essen- 
 tial to the support of life. The internal organs not being 
 repeated, but forming one system, evince a higher type 
 of organization. ^ 
 
 The nervous system of mollusca differs from that of the 
 
224 Nervous System of Mollusca. 
 
 two preceding classes in two respects. In the first place 
 the nodules of the central organ are of disproportionate size, 
 so that the connecting chord appears insignificant ; never- 
 theless the connecting chord is invariably found to exist, 
 uniting all the nodules into a continuous chain. In the 
 second place, the nodules, although generally situated near 
 to the organs which they supply, are found in greatest 
 number and volume near what must be called the head, so 
 as to form something like a brain. Nevertheless, the no- 
 dules which are remote from the head, may be presumed to 
 be of equal force and function to those in the head : in 
 structure at least they are exactly like the latter. In the 
 fresh-water muscle it happens that the nodules in the head 
 are of the brightest yellow colour, the connecting chord and 
 the nerves being white : but the nodules in other parts 
 of the body are equally characterized by this brilliant 
 colour, which I presume is a sufficient proof that they are 
 of the same nature with the first. 
 
 In the three lowest classes of animals, that is to say, 
 in the radiata, the articulata, and the mollusca, the dispo- 
 sition of the double chord has always a certain relation to 
 the opening into the stomach. It is either wholly disposed 
 in a circle round what must be termed the oesophagus, as in 
 several radiated animals ; or the part which extends be- 
 tween the first and second pair of nodules forms a collar 
 through which the oesophagus passes, as in articulated 
 animals and in mollusca. 
 
 In articulated animals, the first pair of nodules, like a 
 brain, is placed above the mouth and commencement of the 
 oesophagus, whilst the remainder are disposed upon the 
 strong integument of the abdomen in the securest region 
 of the frame. 
 
 In the higher mollusca, in the snail for instance, and in 
 the cuttle fish, the upper portion of the nervous centre, or 
 the first pair of nodules, assumes more of the external cha- 
 racter of a brain : still in both of these instances there is 
 found below the oesophagus a second portion (analogous to 
 the spinal marrow and medulla oblongata of the next class), 
 to which the first is united by two chords, which complete 
 the never-wanting collar. 
 
Nervous System of Vertebral Animals. 225 
 
 
 The third and highest type is that 
 which reigns in vertebral animals: 
 the figure which I have given as 
 an example of this type, represents 
 the central organs of the nervous 
 system in the pigeon. 
 
 In vertebral animals, the central 
 organ consists of a double chord, 
 the greater part of which is con- 
 tained in the vertebral canal, and 
 is called the spinal chord, or spinal 
 marrow, while its upper or anterior ex- 
 tremity is prolonged into the cranial 
 cavity, and is called the medulla 
 oblongata. From this double chord, 
 like as in the three preceding classes of 
 animals, nerves are given off in pairs 
 to the successive segments of the 
 frame. So far therefore, parts very 
 strictly parallel are found in ver- 
 tebral animals and in the lower 
 classes. 
 
 It is true that in the greater 
 number of instances the spinal 
 chord is not nodular, as in the arti- 
 culated animals and mollusca. Yet it 
 is observed, that in most there are 
 general swellings and enlargements of the chord at the parts 
 whence the larger nerves, or those of the extremities, arise. 
 Instances likewise are not entirely wanting in which the 
 
 1 
 
 7 
 
 M 
 
226 
 
 Nervous System of Vertebral Animals. 
 
 nodular construction distinctly 
 shows itself. The figure ad- 
 joined represents the upper 
 part of the spinal marrow of a 
 gurnet (from the plates of Des~ 
 moulins and Magendie), in 
 which that portion of the spi- 
 nal chord, from which nerves 
 of finer endowments, those 
 namely which supply the feel- 
 ers, are given off, is found to 
 be nodular. 
 
 The cranial part of the double 
 chord is, however, invariably 
 crowned with hemispherical 
 masses analogous to the no- 
 dules of the lower animals, 
 from which nerves arise in 
 pairs. 
 
 The adjoined figure of the 
 enkephalon of a skait, seen 
 from above, with the nerves 
 arising from it, may serve as 
 an illustration. 
 
 The accumulation of larger 
 nodules in the head, upon the 
 summit of the double chord, 
 is one of the characteristic 
 features of the nervous system 
 in vertebral animals. But ano- 
 ther remarkable point of dis- 
 tinction is never wanting ; 
 there are always found among 
 the nodules which give origin 
 to the cerebral nerves, more 
 than one other nodule from 
 which no nerves arise ; of 
 these in the skait the lar- 
 gest is the cerebellum, which 
 
First appearance of a Brain. 
 
 227 
 
 B 
 
 I have marked with the letter A ; the other parts 
 of this description are placed below ; they are the pituitary 
 gland, and the corpora albicantia. 
 
 In some fish, as for instance in the carp, are other tuber- 
 cular masses not giving origin to nerves, which being placed 
 before the cerebellum, and like it having a superficies of 
 grey matter, constitute a cerebrum. 
 
 The cerebrum is always found in rep- 
 tiles : I have given a representation of 
 it in the toad in the following figure, 
 in which the spinal marrow is likewise 
 shown ; the letters BB mark the two 
 hemispheres of the cerebrum: the 
 letter A the cerebellum, which is sin- 
 gularly small in ophidian and batra- 
 chian reptiles. 
 
 The preceding details may serve to 
 lead us to three important conclusions, 
 respecting the functions of different 
 parts of the nervous system in verte- 
 bral animals. 
 
 I. The higher animals are distin- 
 guished from the lowest in the con- 
 struction of their nervous system, by 
 cerebral masses superadded upon the 
 anterior end of the double chord. 
 They are distinguished also by a 
 larger share of mental endowments. 
 Is it not then probable that the super- 
 added parts are connected with the 
 superadded functions? Or, in the 
 highest and lowest there are found in 
 common a double chord, with nerves 
 arising from it, and the manifestation 
 of sensation and instinct. Is it not 
 therefore likely, that in the highest animals sensation and 
 instinct have their material organs in the common double 
 chord and nerves ; and that the superadded parts have other 
 functions ? 
 
228 Of the Functions of the Chord. 
 
 One to whom this inquiry may be new might think this 
 conjecture ingenious, but would certainly suppose it im- 
 possible to prove its correctness; nevertheless, nothing is 
 more complete than the body of evidence by which it is sup- 
 ported. 
 
 There are extraordinary cases, in which human foetuses 
 are born, having a spinal chord, medulla oblongata, and 
 nerves, but no brain: that is to say, wanting the parts 
 peculiar to vertebral animals, but having those which cor- 
 respond with the entire nervous system of a star-fish, a 
 centipede, or a snail. These acephalous foetuses commonly 
 die in their birth: but occasionally they survive a few hours 
 or days, and when this happens, they are observed to dis- 
 play sensation and instinct. 
 
 The following is an account by Mr. Lawrence of an ace- 
 phalous infant, which lived four days. 
 
 " The brain and cranium of this infant were deficient, 
 and the basis of the latter was covered by the common 
 integuments, except over the foramen magnum, where 
 there existed a soft tumour about equal in size to the end 
 of the thumb. The smooth membrane covering this 
 was connected at its circumference to the skin. The 
 child, as is generally the case in such instances, was 
 perfectly formed in all its other parts, and had attained 
 its full size. It moved briskly at first, but remained 
 quiet afterwards, except when the tumour was pressed, 
 which occasioned general convulsions. It breathed natu- 
 rally, and was not observed to be deficient in warmth until 
 its powers declined. From a fear of alarming the mother 
 no attempt was made to see whether it would take the 
 breast : a little food was given it by the hand. It voided 
 urine twice in the first day, and once a day afterwards. It 
 had three dark-coloured evacuations. The medulla spinalis 
 was found to be continued for about an inch above the fora- 
 men magnum, swelling out into a small bulb, which 
 formed the soft tumour upon the basis of the skull. All the 
 nerves from the fifth to the ninth were connected with this." 
 
 The conclusion deducible from this remarkable instance, 
 that the brain is not necessary for sensation and the com- 
 
Importance of the Medulla Oblongata. 229 
 
 monest instincts, is further confirmed and illustrated by ex- 
 periments made upon living animals. 
 
 M. Magendie mentions, that if after the removal of the 
 upper part of the cranium in a living animal, the cerebrum, 
 the optic tubercles, and the cerebellum be removed in suc- 
 cessive slices, leaving the medulla oblongata entire above 
 the apparent origin of the fifth pair of nerves, the animal 
 is indeed rendered blind ; but it continues to be affected in 
 as lively a manner by pungent odours or tastes, or by irri- 
 tation of the skin, as if no further injury had been sustained 
 than the loss of blood occasioned by the experiment. 
 The animal cries, if a hair of its whisker be plucked, or if 
 vinegar be held to the nose, and strives with its fore feet to 
 rid itself of the object which incommodes it : the move- 
 ments of the body are not more affected than if the cere- 
 bellum alone had been removed. These phenomena may 
 be observed to continue for more than two hours, when 
 the experiment is performed upon an adult hedgehog*. 
 
 II. The next step which we make, if not more wonder- 
 ful, is certainly more unexpected than the preceding. 
 
 It appears by the experiment, which I have last quoted, 
 that the brain may be taken away portion by portion, yet 
 the creature survive, and exhibit sensation and instinct. 
 But let the mutilation be carried a line further ; let that 
 small segment of the medulla oblongata be destroyed, in 
 which the fifth, seventh, and eighth nerves rise, and con- 
 sciousness is at once instantaneously extinguished. Nor is 
 this extraordinary phenomenon to be explained upon the 
 supposition, that it is only necessary that a certain quantity 
 of the cerebral organ be left. It turns wholly upon the 
 destruction of one particular segment : for in an animal in 
 perfect health, and with all the frame entire, if that seg- 
 ment alone be injured, life is at once and utterly over. 
 
 And to mark yet higher the importance of this point in 
 the medulla oblongata, the rest of the nervous system 
 derives its vitality, or, to speak more justly, its participation 
 
 * Anatomie des Syst. Nerv. &c. par F. Magendie et A. Desmoulins, 
 p. 560. 
 
 p 2 
 
230 Importance of the Medulla Oblougata. 
 
 in the phenomena of consciousness, from its continuity with 
 this point being uninterrupted. The proof or disproof of this 
 position turns, however, entirely upon experiments made 
 upon cold-blooded animals. In warm-blooded animals, the 
 vitality of the nervous system depends so directly upon the 
 circulation of the blood, that when the latter is interrupted, 
 no satisfactory results can be obtained. 
 
 But in a frog or a turtle, after the head has been severed 
 from the body, consciousness will yet exist for a time : and 
 whether that principle of consciousness shall remain in the 
 head or the body, depends entirely upon whether the sec- 
 tion of the medulla oblongata have been made above or below 
 the vital point which I have described. As a cook in kill- 
 ing a turtle generally divides the medulla below the vital 
 part, it is the body which is commonly found to be deprived 
 of sensibility, while the separated head continues to exhibit 
 distinct consciousness. If it be so contrived, however, that 
 the section be just above the origin of the fifth and eighth 
 nerves, an opposite result takes place the animal is blind, 
 the head dead, the body alive. 
 
 III. The preceding facts appear to establish an utter dis- 
 similarity between the endowments of the nervous system, 
 as it exists in the vertebral, and in the invertebral animals. 
 That which can be divided, and either half retain its func- 
 tions, is essentially unlike that, all the endowments of which 
 depend upon the continuity of its different segments with 
 one point. Nevertheless, although this important difference 
 cannot be disputed, and it be certain in vertebral animals 
 that all the parts of the nervous system, which are discon- 
 nected with a particular segment of the medulla oblongata, 
 are excluded from participating in consciousness, still it is 
 to be presumed, that as long as the continuity remains, each 
 part exercises an energy of its own, or has its own function. 
 And that, to begin with, each segment of the double chord 
 from which a pair of nerves arises, has in itself a me- 
 chanism of sensation and instinctive action comparable to 
 the parallel parts in articulate animals. The proof of this 
 is contained in the following remarkable experiments made 
 upon the body, a few seconds after it has been deprived of 
 
The Spinal Chord an assemblage of independent segments. 23 1 
 
 life. If the spinal chord be then divided in the middle of the 
 neck and again in the middle of the back, upon irritating a 
 sentient organ connected with either isolated segment, 
 muscular action is produced : if the sole of the foot is 
 pricked, the foot is suddenly retracted, with the same ges- 
 ture as it would have been during life ; that is to say, a 
 sentient organ is excited, and an irritation is propagated 
 through the sentient nerve to the isolated segment of spinal 
 marrow, where it gives rise to some change, which is fol- 
 lowed by an impulse along the voluntary nerves to the 
 muscles of the part. That this is the true explanation of 
 the phenomena observed, is conclusively shown by the fol- 
 lowing experiment. A pigeon being killed, and the head 
 removed, the cerebrum, cerebellum, and medulla oblongata 
 were separated from the optic tubercles and crura cerebri : 
 all the nerves proceeding to the eye, with the exception of 
 the third, were then divided ; and now the stump of the 
 optic nerve adhering to the optic tubercle was pricked, 
 when I found that the iris acted. Thus each segment of 
 the double chord, with the nerves derived from it, may bs 
 fairly compared to a pair of nodules with its nerves in an 
 in vertebral animal. 
 
 We may therefore look at the nervous system as a chain 
 of organs originating nerves in pairs, and make each seg- 
 ment, or group of segments with their nerves, the subject 
 of study ; and consider in succession the spinal chord, the 
 medulla oblongata, and the masses superimposed upon it. 
 Or there is another point of view, under which we may 
 consider the subject. Instead of contrasting one segment, 
 or group of segments, with another, we may study the 
 functions of the nerves as one system of organs, and those 
 of the spinal chord and brain as another. It will be better 
 in fact to adopt both of these modes of distributing the 
 subject. The functions of the nerves will be therefore 
 treated of apart : and in the mean time the functions of 
 the spinal chord, of the medulla oblongata, and of the brain, 
 will be described in succession. 
 
232 
 
 SECTION III. 
 Of the Spinal Chord. 
 
 The spinal chord is the source from which the nerves of 
 the trunk and limbs take their origin. The spinal chord 
 may therefore be viewed as the channel along which im- 
 pressions travel to and from the sentient organs and volun- 
 tary muscles of the body on the one hand, and the brain on 
 the other. Accordingly, if the spinal chord be compressed 
 or divided, the parts supplied with nerves given off below 
 the injured part are totally paralysed, or are cut off from all 
 participation in the functions of consciousness. 
 
 Again, it has been shown by experiment, that in one part 
 of the nervous system, in the nerves themselves namely, im- 
 pressions are transmitted or propagated along or in the di- 
 rection of the threads or filaments of which the nerves are 
 formed. It is interesting to have ascertained (which the 
 method of Reil enabled me to do), that the spinal chord, 
 Jike the nerves, is principally made up of longitudinal 
 threads, part at least of which extend from the medulla ob- 
 longata to the termination of the chord. The effect, therefore, 
 of dividing the spinal chord theoretically ought to be, as it 
 is practically found to be, analogous to the effect of dividing 
 a nerve. 
 
 The white fasciculi which form the spinal chord coalesce 
 continually with each other by means of fine threads 
 which pass obliquely from one fasciculus to another. 
 White threads likewise at intervals detach themselves from 
 the chord, to contribute to the formation of the spinal nerves. 
 The fact which has been last mentioned would lead us to ex- 
 pect to find the spinal marrow of a conical figure, tapering from 
 the neck to the loins in proportion as it parts with nerves. And 
 in fish, in which the body tapers, this is found to be strictly the 
 case. In reptiles, birds, and mammalia, however, the figure 
 of the chord is considerably modified, and a second prin- 
 
Independence of the different Segments of the Chord. 233 
 
 ciple in its construction is brought strikingly into view. 
 The chord consists in truth, not only of threads extend- 
 ing from the medulla oblongata to the nerves, but like- 
 wise of a series of parts analogous to the nodules in the 
 lower animals which are concerned in originating nerves, 
 and the size of which has reference to the size of the nerves 
 given off at each part. Accordingly, although the spinal 
 chord of reptiles, birds, and mammalia, tapers eventually to 
 a fine extremity, yet is its narrowing twice interrupted by 
 sensible enlargements, one of which is at the lower part of 
 the neck, where the large nerves of the upper extremities 
 arise, the other at the lower part of the back, where the 
 nerves of the legs are given off. 
 
 How independent these segments or groups of segments 
 essentially are of each other, is shown by the following cu- 
 rious case. 
 
 A person died at the age of forty-four, seven years after 
 having lost the use of his arms, which had become con- 
 tracted, without however losing their sensibility. The lower 
 part of his body had in no degree participated in the same 
 affection ; and he had been to the last violently addicted to 
 sexual indulgence. Upon dissection, the spinal chord at 
 the lower part of the neck, and upper part of the back, was 
 found converted into a colourless diffluent substance con- 
 taining flakes of nervous matter, all but two narrow bands, 
 one in the line of each anterior lateral furrow, which ap- 
 peared of their natural texture, and joined the sound 
 inferior portion of the spinal chord to the upper part *. 
 The narrow bands of a natural texture, described in this 
 case, served to communicate the vital influence of the enke- 
 phalon to the entire lower segments of the spinal chord. 
 
 But the white filaments of the spinal chord serve not only 
 to connect the brain and medulla oblongata with each seg- 
 ment of the chord, but to associate reciprocally the segments 
 of which the chord itself consists. When the head of a 
 snake has been removed, the body is lifeless, and utterly 
 deprived of sensibility. If, however, before many minutes 
 have elapsed, the experiment be made of puncturing the 
 
 * Magendie, Journ, de Phys. Exper. tome iv. 
 
234 Markings upon the Spinal Chord. 
 
 skin of the tail or of the middle of the animal, the decapi- 
 tated neck is seen to turn menacingly to the point thus irri- 
 tated. The several segments of the spinal chord still co- 
 operate, upon an impression being made upon the nerves 
 derived from one. 
 
 But other questions present themselves : Is the spinal 
 marrow throughout of one structure ? Is either half inter- 
 nally, as it is externally, composed entirely of white matter? 
 Have all its fasciculi one function ? 
 
 The spinal chord exhibits six well-marked furrows upon 
 its surface : two of these, called the anterior and posterior 
 median furrows, mark its division into two symmetrical 
 halves. Two lateral furrows on each half of the chord, near 
 and parallel to the anterior and posterior median furrows, 
 mark the lines at which the two roots of the spinal nerves 
 are attached. Of all these furrows, the anterior median is 
 the coarsest : it alone has a distinct reduplicature of pia 
 mater lining its whole depth. Through this circumstance 
 in the recent state it is readily displayed. The posterior 
 lateral furrows are the next in depth and coarseness. There 
 are no furrows upon the 'sides of the spinal chord. But the 
 furrow, which in the medulla oblongata intervenes between 
 the posterior pyramid and corpus restiforme, is continued 
 down two-thirds of the spinal chord between the posterior 
 median and posterior lateral furrows. 
 
 I made the following measurements, upon the spinal chord 
 of a remarkably muscular body, the age of which was about 
 twenty-five years, the height five feet four inches. Their 
 principal physiological interest consists in their showing, 
 that the depth of the anterior median furrow is greater at 
 the inferior enlargement than at the cervical enlargement 
 of the chord ; that is to say, that the anterior portion of 
 the spinal chord is relatively larger where the nerves of the 
 lower extremities are given off, than at the part where the 
 nerves of the upper extremities arise. 
 
 The entire length of the spinal chord, from the commence- 
 ment of the decussation of the pyramids to its lumbar end, 
 was 18.5. The fine remnant of nervous matter at the infe- 
 rior end extended half an inch beyond the origin of the last 
 nerve. 
 
Disposition of the Grey Matter in the Chord. 235 
 
 Places of measurement. 
 
 Breadth 
 of the entire 
 chord* 
 
 Depth 
 of the entire 
 chord. 
 
 Depth of 
 the anterior 
 median 
 furrow. 
 
 Dimensions of the spinal chord at 
 
 
 
 
 the interval between the origins 
 
 
 
 
 of the sixth and seventh cervical 
 
 
 
 
 nerves 
 
 .57 
 
 .4 
 
 .15 
 
 Dimensions at four inches and a 
 
 
 
 
 half above the origin of the last 
 
 
 
 
 
 36 
 
 .34 
 
 14 
 
 Dimensions at two inches above the 
 
 
 
 
 last filament, or at the thickest 
 
 
 
 
 part of the inferior enlarge- 
 
 
 
 
 ment 
 
 .46 
 
 .38 
 
 .18 
 
 
 
 
 
 The disparity which is thus shown to exist in different 
 regions between the anterior and posterior portions of the 
 spinal chord becomes more remarkable, when the interior of 
 the marrow is displayed by transverse sections. 
 
 The three figures ad- 
 joined, represent transverse 
 sections at the three points 
 of which measurements of 
 the chord have been given. 
 The upper figure corre- 
 sponds with the cervical 
 part, the middle with the 
 dorsal. 
 
 These figures show with 
 tolerable faithfulness the 
 disposition of the grey 
 matter in the interior of 
 the spinal chord. The grey 
 matter is not, as it is com- 
 monly supposed to be, a 
 central solid pillar in either 
 half; but is a capsule only, 
 analogous therefore to the 
 
236 Functions of the Anterior and Posterior Fasciculi. 
 
 corpus fimbriatum in the cerebellum and containing white 
 matter. The figure of the grey matter is different in the dif- 
 ferent portions of the chord. In the back, the figure of the 
 grey matter is perhaps the most regular ; in the inferior part 
 alone does the anterior portion of the grey capsule assume a 
 large and disproportionate size. 
 
 It is easy to explain why the anterior portion of the spinal 
 chord should be principally developed at the lower enlarge- 
 ment of the chord. The conclusive experiments of Ma- 
 gendie, which terminated a long series of inquiries upon 
 this subject, satisfactorily establish, that the anterior por- 
 tion of the spinal chord has to do with voluntary motion 
 exclusively, the posterior with sensation : divide either, 
 and one alone of these functions is disturbed in the parts 
 below the division. But it is in the lower extremities that 
 force of muscular action predominates over fineness of sen- 
 sation, while in other parts of the body, and in the upper 
 limbs, these two endowments may be viewed as nearly ba- 
 lanced. It is for this reason, without doubt, that that part 
 of the chord which gives origin to the nerves of the lower 
 extremities is characterized by the predominant bulk of its 
 anterior portion. 
 
 SECTION IV. 
 Of the Enkephalon. 
 
 The term enkephalon has been appropriately given to the 
 production of the double chord crowned with hemispherical 
 masses, which is contained in the cranium. The lowest 
 portion of the enkephalon, the immediate continuation of 
 the spinal marrow, is in man a cone, 1.3 inches in length, 
 which is called the medulla oblongata. 
 
 To accord with common usage, I here employ the medulla 
 oblongata in a much more limited sense than it is analogi- 
 cally entitled to. Properly, it should comprehend the further 
 production of the double chord to a point at which it ceases 
 to originate nerves. 
 
Of the Shape of the Medulla Oblongata. 
 
 237 
 
 The adjoined figure repre- 
 sents the anterior and inferior 
 surface of the medulla ob- 
 longata. The markings upon 
 the medulla oblongata are, in 
 some respects, different from 
 those upon the spinal chord : 
 the anterior pyramids and the 
 olivary bodies are not conti- 
 nuations of prominences which 
 are seen upon the spinal mar- 
 row. The disposition, like- 
 wise, of the grey matter in the 
 interior of the medulla oblon- 
 gata is considerably more 
 complicated than in the spinal marrow. Accurate figures 
 of sections of the medulla oblongata are given in my work 
 upon the structure of the brain. 
 
 There are two points which especially deserve examina- 
 tion, in the history of the medulla oblongata ; 1st, the lo- 
 cality of that part, the destruction of which is instantly 
 fatal ; 2d, the decussation of the pyramids. The part, the 
 division of which invariably puts a stop to the manifestation 
 of consciousness, is situated near the base of the little 
 cone delineated in the adjoined figure. It seems to be the 
 exact point at which the eighth and fifth nerves take their 
 rise from the medulla oblongata. This point is better shown 
 in a figure in a subsequent section, which represents the 
 origin of the cerebral nerves. 
 
 The decussation of the anterior pyramids, is a subject not 
 to be so briefly dismissed. Its existence, which has so curious 
 a bearing upon pathology, is denied by some modern anato- 
 mists. MM. Magendie and Desmoulins, in their valuable 
 treatise on the nervous system of vertebral animals, assert, 
 that no decussation takes place in the nervous fasciculi at 
 this part, and attribute the appearance which they suppose has 
 misled other observers, to a false view of a succession of 
 oblique and superficial furrows, which they admit exist 
 there *. It is not indeed easy, in every case, by an exami- 
 * Systeme Nerveux, &c. vol. ii, p. 103. 
 
238 Of the Origin of the Anterior Pyramids. 
 
 nation of the recent brain, to obtain conviction upon this 
 question. But if the medulla oblongata, when fresh, be 
 immersed in water, and the pia mater be then carefully re- 
 moved, and the part thus prepared be laid to harden in spi- 
 rits of wine, the structure which i am about to describe be- 
 comes distinct. 
 
 The superficies of the medulla, when hardened, is found 
 to tear into longitudinal filaments, in the same manner as 
 the spinal marrow. At the back part, these run uninter- 
 ruptedly into the longitudinal fasciculi of the chord ; so 
 likewise laterally ; but not so at the fore part. The longi- 
 tudinal fasciculi, of which the anterior pyramids are formed, 
 when they approach the spinal chord, spread in three direc- 
 tions, in the manner represented in the figure : the exterior 
 filaments bend round towards the back part of the medulla 
 oblongata ; the middle filaments descend straight, so as to 
 be continuous with the anterior filaments of the spinal chord : 
 but the inner portion of the anterior pyramid, constituting 
 by far the larger part, throws itself in three or four broad 
 bands obliquely across the median furrow, to the opposite 
 half of the chord, decussating the corresponding series of 
 fasciculi, and becoming continuous thus with the centre of 
 the opposite half of the spinal marrow. As I have found 
 this disposition of parts, not merely in man, but in the ox, 
 the horse, the ass, the monkey, the dog, the kangaroo, the 
 porpesse, I entertain no doubt that it exists in all mam- 
 malia. 
 
 The pathological phenomena, which admit of a satisfactory 
 solution through the decussation of the anterior pyramids and 
 the want of decussation in the other elements of the medulla 
 oblongata, are the following. Injuries of one side of the 
 brain are followed by palsy, which in some cases affects the 
 same side of the body, in others the opposite. But each 
 side of the brain is connected, it appears from what has 
 been stated above, by one set of filaments with the same 
 side of the spinal chord, by another with the opposite. The 
 palsy then, it may be presumed, follows, in the two dif- 
 ferent cases, one or other of these orders of filaments exclu- 
 sively. Nevertheless, M. Magendie found, that division of 
 the anterior pyramids, one or both, in animals, produced no 
 
Shape and Connections of the Cerebellum. 239 
 
 further effect than a slight impediment in their movements 
 forward ; and that division of the entire half of the medulla 
 oblongata produced palsy of the same side of the body. 
 
 The part of the enkephalon which is immediately super- 
 imposed upon the medulla oblongata, is the Cerebellum. 
 The cerebellum, in man, consists of two large hemi- 
 spheres, that are united behind by the vermiform processes, 
 which rest upon the medulla oblongata ; and before, by the 
 tuber annulare, or pons Varolii, which the greater part of 
 the fasciculi of the medulla oblongata either rest upon or 
 pierce through. The hemispheres and vermiform processes 
 are of one structure : they consist, internally, of white ner- 
 vous matter, which divides towards the circumference into 
 arborescent laminae : these are superficially overlaid by one 
 thin uniform layer of grey matter, which if unfolded and 
 spread out would cover a large surface. 
 
 The pons Varolii, with its transverse flutings, looks ex- 
 ternally like a fasciculus of white filaments, extending across 
 to form a great commissure to the hemisphere of the cere- 
 bellum ; where, at either side, its narrowing end appears to 
 plunge into the cerebellum, the term pedicle has been given 
 it. The two ends constitute the middle pedicles of the cere- 
 bellum. Within these, the corpus restiforme seems to stretch 
 upwards from the side of the medulla oblongata, to incorpo- 
 rate itself with the cerebellum. The corpora restiformia are 
 appropriately called the inferior pedicles of the cerebellum. 
 Above, again, the pillars of the valve of Vieussens, directed 
 upwards and forwards from either hemisphere of the cere- 
 bellum to the cerebrum, form the upper pedicles. Each 
 hemisphere of the cerebellum, by its pedicles, is thus united, 
 first, to its fellow ; secondly, to the medulla oblongata ; 
 thirdly, to the cerebrum. 
 
 To determine whether these appearances represent real 
 structure, or are fallacious, it is requisite to employ the me- 
 thod of Reil, and to harden the enkephalon in alcohol pre- 
 viously to its dissection. I am unwilling to enter into the 
 discussion, as to who originated the discoveries, to which 
 Gall and Spurzheim on the one hand have laid claim, and 
 which many on the other hand think are the property of 
 
240 Reil's Exposition of the Structure of the Cerebellum. 
 
 professor Reil. But of this I am certain, that the popular 
 and showy anatomy of Gall and Spurzheim does not carry 
 with it the demonstration which belongs to the researches 
 of their rival ; that the former, in truth, is little more than 
 an expansion of the views of Willis ; and that, where Gall 
 and Spurzheim have been correct, their success is rather to 
 be attributed to bold and fortunate conjecture than to cau- 
 tious and philosophical research. While they were engaged 
 in popularly spreading their views respecting the structure 
 of the brain, Reil was employed in diligently investigating 
 the subject by a more rigorous method ; and year after year, 
 in his Archiven fur die Physiologic, he communicated to 
 anatomists the results of his masterly dissections. 
 
 The adjoined figure may serve to convey an idea of ReiPs 
 discoveries in the structure of the cerebellum. The white 
 nucleus of either hemisphere consists of white filaments, 
 which are collected in three fasciculi. The fasciculus [1], 
 which at the root of the arbor vitae is external, is formed of 
 filaments which extend across, forming the transverse fibres 
 
Of the Structure of the Cerebrum. 241 
 
 of the pons Varolii. Next in order, the filaments [2] derived 
 from the inferior pedicle of the cerebellum enter the nucleus. 
 Internally are [3] the filaments of the upper pedicle ascending 
 towards the cerebrum. All these filaments diverge towards the 
 circumference, and terminate in the peripheral grey matter. 
 Such is the structure of the nucleus, or of the stem of the 
 arbor vitae. The laminated part is much more intricate; 
 for, in addition to the divergent filaments from the triple 
 nucleus, it consists of filaments disposed parallel to the 
 exterior surface, in the manner shown in the upper part 
 of the figure, where a portion of the circumference is sup- 
 posed to be left. These filaments form, it is evident, a new 
 series of bands of communication; they serve to unite adjacent 
 and remote laminae in the same hemisphere : and thus have 
 we the whole scheme of structure displayed: two parts, 
 grey matter and white ; the grey, a thin layer analogous to 
 the retina, folded for convenience of disposition ; the white, 
 four series of filaments, for reciprocally uniting the different 
 points of the grey matter, and placing them in co-operation 
 with the neighbouring elements of the enkephalon. 
 
 The structure of the cerebrum is exactly upon the same 
 principle with that of the cerebellum. The convolutions 
 upon its surface are formed of a layer of grey matter, which 
 contains white : the white matter, as in the cerebellum, is 
 composed partly of filaments parallel to the surface, partly of 
 filaments derived from the nucleus, subdivisible into commis- 
 sural and divergent. The tubercles and the internal masses 
 of grey matter, are, as Gall and Spurzheim conjectured, 
 and as Reil demonstrated, sources from which the fibres 
 ascending from the medulla oblongata receive additions, as 
 from new organs in the nervous system. 
 
 In the figure which is adjoined, I have represented a ver- 
 tical section of a hemisphere of the brain, showing the dispo- 
 sition of some of the white fasciculi which form it. In one 
 small convolution the filaments parallel to the surface are 
 figured, but not with due exactness. At C the great commis- 
 sure is represented throwing its filaments towards and to the 
 circumference. E E represent the cavities of the lateral ven- 
 tricles : and A and B represent the inner and outer portions 
 of the corpus striatum, through which the divergent fasciculi 
 
242 Distribution of the Fasciculi of the great Commissure. 
 
 of the nucleus are shown to ascend, decussating at the 
 upper border of the striated body the filaments of the great 
 commissure. 
 
 I have added another figure, which may not be without 
 interest to the reader. It is taken, like the preceding, from 
 a preparation in the museum of King's College, and from a 
 section nearly at the same part of the brain with the pre- 
 ceding : the letters are the same for both. But the prepa- 
 ration previously figured was made by myself to illustrate 
 the anatomy of Reil, and was made upon the hardened 
 brain. 
 
Theory of Dr. Foville. 243 
 
 The present figure is from a preparation made, when I 
 happened to be present, by Dr. Foville to illustrate his views 
 of the anatomy, and made on the recent brain. Dr. Foville 
 supposes, that the great commissure of the brain does not 
 unite the masses of the hemispheres, but that it rather forms 
 a commissure to the medulla oblongata. By a neat and de- 
 licate manipulation, which it is easy to repeat, he rends down, 
 in the direction shown in the figure, the white substance of the 
 great commissure into the white matter in the middle of the 
 striated body : and it is surprising how clean the surface of 
 the rent is, and how much it resembles a natural separation : 
 nevertheless, the reader may be convinced, on comparing this 
 figure with the last, that the appearance is really produced by 
 a mutilation. The artist dexterously breaks through, at the 
 point where the commissural and divergent fibres intersect 
 each other, the former, and adroitly follows the line of the latter 
 in their descent into the striated body. This, of course it 
 is unnecessary to say, that very excellent anatomist and 
 pathologist, Dr. Foville, does in perfect good faith : he has 
 allowed himself to be deceived by employing an imperfect 
 method. He has used the recent brain ; and the recent 
 brain will not serve for the investigation of structure. The 
 material is then so ductile, yielding like soft dough, that 
 it will allow almost any imaginable structure to be made out 
 in it. 
 
 The simple and analogous structure, which is shown by the 
 method of Reil to pervade the whole of the enkephalon, 
 has not, it must be confessed, as yet thrown much light 
 upon the study of its functions. The whole of our know- 
 ledge upon this interesting subject is derived from physio- 
 logical experiments upon animals, and from comparative 
 anatomy. 
 
 I will first mention the striking, though as yet barren 
 results, which have been obtained through the former 
 channel. 
 
 1. Experiments on the Cerebellum. 
 
 The removal of the cerebellum in fish produces no fur- 
 ther immediate effect than that of weakening the animal : 
 
 Q 
 
244 Experiments on the Cerebellum. 
 
 frogs from which this organ is removed, show an indisposi- 
 tion to move unless irritated or placed in water, when their 
 movements, though less lively than before, are not observed 
 to be otherwise affected. 
 
 In birds and mammalia more important results ensue 
 upon the injury or removal of the cerebellum, which it may 
 be remarked appears not to be sensible to pain from me- 
 chanical lesion. 
 
 If the cerebellum be wounded upon one side, the animal 
 appears to be generally weakened upon the same side : if 
 the wound be deep, the body upon the injured side is ren- 
 dered paralytic. If in a rabbit the upper and middle por- 
 tion of the cerebellum be removed, the hind legs are observed 
 to be spread, the fore legs are extended forwards in a state 
 of rigidity : the whole attitude is that of preparation for 
 moving backward or throwing itself over. After a short 
 time the animal beats the ground with its fore paws, the 
 hind legs not moving, and urges itself backwards. If the 
 tail be pinched, the animal thus excited still exerts its fore 
 legs only, and continues moving backwards. A deeper in- 
 cision causes the animal to fall upon its side, the head is 
 drawn backwards in a state of tension, the feet, and espe- 
 cially the fore feet, which preserve their rigid extension, are 
 moved with violence. 
 
 The flight and the walk of pigeons are not affected by the 
 removal of the upper part of the cerebellum. After a deeper 
 section has been made, the bird totters, falls on its breast, 
 rises again, and is in continual agitation. A deeper section 
 still causes it to walk and to fly backwards. After the 
 entire removal of the cerebellum, the bird when irritated 
 walks almost as usual ; when thrown into the air, it moves 
 its wings regularly, and alights upon its feet. A few mi- 
 nutes afterwards the legs become rigid, but the wings still 
 move regularly if the bird be again thrown into the air : the 
 legs remain in a state of tension, and the head continues 
 drawn backwards till death. M. Fodera saw all these 
 phenomena succeed each other in the same bird, but each 
 may be immediately produced by the fit incision. M. Ma- 
 gendie mentions the case of a young woman, who is affected 
 
Experiments on the Cerebellum. 245 
 
 with a nervous malady that forces her to run rapidly back- 
 wards, disregarding every peril. 
 
 The simplest explanation of the phenomena above de- 
 scribed, is to suppose that an injury of the cerebellum to a 
 certain depth produces a sensation analogous to vertigo; 
 that the animal conceives itself either to be hurried forward, 
 and makes a more or less perfect exertion to repel the ima- 
 ginary force, or to be moving backward, and moves its 
 limbs to a certain degree in correspondence. Either of 
 these suppositions, which rest upon analogy, appear more 
 likely to be just than the hypothesis that an animal exists 
 under the influence of two impulses, one urging it forward, 
 the other backward, and that the organ of one impulse 
 is removed on the partial destruction of the cerebellum. 
 
 M. Fod6ra found similar phenomena to be produced upon 
 the injection of a solution of camphor in oil into the abdo- 
 men in animals, either before or after the removal of the 
 cerebrum, and remarked that they became more intense 
 on removing a part of the cerebellum. 
 
 Lateral pressure of the cerebellum produces no effect that 
 has been observed. 
 
 M. Magendie found results not less unexpected ensue 
 upon a vertical division of the cerebellum, the crura cere- 
 belli, and the pons Varolii. 
 
 If in a rabbit a section through the middle portion of the 
 cerebellum be made in the median plane, the eyes of the ani- 
 mal are observed to be in extraordinary agitation, and as if 
 starting from their sockets : the animal inclines towards 
 one side, then is suddenly thrown towards the opposite, 
 as if unable to balance itself with precision : its fore 
 legs are rigidly extended forwards, as if it were in the act 
 of receding. 
 
 If a vertical section of the cerebellum be made, leaving 
 one-fourth of the whole adhering to the crus of the right 
 side, and three-fourths to the left, the animal rolls over and 
 over incessantly, turning itself towards the injured side. 
 The right eye is directed downwards and forwards, the left 
 eye upwards and backwards. On making a similar section 
 
 Q 2 
 
246 Experiments on tlie Cerebellum. 
 
 upon the left side the animal stops, and the eyes resume 
 their natural direction. 
 
 M. Magendie was led to this discovery by accidentally 
 dividing the crus cerebelli in a rabbit, upon which the same 
 phenomenon occurs as upon dividing the cerebellum une- 
 qually. For eight days that this animal survived the in- 
 jury, it continued to revolve upon its long axis unless stopped 
 by coming in contact with an obstacle : when stopped, it 
 ate upon its back with its mouth upwards. If the opposite 
 crus be subsequently divided, the movement produced by 
 the first experiment is stopped. 
 
 If the cerebellum be divided unequally, so as to produce a 
 constant revolution towards the mutilated side, and the 
 opposite crus cerebelli be subsequently cut through, an 
 equilibrium is not produced, but the animal begins to re- 
 volve towards the side on which the crus is divided. 
 
 The whole of these phenomena are probably attributable 
 to a sensation analogous to vertigo : this conjecture at 
 least appears strongly confirmed by the following case de- 
 scribed by M. Serres. 
 
 A shoemaker sixty-eight years of age, of intemperate 
 habits, after a debauch exhibited a kind of drunkenness 
 which surprised his friends : instead of seeing objects turn 
 around him, he seemed to himself to be turning, and in a 
 few moments commenced revolving : placed in bed he con- 
 tinued to manifest this tendency till he died. Upon ex- 
 amining the head, an extensive lesion was found of one of 
 the peduncles of the cerebellum. 
 
 2. Experiments on the Tubercles. 
 
 The tubercles placed between the cerebellum and the 
 cerebrum, in part give origin to the optic nerves, in part 
 send fibrils to the cerebrum. 
 
 On injuring the optic tubercle of one side in pigeons, 
 blindness ensues of the opposite eye ; and reciprocally on 
 dividing one optic nerve, the under surface of the opposite 
 tubercle, to which the nerve adheres, is found in a few weeks 
 to waste. 
 
Experiments on the Cerebrum. 247 
 
 On injuring deeply the optic tubercle in birds and mam- 
 malia, when the greater part of the brain, especially its 
 base, has been left entire, the animal in flight or in its walk 
 moves continually round towards the same side. In ser- 
 pents and frogs the movement thus produced is towards the 
 opposite side. 
 
 Pain and convulsive movements are produced by wound- 
 ing this part of the enkephalon. 
 
 3. Experiments on the Cerebrum. 
 
 If the cerebrum be removed in frogs and fish, they con- 
 tinue for a time to exhibit voluntary motion, when roused. 
 
 If the upper part of the cerebrum be removed in birds 
 and mammalia, the animal becomes blind, and appears stu- 
 pified ; but when it is roused locomotion is performed with 
 steadiness and precision ; the animal walks when pushed, or 
 if a bird, flies when thrown into the air. No further result is 
 produced by the additional removal of some of the grey matter 
 of the corpus striatum : but if a section be carried through the 
 striated part, the animal springs forward, and continues to 
 advance in a straight line till it meets an obstacle, when it 
 still preserves the attitude of one advancing. This result 
 ensues when the experiment is performed upon dogs, cats, 
 rabbits, Guinea pigs, hedgehogs, and squirrels : the latter 
 only in advancing cross their fore legs as in the action of 
 climbing a branch, and if a stick be placed in their embrace, 
 they ascend it. 
 
 Upon making lateral pressure on the hemispheres of the 
 brain, no effect has been observed to ensue. Upon making 
 vertical pressure upon the brain stupor takes place, which 
 is attributable to the compression of the medulla oblongata. 
 It deserves remark, that when vomiting has been excited by 
 an emetic substance, it is arrested by pressure made upon 
 the medulla oblongata. 
 
 Reil describes his having examined the head of an idiot 
 thirty years of age, who had been employed in the little 
 traffic of neighbouring villages, in whom the middle part of 
 the corpus callosum was entirely wanting, from an original 
 malformation, as it seemed ; for the convolutions were com- 
 
248 Experiments on the Cerebrum. 
 
 plete where a corpus callosuin ought to have emerged to 
 join the inner surface of the hemispheres. 
 
 It is well known that a serous fluid is contained in the 
 ventricles, and that the same is frequently found in greater 
 or less quantity upon the surface of the brain as well as in 
 the theca vertebralis ; but till lately physiologists have been 
 inclined to regard this fluid as a production of disease. 
 M. Magendie has however recently shown that aqueous fluid 
 uniformly exists in animals in full health, upon the surface of 
 the brain and spinal chord and in the ventricles. This fluid 
 serves to fill up the interstices which are left between the 
 irregular surface of the nervous matter and the more even 
 and spacious surface of the cavities which contain it, so as 
 to support with an equal pressure the entire superficies of 
 the brain and spinal chord. When this pressure is sud- 
 denly taken off by letting out the water, M. Magendie 
 found that animals are affected with dulness and stupor : 
 after twenty-four hours they are found to have recovered, 
 the fluid having been reproduced. In two instances a con- 
 trary effect ensued, and for two or three days the animals 
 were in a state of continual agitation and fury. 
 
 The water in the ventricles of the brain was supposed to 
 be secreted by the pia mater which forms their lining mem- 
 brane : upon the surface of the brain it was known to be 
 contained between the arachnoid and pia mater. M. Ma- 
 gendie discovered that the water upon the spine is likewise 
 interposed between the same membranes; and described 
 the channel, by which it flows from the fourth ventricle 
 upon the spinal marrow ; and proved by experiment the 
 ready passage a liquid may find from any point where this 
 water is found to all the rest 5 *. 
 
 Let us now turn to the physiological conclusions which 
 are suggested by a comparison of the brains of vertebral 
 animals of different orders with each other and with that 
 of man. 
 
 Whenever our knowledge of any branch of natural phi- 
 losophy is sufficient to enable us to study with success the 
 uses of a part of the animal frame, we invariably discover 
 
 * Journal de Pliys. Exper., torn, 7. 
 
Relation of the size of the Brain to Mental Power. 249 
 
 the most exact adaptation of the physical structure to the 
 office of the part. In the form and disposition of the bones, 
 for instance, or in the structure of the eye, we find more and 
 more occasion for wonder at the perfect art displayed, in 
 proportion as we more deeply study mechanics and the nature 
 and properties of light. It is impossible for us therefore to 
 doubt, that in the brain there is the same exquisite 
 fitness to the purposes for which it is designed. And 
 as experiment and observation lead us to think, that 
 the brain is the organ through which the mind influ- 
 ences and is influenced by the body, we naturally con- 
 clude that its whole structure has a direct and imme- 
 diate relation to the endowments and workings of the 
 mind. The composition of the brain is doubtless as 
 exactly suited to the phenomena of thought and feel- 
 ing, as the structure of the eye to the properties of light. 
 What inquiry is likely to prove more interesting, than to 
 trace the relation which exists between an improving mental 
 nature and its appropriate bodily instrument ? 
 
 It does not appear that an increase in the absolute weight 
 of the brain confers a superiority in mental endowments. 
 Were this the case, the intellects of the whale and of the 
 elephant should excel the rational nature of man. Neither 
 does the relative weight of the brain to the whole body 
 appear the measure of mental superiority. The weight of 
 the human brain is but VTT of the frame ; while that of a 
 canary-bird is -rV. Nor, in conjunction with parity of form 
 and structure even, does this relation appear of any value. 
 The eagle is probably as sagacious as the canary-bird ; but 
 the weight of its brain is but TB-O- of its entire weight. 
 
 We may next inquire, whether an increasing number 
 and complication in the parts of the brain is essentially 
 connected with improved mental functions. The first in- 
 stances which occur to the mind are in favour of the affirm- 
 ative of this supposition. It may be inferred from their 
 docility and surprising capability of receiving instruction, 
 that birds have higher mental endowments than fish ; and 
 accordingly, in place of the nodules of the fishes brain, 
 which are scarcely more than tubercles to originate nerves, 
 
250 Of the Brains of the Cetaceous Mammalia. 
 
 birds possess an ample cerebrum and cerebellum. But in 
 pursuing this argument, if we compare, on the other hand, 
 the brain of birds with those of alligators and tortoises, we 
 find no striking difference or physical superiority in the 
 former over the latter ; yet in mental development the tor- 
 toise and alligator are probably much nearer to fish than to 
 birds. The instantia crucis, however, upon this question, 
 is found in the comparison of the brain of the cetaceous 
 mammalia with the human brain on 'the one hand, and with 
 that of fish on the opposite. 
 
 The cetaceous mammalia have brains which, besides being 
 of large size, are nearly as complicated as those of human be- 
 ings; they might therefore be expected, if the opinion which I 
 am combating were true, to manifest a remarkable and distin- 
 guishing degree of sagacity. Endowed with a brain approach- 
 ing nearly in complexity and relative size that of man, the 
 dolphin should resemble in his habits one of the transformed 
 personages in eastern fable, who continued to betray under 
 a brute disguise their human endowments. Something there 
 should be very marked in his deportment which should stamp 
 his essential diversity from the fishes, in whose general 
 mould he is cast. His habits too, not shunning human 
 society, render him especially open to observation ; and the 
 class of men who have the constant opportunity of watching 
 his gambols in the deep are famed for their credulity, and 
 delight to believe in the mermaid, the sea-snake, and the 
 craken. Yet the mariner sees nothing in the porpesse or 
 the dolphin but a fish, nor distinguishes him, except by his 
 unwieldy bulk, from the shoal of herrings he pursues. The 
 dolphin shows, in truth, no sagacity or instinct above the 
 carp, or the trout, or the salmon. It is probable even that 
 the latter, which have but the poorest rudiment of a brain, 
 greatly exceed him in cunning and sagacity. 
 
 I am afraid that the instance which I have last adduced, 
 is sufficient to overthrow most of the received opinions re- 
 specting the relation of the size and shape and organization 
 of the brain to mental development ; nor is it easy to find a 
 resting place for conjecture upon this subject. 
 
 Is there, we may ask, any ascertained relation between a 
 
Other relations of the size of the Brain. 251 
 
 single division of the enkephalon, and any class of mental 
 affections? It is often asserted, that some ratio exists 
 between the size of the cerebellum and the force of the 
 sexual appetite : yet, how opposite to this conclusion are 
 the most obvious facts. The cerebellum of frogs, which are 
 remarkable for their salacity, is so small, that its exist- 
 ence has been disputed. Fish, on the other hand, have 
 the cerebellum of great size. And in mammalia, in which 
 the sense of smell certainly contributes principally to excite 
 the sexual appetite, the olfactory nerve, which is of prodigious 
 size, instead of having any visible connection with the cere- 
 bellum, appears to be an actual production of the cerebrum. 
 Or can any relation be traced between the development 
 of the brains of animals and the caste of their other organs ? 
 We naturally suspect that such may be found, when we 
 observe, that animals so unlike in their habits (at least as 
 far as regards their mode of progression) as the frog and the 
 snake, have brains precisely similar. We are led to think, 
 by such instances, that the formation of the brain may have 
 a greater reference to the physical character of the general 
 frame than to the mind. Yet the brain of the ornithorhyn- 
 cus, as it is delineated by Meckel, resembles not the brains 
 of reptiles and birds, to which by its generative organs the 
 animal seems allied, but the brains of mammalia. 
 
 The brains of monkeys have a strong general resemblance 
 to the human brain. This must surely refer to the resem- 
 blance of their physical organs to those of man, not to 
 their sagacity : the dog should else have a brain shaped like 
 that of the monkey. 
 
 It is a common opinion, that the front of the brain is the 
 seat of the intellectual faculties : yet in monkeys and in man 
 the back part of the brain is that which has the largest rela- 
 tive size. The sheep, on the other hand, has an ample front 
 to its brain, a large intellectual region, according to the 
 phrenological theory, while its instinct of attachment to its 
 young has a poor locality in its moderate posterior cerebral 
 lobe. 
 
 M. Magendie makes the curious remark, that the brains 
 of adult human beings exceed those of aged persons fifteen 
 per cent, in specific gravity. 
 
252 Nerves. Their Structure, Origin, and Termination. 
 
 Has nothing then been discovered to mark an essential 
 superiority in the brain of man ? The question must, I believe, 
 be answered in the negative. No physical condition, distin- 
 guishing the human brain from that of animals, and therefore 
 fitting it to co-operate with a rational soul r has as yet been as- 
 certained, or even plausibly conjectured, to exist. We are as 
 yet free to suppose, that a mental nature of a higher caste 
 may possibly work with materials as gross as those which 
 are suited to the instincts and small sagacity of brutes ; or 
 that some delicate difference of organization, finer than we 
 yet have the means of testing, and independent of the 
 relative size and volume of the brain, may be the material 
 cause, especially qualifying the human brain to be the seat 
 of reason. 
 
 SECTION V. 
 
 Of the Functions of the Nerves. 
 
 There are forty pairs of nerves in the human body, of 
 which thirty-one rise from the spinal marrow, and nine from 
 the medulla oblongata. The former are called Spinal, the 
 latter Cerebral nerves. 
 
 Nerves consist of the same material as the white matter of 
 the brain : it is here as in the brain wrought into delicate 
 filaments contained in sheaths of the finest membrane ; 
 several of these are contained in a common sheath, and form 
 nervous fibrils : and a nerve consists of more or fewer fibrils 
 connected by processes of the membrane already described, 
 which is termed the neurilema : it is very vascular, and may 
 be compared with the pia mater in the brain. A nerve has 
 an outer tunic of a dense white glistening membrane, which 
 is called its cellular tunic. The fibrils of a nerve are dis- 
 posed parallel to each other, but they continually give off 
 filaments, which join the adjacent fibrils : so that when u 
 nerve is drawn out laterally, its structure appears rcticular. 
 
j: Of Plexuses and Ganglia. 253 
 
 All nerves partake of this structure. In the long nerves 
 it is most evident near their origin. The optic nerve, which 
 is short, is so reticular, that the appearance of strictly pa- 
 rallel fibrils is nowhere distinguishable in it. 
 
 Nerves extend from the spinal marrow and medulla ob- 
 longata to sentient surfaces and irritable parts. The first of 
 these attachments is called their origin, the opposite their 
 termination. The origin of a nerve is always in part from 
 grey matter. The mode in which nerves terminate is not 
 satisfactorily known, with the exception of the instance of 
 the optic nerve, which expands within the eyeball into a 
 sheet of grey matter ; and of the instances, yet more cu- 
 rious, in which voluntary nerves coalesce directly with fibrils 
 of sentient nerves, a fibril originating at one part of the me- 
 dulla oblongata, appearing to return under another character 
 to attach itself again to the same part. 
 
 The tendency to a reticular structure which is met with 
 in the composition of each single nerve, shows itself again 
 in the manner of their distribution. 
 
 In several remarkable instances, the fibrils of which ad- 
 jacent nerves are composed are reciprocally thrown across 
 from one to the other, forming what is termed a plexus. 
 The nerves which proceed from the further side of a plexus 
 may be more or fewer in number than those which enter it ; 
 but the essential result is, that nervous fibrils from different 
 sources are brought together to form new trunks. What are 
 termed ganglia have been thought by many to be exactly 
 of the nature of plexuses. A ganglion is a small nodule, 
 usually flattened, of an oval or circular shape, and of a red- 
 dish grey colour, which is found either on the trunk of a 
 single nerve, or where two or more branches coalesce. 
 Scarpa supposes, that a ganglion is but a bed of gelatinous 
 membrane, in which the smallest fibrils of the nerves that 
 enter it are arranged in new combinations. Others have 
 supposed that nervous filaments originate in the grey matter 
 of ganglions. It is not improbable that this may be the 
 case, but the extreme minuteness of the fibrils in a gan- 
 glion renders it very difficult to determine whether it be so 
 or not. 
 
254 Of the Origin of the Spinal Nerves. 
 
 1. The nerves which rise from the spinal marrow are more 
 uniform in their mode of origin, and simpler in their distri- 
 bution, than those which rise from the medulla oblongata. 
 Each spinal nerve arises alike by two roots, one from the 
 anterior lateral, the other from the posterior lateral furrow. 
 The filaments, which compose the anterior root, are more 
 slender and more numerous than those of the posterior root. 
 The filaments which form the roots of the spinal nerves are 
 followed with great difficulty into the substance of the chord. 
 They appear partly to be continuous with the white fasciculi 
 of the chord, partly to originate in the interior grey matter *. 
 The two roots perforate the theca vertebralis by separate 
 openings; then a spherical ganglion is formed upon the 
 posterior root, and afterwards tKe two roots unite to form 
 one nerve, which takes its name from the bone below 
 which it emerges. 
 
 When a spinal nerve is divided in its course through the 
 body, the parts supplied by it beyond the division are para- 
 lyzed they lose sense and motion. If the two origins of 
 the spinal nerves be exposed in a young animal, and sepa- 
 rately divided, different effects are produced. The section 
 of the anterior root deprives the part supplied by the nerve 
 of voluntary motion, sense remaining; the section of the 
 posterior root deprives the corresponding part of the body 
 of sensation, voluntary motion being left. 
 
 These experiments were made by M. Magendie, and pub- 
 lished by him in his Journal of Experimental Physiology. 
 
 * Among the anomalies mentioned by Magendie and Desmoulins 
 respecting the spinal nerves, the principal are the two following. They 
 state, that, in serpents, the spinal nerves have each but one root. Upon 
 carefully opening the vertebral canal in a Python, I ascertained that 
 this is not the fact, but that the nerves rise, as in other vertebral ani- 
 mals, by two roots. The second is, however, as correctly stated as it is 
 extraordinary. In the lamprey, the spinal nerves appear to rise from 
 the theca, not from the chord ; that is to say, upon slitting up the 
 theca, no filaments are seen extending to or from the chord. This I have 
 found in the lamprey examined immediately after decapitation. I was 
 greatly surprised to observe, upon irritating the skin of its tail, under 
 these circumstances, the caudal muscles act. 
 
Of the First and Second Cerebral Nerves. 255 
 
 But many years earlier, Sir C. Bell had made experiments 
 upon the spinal nerves, some account of which had been 
 printed and circulated among his friends, as well as deli- 
 vered in his Lectures. The following is an extract from this 
 account : " On laying bare the roots of the spinal nerves/' 
 observes Sir C. Bell, " I found that I could cut across the 
 posterior fasciculus of nerves, which took its origin from 
 the posterior portion of the spinal marrow, without con- 
 vulsing the muscles of the back ; but that on touching the 
 anterior fasciculus with the point of the knife, the muscles 
 of the back were immediately convulsed." Sir C. Bell was 
 carried by these experiments very near to the truth, but he 
 failed at that time to ascertain it : he inferred from his ex- 
 periments, indeed, that the anterior and posterior roots of 
 the spinal nerves have different functions ; but in the nature 
 of these functions he was mistaken. Upon the anterior root 
 he supposed both sensation and motion to depend : the 
 posterior root he considered an unconscious nerve, which 
 might control the growth and sympathies of parts. Before 
 Sir C. Bell published any other account of the functions of 
 these nerves, M. Magendie had given to the world the true 
 theory of their uses. 
 
 The cerebral nerves taken together are by no means so 
 simple or uniform, either in their origin or their distribution, 
 as the spinal nerves. Yet the uses of several of them have 
 long been thought sufficiently explained by reference to the 
 parts which they supply : and modern experiments have 
 thrown no permanent doubt upon the correctness of opinions 
 thus originally deduced from the consideration of anatomical 
 structure. The cerebral nerves, the uses of which have long 
 been known, belong either to sense or motion. 
 
 II. The nerves of sense, included in this class, are, the 
 first, the second, and the soft portion of the seventh. 
 
 The first nerve rises by three roots from the fore and under 
 part of the corpus striatum, a layer of grey matter from 
 which is contained within it, and extends as far as to the 
 cribriform lamella of the ethmoid bone, where the size of the 
 nerve is greatly increased by an additional volume of cine- 
 
. 
 
 256 Of the soft portion of the Auditory Nerve. 
 
 ritious substance. The nerve now terminates in numerous 
 fibrils, which pass through the foramina of the ethmoid bone, 
 and are distributed upon the septum narium and the adja- 
 cent surface of the upper turbinated bone. 
 
 As this nerve is the only nerve exclusively distributed to 
 the nose, and as the sense peculiar to the nose is that of 
 smell, anatomists consider this nerve to be the olfactory 
 nerve. 
 
 The second nerve may be traced to the back part of the 
 crus cerebri : it rises by a flat band of white fibrils, termed 
 the tractus opticus, from the corpora geniculata and the 
 thalamus nervi optioi. The tractus optici unite at their 
 commissure, and the second nerve is properly that part of 
 the chord which extends from the commissure to the globe 
 of the eye. Reasoning in the same manner as in the former 
 instance, anatomists justly considered the second nerve to 
 be the nerve of vision. There is much that is curious in the 
 structure of the commissure : it may be better understood 
 by reference to the figure at the end of this section than by 
 any description in words. It appears that the outermost 
 fibres of the tractus go to form the outermost fibrils of the 
 optic nerve of the same side ; that the next in order cross 
 over to the optic nerve of the other side : that the innermost 
 fibrils of the tractus of one side are continuous with the 
 innermost fibrils of the opposite ; and that in a similar man- 
 ner a sort of loop is formed by the innermost fibres of either 
 optic nerve. 
 
 The soft portion of the seventh nerve rises by two roots 
 from the medulla oblongata. One set of fibrils passes be- 
 tween the corpus restiforme and the production of the oli- 
 vary tubercle to the floor of the fourth ventricle : another, 
 which is more known, turns round the corpus restiforme, 
 and reaches by a circuitous route the same origin with the 
 first : the white striae which form this second origin are an 
 essential part of the calamus scriptorius. It is perhaps 
 worthy of remark, that some of these coalesce at the median 
 plane with fibrils from the opposite side, in a manner exactly 
 resembling the junction of the innermost fibres of the two 
 optic nerves : these nerves are probably the only nerves, 
 
Of the third, fourth, Jifth, and ninth Cerebral Nerves. 257 
 
 which, when the two are simultaneously excited, convey but 
 a single impression. 
 
 III. The cerebral nerves, which upon anatomical evidence 
 have been considered voluntary nerves, are the third, the 
 fourth, the sixth, and the ninth. 
 
 The third nerve rises by many filaments from the black 
 matter in the crus cerebri : it is distributed to five muscles 
 in the orbit, and sends a branch to assist in supplying the 
 iris. 
 
 The fourth nerve rises from the opposite surface of the 
 medulla oblongata, and supplies the superior oblique muscle 
 of the eye. 
 
 The sixth nerve takes its apparent origin from the outside 
 of the anterior pyramid at the edge of the pons Varolii, and 
 supplies the abductor muscle of the eye. 
 
 It is remarkable, that the muscles of the eyeball have no 
 separate nerves of touch. Is not this because their action 
 is regulated by vision instead of by touch ? 
 
 The ninth nerve rises from the fore part of the olivary tu- 
 bercle : its numerous filaments are collected into two fasci- 
 culi, which unite to form one nerve. This nerve has long 
 been termed the motor linguae ; it supplies the flesh of the 
 tongue, and several muscles of the throat. 
 
 IV. We may next inquire into the history of the fifth 
 nerve, and of the hard portion of the seventh. 
 
 The fifth nerve, the largest of the cerebral nerves, emerges 
 from the side of the pons Varolii, in two fasciculi, or roots, 
 upon the larger of which a ganglion, termed the Gasserian, 
 is formed ; afterwards the fibrils of the nerve separate into 
 three divisions. The smaller fasciculus passes below the 
 ganglion, and afterwards associates itself with the third di- 
 vision of the larger. The correspondence in their mode of 
 origin between the fifth and the spinal nerves has long been 
 known to anatomists : Soemmering thus notices it ; after 
 describing the larger portion of the nerve, he adds, " minor 
 nervi pars, majorem portionem descendendo oblique prse- 
 
258 Origin of the Fifth Cerebral Nerve. 
 
 terit, neque ei fibras addit, eumfert in modum, quo prior ra- 
 dix nervorum spirit medulla ganglion non intrat *. 
 
 The first division of the fifth nerve is distributed to the 
 ball of the eye and iris, to the lachrymal gland, to the 
 Schneiderian membrane in the nose, and to the muscles and 
 integuments of the forehead. 
 
 The second division of the fifth is distributed to the 
 Schneiderian membrane, to the cheek and nostrils, to the 
 palate, and to the alveoli of the upper jaw. 
 
 The third division of the fifth is distributed to the alveoli 
 of the lower jaw, to the tongue, and the submaxillary and 
 sublingual glands, to the integuments of the temple and of 
 the chin, to the masseter, the pterygoid muscles, the tem- 
 poral, and the circumflexus palati. 
 
 The hard portion of the seventh rises apparently between 
 the corpus restiforme and corpus olivare. Having emerged 
 from the cranium it reaches the cheek, through the sub- 
 stance of the parotid gland, in which it divides into many 
 branches, that radiate to be distributed to the cutaneous 
 muscles and to the integuments of the face. These branches 
 are noted for their frequent reticular junctions, which have 
 obtained for the whole the name of pes anserinus ; and are 
 yet more remarkable for the occasional direct continuity 
 (resembling that between the ninth and the gustatory in the 
 tongue) of their finer fibrils with those of the facial branches 
 of the fifth. 
 
 Not more than twelve years since, when the functions of 
 the first, the second, and the auditory, of the third, fourth, 
 and sixth, of the ninth and of the gustatory branch of the 
 fifth were understood, and described in anatomical trea- 
 tises, the functions of the greater part of the fifth and of 
 the hard portion of the seventh nerves remained unknown, 
 and lecturers on anatomy passed the subject over, as one 
 which had hitherto baffled research. 
 
 It was in the year 1821 that the inquiries of Sir C. Bell into 
 
 * S. T. Soemmering de Corp. Hum. Fabrica, torn, iv, p. 214. Tra- 
 jecti ad Mcenuna, 1798. 
 
Sir Charles Be/l's Experiments. 259 
 
 the uses of the fifth nerve, and of the portio dura of the 
 seventh, were published in the Philosophical Transactions. 
 Sir C. Bell's experiments were the following : 
 
 " An ass being thrown, and its nostrils confined for a few 
 seconds, so as to make it pant and forcibly dilate the nos- 
 trils at each inspiration, the portio dura was divided on one 
 side of the head; the motion of the nostril of the same side 
 instantly ceased, while the other nostril continued to ex- 
 pand and contract in unison with the motions of the chest. 
 
 " On the division of the nerve, the animal gave no sign 
 of pain ; there was no struggle or effort made when it was 
 cut across. 
 
 " The animal being untied, and corn and hay given to 
 him, he ate without the slightest impediment. 
 
 " An ass being tied and thrown, the superior maxillary 
 branch of the fifth nerve was exposed. Touching this nerve 
 gave acute pain. It was divided, but no change took place 
 in the motion of the nostril ; the cartilages continued to ex- 
 pand regularly in time with the other parts which combine 
 in the act of respiration ; but the side of the lip was observed 
 to hang low, and it was dragged to the other side. The same 
 branch of the fifth was divided on the opposite side, and 
 the animal let loose. He could no longer pick up his corn ; 
 the power of elevating and projecting the lip, as in gathering 
 food, was lost. To open the lips, the animal pressed the 
 mouth against the ground, and at length licked the oats 
 from the ground with his tongue. The loss of motion of the 
 lips in eating was so obvious, that it was thought a useless 
 cruelty to cut the other branches of the fifth *. 
 
 The inference, which Sir C. Bell drew from these experi- 
 ments, was, that the branches of the fifth, which emerge 
 upon the face to supply the muscles and integuments, are 
 for sensation and voluntary motion jointly ; and that the use 
 of the seventh (the branches of which are distributed to the 
 
 * Phil. Trans. 1821, p. 413. The passages in this extract which I 
 have printed in italics mark the particular points in which Sir C. BelPs 
 experiments either were incomplete, or admitted of a different explana- 
 tion to that which he adopted. 
 
260 Experiments showing the true Function of the 
 
 same parts) is to " govern the motions of the lips, the nos- 
 trils, and the velum palati, when the muscles of these parts 
 are in associated action with the muscles of respiration." In 
 other words, according to Sir C. Bell, the seventh is the nerve 
 of instinctive motion to the face, and the fifth of voluntary 
 motion and sensation. Sir C. Bell, indeed, supposed that the 
 hard portion of the seventh nerve was one of a system of 
 nerves, which he termed superadded or respiratory (the others 
 belonging to the system being the nervus vagus, the spinal 
 accessory, the phrenic, and the posterior thoracic), that had 
 the common office of ministering in different parts to in- 
 stinctive action ; and he appears to have relied especially 
 upon the experiments which I have quoted, to illustrate and 
 to support his theory. 
 
 The reader will see, that I have here quoted in Sir C. Bell's 
 own words those experiments and conclusions of his, to 
 which I adverted in a former section. I have, therefore, in 
 addition, briefly to describe again my own counter-experi- 
 ments, which were published in the first part of my anato- 
 mical and physiological commentaries in 1822. 
 
 1 . I divided the portio dura in an ass, not on one side 
 only, but on both : the instantaneous effect of the operation 
 was to paralyze the nostrils and lips completely : the lips 
 dropped from the teeth, and hung pendulous, not having 
 muscular tone left to support their own weight. The lips 
 remained perfectly sensible, but the animal made no use of 
 them in attempting to take its food, or on any other oc- 
 casion. 
 
 2. I divided the branches of the second and third division 
 of the fifth at the foramina, where they emerge upon the 
 face, in another ass : the result was, that the lips lost sen- 
 sation ; but although their apposition did not remain quite 
 as exact as before, they did not lose their tone, or fall from 
 the teeth, as in the first experiment. The animal, however, 
 ceased to use its lips in taking up its food, and employed 
 for this purpose the method described by Sir C. Bell. 
 
 No doubt I believe is now entertained, that the inference 
 which I drew from these experiments is correct ; namely, 
 that the portio dura of the seventh nerve is a simple volun- 
 
Facial Branches of the Fifth and Seventh Nerves. 261 
 
 tary nerve, and that the facial branches of the fifth are ex- 
 clusively sentient nerves. The only circumstance which 
 seemed to throw a doubt upon these conclusions, was the 
 uselessness of the lips to the animal in gathering food, after 
 the fifth alone had been divided. If the facial branches of 
 the fifth be not, as Sir C. Bell supposed, nerves of motion 
 as well as of sensation, how happens it that muscles, which 
 they supply, cease to be of use on their division ? 
 
 This seeming difficulty I discovered to be entirely 
 removed upon referring to the history of cases of anaes- 
 thesia. In this disease, the sensation of the extremities 
 is wholly lost, while their muscular power remains. Now 
 it is remarkable, that in persons thus affected, the mus- 
 cles of the insensible part can only be exerted efficient- 
 ly, when another sense is employed^ to guide them and 
 to supply the place of that which*' has been lost. A person 
 afflicted with anaesthesia is described, in a case quoted by 
 Dr. Yelloley in a very interesting memoir upon this disease, 
 as liable " on turning her eyes aside to drop glasses, plates, 
 &c., which she held in safety as long as she looked at 
 them*." Instead, therefore, of being surprised that the ani- 
 mal in the experiment should cease to use its lips as before, 
 supposing they had been deprived of sensation only, we 
 could not consistently with analogy expect any other result. 
 In pursuing this subject, I was led to observe, that there 
 were muscles which received no branches from any nerve 
 but the fifth ; these muscles are the masseter, the temporal, 
 the two pterygoi'ds, and the circumflexus palati. These 
 muscles again I remarked are supplied with branches from 
 the third division of the fifth, that is to say, from the par- 
 ticular division of the fifth, with which the smaller fasciculus 
 or root of the nerve is associated. After some careful dis- 
 section, in the greater part of which I afterwards found that 
 I had been anticipated by Palletta, I made out, that the 
 smalkr fasciculus of the fifth is entirely consumed upon the 
 supply of the muscles I have named ; to which it is to be 
 
 * Medico-Ckirurgical Transactions, vol. iii, p. 99. 
 
262 Uses of the remaining parts of the Fifth Nerve. 
 
 borne in mind, that twigs from the ganglionic portion of the 
 nerve are likewise distributed. 
 
 But I had already ascertained by experiment, that al- 
 most all the branches of the larger or ganglionic portion of 
 the fifth were nerves of sensation. I proved this point by 
 experiments upon the ass, the dog, and the rabbit, respect- 
 ing the second and third division of the fifth ; in the pigeon, 
 respecting the first division. It was therefore thoroughly 
 improbable that the twigs sent from the same part of the 
 nerve to the muscles of the lower jaw should have a dif- 
 ferent quality, and be nerves of motion. For this function 
 it was reasonable to 'look to the other nervous fibrils, which 
 the masseter and temporal and pterygoid muscles receive ; 
 in other words, to the branches of the smaller fasciculus, or 
 to the ganglionless portion of the fifth. 
 
 By the experiments and reasoning which I have de- 
 scribed, I thus established that the ganglionless portion of the 
 fifth and the hard portion of the seventh nerve are voluntary 
 nerves to parts, which receive sentient nerves from the larger 
 or ganglionic portion of the fifth. This happened before 
 the publication of M. Magendie's discovery of the parallel 
 functions of the double roots of the spinal nerves; and 
 without wishing to assert the least claim to that discovery, 
 I will yet observe, that 1 was led by the well-known ana- 
 tomical analogy between the fifth and spinal nerves, to con- 
 jecture nearly what M. Magendie proved, and was indeed 
 actually engaged in experiments to determine the point, 
 when M. Magendie's were published. I say nearly, inas- 
 much as subsequently to the publication of my experiments 
 upon the facial branches of the fifth and seventh, I had 
 been misled by the analogy of the third, fourth, and sixth 
 nerves, to adopt an opinion respecting muscular sensation, 
 which I did not correct till after I had seen M. Magendie 
 repeat his experiments on the spinal nerves in this country. 
 
 IV. The eighth nerve consists of three parts, the glosso- 
 pharyngeal nerve, the pneumo-gastric nerve or nervus vagus, 
 and the spinal accessory. 
 
 The two first of these rise by many fibrils disposed in a 
 
Of the Pneumo-gastric Nerve. 263 
 
 line from the fore part of the corpus restiforme : upon each 
 a small ganglion is formed. The smaller, which consumes 
 the uppermost four or five fibrils, is the glosso-pharyngeal : 
 it terminates in twigs distributed to the root of the tongue, 
 and to the upper part of the pharynx. The latter branches 
 are probably sentient and voluntary; the former sentient 
 only. This inference I ground upon the following facts. 
 
 In every case where muscular action is proved to be under 
 the voluntary control of a particular nerve, the mechanical 
 irritation of that nerve directly 'after death will cause the 
 muscle it controls to act : on the other hand, if a sentient 
 nerve that is distributed in a muscle be thus irritated, no 
 action of the muscle follows. Now I observed, that on thus 
 irritating the glosso-pharyngeal nerve in an animal recently 
 killed, the muscular fibres about the pharynx acted, but 
 not those of the tongue. 
 
 The nervus vagus, or pneumo-gastric nerve, distributes 
 branches to the larynx, trachea, and lungs, to the pharynx, 
 oesophagus, stomach, and duodenum, to the liver, the 
 spleen, the kidneys. The fibrils which it distributes to the 
 larynx and pharynx and oesophagus are nerves of sensation 
 and motion. 
 
 The spinal accessory nerve, which is associated with the 
 two preceding, rises remotely from them : its origin takes 
 place by many fibrils from the side or rather from the back 
 part of the spinal marrow in the upper part of the neck, 
 behind the ligamenta dentata, and not far from the poste- 
 rior roots of the spinal nerves, which furnish a few filaments 
 to it. It gives a branch to the nervus vagus, and fibrils to 
 the pharynx, but the greater part of the nerve assists the 
 spinal nerves in supplying the sterno-cleido-masto'ideus and 
 the cucullaris muscles. Upon irritating this nerve in a living 
 animal, pain is excited : upon irritating it in an animal re- 
 cently killed, the muscles it supplies are convulsed. We 
 may suppose, that rising between the two roots of the spinal 
 nerves, it partakes of both their functions ; but why it 
 should not, like the phrenic or the ulnar nerve, rise in the 
 ordinary manner from the spinal nerves, no cause that will 
 bear examination has been assigned. 
 
264 Of the Sympathetic Nerve. 
 
 V. Of the sympathetic nerve. 
 
 The sympathetic is a slender nerve which descends upon 
 or near the side of the vertebrae, from the foramen caroticum 
 in the temporal bone to the os coccygis. Its colour is 
 greyer than that of other nerves, and its texture seems 
 to contain throughout a portion of the substance, which is 
 elsewhere peculiar to ganglia. The whole nerve is indeed 
 studded with ganglia : there are three in the neck, and one 
 to each of the vertebrae below ; on the os coccygis the nerve 
 on one side joins with its fellow to form a single ganglion. 
 In the canalis caroticus the nerve which ascends as a plexus 
 round the artery has again one or more small ganglia. 
 
 From this nerve are derived in the neck and canalis 
 caroticus, branches to the great vessels and to the heart ; 
 in the chest, branches which supply the viscera of the ab- 
 domen ; in the abdomen, branches which supply the pelvic 
 viscera. Their function is unknown. I have divided the 
 nerve on each side in the neck, but no symptom followed. 
 The ganglions and the nerve itself appear to be sensible in 
 a very low degree, if at all. Yet the sensations which we 
 experience in the viscera must be communicated through 
 this nerve ; and the action of the fibres of the bowels may 
 be influenced through it ; and the impression which can be 
 made upon the action of the heart after decapitation, by 
 crushing a portion of the spinal chord, must be transmitted 
 through its influence. The name of the nerve expresses the 
 conviction of anatomists that it is used to associate the 
 affections of different parts ; and till the real functions of 
 the nerves were ascertained, physiologists were pleased with 
 dilating upon the connections, which in health and disease 
 are kept up between all the organs of the frame through 
 the agency of this nerve and the nervous system generally. 
 But the shallowness and conjectural nature of such remarks 
 becomes strikingly apparent, when they are placed by the 
 side of rigorous deduction from experiment ; and it be- 
 comes proportionately easier to understand, that a plain 
 avowal of ignorance is more creditable and more useful to 
 the progress of science, than pages of the most ingenious 
 hypothesis. 
 
Of the Sympathetic Nerve. 
 
 265 
 
 But will not the origin of the sympathetic throw some 
 light upon its function ? It seems to spring from the sixth 
 nerve, and from the Vidian branch of the fifth, and to be 
 reinforced by fibrils from the portio dura, the eighth, the 
 ninth, and all the spinal nerves, and from both their roots, 
 but principally the anterior. The nerve then is in fact but 
 a collection of branches from almost every nerve in the 
 frame, which join it at the adjacent ganglia ? This may 
 appear to be true, but it is not the whole truth. The 
 sympathetic certainly gives branches to different nerves as 
 well as receives them from the same. The adjoined drawing, 
 which I made from two very careful dissections, will serve 
 to illustrate this remark. 
 
 Fig. 1, represents the junction of the sympathetic with 
 the sixth in the cavernous sinus. , is the carotid artery ; 
 c, the sympathetic nerve distributed upon and to it; and b, 
 the sixth nerve (the letter being placed at its cerebral end), 
 both giving and receiving filaments. 
 
 Fig. 2, represents the junction of the sympathetic with 
 the second lumbar nerve, d, is a ganglion of the sympa- 
 thetic : e, the spinal nerve ; 1, its anterior root ; 2, its pos- 
 
266 Plate of the Origins of the Cerebral Nerves. 
 
 terior root with the ganglion. The connection between 
 the nerves is of the same description as in the former in- 
 stance. 
 
 I am tempted to add a figure of the origins of the cere- 
 bral nerves, as they appear when made out in the substance 
 of a brain hardened in alcohol. It will serve to illustrate 
 several of the remarks which I have already had occasion 
 to make, and I shall,, again find advantage in having it to 
 refer to. 
 
Of the Cerebral Nerves. 267 
 
 A. Represents the under part of the corpus striatum. 
 
 B. The thalamus nervi optici. 
 
 C. The corpus geniculatum externum. 
 
 D. The corpus geniculatum internum. 
 
 E. The corpus bigeminum superius. 
 
 F. The corpus bigeminum inferius. 
 
 G. The exterior stratum of the crus cerebri cut through 
 so as to show the termination of 
 
 H. The upper pedicle of the cerebellum. 
 
 I. The pons Varolii cut through at the part where the 
 fifth nerve perforates it. 
 
 K. The corpus restiforme. 
 
 L. The corpus olivare. 
 
 M. The anterior pyramid : the letter is placed just above 
 the decussation of the pyramids. 
 
 The nerves are marked with the numbers which designate 
 them : it is only necessary to observe, that 50, represents the 
 larger portion of the fifth with the ganglion of Gasser upon it; 
 and 5b, the smaller portion, which, passing below the gan- 
 glion, afterwards forms part of the third division of the 
 fifth ; that 70, is the portio dura, 7b, the portio mollis of 
 the seventh. 
 
 I believe that the observation will be found to be correct, 
 that nerves of motion take their rise from the same region 
 or segment with those sentient nerves which transmit the 
 impressions, by which their action is usually regulated. 
 The correctness of this remark, as it respects the spinal 
 nerves, will not be disputed. It is owing to this circum- 
 stance, that if in an animal just killed, the spinal chord be 
 divided in the neck and in the back, on irritating the in- 
 tegument of either foot, that foot is retracted as promptly 
 and to the same extent, as if the spinal chord and medulla 
 oblongata were entire. Upon the same principle, if a pi- 
 geon's enkephalon be removed, with the exception of the 
 tubercles and crura cerebri, which are to be left attached to 
 the eyeballs by the third pair of nerves, on irritating the 
 part of the divided optic nerve adherent to the insulated 
 segment of enkephalon, the iris acts. In the preceding 
 
268 Principle observed in the Origin of Nerves. 
 
 figure, the third and fourth nerves, one of which governs 
 the motion of the iris, while both guide the eye to suit the 
 wants of vision, are seen to rise near the optic. But 
 the principle which I have laid down is more strikingly 
 illustrated by referring to the origin and uses of other 
 nerves. 
 
 We observe, that the smaller portion of the fifth rises 
 from the upper part of the medulla oblongata close upon the 
 greater portion ; and we recollect, that the sense of pressure 
 upon the teeth and gums, and of muscular exertion attend- 
 ing it, depends upon the latter, the muscular effort itself 
 upon the former. 
 
 We observe, that the large root of the fifth, and the portio 
 dura, rise together ; and we recollect, that the delicate sense 
 of touch upon the eye and eyelids depends upon the first, 
 and the action of the orbicularis palpebrarum on the second ; 
 that the sense of touch in the nostrils depends upon the 
 first, and the action of the muscles of the nostrils upon the 
 second ; that feeling in the lips depends upon the first, and 
 the action of the muscles of the lips upon the second ; and, 
 finally, that the sensation of those muscles, which the 
 second sets into action, depends upon the first. 
 
 We observe, that the portio dura rises near the portio 
 mollis ; and we recollect, that the motions of the ear de- 
 pend upon the former, and the sense of hearing upon the 
 latter. 
 
 We observe again, that the sixth nerve rises near the 
 fifth ; and we recollect, that it directs the eye outwards to- 
 wards the orifice of the lachrymal gland, the secretion of 
 which is under the control of the fifth. 
 
 It is unnecessary to point out in detail how completely 
 the glosso-pharyngeal and the pneumo-gastric nerves support 
 the principle which I have endeavoured to establish. That 
 every nerve cannot be arranged under it (for I know not by 
 what means it can fairly be made to include the first and the 
 ninth) does not, I hope, render the observation valueless. 
 
 It may appear to some of my readers, that I should have 
 defined exactly the terms sentient and voluntary nerves, 
 
Nerves probably Media of Transmission only. 269 
 
 which I have frequently had occasion to employ. Let me 
 repair the omission. By sentient nerves, I mean those, the 
 division of which is followed by instantaneous loss of sensation 
 in a part ; by voluntary, those, upon the division of which, the 
 will ceases to influence the muscles they supply. What part 
 nerves play in sensation and voluntary motion, whether they 
 merely transmit impressions, or have some further agency, 
 is a matter of speculation. The former opinion is perhaps 
 the most plausible : it is borne out by the analogy of the 
 general structure of the nervous system ; and it is strikingly 
 consistent with the very curious fact, that after the amputa- 
 tion of a limb the patient always experiences for a 
 time sensations, which, taken alone, would persuade him 
 that his limb was still alive, and still formed part of his 
 frame. 
 
 In this account of the offices of the nerves, I have viewed 
 them in their relation to the phenomena of consciousness 
 alone. The influence which they exert upon vegetative life, 
 the reader will find that I have noticed in connection with 
 the history of the different automatic functions, which the 
 nerves control or minister to. A single remark, however, I 
 am tempted to conclude this section with, referring to the 
 unconscious agency of nerves, yet illustrating the common 
 nature of those which have been supposed to be most unlike. 
 Sir Charles Bell, it will be remembered, represents the eighth 
 nerve as being essentially different from the fifth and spinal 
 nerves. That it is not so, as far as it regards sense and vo- 
 luntary motion, I have already shown. But consider the 
 eighth in relation to a function of another class : place it, 
 for instance, in contrast with the fifth and the spinal nerves, 
 in animals which have electric organs superadded to their 
 frame ; what is the deduction obtained ? The electric organ 
 of the gymnotus electricus is supplied from the spinal nerves 
 alone. The electric organ of the raya torpedo is supplied 
 with nerves from the fifth. So far Sir C. Bell's distinc- 
 tion is supported by the instances before us : but this, al- 
 though the truth, is not the whole truth : the electric organ 
 of the raya torpedo is in fact not more supplied by the fifth 
 than it is by the eighth. In other words, as far as we can 
 
270 What Nerves are distributed to the Electric Organs. 
 
 learn from anatomy, the regulation of this one most remarkable 
 function is equally and together conducted through nerves, 
 which have been theoretically opposed to each other. The 
 eighth, the fifth, the spinal nerves, seem equally adequate 
 to this office, and the only ground of selection of one or 
 other of these nerves in the different cases, seems to have 
 been the casual vicinity of the electric organ to one system 
 or the other. 
 
CHAPTER XII. 
 
 OF THE ORGANS OF THE SENSES. 
 
 THE sensations which we experience are of two kinds; one 
 relating to the condition of our bodily frame instructing us 
 when it is threatened with injury, and when its wants require 
 to be relieved the other, conveying to us ideas of the ex- 
 ternal world, and of the qualities of the matter which sur- 
 rounds us. 
 
 The conservative sensibility of the frame is strictly ad- 
 justed to the situation and nature of different parts. The 
 skin is acutely alive to most varieties of mechanical or che- 
 mical lesion. But this mode of sensibility is more sparingly 
 allotted to internal parts, where it is evidently not needed, 
 as such parts can be reached only through the previous de- 
 struction or laceration of the integuments. On the other 
 hand, no sensation is excited in the skin by many impres- 
 sions, which yet are strongly felt on other parts ; as, for 
 instance, by the contact of a weak acid, or by a very consi- 
 derable degree of stretching and extension of its tissue. 
 Neither of these causes are calculated to injure the skin. 
 But one texture that of the teeth would be impaired by 
 the first cause which I have named, and the ligaments 
 around the joints would be rendered useless by the second. 
 Accordingly, the teeth are acutely sensible to the contact of 
 acids ; and the ligaments, which have no feeling when cut 
 through, when strained give rise to the most overwhelming 
 pain. Every part aches, when fatigued by protracted ex- 
 ertion. When the stomach craves food, we feel sensations 
 of hunger; when the bladder should be emptied, a sensation 
 calls our attention to it. 
 
 The sensations, which convey to us a knowledge of the 
 
272 Of the Nature of Light. 
 
 external world, are referable to five kinds ; namely, sight 
 touch, smell, taste, and hearing. The parts of the frame in 
 which these sensations are excited, are the organs of our 
 senses. 
 
 The organs of the senses consist of expansions of nervous 
 matter, disposed in such a form and situation, and behind 
 such media, as are calculated to collect upon each the im- 
 pressions it is fitted to appreciate. 
 
 It may be remarked, in general, that the exercise of an 
 organ of sense, as well as the excitement of the conservative 
 sensibility, always conveys with it a notion of definite lo- 
 cality ; and that, in proportion to the knowledge which sen- 
 sations communicate to us, they are themselves overlooked, 
 and the bodily feeling is lost in the ideas which it suggests. 
 
 SECTION I. 
 Of the Organ of Vision. 
 
 A 
 
 The expansion of the optic nerve, or the retina, which is 
 disposed as a cup at the bottom of the eyeball, has the won- 
 derful property of communicating to us sensations of colour, 
 when adequate impressions are made upon it. A blow upon 
 the eye causes it to appear to flash fire j and pressure on 
 the side of the eyeball excites a sensation of coloured circles. 
 The impressions by which we s.ee, although of an incompa- 
 rably more delicate nature than the preceding, yet, like 
 them, are mechanical impulses upon the retina. They are 
 produced by light. 
 
 Light consists either of imponderable and infinitely mi- 
 nute material particles emitted from luminous bodies, or of 
 undulations of an ethereal medium supposed to pervade all 
 space. A succession of particles on the one theory, or of 
 undulations on the other, constitutes a ray of light. Rays 
 of light move only in straight lines : their velocity is so 
 great, that they travel from the sun to the earth, a distance 
 of 95,000,000 miles, in 8i minutes. 
 
Of Reflection and Refraction. 273 
 
 Luminous bodies are such as continually throw off par- 
 ticles of light. Transparent bodies are those which permit 
 the passage of light ; opaque bodies, those which obstruct 
 it. No material substances appear to be perfectly opaque 
 or transparent. Leaf gold sensibly transmits a greenish 
 light ; and, on the other hand, a depth of seven feet of 
 water intercepts one half of the light which passes through 
 it. Light moves in right lines ; but its path is liable to be 
 altered in two ways -by reflection namely, and by re- 
 fraction. 
 
 All visible bodies that are not luminous, are seen by means 
 of rays thrown back from their surface. If a ray of light 
 fall upon a surface perpendicularly, it is reflected perpendi- 
 cularly. If a ray of light fall upon a surface obliquely, and 
 is reflected, the angles which it forms with a line vertical 
 to that surface, are called the angles of incidence and re- 
 flection. The law of reflection requires that the angles of 
 incidence and reflection be equal, and that the incident and 
 reflected ray be in the same plane with the imaginary ver- 
 tical line. The term reflection is usually confined to those 
 cases in which the rays are thrown back in a definite order, 
 either in lines parallel to each other, or uniformly conver- 
 gent or divergent. To produce this species of reflection, a 
 surface must be highly polished, in order that there may be 
 uniformity in the angles at which the greater part of the 
 rays are returned. 
 
 Refraction takes place, when a ray of light passes from 
 one transparent medium into another of different density at 
 any but a right angle. If the direction of the ray be ver- 
 tical to the surface of the new medium, no refraction takes 
 place, and the continued path of the ray is a right line con- 
 tinuous with its former course. If the ray enter the new 
 medium obliquely, it pursues a new course, being turned or 
 refracted towards the perpendicular, when the second medium 
 is of greater density than the first ; but refracted from the 
 perpendicular, in the opposite case. Transparent substances 
 have been supposed to refract, in the ratio of their density 
 and their combustibility. The extent of the refraction pro- 
 duced by the same medium depends upon the angle at 
 
274 Of Colour. Of Complementary Colours. 
 
 which a ray enters it. All rays of the same kind transmitted 
 by the same substance, form with the perpendicular an 
 angle of refraction, the sine of which has a constant propor- 
 tion to the sine of the angle of incidence. 
 
 Light is not simple. The white light of the sun admits of 
 being decomposed, through the different refrangibility of its 
 elements, into rays of different colours ; which again are 
 capable of being recombined, when they form again white 
 light. The primitive colours which form white light, are 
 three red, yellow, and blue. The intermediate tints of 
 orange, green, indigo, and violet, are combinations of the 
 primitive colours. The colour of luminous bodies depends 
 upon the quality of the light they emit. The colour of bodies 
 that are not luminous, when seen by white light, results 
 from their absorbing some and reflecting others of the ele- 
 mentary rays. 
 
 The compound nature of white light is physiologically 
 illustrated by the phenomena of convertible colours. If the 
 retina be fatigued by fixing the eye for some seconds upon 
 a coloured spot strongly illuminated, upon averting it the 
 field of vision appears haunted by a spot of the size of that 
 recently looked at, but of a different colour. If the experi- 
 ment be repeated with different colours, the eye being 
 directed after each trial to a perfectly white surface, the 
 colour of the spectrum is found to have an invariable rela- 
 tion to the colour of the spot by which the eye has been fa- 
 tigued. The secondary colour is called the convertible or 
 accidental colour of the first. The term complementary, 
 often used as synonimous with the terms already mentioned, 
 is better than either. The new colour is, in fact, the com- 
 plement of the original colour to white ; or deduct the colour 
 with which you would fatigue the eye from white, the con- 
 vertible colour will certainly be composed of the remaining 
 elements of white light. Fatigue the eye with red, for in- 
 stance, the colour of the spectrum produced will certainly 
 be a blueish green. Each point of the retina, it thus ap- 
 pears, has a separate perception of the different elements of 
 white light, at the same time that it receives their collective 
 impression ; so that when its sensibility to one is exhausted, 
 
Of defective Vision of Colours. 275 
 
 it can discern, with unimpaired distinctness, the rest of the 
 group. 
 
 The effect produced upon the retina by rays of light of 
 different refrangibility, may, in one sense, be considered ar- 
 bitrary. We may imagine, on the one hand, that there are 
 beings who would derive sensations of light from the de- 
 oxydizing ray, beyond the violet of the prismatic spectrum ; 
 and we find, upon the other, that there exist human beings 
 to whom either extreme of the spectrum is alike. The fol- 
 lowing statement, which I extract from the Medico-Chi- 
 rurgical Transactions, describes the common form of defec- 
 tive vision. 
 
 " My eyes (says the writer of this narrative) are grey 
 with a yellow tinge round the pupil. The colour I am most 
 at a loss with is green, and in attempting to distinguish it 
 from red, it is nearly guess-work. Scarlet in most cases I 
 can distinguish, but a dark bottle-green I could not with 
 any certainty tell from brown. Light yellow I know ; dark 
 yellow I might confound with light brown, though in most 
 cases I think I should know them from red. All the shades 
 of light red, pink, purple, &c., I call light blue : but dark 
 blues and black I think I know with certainty. Though I 
 see different shades in looking at a rainbow, I should say it 
 was a mixture of yellow and blue, yellow in the centre and 
 blue towards the edges. I have red crimson curtains in the 
 window of my bed-room, which appear red to me in candle- 
 light and blue in day-light. The grass in full verdure ap- 
 pears to me what other people call red, and the fruit on 
 trees when red I cannot distinguish from the leaves, unless 
 when I am near it, and then more from the difference of 
 shape than colour. A cucumber and a boiled lobster I 
 should call the same colour, making allowance for the va- 
 riety of shade to be found in both ; and a leek in luxuriance 
 of growth is to me more like a stick of red sealing-wax than 
 any thing I can compare it with." 
 
 The writer of this narrative mentions that a similar defect 
 -in vision had occurred in other instances in his family. 
 At Dr. NicholPs suggestion he made the curious observa- 
 tion, that on fatiguing his sight at different times with 
 
276 Perception of the Blood-vessels of the Retina. 
 
 gazing upon spots of red and green on a white ground, the 
 eye became painfully affected, but no accidental colour made 
 its appearance *. 
 
 The simplest instance of vision is the perception of the 
 blood-vessels upon the retina. They may be brought into 
 view in the following manner : Let one eye be closed, and 
 a candle held near to the other, but to one side, so that the 
 flame may not occupy any of the central part of the field of 
 view. If the candle thus held be kept stationary, nothing- 
 occurs but a diminution of the sensibility of the retina to 
 light : but if the flame be continually moved up and down 
 through a small space for a short period of time, the blood- 
 vessels of the retina, with all their ramifications, and exactly 
 as they are represented by the accurate Soemmering, are 
 projected in the field of view, and become distinctly seen. 
 This curious phenomenon, observed by Purkinje, has been 
 best explained by Mr. Wheatstone. 
 
 Mr. Wheatstone supposes, that the appearance seen is the 
 shadow of the vascular network ; and that it becomes vi- 
 sible through being made to fall intermittently upon the 
 same points of the retina, or in succession upon different 
 points. 
 
 Mr. Wheatstone recommends the following contrivance 
 for showing a variation of this experiment. A circular plate 
 of metal is to be used, about two inches in diameter, black- 
 ened upon one side, and perforated at the centre with an 
 aperture of the size of an ordinary pinhole : to this is fixed 
 a similar plate of ground glass. On placing the aperture 
 between the eye and the flame of a candle, and keeping the 
 plate in motion, so as to displace continually the image of 
 the aperture on the retina, the blood-vessels are seen distri- 
 buted as before, but more brightly, and the spaces between 
 their ramifications appear filled with innumerable minute tor- 
 tuous vessels before invisible. It is remarkable, that in this, 
 as well as in the former experiment, in the very centre of 
 the field of vision, there is a small space in which no trace 
 whatever of vessels appears. 
 
 * Medico-Chirurgical Trans, vol. ix, p. 363. 
 
Fundamental Law of Vision. 277 
 
 It has been stated to be the particular endowment of the 
 retina, that, when adequate impressions are made upon it, 
 sensations of colour are produced. A very trifling addition 
 to this statement contains the enunciation of a principle, 
 upon which almost all the phenomena of vision depend, and 
 to which the entire construction of the eye has reference. 
 When an impression es made upon the retina sufficient to pro- 
 duce sensations of colour, the colour appears projected in a line 
 vertical to the point of the retina which has been excited* 
 Thus, if pressure be made with the finger upon the out- 
 side of the eyeball, a circular spectrum is seen in the 
 
 direction of the nose ; if the pressure be made at the upper 
 part of the eyeball, the spectrum appears towards the cheek ; 
 if below, towards the eyebrow. The spectrum is always op- 
 posite to the point compressed, or is projected in a line ver- 
 tical to the point of the retina which is excited to sensation. 
 I shall have occasion, afterwards, to mention the conclusive 
 experiment made by Scheiner, through which this law of 
 vision was established. In the mean time, the ruder experi- 
 ment of my own, which I have mentioned, may serve to 
 satisfy the reader of its justness. 
 
 It appears that by this endowment of the retina the di- 
 rection is rigorously determined, in which we can see by 
 each point of its surface. The upper part, when excited, 
 sees downwards, the lower part upwards, the inner out- 
 wards, the outer inwards. Now the retina is to be used in 
 giving us notions of the visual direction of objects, which 
 are to correspond exactly with the notions which we derive 
 from the sense of touch. Accordingly, we find placed before 
 the retina a series of media, the effect of which is to pro- 
 
278 Use of the Inversion of the Picture on the Retina. 
 
 duce true vision by means of the law of direction above 
 stated. 
 
 The globe of the eye is filled with transparent humours : 
 the effect of these humours is parallel to that of a common 
 double convex lens of glass. Interpose such a lens between 
 the flame of a candle and a sheet of paper, and if the latter 
 be at the proper focal distance, the result is the arrange- 
 ment of the rays entering the lens from the candle in an 
 inverted position, thus 
 
 Let me substitute for this diagram, one of the eye in 
 vision. 
 
 The rays from the object towards which the eye is turned, are 
 represented as reversed upon the retina. This fact, which is 
 easily shown in the eye of a dead animal, is commonly 
 considered as a defect in the mechanism of sight requiring 
 compensation. So far, however, is this from being true, 
 that the inversion of the picture is the only means by which 
 correct vision could have been attained. For the upper 
 part of the retina is that which alone, by the law of vision 
 above stated, can see downwards. The rays from the lower 
 part of the object must therefore be brought to the upper 
 
Further Offices of the Humours of the Eye. 279 
 
 part of the retina, as the only part at which they can ex- 
 cite a just impression of the direction of the point from 
 whence they have come. To refer to the diagram : Excite 
 the point A of the retina any how, so as to produce sensa- 
 tions of colours, they will be projected in the line AB: 
 excite C, the colours will be seen in the direction CD. But 
 A B is in the true direction from the upper part of any ob- 
 ject looked at : the ray of light from the upper part of the 
 object must therefore be brought to A. CD again is the true 
 direction from the lower part of the object; the ray pro- 
 ceeding from the lower part must therefore be brought 
 to C. 
 
 In the diagrams which I have given, I have represented 
 a single ray as proceeding from each point; but it is evident 
 that many rays enter the eye from each point of an object. 
 It is another office of the refractive media of the eye, to 
 bring all the rays which enter the pupil from a single point 
 to a focal point upon the retina. A diagram, therefore, of 
 the passage of each ray of light through the humours of 
 the eye must be at least as complicated as the subjoined 
 figure, to convey an adequate notion of their agency. 
 
 It is evident how essential it is to vision, that the rays of 
 light from each point of an object should be collected upon 
 one point of the retina ; for, if they reached several points with 
 perceptible intervals, they would necessarily give rise to as 
 many different perceptions of the object, and all in different 
 directions, as the points upon which they might fall ; or, if 
 they were vaguely spread over a circle instead of occupying 
 a point, there would be an end, through their mutual in- 
 tersections, of distinct vision. The second of these two 
 consequences is illustrated by the defective vision of myopic 
 and presbyopic eyes. 
 
 s 2 
 
280 Of Myopic and Presbyopic Eyes. 
 
 The myopic eye is the common cause of short sight in 
 young persons ; in it the aqueous humour is too convex, 
 and the lenses of the eye are therefore too highly refractive. 
 The result is, that parallel rays of light entering the 
 pupil are brought to a focus before they reach the retina ; 
 and having crossed and begun to disperse again, are spread 
 upon the retina in a circle instead of a point. This defect is 
 corrected by the use of glasses of a divergent quality, which 
 spread the rays a little before they enter the too powerfully 
 refractive eye. Without glasses the myopic eye sees dis- 
 tinctly objects which are near; for from these the rays which 
 enter the pupil are already divergent. 
 
 The presbyopic eye is the cause of imperfect vision in 
 old people: in it the aqueous humour is not sufficiently con- 
 vex ; the humours of the presbyopic eye are therefore not 
 sufficiently refractive, and can bring to a focus upon the 
 retina no rays that are at all divergent when they reach 
 the pupil. Distant objects however, from which the rays 
 are parallel, the presbyopic eye sees without assistance. 
 To enable such an eye to see near objects, a lens of a con- 
 vergent quality must be made use of. 
 
 The former point to which I adverted the consequence, 
 namely, of the rays of light from a single point of the ob- 
 ject reaching the retina at different points with perceptible 
 intervals is illustrated by, and gives me a fitting opportu- 
 nity of describing the experiment made by Scheiner, through 
 which the law of visual direction was originally shown. 
 
 If the head of a pin be viewed with one eye at the dis- 
 tance of three inches, that is to say at a distance nearer 
 than the limits of distinct vision, the pin-head appears large 
 and imperfectly defined, the outermost part of the cone of 
 rays, which enters the pupil from each point of the object, 
 having been too divergent to be brought to a focus on the 
 retina. A well-constructed eye looking at an object at this 
 distance is in the situation of a presbyopic eye directed to 
 any but remote objects. Now, if a card pierced with a 
 single pin-hole be interposed between the eye and the head 
 of the pin, the outline of the latter is at once rendered 
 clear and definite. The minute hole through which it is 
 
Experiment of Scheiner. 
 
 281 
 
 seen excludes the cone of rays, allowing one ray alone from 
 each point of the object to reach the retina. 
 
 But the object may be seen by rays passing through the 
 upper part, or the middle, or the lower part of the pupil, 
 according as the card is raised or lowered ; and the apparent 
 place of the object may by this means be made to shift: 
 the object appears to rise when the card is lowered, to sink 
 when it is raised. Or, instead of one, let three minute pin- 
 holes be made close to each other on a vertical line. The 
 diagram which is adjoined is meant to illustrate all the phe- 
 .nomena which are then observed. 
 
 k-~H 
 
 By this experiment a clear picture of the object is pro- 
 duced upon three parts of the retina. The consequence is, 
 that three distinct objects are seen; when it is easy to ascer- 
 tain, by closing the pin-holes in succession, that the lowest 
 of the three objects results from the impression made upon 
 the upper part of the retina, and vice versa. In other words, 
 each point of the retina upon which you collect the rays 
 from the object, sees the object in a direction vertical to it, 
 agreeably with the law which has been already introduced 
 to the reader's notice on other evidence. 
 
 Let me now describe the nature of the refracting media 
 within the eye, which I have hitherto viewed as comparable 
 to an ordinary double convex lens. 
 
 The refracting media in the eyeball are the cornea, the 
 aqueous humour, the lens or crystalline humour, and the 
 vitreous humour. 
 
 The cornea is formed of a transparent dense elastic latni- 
 
282 Of the Humours of the Eye. 
 
 nated substance, being a segment of a smaller sphere tha 
 the globe of the eye. As its surfaces are nearly parallel, it 
 deserves perhaps rather to be described as a piece in the 
 case of the eye, than as part of the mechanism by which 
 light is modified in its passage to the retina. 
 
 The aqueous humour is a liquid, which consists of water 
 impregnated with albumen, gelatin, and muriate of soda : 
 its refractive power, according to the researches of Dr. Brew- 
 ster and Dr. Gordon, may be estimated at 1.3366, that of 
 water being 1.3358. 
 
 The form of the aqueous humour depends upon the parts 
 which confine it. The aqueous humour is contained be- 
 tween the cornea and the lens, and forms a meniscus. Its 
 specific gravity is 1.0088. 
 
 The crystalline is a double convex lens, of which the an- 
 terior surface is flatter than the posterior : its substance is 
 gelatinous, and of much denser consistence at the centre 
 than near the surface ; it is contained in a thin capsule. 
 Its composition, according to the analysis of Berzelius, is 
 as follows : 
 
 Water 58 
 
 Peculiar matter 35.9 
 
 Muriates, lactates, and animal matter soluble in alcohol 2.4 
 
 Animal matter soluble only in water with some phosphates ... J.3 
 Portions of the remaining insoluble cellular membrane 2.4 
 
 100.0 
 
 The refractive power of the different parts of the crystal- 
 line humour, according to Dr. Brewster and Dr. Gordon, is 
 as follows . 
 
 Refractive power of the outer coat of the crystalline 1.3767 
 
 Refractive power of the middle coat of the crystalline 1.3796 
 
 Refractive power of the central part of the crystalline 1.3990 
 
 Refractive power of the whole crystalline 1.3839 
 
 The specific gravity of the crystalline is 1.0765. 
 
 The vitreous humour is a liquid resembling the aqueous 
 humour ; but it is contained in a proper capsule termed the 
 hyaloid membrane, from which innumerable membranous 
 processes pass inwards to form a series of cells in which the 
 liquid is lodged ; the vitreous humour nearly fills the eye- 
 
The Eye Achromatic. 283 
 
 ball. The lens is imbedded in its fore part; the hyaloid 
 membrane upon approaching the margin of the lens splits 
 into two layers, one of which passes behind the lens adhering 
 to its capsule, the anterior passes upon the fore part of the 
 lens and becomes identified with its capsule. Air may be 
 blown into the circular channel between the two layers of 
 the hyaloid membrane at the margin of the lens : this chan- 
 nel is termed the canal of Petit. 
 
 The refractive power of the vitreous humour is 1,3394. 
 In specific gravity and chemical composition it resembles 
 the aqueous humour. 
 
 The object sought and attained by the employment in 
 the eye of several media of different density and refractive 
 power appears to be the following. 
 
 Light by refraction through any single transparent sub- 
 stance is more or less separated into different colours ; but 
 this dispersive power, as it is called, is not the same in all 
 transparent substances, nor is it proportioned to the power 
 of refraction. Accordingly by combining, or rather oppos- 
 ing to each other lenses of different dispersive powers, a 
 certain amount of refraction may be obtained, at the same 
 time that the opposite dispersions are neutralized. This is 
 the principle upon which achromatic telescopes are con- 
 structed. In the structure of the eye a parallel adjustment 
 is certainly made, although in what way exactly has not 
 yet been explained in a satisfactory manner, 
 
 As the joint effect of the transparent media above de- 
 scribed and of the figure of the retina, the rays that enter the 
 pupil from a given point of an object are collected without 
 dispersion into a focus upon that part of the retina, which is 
 vertically opposite to that point : and thence, through the 
 operation of the law before explained, we have intuitive 
 knowledge of the true direction of any point of an object 
 at which we look, that is at a proper distance and ade- 
 quately illuminated. These premises being admitted, it is 
 evident, that every object, at which we look, must have 
 a definite visual magnitude, inasmuch as the apparent 
 size of an object must exactly depend upon the space 
 which its outline occupies upon the retina* Now the same 
 
284 Of the Knowledge directly obtained by Vision. 
 
 object at different distances will, it is easily shown, occupy 
 a larger or smaller area in the retina. The nearer it is, the 
 larger will be that area ; the more remote, the less. Here 
 then is a provision by means of which we may learn to 
 judge of the relative distance of a known object. But 
 has the eye no original measure for, or perception of dis- 
 tance ? It appears by a remarkable case, recorded by Che- 
 selden, that it has not. This philosophic surgeon, after 
 performing the operation of couching, studied the effect of 
 the first visual impressions upon his patient, which he de- 
 scribes in the following words. 
 
 " This young gentleman either had been born blind, or 
 had lost his sight so early, that he had no remembrance of 
 ever having seen : the blindness arose from a cataract, or 
 opaque crystalline, in both eyes. Like other persons who 
 have ripe cataracts, he was not so blind but that he could 
 discern day from night, and for the most part in a strong 
 light distinguish black and white and scarlet. When he 
 first saw, he was so far from making any judgment about 
 distances, that he thought all objects whatever touched his 
 eye (as he expressed it), as what he felt touched his skin. 
 He knew not one thing from another, however different in 
 shape or magnitude ; but upon being told what things were, 
 whose form he before knew from feeling, he would carefully 
 observe that he might know them again. Two months after 
 being couched, his attention seems to have been drawn to 
 the effects of painting, which he then first and at once com- 
 prehended : but even then he was no less surprised, expect- 
 ing the pictures would feel like the things they represented, 
 and was amazed when he found those parts, which by their 
 light and shadow appeared round and uneven, felt only flat 
 like the rest ; and asked which was the lying sense, feeling 
 or seeing ? 
 
 " Being shown a small miniature of his father, and told 
 what it was, he acknowledged a likeness, but was vastly 
 surprised, asking how it could be that a large face could be 
 expressed in so little room, saying it should have seemed 
 as impossible to him, as to put a bushel into a pint. At 
 first he could bear but very little light, and the things he 
 
Case mentioned by Cheselden. 285 
 
 saw he thought extremely large ; but upon seeing things 
 larger, those first seen he conceived less, never being able 
 to imagine any lines beyond the bounds he saw. The room 
 he was in, he said, he knew to be but part of the house, 
 yet he could not conceive that the whole house could look 
 bigger. Before he was couched, he expected little advan- 
 tage from seeing worth undergoing an operation for, except 
 reading and writing ; for he said, he thought he could have 
 no more pleasure in walking abroad than he had in the 
 garden, which he could do very safely and readily; and 
 even blindness, he observed, had this advantage, that he 
 could go anywhere in the dark, much better than those 
 who can see : and after he had seen, he did not soon lose 
 this quality, nor desire a light to go about the house in the 
 night. He said every new object was a new delight, and 
 the pleasure was so great that he wanted ways to express it : 
 but his gratitude to Mr. Cheselden he could not conceal, 
 never seeing him for some time without tears of joy and 
 other marks of affection. A year after first seeing, being 
 carried upon Epsom Downs, and observing a large prospect, 
 he was exceedingly delighted with it, and called it a new 
 kind of seeing. And now being lately couched of his other 
 eye, he says that objects at first appeared large to this eye ; 
 but not so large as they did at first to the other ; and looking 
 upon the same object with both eyes, he thought it looked 
 about twice as large as with the first couched eye only, but 
 not double that he can any ways discover 5 *." 
 
 By part of these interesting details it appears evident, 
 that the sense of sight originally gives us no information 
 respecting either the distance or real magnitude of objects, 
 and that there is no essential resemblance between the ideas 
 communicated by vision and by feeling. The early years of 
 life are instinctively employed in learning to interpret the 
 visible signs of external objects. For this purpose, as soon as 
 there is intelligence in an infant's gaze, it extends its hands 
 to touch and examine each object in succession which at- 
 tracts its notice. 
 
 * Phil. Trans, abridged, vol. vii, p. 491. 
 
286 Knowledge of the Magnitude and Distance 
 
 The eye has no original measure for distance, and gives us 
 no certain notion of real magnitude. When the eye is fixed 
 upon a point on the wall of a narrow chamber, or in the 
 vault of heaven, it seems to command an oval or circular 
 area of equal visual dimensions : a foot-rule under these cir- 
 cumstances held at the distance of a few inches before the 
 eye measures equally the side of the room or a segment of 
 the firmament. 
 
 When the actual size of an object is unknown to us, 
 and we look at it, if at a certain degree of remoteness, with 
 both eyes, or if near with one eye only, we judge of its dis- 
 tance by the greater Or less indistinctness of its colour and 
 outline. We judge of its real magnitude by a calculation 
 founded upon its apparent size and probable distance. 
 Hence we are liable to continual mistakes on these points. 
 An Englishman in the clear atmosphere of Italy supposes 
 distant objects to be nearer to him than they are. We 
 think the moon larger when near the horizon than when 
 above our heads ; near the horizon the moon is more dim, 
 we therefore by analogy suppose her more remote ; but her 
 visual diameter being really the same, we therefore are 
 persuaded that her disk is broader. 
 
 Hitherto we have considered sight in reference to vision 
 with a single eye ; but habitually we employ both eyes ; 
 and it is interesting to inquire what are the conditions 
 which render vision under these circumstances single or 
 double. 
 
 It is to be borne in mind that the centre of the retina, 
 from whatever cause it proceed, furnishes the most distinct 
 vision. Hence in looking at a point of an object we in- 
 variably direct the axis of the eye towards it ; and when we 
 look with one eye at a succession of objects placed in a line 
 directly before us, but at different distances, the optic axis 
 is seen to incline inwards when we regard the nearest object, 
 and to increase its direction outwards as we view those which 
 are more remote. 
 
 Now when we look with both eyes at any one of such 
 a series of objects, it appears single, the rest appear double. 
 This familiar but remarkable phenomenon has given rise to 
 
of Objects, how obtained. 287 
 
 the hypothesis that there are corresponding points in either 
 retina; it is supposed that when an object is delineated 
 upon those points of the two retinae which are naturally 
 associated, it appears single, and double under other cir- 
 cumstances. But it seems unnecessary to resort to this 
 explanation of the fact. It has been already shown that 
 objects are seen in a definite direction; when therefore it 
 happens that the visual direction of an object is the same or 
 nearly the same for both eyes, that object appears single ; 
 when different, the object appears double. In both cases 
 two objects are seen : but in single vision they are seen in 
 the same place, and therefore necessarily appear to form but 
 one : the images coincide, and are therefore essentially in- 
 distinguishable. 
 
 It is easy through another simple artifice to render vision 
 double. By pressure with the finger we may raise or de- 
 press one eyeball, when the object seen by that eye appears 
 to shift its place, as the position of the organ is varied. 
 The effect, which is thus produced at will in an experiment, 
 sometimes occurs as the result of disease. M. Magendie 
 mentions the case of a gentleman in whom, from palsy of 
 the third nerve, the left eye is permanently drawn outwards ; 
 the consequence of which, he observes, is, that with that 
 eye the patient sees objects in their wrong place, " deplaces 
 de vingt a vingt cinq degres a droite de leur position." The 
 case is curious, but not without its parallel ; and the ac- 
 count of the result of the displacement of the eye is incor- 
 rect. It is not true that the object is seen by the averted 
 eye out of its true position ; the proof of which is, that an 
 eye thus affected, or similarly pushed aside for experiment's 
 sake, will take as true an aim as before, or look along a line 
 as justly towards a remote object. The object is seen appa- 
 rently in two places, yet both eyes see truly. This para- 
 doxical circumstance renders evident one of the most curious 
 provisions in our frame, namely, the extreme nicety with 
 which the two eyes are co-adjusted, so that their impressions 
 may exactly tally. 
 
 The convergence of the optic axes has to do in a certain 
 degree with our appreciation of distance and real magni- 
 
288 Convergence of the Optic Axes. 
 
 tude. When, indeed, objects are placed at such a distance 
 that in regarding them the optic axes remain parallel, our 
 notions upon these points are entirely derived in the ways 
 already explained. But when they are situated nearer, the 
 sensation attending each degree of inclination of the optic 
 axes enters as an important element into our estimate. 
 Mr. Wheatstone has shown, in a paper he is about to pub- 
 lish, that if by artificial means the usual relations which 
 subsist between the degree of inclination of the optic axes 
 and the visual angle which the object subtends on the 
 retina be disturbed, some extraordinary illusions may be 
 produced. Thus the magnitude of the image remaining 
 constant on the retina, its apparent size and distance may 
 be made to vary with every alteration of the angular incli- 
 nation of the optic axes. The author also proves, that the 
 adaptation of the eye to distinct vision exercises no modify- 
 ing influence on these perceptions ; and, contrary to the 
 opinions of Dr. Wells and other eminent optical writers, 
 that there exists no necessary connection between this adap- 
 tation and the convergence of the axes. 
 
 One of the most remarkable results of Mr. Wheatstone's 
 investigations respecting binocular vision is the following. A 
 solid object being placed so as to be regarded by both eyes, 
 projects a different perspective figure on each retina ; now if 
 these two perspectives be accurately copied on paper, and 
 presented one to each eye so as to fall on corresponding 
 parts, the original solid figure will be apparently reproduced 
 in such a manner that no effort of the imagination can 
 make it appear as a representation on a plane surface. This 
 and numerous other experiments explain the cause of the 
 inadequacy of painting to represent the relief of objects, 
 and indicate a means of representing external nature with 
 more truth and fidelity than have yet been obtained. It 
 .would require too much space to enter upon the physiological 
 views to which these experiments have led their author. 
 
 For perfect vision with the human eye, it seems requisite 
 that the rays of light should undergo no reflection after 
 reaching the retina. To provide for this object, the delicate 
 membrane called the chorioi'd, which immediately contains 
 
Use of the Pigmentum Nigrum. 289 
 
 the retina, secretes in the human eye a black mucus called 
 the pigmentum nigrum, which has the effect of absorbing 
 the rays of light which have once reached the retina. 
 Those in whom this black pigment is wanting have a weak 
 sight, and only see distinctly in an obscure light. We may 
 suppose the retina in such cases liable to be dazzled by the 
 reflection of part of the light from the vascular chorioi'd. 
 On the other hand there are animals, which habitually seek 
 their prey in the dusk ; in these and in several instances 
 where the final cause of the peculiarity of structure is not 
 equally obvious, the back part of the chorioi'd is covered 
 with a membrane termed the tapetum lucidum, which pre- 
 sents a brilliant reflecting surface. The lustre of the eyes 
 of cats in an obscure place results from this cause. It is 
 supposed that the double impression of a low degree of 
 light upon the retina may be equivalent to the single im- 
 pingement of brighter light. M. Magendie ingeniously 
 compares with this disposition of parts a structure observed 
 by himself in the eyes of birds remarkable for their acute 
 vision. In the eagle, the retina lies in numerous folds, so 
 that we may suppose it several times perforated by the rays 
 of light. 
 
 The eye of the Albino is remarkable for its want of pig- 
 mentum nigrum, in consequence of which the pupil and the 
 iris are coloured of different shades of red. In such persons 
 vision is weak in the ordinary light of day, and distinct 
 only in a darkened room or at twilight. The eyes of 
 Albinoes are likewise observed to be in perpetual motion, 
 unconsciously oscillating from side to side, even when their 
 sight is most steadily bent upon an object. There can be 
 little doubt that this provision is intended to save the un- 
 protected retina, by preventing a continued impression of 
 undue intensity upon one point. Other people use one part 
 of the retina for perfect vision, and direct it successively 
 towards the different points of an object while examining 
 it : the Albino uses several, continually alternating from one 
 to the other. The motion is unattended with any apparent 
 change of place in the object (such as that adverted to 
 when the eye is pushed or drawn aside), upon the same 
 
290 The Action of the Iris 
 
 principle as when for experiment's sake we intentionally 
 roll the eye from side to side : the scene before us in either 
 case remains visibly stationary, because the parts of the 
 retina upon which each point of an object is successively 
 delineated, are in their turn brought opposite to the same 
 point in space. 
 
 The principal use of the iris appears to be, to equalize the 
 quantity of light admitted within the eye under different 
 circumstances. It is well known that the aperture of the 
 iris, or the pupil, is diminished when light is more intense, 
 and enlarges under a more obscure light. What principally de- 
 serves attention in this phenomenon, is the mechanism through 
 which a change in the diameter of the pupil is produced. 
 
 The most ready manner of accounting for the alteration of 
 the size of the pupil is to suppose the substance which 
 forms the unattached margin of the iris irritable. In many 
 instances the iris distinctly consists of two portions, which 
 appear from their colour to be differently organized of an 
 outer broader part, and an inner narrow ring. In birds 
 especially, in which the pupil is as mobile as their vision is 
 perfect, the inner ring of the iris generally presents a hue 
 totally different from the outer, and beginning at an abrupt 
 line. In a parrot belonging to Mr. Hawes, of which I do 
 not know the species, the inner ring is grey or slate-coloured, 
 the outer ring yellow or orange. If the eye of this animal 
 is attentively watched, the grey inner ring of the iris may 
 be observed, when the pupil contracts, to become sensibly 
 narrower, as if it were the part that acted. I have not 
 observed a similar change, however, in the iris of any other 
 bird, though many have the iris similarly coloured. 
 
 Upon watching the eye of a cat or of a hawk, the con- 
 traction of the pupil appears often to be voluntary. When 
 the eye of the animal is bent upon an object that excites its 
 attention, yet which does not shift its position, the pupil 
 may be seen to enlarge and to contract alternately. The 
 animal is probably employed in examining the object under 
 different lights by intentionally admitting more or fewer 
 rays through the pupil. 
 
 Another remarkable circumstance concurs with the pre- 
 
in certain Animals distinctly voluntary. 291 
 
 ceding in establishing a resemblance between the action of 
 the iris and that of voluntary muscles. The iris receives 
 nerves from two sources, from the sentient part of the fifth, 
 and from the third : the main part of the latter is distri- 
 buted as a voluntary nerve to the muscles of the eye. Now 
 if the head of a pigeon be cut off, and, instantly after, the 
 upper part of the cranium be removed, and the entire brain 
 be taken out, on pinching the portion of the third nerve 
 which remains attached to the eye, I observed that the pu- 
 pil is contracted suddenly, just as the biceps flexor cubiti 
 acts in an animal recently killed, when the nerve which 
 supplies that muscle is pinched. A similar injury to the fifth 
 nerve produces no visible effect. 
 
 If the third nerve be divided in the cranial cavity, while the 
 animal is alive, the pupil immediately dilates to the utmost, 
 and remains afterwards immoveable, the iris being seemingly 
 paralysed. When again the third nerve is pinched in the 
 cranial cavity of a young cat instantly after death, the iris 
 will occasionally act as in the pigeon. In either case the ex- 
 posure of the nerve must be very promptly executed, or the 
 effect described does not happen. 
 
 I have already mentioned the curious changes which 
 M. Magendie observed to ensue gradually in the eyes of 
 rabbits after the division of the fifth nerve ; but another re- 
 markable effect followed instantaneously : the pupil became 
 diminished to a point, arid the eye was* apparently blind. 
 Blindness, however, had not appeared to ensue in pigeons 
 in which I had before this made the division of the fifth 
 nerve, and I have subsequently ascertained that the divi- 
 sion of the fifth nerve in the cranial cavity of a cat produces 
 no such effect ; and M. Magendie has likewise since found, 
 that if a bright light be concentrated with a lens upon the 
 eye of the rabbit after the same experiment, the retina is 
 evidently sensible to the impression. But the contraction 
 of the pupil in this experiment remains unexplained; a 
 singular anomaly, placed perhaps in a still stronger light by 
 the following experiment which I have repeated several 
 times. A young rabbit being killed, the upper part of the 
 cranium was immediately removed, together with the cere- 
 
292 State of the Pupil in Death. 
 
 brum. The optic nerve thus exposed was pricked, and then 
 divided ; no movement of the iris ensued : the third nerve 
 was pricked and then divided ; the iris exhibited no change : 
 the fifth nerve was then slightly compressed, when the pupil 
 became contracted, not suddenly, but slowly and gradually, 
 and then slowly dilated again : upon now dividing the fifth, 
 the pupil became contracted to the utmost, but in a gradual 
 manner, although more promptly than when compressed only, 
 and remained in this state. It is difficult to explain this 
 singular phenomenon. But it should be mentioned in con- 
 nection with it, that in the cat and pigeon, in which the 
 iris is paralysed by the division of the third nerve, and the 
 pupil remains permanently dilated afterwards, the pupil 
 dilates likewise in death. In the rabbit, on the contrary, 
 the pupil contracts as soon as life is entirely extinguished. 
 
 It remains uncertain what properties the human iris is 
 endowed with. It is probable that its inner unattached edge 
 is capable of voluntary contraction : but being accustomed to 
 employ it on two occasions alone (when the light thrown on 
 objects or their distance varies), we lose part of our original 
 control over it. Such appears to be the condition of the 
 muscles of the soft palate, which most persons are capable 
 of moving in one or two combined actions only ; but they 
 are not the less under the influence of the will ; and some 
 persons are found, according to M. Magendie, who can 
 move them separately at pleasure. 
 
 If light be too intense, the eye is dazzled, and objects are 
 no longer distinguished : if the quantity of light be very in- 
 considerable, no adequate impression is made upon the re- 
 tina, and vision does not take place. If again we enter sud- 
 denly an obscure chamber not absolutely dark out of bright 
 daylight, for a few seconds we discern nothing ; but the eye 
 quickly accommodates itself to the obscurer light, and vision 
 is restored. 
 
 Under any advantage of light it appears that objects are 
 only perfectly seen when within a certain range of distance. 
 The image of an object upon the retina is diminished in 
 proportion as its distance is increased ; and when the space 
 the image occupies is reduced to less than a certain dimen- 
 
The Eye adjusts itself to Vision at different Distances. 293 
 
 sion, it wholly ceases to produce sensation. This remark, 
 it will be seen, bears upon an expression that has been em- 
 ployed in the preceding pages, and which, though it be 
 convenient to retain it, must be taken with some modifica- 
 tion of its meaning. The cone of rays which enters the pupil 
 from any visible point of an object is said to converge to a 
 focal point upon the retina ; it is obvious, that such a focal 
 point is very different from a point in the strict mathe- 
 matical sense of the word ; it signifies only a very small 
 circle. 
 
 But there is another cause, why the range of perfect vi- 
 sion has its limits, which has been already in part illus- 
 trated. It appears by the phenomena of myopic and pres- 
 byopic eyes, that a very nice arrangement of the rays of 
 light upon the retina is necessary for distinct vision ; it is 
 not therefore wonderful that we cannot see perfectly at all 
 distances ; but on the contrary it ought rather to excite our 
 admiration, that we are able to see objects with any degree 
 of distinctness at more distances than one. When we con- 
 sider how different the angle must be at which the marginal 
 rays of each cone reach the eye from objects at different 
 distances, it is reasonable to suppose that the focal length 
 of the eye adapted to one case must be essentially unfit for 
 any other. Nevertheless we are not conscious of making an 
 effort to produce a change in the refractive power of the eye, 
 at the time we direct our attention from a near object to one 
 more remote. 
 
 A simple experiment, however, serves at once to prove, 
 that when the eye is capable of seeing distinctly objects at 
 one distance, it is unfit to distinguish objects at any other, 
 and that we possess a voluntary power of instantaneously 
 altering the focal length of the eye. 
 
 If a clear straight line be drawn with a pen upon a plane 
 white surface from a foot to two feet in length, and the eye 
 be placed just above the level of the white surface, and be 
 directed along the black line, the latter will appear distinct 
 at one point only, on either side of which it appears con- 
 fused, and spread over a widening space. If the eye be fixed 
 upon a point nearer than that first looked at, but within the 
 
 T 
 
294 Mechanism by which the Eye alters its focal Length. 
 
 limits of distinct vision, the nearer point becomes defined, 
 and the remote point confused. 
 
 In Dr. Young's optometer a single line is seen through 
 several narrow slits in a thin brass plate, two or more of 
 which correspond with the aperture of the pupil. Hence it 
 happens, that except at the point to which the eye is ad- 
 justed, the line appears double or triple : or the lines are 
 seen to cross at the point at which vision is distinct ; and 
 the crossing of the lines may be made to appear more or less 
 remote by directing the attention successively to different 
 points of the surface. By means of a convergent lens, the 
 effect of infinite distance is given to the length of a few 
 inches upon the optometer, and a graduated scale shows the 
 true distance at which vision is distinct. 
 
 At eighteen or nineteen years of age, a good eye should 
 be capable of adjusting itself to objects situated at any 
 point between five or six inches from the eye and infinite 
 distance, or even of bringing to a focal point upon the retina 
 convergent rays. As life advances, the power of adjusting 
 the eye is continually diminished by an increasing inability 
 to distinguish near objects. Between fifty and sixty, the 
 refractive power of an eye originally perfect is qualified to 
 bring to a focus parallel rays only, or the power of adjust- 
 ment is wholly lost. A myopic eye does not, as it is usually 
 supposed, acquire a long sight in the advance of life ; it 
 possesses at first a certain power of adjustment, as for in- 
 stance, between four and twelve inches ; and when the power 
 of adaptation is lost, its vision, like that of an eye origi- 
 nally good, continues perfect at the remotest point to which 
 its powers of adj ustment originally extended. 
 
 The mechanism by which the eye alters its focal length 
 remains in obscurity, notwithstanding the numerous attempts 
 that have been made to explain it. 
 
 An experiment made by Dr. Young, contravenes the sup- 
 position that the change produced consists in an alteration 
 of the form of the cornea. A convex lens fixed in a socket, 
 which contained water, and the edges of which were secured 
 with wax, was applied to the eye, so that the cornea entered 
 half way into the socket, and was everywhere in contact 
 
Mechanism by which the Eye alters its Focal length. 295 
 
 with the water : the eye immediately became presbyopic ; 
 but upon the addition of another convex lens to make up 
 for the loss of the convexity of the cornea, vision was re- 
 stored to its natural state, and the eye regained the power of 
 adjustment *. 
 
 Other experiments, made by Dr. Young, set aside the 
 supposition that a change takes place in the length of the 
 axis of the eye, to fit it for vision at different distances ; 
 if experiments are indeed necessary to disprove the applica- 
 tion to this delicate organ of any considerable pressure, of 
 which we have no consciousness at the time when upon this 
 hypothesis it should take place. 
 
 Dr. Young himself concludes that the means of adjust- 
 ment consist in a change of form in the crystalline, the fibres 
 of which he describes, and which he supposes to be irritable. 
 But it does not appear from direct experiment that the crys- 
 talline possesses irritability ; and if faith can be attached to 
 a single well-attested observation upon a point so delicate, 
 the instance of Henry Miles, recorded by Sir Everard Home, 
 proves that the eye may retain its power of adjustment after 
 the removal of this part f 
 
 The only evident change in the eye, when adjusting its 
 focal length to different distances, is an alteration in the 
 diameter of the pupil. The pupil enlarges when a distant 
 object is seen, and diminishes when we look at a nearer 
 point. Upon a superficial analogy we might conclude, that 
 these changes are sufficient to produce the requisite altera- 
 tions of the focal length of the eye : for by viewing objects 
 through a series of pinholes in a card, the largest smaller 
 than the aperture of the pupil and each of the rest in suc- 
 cession smaller than the last, the eye is rendered capable of 
 seeing distinctly at the distance of four, of three, and even 
 of two inches. When, however, the correctness of this hy- 
 pothetical explanation is put to the test of direct experi- 
 ment, it proves to be fallacious. 
 
 * Phil. Trans, vol. xci, p. 58. 
 t Phil. Trans, vol. xcii, p. 8. 
 T 2 
 
296 The Eye adjusts itself to different Distances. 
 
 In investigating the point under consideration, I availed 
 myself of the assistance of Mr. Robinson, of Devonshire 
 Street, a very ingenious artist, who makes the optometer 
 contrived by Dr. Young, and who is conversant with the use 
 of that instrument. 
 
 A room was darkened by half closing the shutters, and I 
 attentively observed the state of the pupil, when Mr. Ro- 
 binson directed his eye to a definite point upon the opto- 
 meter : the pupil was of course considerably dilated : the 
 shutters being then opened, the pupil instantly contracted, 
 but the point upon the optometer at which the lines crossed 
 did not shift its place. 
 
 When by some practice I had accustomed my own eye to 
 the use of the optometer, I compared its range in the 
 brightest and in the obscurest light in which the lines were 
 visible, and observed no apparent difference in the two 
 cases. Mr. Robinson made a similar observation. Either of 
 these experiments prove that the change in the size of the 
 pupil is not the means by which the adjustment of the eye 
 to distances is effected. But an additional fact may be 
 mentioned. In an old lady of sixty-seven, whose sight in 
 early life was remarkably good, but whose eyes can now 
 only bring to a focus parallel rays, the pupil retains its mo- 
 bility perfectly under variations of light; and even sensibly 
 moves upon her making ineffectual attempts to read without 
 spectacles a page held at different distances from her. 
 
 It deserves remark, that after the eye has had some prac- 
 tice in accommodating itself to exact vision at different 
 distances, it is easy when an object, as for instance a 
 screen, is held at the distance of six or seven inches, and 
 has been for a few seconds distinctly seen, to adjust at plea- 
 sure the focal length of the eye for vision at a remoter point : 
 under these circumstances the object held before the eye 
 becomes confusedly seen ; the optic axes diverge, and the 
 pupil dilates. In a similar way the eye may be adjusted at 
 pleasure to a shorter distance, at which no visible object is 
 situated : thus a power appears to be acquired of voluntarily 
 influencing the action of the iris. 
 
Extent of the Field of Vision. 297 
 
 I have already observed that one part of the retina appears 
 habitually used for accurate vision : I cannot better illustrate 
 this subject than by making the following extract from a 
 paper of Dr. Young's in the Philosophical Transactions. 
 
 " The visual axis (observes Dr. Young) being fixed in any 
 direction, I can at the same time seeffa luminous object 
 placed laterally at a considerable distance from it ; but in 
 various directions the angle is very different. Upwards it 
 extends to 50 degrees, inwards to 60, downwards to 70, and 
 outwards to 90 degrees. These internal limits of the field 
 of view nearly correspond with the external limits formed 
 by the different parts of the face, when the eye is directed 
 forwards and somewhat downwards, which is its most na- 
 tural position ; although the internal limits are a little more 
 extensive than the external ; and both are well calculated 
 for enabling us to perceive the most readily such objects as 
 are likely to concern us. Dr. Wollaston's eye has a larger 
 field of view, both vertically and horizontally, but nearly in 
 the same proportions, except that it extends further up- 
 wards. It is well known that the retina advances further 
 forwards towards the internal angle of the eye than towards 
 the external angle; but upwards and downwards its extent 
 is nearly equal, and is indeed every way greater than the 
 limits of the field of view, even if allowance is made for the 
 refraction of the cornea only. The sensible portion seems 
 to coincide more nearly with the painted chorioid of qua- 
 drupeds; but the whole extent of perfect vision is little more 
 than ten degrees ; or more strictly speaking, the imperfec- 
 tion begins within a degree or two of the visual axis, and at 
 the distance of five or six degrees becomes nearly stationary, 
 until at a still greater distance vision is wholly extinguished. 
 The imperfection is partly owing to the unavoidable aberra- 
 tion of oblique rays, but principally to the insensibility of 
 the retina ; for if the image of the sun itself be received on 
 a part of the retina remote from the axis, the impression 
 will not be sufficiently strong to form a permanent spec- 
 trum, although an object of very moderate brightness will 
 produce this effect when directly viewed. The motion of 
 the eye has a range of about 55 degrees in every direction, 
 
298 Retina insensible to the ordinary Impressions of Light. 
 
 
 
 so that the field of perfect vision, in succession, is by this 
 motion extended to 110 degrees *. 
 
 Mariotte discovered the curious fact, that there is a cer- 
 tain part of the retina insensible to the ordinary impressions 
 of light. The most ready way of making the experiment 
 which proves this, is to look steadfastly with one eye, the 
 other being closed, at a mark on a sheet of white paper, 
 placed at the ordinary reading distance from the eye ; and 
 whilst the eye thus remains stationary, to move a coloured 
 wafer along the surface of the paper on the external side of, 
 and on the same horizontal line with the mark. At a cer- 
 tain point in this line, the wafer will completely disappear ; 
 but it may be rendered again visible, by moving it either 
 farther from or nearer to the fixed mark. This insensible 
 part may be shown to correspond with the place at which 
 the optic nerve enters. This circumstance induced Mariotte 
 to consider the chorioi'd as the seat of vision rather than 
 the retina; for, argues he, here is no deficiency of that 
 nervous matter of which the retina is the expansion, but 
 the chorioi'd is wanting. The following experiment of 
 Purkinje's will show the erroneousness of this conclusion, 
 which has not wanted supporters among modern physiolo- 
 gists. By repeating the above experiment, substituting the 
 flame of a candle for the wafer, he has proved, that though 
 no image of the object is formed at this part, it is still not 
 insensible to light, for a diffused reddish light appears to 
 occupy the place of the flame. It is not the optic nerve 
 which is insensible, as Mario tte's hypothesis supposes ; but 
 the objects are invisible, in consequence of being placed in 
 the projection of the central artery which accompanies it. 
 The red nimbus results from the passage of light through 
 this blood-vessel, the irregularity and semi-transparency of 
 which prevents it from transmitting the image. 
 
 Dr. Wollaston described a partial and temporary insensi- 
 bility of the retina in both eyes which twice occurred to him- 
 self, and which has directed attention to similar cases. The 
 following are Dr. Wollaston's words. 
 
 * Phil. Trans, vol. xci, p. 46. 
 
Remarkable simultaneous Affection of both Retina. 299 
 
 " It is now more than twenty years since I was first af- 
 fected with the peculiar state of vision to which I allude, 
 in consequence of violent exercise I had taken for two or 
 three days before. I suddenly found that I could see but 
 half the face of a man whom I met ; and it was the same 
 with respect to every object I looked at. In attempting to 
 read the name JOHNSON over a door, I saw only SON ; 
 the commencement of the name being wholly obliterated to 
 my view. In this instance the loss of sight was toward my 
 left, and was the same whether I looked with the right eye 
 or the left. This blindness was not so complete as to amount 
 to absolute blackness, but was a shaded darkness without 
 definite outline. The complaint was of short duration, and 
 in about a quarter of an hour might be said to be wholly 
 gone, having receded with a gradual motion from the centre 
 of vision obliquely upwards toward the left. 
 
 " Since this defect arose from over-fatigue, a cause com- 
 mon to many other nervous affections, I saw no reason to 
 apprehend any return of it, and it passed away without need 
 of remedy, without any further explanation, and without my 
 drawing any useful inference from it. 
 
 " It is now about fifteen months since a similar affection 
 occurred again to myself, without my being able to assign 
 any cause whatever, or to connect it with any previous or 
 subsequent indisposition. The blindness was first observed, 
 as before, in looking at the face of a person I met, whose 
 left eye was to my sight obliterated. My blindness was in 
 this instance the reverse of the former, being to my right 
 (instead of the left) of the spot to which my eyes were di- 
 rected ; so that I have no reason to suppose it in any man- 
 ner connected with the former affection. 
 
 " The new punctum caecum was situated alike in both 
 eyes, when at an angle of about three degrees from the 
 centre; for when any object was viewed at the distance of 
 about five yards, the point not seen was about ten inches 
 distant from the point actually looked at. 
 
 " On this occasion the affection, after having lasted with 
 little alteration for about twenty minutes, was removed sud- 
 denly and entirely by the excitement of agreeable news re- 
 
300 Remarkable simultaneous Affection of both Retina. 
 
 specting the safe arrival of a friend from a very hazardous 
 enterprise." 
 
 Dr.Wollaston was led to infer from the symptoms which 
 have been described, a peculiarity of structure in the com- 
 missure of the optic nerves, the existence of which has been 
 confirmed by anatomical examination. It has been already 
 mentioned, that the outer fibrils of the tractus opticus of one 
 side are continued to form the outer part of the optic nerve 
 of the same side, and that the fibrils next in order pass over 
 to the inner and central part of the opposite nerve : thus 
 the parts of the two retinae, on which the same part of an 
 object is delineated, are probably supplied from one nerve. 
 
 In the plate which I have given in a former section of the 
 origins of the cerebral nerves, I have delineated the structure 
 of the commissure of the tractus optici. Not the least cu- 
 rious part in it, is its containing fasciculi which do not 
 reach either eye, but pass from one thalamus to the oppo- 
 site. I introduce in the present section, having accidentally 
 omitted it in the preceding, a figure of the brain of the 
 mole, which explains the nature of these fasciculi. In the 
 mole, the optic nerve, with the third nerve, the fourth, and 
 sixth, are entirely wanting. The little rudimental eye is 
 probably an organ of touch alone : it is supplied by a 
 branch of the fifth : the letter V in the figure on the next 
 page is placed on the fifth nerve. The letter C represents 
 commissural fasciculi, which correspond with the posterior 
 fasciculi above adverted to, in the commissure of the optic 
 tracts in man. Traced in their retrograde course, these fas- 
 ciculi pass as tractus optici to thalami, in this instance mis- 
 called thalami nervorum opticorum. Or the thalami nervo- 
 rum opticorum are thus shown to be of much less import- 
 ance as matrices of the optic nerves, than as cerebral organs, 
 which originate masses of divergent fasciculi in the brain. 
 
Remarkable simultaneous Affection of both Retina. 301 
 
 
 The eyes of different animals vary remarkably in their ca- 
 pability of being directed at the same time to the same ob- 
 ject. In some again a connection exists between the two 
 optic nerves ; in others the optic nerves are separate, from 
 their origin to their termination. In several species of fish 
 the nerves distinctly cross without intermixture from the 
 thalamus of one side to the eye of the opposite. In birds 
 the optic nerves cohere near their origin. It has been ob- 
 served in birds, that the degree of blindness, which is pro- 
 duced by opacity of the cornea, is alone sufficient in the 
 space of three weeks to produce wasting and discoloration 
 of the optic nerve, which extends to the tubercle of the op- 
 posite side ; and conversely, that if the optic tubercle be in- 
 jured on one side, blindness of the opposite eye immediately 
 ensues. In human beings, atrophy of the optic nerve fol- 
 
302 Of the Action of the Recti Muscles. 
 
 lows blindness very slowly, and the same alteration is not 
 supposed to be continued beyond the commissure. Never- 
 theless I have witnessed in one instance a discoloration of 
 the optic nerve on one side joined with a similar appearance 
 for a short extent upon the opposite tractus ; but the inter- 
 mediate portion of the commissure was white, and of the 
 previous history of the case nothing was known. 
 
 In the preceding details the movements of the eyeball 
 have been occasionally referred to : we may now examine 
 the contrivances provided for this purpose, and the nature 
 of the external parts intended for the protection of the organ 
 of vision. 
 
 The optic nerve, of which about an inch is interposed 
 between the foramen opticum and the eyeball, contributes 
 to hold the eye forward towards the front of the orbit. The 
 intervals between the different parts contained in the orbit 
 are filled with adipose substance. 
 
 Six muscles are inserted into the sclerotic coat of the eye, 
 of which four are termed recti, and two obliqui. 
 
 The recti are thin flat muscles which rise from the margin 
 of the foramen opticum, and extend, one over the upper 
 part, one upon the outside, a third upon the inside of the 
 eyeball, and a fourth below it, to be inserted each by a broad 
 thin tendon into the sclerotic at about five lines from the 
 edge of the cornea. 
 
 The four recti are distinguished individually by the 
 names of, superior, inferior, internus, and externus, with 
 which the terms attollens, deprimens, adducens, and abdu- 
 cens, are used synonymously. By careful dissection a layer 
 of membrane may be separated from the part of the sclerotic 
 between the insertion of the recti and the cornea. This 
 membrane is termed the tunica albuginea, and is considered 
 to be the aponeurosis of the recti muscles. 
 
 It is easy to understand that these muscles acting singly 
 would direct the eye to four equidistant points in a circle, 
 and acting in concert might turn the axis of the eye towards 
 all the intermediate points : and it is equally obvious that 
 they must exert a constant effort to retract the eye, against 
 which the elasticity of the optic nerve, and of the adipose 
 
Of the Action of the Obliqui. 303 
 
 substance in the orbit, would make very inadequate re- 
 sistance. 
 
 The two remaining muscles of the six appear intended to 
 counteract the effect last adverted to. 
 
 The obliquus superior or trochlearis rises from the upper 
 and inner part of the edge of the foramen opticum, and 
 advances obliquely forwards and inwards towards the mar- 
 gin of the orbit, where a loop of membrane is attached, 
 through which its tendon passes ; the tendon is subse- 
 quently reflected downwards, backwards, and outwards, to 
 be inserted into the upper part of the eyeball behind its 
 vertical axis. 
 
 The obliquus inferior oculi rises from the nasal process 
 of the superior maxillary bone, and passes obliquely outwards 
 and backwards below the eyeball, to be inserted into the 
 sclerotic within the rectus externus, and behind the trans- 
 verse axis of the eye. 
 
 The action of the obliqui is involved in some obscurity : 
 there can indeed be no doubt respecting their principal use; 
 by drawing the eye forwards they prevent that constant re- 
 traction which would otherwise be produced by the recti. 
 But individually they are calculated to give each its specific 
 direction to the eye : the obliquus superior points the optic 
 axis downwards and outwards ; the obliquus inferior, on the 
 other hand, directs the eye upwards and outwards. 
 
 What renders this question still more intricate, is, that 
 three nerves are employed to supply the six muscles that 
 have been described. The fourth nerve supplies the obli- 
 quus superior, the sixth supplies the rectus externus, and 
 the third supplies the remaining muscles. 
 
 It is remarkable again, that of the six muscles of the eye- 
 ball, three turn the optic axis directly or obliquely outward, 
 and that each of these three muscles is supplied by a dif- 
 ferent nerve ; two indeed have an entire nerve exclusively 
 distributed to each of them. 
 
 The intricacy of the muscular nerves of the eye admits, 
 however, of a conjectural explanation. We may remark, 
 that their distribution is not such as to allow of our op- 
 
304 Intricacy of the Nerves of the Orbit considered. 
 
 posing the recti to the obliqui : in following this indication 
 we are stopped by the fact, that the third nerve supplies 
 half or the greater part of each class. But from the close 
 anatomical relation between the origins of the third nerve 
 
 O 
 
 and of the fourth, we may conclude their function to be not 
 materially different ; whereas the sixth nerve rising from a 
 remote point, seems distinguished essentially from both the 
 others. 
 
 It appears to be a principle universally observed in the 
 construction of the nervous system, that nerves of motion 
 rise near the origin of those sentient nerves, through which 
 the actions they control are habitually guided or called into 
 play. 
 
 This principle, as I have already shown, is remarkably 
 exemplified in all the spinal nerves ; and in the distribution 
 of the fifth and seventh cerebral nerves ; and the origin of 
 the third and fourth nerves is perhaps sufficiently near that 
 of the optic nerve to bring them both under the same law. 
 Now when we investigate the origin of the sixth nerve, we 
 find it passing to the back part of the medulla oblongata, 
 so as to rise near the fifth and the seventh in other words, 
 it rises near those nerves which comprehend within their 
 functions the sensibility of the surface of the eye, an influ- 
 ence over the secretion of the lachrymal gland, and the 
 sense of hearing. When again we examine the distribution 
 of the sixth nerve, we find it forming the sole supply of a 
 muscle which has a remarkable consent with the three offices 
 alluded to. The rectus externus or abducens oculi, which 
 it supplies, directs the axis of the eye outwards. And we 
 may remark, 1, that when the optic axis is directed out- 
 wards, the surface of the eye is carried towards the orifices 
 of the ducts of the lachrymal gland : 2, that the reversion 
 of the eye for vision is commonly suggested by impressions 
 upon the organ of hearing : and, 3, as an instance of the 
 consent between the common feeling of the eye and the ac- 
 tion of the abductor, that when an animal is destroyed by 
 pithing, if while imperfect life yet remains in the head the 
 eyelids be rendered incapable of closing by the division of 
 
Of Squinting. 305 
 
 the portio dura, and the surface of the eye be then touched, 
 the motion of the eye to avoid the offending substance is in 
 a direction outwards. 
 
 When the eyelids are kept shut, the eyes are often in 
 motion. " Inter somnum quietum atque placidum (observes 
 Soemmering in his Icones Oculi Humani), bulbus oculi, ut 
 in ipsis somnolentis videre licet, paullo plus sursum tra- 
 hitur." In some instances this elevation of the axis of 
 the eye during sleep is very considerable, in others it is 
 very slight. 
 
 Squinting consists in a want of consent between the mus- 
 cles of the two eyes, through which defect the optic axes 
 are habitually directed towards different points. The incli- 
 nation of one eye inwards may be so great as to exclude it 
 from the vision of objects towards which the other is turned, 
 or may be so slight as to allow of the distorted eye taking 
 in part of the same field of vision with its fellow. In either 
 case it appears that those who squint, habitually neglect 
 the impressions upon the distorted eye, and see with but 
 one. 
 
 The cause of squinting is obscure : for though it fre- 
 quently happens that the eye which squints has an imper- 
 fect vision, so as to favour the supposition that it is in- 
 stinctively averted in order to prevent the perception of ob- 
 jects becoming confused ; yet in other cases, vision with 
 either eye is equally good, and the patient can at will em- 
 ploy either singly, but cannot prevent the other from turn- 
 ing away from the object of vision. 
 
 Perhaps in cases of the latter description the original ad- 
 justment of the two eyes is not true; so that if both were 
 directed towards the same object, it might necessarily ap- 
 pear double, upon the same principle as in the case recently 
 quoted from M. Magendie's works. 
 
 The parts employed for the protection of the eye are, the 
 eyelids with their muscles, the tunica conjunctiva, and the 
 lachrymal gland. 
 
 The eyelids are two folds of skin, to which shape and 
 firmness are given by two slips of cartilage termed the tarsi. 
 
306 Of the Eyelids and Tunica Conjunctiva. 
 
 Upon the surface at which the eyelids meet, the skin is 
 gradually transmuted into a mucous membrane termed the 
 conjunctiva, which lines the tarsal cartilages, and is re- 
 flected from the inner surface of the eyelids upon the 
 sclerotic coat, to cover the front of the eye, the tunica 
 albuginea, and the cornea. The tarsal cartilages have a 
 membranous joint at either corner, from which a ligament 
 extends to the adjoining bone : the ligament on the inside 
 is well denned, and* of a bright silvery colour, and is called 
 the tendo oculi ; it extends to the nasal process of the 
 superior maxillary bone : the external ligament is broader 
 and of a membranous character ; it extends to the frontal 
 process of the malar bone. 
 
 The opposed edges of the tarsal cartilages are so grooved 
 and sloped internally, as to form when they meet a 
 channel, which is closed at the back part by the eyeball. 
 The external edge of this groove is guarded by the strong 
 hairs which form the eye-lashes, and upon its inner edge 
 from thirty to forty thin white ducts open, which are termed 
 glands of Meibomeus ; they are filled with a white seba- 
 ceous or albuminous material. At the inner canthus of the 
 eye the tunica conjunctiva is reflected over a fleshy fold 
 termed the caruncula lachrymalis. The liquid which lubri- 
 cates the surface of the eye appears raised by this fold of 
 membrane to the apertures of the puncta lachrymalia, as the 
 two capillary tubes are termed, which absorb the liquid 
 from the surface of the eye ; they terminate in an oval bag, 
 termed the lachrymal sac, which is lodged in a fossa common 
 to the os unguis and superior maxillary bone, and transmits 
 the tears onward towards the nose. 
 
 The tears are a salt transparent liquid, a hundredth part 
 only of which consists of saline ingredients. Soda and 
 muriate of soda, phosphate of lime, and phosphate of soda, 
 with mucus and water, are the component parts of the 
 tears, according to Fourcroy and Vauquelin. The tears are 
 secreted by the lachrymal gland, a flattened circular body, in 
 structure and appearance resembling a salivary gland, 
 which is placed at the outer and upper part of the orbit : its 
 
Of the Tears. 307 
 
 five or six small ducts open at the neighbouring angle of 
 reflection of the tunica conj unctiva from the upper palpebra 
 upon the eyeball. 
 
 The lachrymal gland is supplied with two nerves from the 
 first division of the fifth : its secretion is remarkably under 
 the influence of the mind. Yet the surface of the eye does 
 not seem less moist than usual when the fifth nerve has 
 been divided, and it is questionable whether the liquid with 
 which it is generally lubricated be derived from the lachry- 
 mal gland or from its mucous covering. The remarkable 
 effect of dividing the fifth nerve upon the nutrition of the 
 eye has been already described : it deserves remark, that 
 the eye is rendered insensible to common stimuli by this 
 operation. Diluted liquor ammonise applied to the eye in 
 this state produces no inflammation of its surface, a 
 phenomenon extremely curious, when viewed in connec- 
 tion with the fact, that the operation itself produces a 
 violent inflammation of the tunica conjunctiva in twenty- 
 four hours. 
 
 When the optic axis is directed forwards, the eyelids 
 meet at the lower margin of the cornea. The lower eyelid 
 has little motion ; the upper eyelid alone is concerned in 
 the ordinary opening and shutting of the palpebrse. 
 
 The muscle which raises the upper eyelid is termed the 
 levator palpebra? superioris ; it rises from the margin of the 
 foramen opticum immediately above the rectus superior 
 oculi, and is inserted into the upper tarsal cartilage : it is 
 supplied by the third nerve. 
 
 The muscle which closes the eyelids is called the orbicu- 
 laris palpebranim ; it is disposed for some breadth beneath 
 the skin of the eyelids in concentric fasciculi. This mus- 
 cle is supplied by the fifth nerve and by the portio dura of 
 the seventh, and is paralized by the division of the latter. 
 The fifth nerve and the seventh rise together : the fifth im- 
 parts sensibility to the surface of the eye, to the eyelids and 
 eyelashes ; and the least irritation of these parts calls into 
 action the orbicularis palpebrarum, which receives its 
 stimulus through the portio dura of the seventh. If the 
 hand be moved rapidly before the eye at three inches dis- 
 
308 Of the Sensation of Touch. 
 
 tance from its surface, we are scarcely tempted to close the 
 eyelids ; but if it approach so near as sensibly to affect the 
 eyelashes by the displacement of the air, though we are 
 conscious that it threatens no injury, we find it scarcely 
 possible to refrain from winking. The consent between the 
 fifth and the seventh nerve in this instance seems as close as 
 that between the second and the third, or as the connection 
 between a vivid impression upon the retina and the contrac- 
 tion of the pupil. 
 
 SECTION II. 
 Of the Organ of Touch. 
 
 When the temperature of the media next to us varies 
 considerably from our own, we feel heat or cold : when 
 the pressure of surrounding substances is actually or re- 
 latively increased above that which we habitually sustain, 
 we feel the contact of bodies, their hardness, softness, 
 and the like. The preceding modes of sensibility consti- 
 tute the sense of touch. Parts which enjoy the sense 
 of touch are exquisitely alive to mechanical injury or chemi- 
 cal action. 
 
 The skin is the principal seat of touch ; but this sense is 
 shared by the mucous surfaces of the eyes and nose and 
 fauces, of the larynx, pharynx, and oesophagus, of the 
 rectum and urinary canal, and of the external part of the 
 uterine system, as well as by the voluntary muscles. 
 
 In some of the latter instances, the eye namely and the 
 larynx, the surface is much more acutely sensible than the 
 skin ; but it conveys not the same defined and accurate 
 impression as the skin itself. Different parts of the skin 
 likewise enjoy the sense of touch in different degrees. The 
 hand and fingers, the tips of the latter especially, have 
 practically the finest discrimination of the tangible qualities 
 of bodies; but it is difficult to determine how much of the 
 
Of Sensations of Heat and Cold. 309 
 
 superiority of the hand in touch may result from the happy 
 flexibility of its joints and the number of its muscles, by 
 which it can vary its form and pressure to suit the nature of 
 different substances. 
 
 Sensations of heat and cold are relative : the weather 
 which is mild in winter, appears cold to us in summer. 
 Like other sensations, these again essentially depend not 
 merely upon the present impression, but upon the condi- 
 tion of the sentient organ. Thus a patient occasionally 
 feels chilly, when the surface of his body seems to a by- 
 stander more heated than usual. The sensation of cold 
 in the preceding instance is analogous to the perception of 
 flashes of light before the eyes, when an apoplectic attack is 
 threatened. 
 
 Custom enables the skin to sustain without inconveni- 
 ence a degree of heat which naturally gives pain, and even 
 to resist the physical injury which it commonly produces. 
 Some extraordinary exhibitions have been presented to the 
 public, in which there evidently has been no deception, yet 
 in which the operator has applied heated liquids or heated 
 metals to the skin or tongue, without producing that vesi- 
 cation of the surface which another would have expe- 
 rienced under the same circumstances. 
 
 It is interesting to speculate upon the order in which the 
 sense of touch may be supposed to communicate to us 
 our first impressions respecting an external world, or to 
 analyze the precise evidence upon which our notions of 
 what are termed the primary qualities of matter are founded. 
 
 A sensation of touch resulting from the contact of a 
 foreign substance with the skin communicates a distinct 
 impression of its place. If sensations of touch be excited 
 at different parts of the surface of the body, and continue 
 long enough for the mind to compare them, the notion of 
 an intermediate space, together with the abstract idea of 
 extension, follows. If a foreign substance be moved upon 
 the surface of the body from one point to another, the 
 consciousness we have of its change of place gives origin to 
 the idea of motion. What we term roughness, smoothness, 
 
 u 
 
310 Influence of the Nerves of Touch over Nutrition. 
 
 and the like, are sensations produced by moving different 
 substances in contact with the skin. 
 
 Branches of the same sentient nerves, which supply the 
 skin, are distributed to voluntary muscles in conjunction 
 with their voluntary nerves : and muscles of this description 
 appear to enjoy in a very high degree a modified sense of 
 touch ; a peculiar sensation independent of that which is 
 felt upon the skin is produced by resistance to our mus- 
 cular efforts. It is from this muscular sense that we im- 
 mediately derive our notions of the hardness or softness, 
 and of the weight and momentum of bodies. 
 
 The something external, which is the cause why sensa- 
 tion occurs in us, we call matter. By combining the dif- 
 ferent sensations, which arise in us on the same occasions, 
 we form our notions of different material substances. We 
 suppose matter to be impenetrable, since we find that two 
 material substances cannot occupy the same place at once. 
 We suppose matter to be infinitely divisible, since we 
 cannot conceive a particle so minute as not to have two 
 surfaces that might admit of separation, much in the same 
 manner that we suppose space to be infinite, since the 
 imagination can always frame the idea of extension beyond 
 the greatest assignable distance. 
 
 The nerves which minister to the sense of touch are the 
 posterior roots of the spinal nerves, the large division 
 of the fifth, the nervi vagi, and the glosso-pharyngeal 
 nerves. 
 
 The body, the neck and occiput, and the limbs, are sup- 
 plied by the spinal nerves ; the face, temples, and fauces by 
 the fifth; the pharynx and oesophagus by the nervi vagi 
 and glosso-pharyngeal nerves. 
 
 It is remarkable that the nerves of touch have ganglions 
 near their origin. It is to this class of nerves that physio- 
 logists have commonly attributed the unconscious influence, 
 which is exercised by the nervous system over nutri- 
 tion. This conjecture does not appear to be without founda- 
 tion. 
 
 In an interesting case of anaesthesia mentioned by 
 
Influence of the Nerves of Touch. 311 
 
 Dr. Yelloly, in which, though sensation was almost wholly 
 extinguished in the fore-arms and hands and in the legs 
 and feet, yet the power of voluntary motion was not much 
 diminished, it was observed that an elevated temperature 
 more readily produced vesication of the skin than in healthy 
 persons ; that is to say, the palsy of the nerve, which ex- 
 periment has proved to be the nerve of touch, had deprived 
 the part of its physical capacity of resisting heat. 
 
 I have already mentioned M. Magendie's experiments of 
 dividing the fifth nerve in the cranial cavity, both at the 
 ganglion of Gasser and at a part nearer to the brain, and 
 the injurious effect in each case upon the structure of the 
 eye ; extending in the former to destructive ulceration, 
 in the latter producing a partial opacity of the cornea 
 only. 
 
 What renders these experiments of more than usual 
 value, is the light which they have directly thrown upon 
 pathology and the practice of surgery. In my Anatomical 
 Commentaries I have described a case, which was treated 
 by Dr. Macmichael, and which presented the anomalous 
 circumstance of inflammation of the 'eye combined with 
 palsy of the fifth nerve, that admitted of a satisfactory ex- 
 planation by reference to Magendie's experiments on 
 animals ; and M. Serres has subsequently published a case 
 of a very similar nature, and of the highest interest : for 
 the patient died, and the opportunity was taken to examine 
 the change which had ensued in the fifth nerve. The 
 sentient portion of the fifth together with the ganglion was 
 found discoloured, softened, and loaded with a quantity of 
 serosity ; this change extended to the origin of the nerve, 
 and was the more distinct, as it happened that the muscular 
 portion of the fifth was unaffected. 
 
 In this case M. Serres observed, that in addition to the 
 change produced in the eye (a thickening namely aad 
 opacity of the cornea with adhesion of the iris to its sur- 
 face), other parts had likewise suffered in their texture. 
 The mucous membrane of the tongue was softer and more 
 spongy on the affected side ; and though the gums were in 
 
 u 2 
 
312 Of the Organ of Taste. 
 
 a scorbutic state on both sides, yet this appearance was 
 far more marked upon the side which had been insensi- 
 ble*. 
 
 SECTION TIL 
 
 Of the Organ of Taste. 
 
 The organ of taste is situated at the commencement of 
 the digestive canal, and appears originally intended to 
 provide us with the means of distinguishing wholesome 
 food. 
 
 The seat of the sense of taste is the tongue and palate. The 
 mucous membrane which covers the tongue is marked by a 
 vast variety of little elevations. For an inch from its root 
 the tongue is covered with mucous follicles : before these, 
 fourteen or fifteen broad papillae, termed papillae conicse, 
 are found, that are contained in fossulae, to which they ad- 
 here by their apices, while they present a broad and slightly 
 cupped surface level with the dorsum of the tongue ; 
 about seven of th^se advance on either side from the centre 
 to the edges of the tongue, the whole remaining sur- 
 face of which is covered with oval papillae that proceed in 
 ranks parallel to the papillae conicae; these are termed 
 papillae conoideae : at the edges of the tongue some of 
 similar fabric seemingly to the last assume a shred-like ap- 
 pearance, and are called papillae filiformes ; while a fourth 
 class remains, that are interspersed among the papillae co- 
 noideae ,* they are termed papillae fungiformes : they are 
 dispersed in great numbers along the sides and towards the 
 tip of the tongue. Of these papillae the last alone are 
 thought to belong to taste ; they are vascular and erectile, 
 and may be observed to shoot up upon the surface of the 
 tongue, when it is touched by a sapid substance. No 
 papillae are discoverable on the palate. 
 
 When sapid substances, such as salt, sugar, aloes, tar- 
 
 * Medico-Chirurgical Trans, vol. iii, p. 94 ; Magendie, Journal de 
 Phys. torn, v, p. 248 
 
Impressions included under the term Taste. 313 
 
 taric acid, are applied to different parts of the interior of 
 the fauces, they are found to excite the most acute sensa- 
 tion at the tip and edges of the tongue : they produce no 
 sensation at the fore and upper part of the tongue, or 
 on the hard palate. But at the back of the tongue they 
 again excite sensation enough to be distinguishable, and 
 they are still more perfectly tasted upon the middle of the 
 soft palate and uvula. The participation of the soft palate 
 in the sense of taste has been recently pointed out by 
 MM. Guyot and Admyrauld, and has been carefully verified 
 by Mr. Wheatstone and myself. We did not find that one 
 taste was perceived more distinctly than another at any 
 point of the tongue or soft palate. 
 
 In order that a substance may excite the sensation of 
 taste, it must be presented to the tongue in a liquid state : 
 to promote this object, when a solid is placed in the mouth, 
 the saliva flows abundantly; the sapid qualities of the 
 food are perceived in proportion as it dissolves : in like 
 manner an aeriform fluid is tasted as soon as the moisture of 
 the mouth becomes impregnated with it. 
 
 Various substances, after exciting the sense of touch on 
 the fauces, and that of taste upon the tongue, are capable 
 of producing a third impression, which is popularly referred 
 to the palate, but is really felt upon the sentient membrane 
 of the nostrils : the fume of certain kinds of food ascends 
 into the cavities of the nose, and produces this third and 
 distinct sensation : in administering medicine to children, 
 it is well known that the greater part of what is disagree- 
 able in its flavour may be avoided, by closing the nostrils 
 while the draught is swallowed : and by repeating this ex- 
 periment upon various articles of food, it is easy to ascer- 
 tain how much of their flavour depends upon one sense, 
 and how much is appreciated by the other. Hence it is 
 that the senses of taste and smell have been often compared 
 as having a resemblance, the odour of many substances 
 being supposed to resemble their flavour j while the fact is, 
 that the flavour of such bodies consists in their scent, and 
 that the two impressions, which are compared, are one and 
 the same. 
 
Impressions included under the term Taste. 
 
 It follows, from what has been said, that substances taken 
 into the fauces may be such, as either, 
 
 1. To excite sensations of touch alone ; of this nature are 
 rock-crystal, sapphire, or ice : 
 
 2. Or to be felt upon the tongue, and in addition to ex- 
 cite sensation in the nostrils, as for instance tin and other 
 odorous metals : 
 
 3. Or to be felt upon the tongue, and in addition to ex- 
 cite sensations of taste, as for instance sugar and salt : 
 
 4. Or, finally, to be felt upon the tongue, to be tasted by 
 the tongue, and in addition to excite a sense of flavour in the 
 nostrils, as for instance bread, manna, and other substances. 
 
 It may be remarked, in addition, that some substances of 
 a penetrating nature, such as peppermint, appear to produce 
 another distinct impression, the seat of which seems to be 
 the back part of the fauces. 
 
 Sensations of taste are not perfect until the mouth is 
 closed and the tongue pressed against the palate, by which 
 means the sapid liquid is brought into more exact contact 
 with the surface of the tongue, and perhaps forced into the 
 texture of its mucous membrane, at the same time that its 
 fumes are driven through the posterior fauces into the cavi- 
 ties of the nostrils. 
 
 The tongue is supplied by the ninth nerve, which is dis- 
 tributed through its muscular texture : by the gustatory, a 
 branch of the ganglionic portion of the third division of the 
 fifth, which is distributed not merely to the muscles of the 
 tongue, but to its mucous surface likewise and to two of the 
 salivary glands : by the glosso-pharyngeal nerve, which gives 
 branches to the surface of the root of the tongue. 
 
 After the division of the ninth nerve on both sides in dogs 
 and rabbits, the tongue loses the power of motion, so that 
 when a little drawn out of the mouth it remains protruded, 
 and is not retracted when acrid substances are applied to 
 it, which at the same time evidently produce the usual de- 
 gree of sensation. 
 
 Upon dividing the gustatory nerve, the tongue loses sen- 
 sation, but its muscles appear to retain their tone. 
 
 Upon pinching the gustatory nerve in animals immediately 
 
Of Odorous Impressions. 315 
 
 after death, no movement follows of the fibres of the tongue : 
 but each time that the ninth nerve is pinched, the muscles 
 of the tongue are convulsed. 
 
 In a case that I witnessed in which the symptoms pre- 
 sent showed that every portion of the fifth had lost its in- 
 fluence, the peculiar sensibility of the root of the tongue 
 remained; a vague sensation of touch, attended with a 
 momentary nausea and effort to vomit, ensued, as in healthy 
 persons upon pressing the surface of the root of the tongue 
 with a probe. Upon pinching the glosso-pharyngeal nerve 
 in animals immediately after death, no spasm follows of 
 the muscles of the tongue. 
 
 SECTION IV. 
 Of the Organ of Smell. 
 
 Particles are continually flying off from the surfaces of 
 bodies : or the air seems to dissolve minute portions of 
 every substance with which it is in contact. Hence arise 
 the virtues of salubrious situations, or the poisonous quali- 
 ties of such as are noxious ; the atmosphere becoming im- 
 pregnated with the elements of the soil in proportions too 
 delicate to be tested except by the animal frame, into which 
 they find admission through pulmonary absorption. The 
 atmospheric solution of many substances is distinguishable 
 by the sense of smell. The organ of this sense forms the 
 commencement of the respiratory tube, so that each time we 
 breathe, the olfacient qualities of surrounding substances 
 are submitted to our senses. 
 
 The sense of smell is calculated to give warning of the 
 vicinity of unwholesome objects, and to minister to the ap- 
 petites ; or like the sense of hearing may be employed to 
 furnish a succession of impressions that are merely grateful. 
 The influence of this sense over the frame is very remark- 
 able : one odour will instantly produce loathing, nausea, 
 and vomiting j another, like the pleasant fragrance of the 
 
316 Form of the Nostrils. 
 
 country on a spring morning, has a part in producing an ex- 
 hilarating influence upon the mind. 
 
 The organ of smell is separated into two chambers, by a 
 partition, which is seldom exactly in the median plane of 
 the head. This partition consists of the nasal processes of 
 the ethmoid and sphenoid bones, of the vomer, and of the 
 cartilago septi narium. The floor of each chamber or nostril 
 is formed by the superior maxillary and palate bones. The 
 outside by the superior maxillary bone, the palate bone, the 
 os unguis, the os planum, the cartilago nasi lateralis, and 
 the cartilago alse nasi. The floor of the nostril is horizontal 
 and slightly hollowed ; the septum is nearly vertical and 
 plane : at the upper part is the narrow cribriform plate 
 of the ethmoid bone ; upon the outside the lower cornu 
 of the ethmoid bone and the inferior turbinated bone fall 
 like curtains, leaving a passage toward the pharynx, the 
 upper and outer part of which is divided into three chan- 
 nels. The frontal sinuses open through the anterior cells 
 of the ethmoid bone into the middle channel of the nostrils : 
 the sphenoid cells and the antrum of Highmore open through 
 the posterior cells of the ethmoid bone into the superior 
 channel. The lachrymal duct opens into the inferior channel. 
 
 The thick and vascular mucous membrane, which invests 
 this extensive surface of bone and cartilage, is termed the 
 Schneiderian membrane. Over the whole of it are distri- 
 buted branches of the fifth nerve ; upon the fore part, a branch 
 from the nasal portion of the first division of the fifth ; upon 
 the remaining surface, branches derived from the ganglion 
 of Meckel. The distribution of the first nerve is more li- 
 mited. The first nerve enlarges into an oval bulb, containing 
 grey matter, upon the lamina cribrosa of the ethmoid bone, 
 which it perforates in numerous filaments, that are spread 
 over the septum narium and the internal surface of the 
 ethmoid bone. 
 
 The simple contact of an atmosphere laden with odours 
 is not sufficient to produce sensation in the nostrils. In 
 order that smelling may take place, it is necessary that air 
 impregnated with the odour be carried with some velocity 
 against the surface of the Schneiderian membrane. 
 
Experiments on the Olfactory Nerves. 317 
 
 The upper part of the nostril appears to be the region 
 to which the sense of smell is limited, or at which it is 
 most exquisite. The apertures of the nostrils, and the in- 
 clination of the nose, are obviously adapted to direct the 
 stream of air in that direction. Accordingly, when the nose 
 has been destroyed by disease, smell is found to be greatly 
 impaired or lost. 
 
 It is usual and reasonable to suppose the first nerve to be 
 that employed in the sense of smelling. The nostrils are 
 the only parts which distinguish odours, and although 
 two nerves are distributed upon their sentient surface, one 
 alone has its distribution confined to this organ. The acute 
 sense of touch which the nostrils enjoy in addition seems a 
 sufficient use for the remaining nerves which are spread 
 upon the Schneiderian membrane ; they are one and all de- 
 rived from trunks, the other branches of which are nearly 
 all nerves of common feeling. 
 
 M. Magendie has recently tried the effect of the separate 
 division of the first and fifth nerve in animals ; and has 
 thus more precisely pointed out, how much of the impres- 
 sion received upon the nostrils belongs to smell properly so 
 called, and how much to touch. It appears that upon the 
 division of the first nerve the animal remains as sensible to 
 the disagreeable impression of odours which act pungently, 
 as before ; a young dog thus mutilated appeared conscious 
 of an unpleasant impression when ammonia, acetic acid, oil 
 of lavender, or DippeFs oil, were held to its nose : on the 
 other hand, after the division of the fifth, the first nerve re- 
 maining entire, an animal is not affected by the presence of 
 the substances above mentioned. But M. Magendie men- 
 tions, that a dog, which survived the division of the fifth 
 nerve for a considerable period, would at times, when food 
 was offered to it rolled up in paper, unrol the paper, and 
 expose and eat the food ; although at other times he ap- 
 peared to want the power of distinguishing by smelling the 
 presence of objects placed near to it*. 
 
 * Magendie, Journal de Phys. Exper. vol. iv, p. 1?3. 
 
318 Of the Nature of Sound. 
 
 Pungent odours seem to offend the nose upon the same 
 principle that they irritate the surface of the eye, their 
 acrid impression, without their scent, being perceived, when 
 the influence of the first nerve is artificially destroyed : such 
 at least appears to be the inference justly deducible from 
 the facts which M. Magendie has added to our knowledge 
 upon this subject, and which leave the first pair of nerves 
 in full possession of the faculty of smelling. 
 
 SECTION V. 
 Of the Organ of Hearing. 
 
 The physical impressions upon the organ of hearing, 
 which produce sensations of sound, consist in impulses re- 
 gularly recurring within certain limits of frequency. In all 
 ordinary cases of the production of sound, these impulses 
 originate from vibrating bodies, and are communicated to 
 the organ of hearing by means of undulations excited in the 
 air. 
 
 The limits between which regularly recurring impulses are 
 perceptible as sounds have been generally stated at 30 in a 
 second on the one extreme, and from 8000 to 12000 on the 
 other : but some recent investigations by Savart show that 
 acute, sounds may be perceived resulting from 24000 im- 
 pulses in a second, and that grave sounds may be appre- 
 ciated arising from 7 or 8 impulses only. He has found 
 such sounds in either extreme capable of being rendered 
 appreciable by the senses upon increasing their loudness. 
 Dr. Wollaston conceived, from trials made with very acute 
 sounds on a number of persons, that the limit of audition 
 with regard to acuteness of sound is variable in different 
 individuals : but Savart has shown, that these experiments 
 only prove different degrees of sensibility in the individuals 
 with respect to the intensity of sound, and that had the 
 
Of the Nature of Sound. 319 
 
 intensity of the sounds excited been greater, the limits of 
 hearing would have been the same in all. 
 
 The length of the interval between two successive im- 
 pulses, or, which is the same thing, the number of impulses 
 in a given time (a second is the time generally assumed), 
 constitutes the pitch or musical degree of the sound. Grave 
 sounds are those in which the interval between the impulses 
 is greater, and acute sounds those in which it is less : these 
 are merely terms of comparison ; and the same sound may 
 be acute compared with one grave, and grave compared 
 with one more acute. 
 
 It does not appear that a continued series of isochronous 
 impulses is necessary to constitute a comparable musical 
 sound : two successive beats are sufficient to give rise to the 
 sensation, and the pitch of the sound is solely determined 
 by the duration of the interval between them. It follows, 
 therefore, that in the most extreme limit of acute sound 
 which has yet been determined, a sound is perceptible which 
 lasts only the 24000th of a second. 
 
 A phenomenon analogous to the duration of luminous im- 
 pressions on the retina has been observed with regard to 
 sound ; in a continuous series of isochronous impulses, a 
 very considerable number may be intermitted without im- 
 pairing in the slightest degree the apparent continuity of 
 the sound. 
 
 These curious facts never could have been ascertained, 
 had we been confined to experimenting on sounds produced 
 by vibrating bodies : but a means of investigation originally 
 proposed by Dr. Hooke, and successively improved by Ro- 
 binson, Cagniard de Latour, and Savart, enables us to ob- 
 tain every possible arrangement of impulses, and every re- 
 quisite degree of intensity. By the extension of these means, 
 our knowledge with regard to audition may be yet much 
 extended. 
 
 The undulations arising from sonorous impulses are trans- 
 mitted more rapidly through solids than through liquids, 
 and by liquids than by aeriform fluids. Sound travels 
 through air with a velocity equal to 1142 feet per second; 
 
320 Of the Organ of Hearing. 
 
 and it is calculated, that it would be transmitted through 
 water with a velocity of 4900 feet, and through glass, iron, 
 or deal wood, with a velocity of about 18000 feet per 
 second. 
 
 Sound transmitted through a fluid spreads spherically in 
 every direction. Hence it may be understood how sound, 
 when moving through a fluid, is diminished in intensity 
 (like light) in the ratio of the square of the distance. Sound 
 likewise admits of being reflected like light : upon this prin- 
 ciple depend the phenomena of echoes. Sound is deadened 
 by passing from one medium to another. Sound perishes 
 when no material substance fit for its transmission is pre- 
 sent. A bell struck in an exhausted receiver is scarcely 
 audible. 
 
 The essential part of the organ of hearing consists of a 
 series of cavities, termed the labyrinth, hollowed in the pe- 
 trous bone, within which is a membrane containing a liquid, 
 in contact with which the portio mollis of the seventh nerve 
 is expanded. 
 
 The labyrinth is divided into the vestibule, cochlea, and 
 semicircular canals, a particular description of which would 
 be superfluous, as the specific advantages resulting from 
 their shape is unknown. But it is to be remarked, that a 
 provision is made for the free vibration of the fluid which 
 they contain by means of two apertures, the fenestra ro- 
 tunda and fenestra ovalis, that are closed by a membrane 
 only. 
 
 As long as the labyrinth is perfect, no degree of obstruc- 
 tion of the external passages or removal of the external 
 
 i O 
 
 parts can prevent hearing from taking place. In a total ob- 
 struction of the external passages, sound may still be con- 
 veyed through the bones of the head to the auditory nerve, 
 as for instance upon applying a tuning-fork to the teeth ; and 
 thus in deafness may be attained an accurate criterion to de- 
 termine whether the disease be seated in the labyrinth or in 
 the passages leading to it. In a total loss of the external 
 parts, on the other hand, sound is capable of being commu- 
 nicated through the air to the membranes and liquid of the 
 
Of the Tympanum. 321 
 
 labyrinth if they remain entire, nearly as perfectly, it should 
 seem, as when the outer parts are complete*. 
 
 The chambers of the ear external to the labyrinth are the 
 cavity of the tympanum and the meatus auditorius ex- 
 ternus. 
 
 The tympanum is a narrow chamber, which opens for- 
 wards into the posterior fauces through the Eustachian tube, 
 and is continued backwards into the cells of the mastoi'd 
 process of the temporal bone. The membranes of the fe- 
 nestra ovalis and fenestra rotunda prevent communication 
 between the cavities of the tympanum and of the labyrinth. 
 The membrana tympani on the opposite side is interposed 
 between the tympanum and the meatus auditorius externus. 
 A chain of bones, the malleus, the incus, the os orbiculare, 
 and the stapes, extend from the membrana tympani to the 
 membrana fenestrse ovalis ; and four little muscles, the ten- 
 sor tympani, the laxator tympani, the externus mallei, and 
 the stapedius, by drawing upon the ossicula auditus, give 
 greater or less tension to the membranes which those bones 
 unite. 
 
 The membrana tympani is very vascular, but presents a 
 dry shining cuticular surface. It appears to contain fibres 
 that converge towards its centre ; which part is drawn in- 
 wards, and has attached to it the handle of the malleus. 
 It is worthy of remark, that the ossicula with their muscles 
 are situated to the inside of the tipper half of the membrana 
 tympani, or are placed at the upper part of the cavity of the 
 tympanum : the practical application of this fact is the fol- 
 lowing. 
 
 One sort of deafness to sounds transmitted in the common 
 way results from an obstruction of the Eustachian tube : 
 when this happens through any cause, the air confined in 
 the cavity of the tympanum cannot vibrate, and therefore 
 cannot transmit sound. An obstruction of the Eustachian 
 tube is therefore supposed to exist, when those sounds alone 
 
 . 
 
 * It is to be observed, that the stapes is so strictly applied to the 
 membrana fenestrse ovalis, that the loss of this bone necessarily pro- 
 duces incurable deafness by the attendant injury of the labyrinth. 
 
322 Of the External Ear. 
 
 are heard, that are transmitted through the bones of the 
 head, at the same time that the meatus auditorius externus 
 is perfectly free, and the patient is unable to inflate the tym- 
 panum by impelling air into it from the fauces. As long as 
 the Eustachian tube remains obstructed, and the membrana 
 tympani perfect, the vibrations of sound are in vain trans- 
 mitted along the air in the external meatus : the ossicula 
 auditus form an insufficient medium of communication be- 
 tween the membrana tympani and the membranes of the 
 labyrinth : and hearing is only restored by the operation of 
 perforating the membrana tympani. 
 
 All that is known of the office of the membrana tympani 
 is, that it opposes an obstacle to the entrance of foreign sub- 
 stances, at the same time that it presents no impediment to 
 the communication of the sonorous undulations. 
 
 The meatus auditorius externus including the cartila- 
 ginous part is an inch in length : it is curved in two 
 senses like an italic f, its general direction is horizontally 
 outwards and backwards. This canal is fenced with short 
 strong hairs, and its surface secretes a peculiar substance 
 termed cerumen, which is of an orange-yellow colour and 
 bitter taste, consisting of albumen, an oil, colouring mat- 
 ter, soda, and phosphate of lime *. The cerumen is liable 
 to collect in thick inspissated masses, sufficient to ob- 
 struct the passage of sound along the meatus auditorius 
 externus. 
 
 The external ear is formed of an expansion of the carti- 
 lage, which forms the outer half of the external meatus : its 
 several folds and margins are distinguished by separate 
 names : the helix is the outer folded edge ; the antihelix is 
 the fold parallel to the former : the deep hollow below and 
 before the antihelix is called the concha, the anterior edge 
 of which is formed by the fold termed the tragus, the poste- 
 rior edge by the antitragus. The attollens, the retrahentes, 
 and the anterior auris, are muscles which carry the outward 
 ear in the directions which their names specify. The he- 
 licis major and minor, the tragicus and the antitragicus, 
 
 * Thomson's Chemistry, vol. iv, p. 513. 
 
Of the Nerve of Hearing. 323 
 
 and the transversus auris, are thin muscular slips, which 
 extend from one point to another of the external ear, and 
 are calculated to expand the different hollows and fossulse 
 into which the surface of the ear is thrown. Among savage 
 tribes the outward ear is prominent, and moveable like the 
 ears of animals ; their hearing is more acute than that of 
 civilized nations, and it is probable that the motions of the 
 external ear assist them in discriminating the direction and 
 nature of different sounds. 
 
 The portio mollis of the seventh nerve we may infer from 
 its distribution to be the nerve of hearing. The portio dura 
 of the seventh traverses a canal in the temporal bone : it is 
 joined in its course by a branch from the second division of 
 the fifth nerve, and from the united trunk filaments are 
 given to the muscles within the tympanum. But the portio 
 dura is a nerve of voluntary motion, and the second division 
 of the fifth is a sentient nerve ; thus the circuitous route of 
 the portio dura and its junction with the Vidian nerve are 
 explained. The division of the trunk of the fifth nerve in 
 cats within the cranial cavity does not seemingly affect the 
 acuteness of hearing on the same side. 
 
CHAPTER XIV. 
 OF VOLUNTARY MOTION. 
 
 IN describing the offices of the chest, as well as on several 
 other occasions, I have had to advert to voluntary muscular 
 action ; but its most remarkable phenomena yet remain to 
 be considered : they may be arranged under two heads 
 the history namely of the attitudes and movements of man, 
 and of the production of vocal sounds, or more generally of 
 the uses of the larynx. Under the first head I shall speak 
 of the bones and joints or of the mechanism of the ske- 
 leton, of the voluntary muscles of the trunk and limbs, and 
 of the chords or tendons through which they operate on re- 
 mote parts. 
 
 SECTION I. 
 
 On the Attitudes and Movements of Man. 
 
 The skeleton first merits onr attention. With a theme 
 susceptible of the most varied illustration, I shall at present 
 confine myself to a brief and elementary notice of the broad- 
 est features which it presents. 
 
 When sections are made of a dry bone, it is found to be 
 composed of two parts ; externally, of a compact crust of 
 greater or less thickness, and internally, of a series of deli- 
 cate bony threads, which form a close net- work, or lattice- 
 work, or cancellated structure ; the spaces or cells between 
 the bony threads freely communicate. 
 
 The bones of the skeleton affect three principal forms ; 
 
Of tJie different kinds of Bones. 325 
 
 each of which has some peculiarity in its structure, adapted 
 to the object upon which it is employed. 
 
 The flat bones are those which form the walls of the 
 great visceral cavities, the cranium, the chest, the pelvis. 
 In these bones the crust is thin, and forms what are termed 
 tables, an outer and an inner : the interposed cancellated 
 structure is termed the diploe. The two tables of the flat 
 bones are for the most part parallel. In the skull the inner 
 table is of a closer grain and of greater density than the 
 outer. The flat bones are externally convex, a circumstance 
 which contributes with the alternating compactness and po- 
 rousness of their texture to increase their strength. 
 
 The round or cuboid bones are small irregular cubes or 
 portions of cylinders, one series of which forms the vertebral 
 column, another the wrist, and a third the instep : their 
 crust is yet thinner than that of the flat bones ; their in- 
 ternal structure varies in different instances : the cancelli 
 are fine in the vertebrae, coarse in the tarsal and carpal 
 bones. The texture of cuboid bones is therefore any thing 
 but brittle, and is well calculated to deaden the force of 
 jars and concussions of all sorts. To promote the latter 
 object, the cuboid bones are placed not singly but in 
 groups, so that the elasticity resulting from many joints 
 and intervening layers of cartilage may add to that resulting 
 from their texture. Another advantage is obtained by form- 
 ing the parts described of many bones ; a considerable ex- 
 tent of motion may exist in the entire part, at the same time 
 that no single joint has play enough to risk its security. 
 
 The long or cylindrical bones are employed as levers upon 
 which the muscles act when supporting or propelling the 
 body. The extremities of a cylindrical bone, where it is 
 articulated to those adjoining, as they have the office, so 
 likewise have they the structure of the cuboid bones a thin 
 outer crust, and strong cancelli : they likewise generally 
 affect a considerable breadth, which increases the strength 
 of the joints. But the intermediate part or shaft of a long 
 bone is constructed differently ; its crust is of great thickness, 
 from one-fourth to one-third of an inch; while the inter- 
 nal cancellated structure is remarkably fine and delicate. 
 
326 Chemical Composition of Bone. 
 
 The bony matter, spread out in innumerable plates and 
 fibres in the broad articular extremities, in the shaft is con- 
 densed into a close and compact structure, in order that 
 the lever which it forms may not be flexible : the shaft is 
 hollow, to give the greatest strength to a determinate weight 
 of bony substance. 
 
 If a bone be calcined, the earth which remains has the 
 same form and structure as the bone possessed ; but it is 
 brittle, and falls in pieces almost from its own weight. If 
 a bone be steeped in acid, it retains its form and structure, 
 but becomes flexible. 
 
 The following table exhibits the composition of calcined 
 human bones, according to the analysis of Berzelius. 
 
 Phosphate of lime 81.9 
 
 Fluate of lime 3.0 
 
 Lime 10.0 
 
 Phosphate of magnesia 1.1 
 
 Soda 2.0 
 
 Carbonic acid 2.0 
 
 100.0 
 
 Bones when forming part of the living body are covered 
 with a membrane termed their external periosteum, which 
 is easily detached from their surface; it is thin, except 
 where tendons or ligaments are inserted. All the cavities in 
 a bone again are lined with a fine membrane termed the 
 internal periosteum; from the surface of which, or from a 
 membrane within it, is secreted the marrow which fills the 
 cancelli. 
 
 Upon examining the bones in a favourable subject mi- 
 nutely injected with size and vermilion, blood-vessels may 
 be traced through their entire substance. Neither lym- 
 phatics nor nerves have been followed into bone ; but ab- 
 sorption evidently takes place during the growth of bone, 
 or the cavities of the long bones could not enlarge propor- 
 tionally. During health bones are perhaps insensible : during 
 disease they exhibit acute sensibility. 
 
 The modes, in which the bones of the skeleton are joined 
 together, are very various ; in some instances no motion is 
 allowed between adjoining bones, and they seem to have 
 
Of the Joints. 327 
 
 been left disunited with the sole object of diminishing the 
 liability to fracture in the part they form. Upon this prin- 
 ciple it is supposed that the bones of the cranium are left 
 disunited after their growth is completed. The strength of the 
 immoveable joints which are thus left is'determined by the 
 shape of the bony edges. In general these are wrought into 
 alternating projections and hollows ; so that, to use a term 
 of carpentry, the bones are dovetailed together. In other 
 instances a plate of one bone overlaps a plate of another. 
 The former kind of junction is termed a suture proper; the 
 latter a squamous suture. 
 
 In other instances again, where no sensible motion is in- 
 tended to take place, but where a part has often to resist 
 considerable violence, a portion of white elastic substance 
 termed fibrous cartilage is additionally interposed between 
 two bones, with the extremities of either of which it is con- 
 tinuous ; in this manner the ossa innominata are joined to 
 each other and to the sacrum. As a variety in this sort of 
 articulation we may remark, that the true ribs are joined to 
 the sternum by portions of fibrous cartilage, which are re- 
 ceived into sockets at the side of the breast-bone, but are 
 not continuous with it : a layer of cellular membrane is in- 
 terposed between the cartilages of the ribs and the breast- 
 bone, so as to allow a certain degree of motion to take place 
 at the sterno-costal joints during the dilatation of the chest. 
 
 In the kind of joint last described another substance 
 called ligament is generally found in addition. Ligaments 
 are white silvery bands composed of very delicate fibres, 
 that are very flexible, but have little extensibility : they are 
 composed nearly wholly of gelatin : they have little sensi- 
 bility to common stimuli, but when strained they give rise 
 to acute pain. 
 
 The joints of the bodies of the vertebrae deserve to be 
 particularly described. In fish, in which the spine is very 
 flexible, the articular surfaces of the bodies of the vertebrae 
 are so excavated, that when two meet they inclose a cavity, 
 the shape of which may be called spherical. This cavity 
 is filled with fluid, which we will suppose to be incompres- 
 sible, while the margins of the two vertebrae are joined toge- 
 
 x 2 
 
328 Nature of Sinovia. 
 
 ther by the intervention of a ligamentous substance which 
 is highly elastic ; thus a double ball and socket joint exists 
 between every two vertebrae, each of which is capable of 
 rolling in every sense upon the ball of liquid contained be- 
 tween the two. In the human spine the same type is fol- 
 lowed, but with a provision for much less latitude of mo- 
 tion ; the excavation is shallow, the central substance semi- 
 fluid, and the surrounding fibrous cartilage is confined by 
 ligamentous bands of less elastic substance. 
 
 In the two preceding kinds of joints (at least in the human 
 frame), there is no absolute discontinuity ; a layer of ani- 
 mal membrane or df fibro- cartilage directly unites the op- 
 posed ends of bone. In other joints the bones otherwise 
 disconnected are held in apposition by ligaments. The ends 
 of such bones are covered with a layer of elastic cartilage, 
 that their reciprocal pressure may not injure the osseous 
 tissue. And to facilitate their motion on each other, the whole 
 inner surface of the joint is lubricated with a peculiar fluid. 
 The lining surface may be viewed as one continuous mem- 
 brane. Membranes of this description in many respects re- 
 semble serous membranes : they form shut sacs of the finest 
 texture : they can be separated, though not without difficulty, 
 from the ligaments and periosteum which they cover ; but 
 they rarely admit of being detached from the surface of 
 cartilages. I have one preparation, however, in which I ac- 
 cidentally succeeded in raising an uniform membrane from 
 the cartilage covering the head of the humerus. Membranes 
 of this description take their name from the viscid fluid 
 called sinovia, which they secrete, and which lubricates their 
 internal surfaces. 
 
 From an analysis by M. Margueron it appears that sinovia 
 is composed of the following ingredients : 
 
 Fibrous matter 11.86 
 
 Albumen 4.52 
 
 Muriate of soda 1.75 
 
 Soda O./l 
 
 Phosphate of lime 0.70 
 
 Water 80.46 
 
 100.00 
 
Analogical Design in the Skeleton. 329 
 
 Joints which combine these various elements are divided 
 into classes, according to the form which they affect and the 
 kind of motion of which they allow. 
 
 A ball and socket joint, or enarthrosis, like that of the 
 hip, has great security, and at the same time permits very 
 extensive motion. 
 
 A joint, in which surfaces nearly plane are opposed to each 
 other, is termed an arthrodia ; the motion allowed in such a 
 case is very limited, but takes place in every sense. 
 
 A joint which allows of motion in one plane only is 
 termed a ginglymus or hinge joint. Of this joint there are 
 two kinds ;, in one the motion is angular, as in the knee, in 
 the other rotatory, as in the joints of the atlas and dentata. 
 
 Such are the materials of the skeleton, and the different 
 modes in which they are joined together to form one frame. 
 
 When we seek in the skeleton for illustrations of that ana- 
 logical design, which is evident not merely in entire classes 
 but in single objects of Nature's workmanship, we remark 
 that the head is not a part which corresponds with any 
 subdivision of the frame, but that it rather seems an epitome 
 of all the rest. 
 
 When we compare together the several regions of the 
 trunk, we observe that it is laid out in corresponding organs 
 on either side of a centre, which consists of the five lumbar 
 vertebrae. Above the lumbar vertebrae are the dorsal ver- 
 tebrae, above these the cervical ; below the lumbar vertebras 
 are the sacral bones, below these the coccygeal. To the 
 dorsal vertebrae and to the sacrum bones are articulated, 
 which have the double office of forming a visceral cavity, 
 and of throwing to a convenient distance from the median 
 plane the bones of the extremities. The ribs and sternum, 
 the clavicles and scapulae, form with the dorsal vertebrae an 
 organ strictly analogous to that formed by the ossa inno- 
 minata and the sacrum. But the chest for the function of 
 respiration requires to be continually altering its dimensions, 
 and the upper extremity is characterized by the extent and 
 velocity of its movements rather than by its strength : to suit 
 both these objects, the chest and shoulder are formed of 
 many bones, that are moveable in various senses ; the ribs 
 are capable of rotating upon their sternal and vertebral 
 
330 Analogical Design in the Skeleton. 
 
 joints, and of being raised or depressed upon their vertebral 
 joints, carrying with them the sternum ; the clavicle again 
 revolves upon the sternum, and the scapula rolls upon the 
 convexity of the ribs. On the other hand the pelvis, as 
 regards the viscera, is intended merely for their support ; 
 and if during labour a temporary enlargement of its lower 
 aperture be requisite, the flexibility of the joints of the os 
 coccygis in the female skeleton, with the temporary yielding 
 of the ligaments, affords a sufficient provision for this object: 
 the inferior extremities again require to be articulated to a 
 solid unyielding platform, upon which they may poise the 
 incumbent weight of the trunk and head. The bones of 
 the pelvis are for these reasons few, weighty, massive, 
 and knit together immoveably. Thus accurately do the 
 points, in which a resemblance is wanting between the 
 chest and pelvis, preserve the analogy between these parts. 
 
 It is needless to dilate upon the correspondence of the 
 femur with the humerus, of the tibia, patella, and fibula 
 with the radius and ulna, of the tarsus with the carpus, of 
 the bones of the foot with those of the hand. As mobility 
 is the prevailing character of the upper extremity, the 
 radius plays upon the ulna, the bones of the wrist are so 
 disposed as to form three ball and socket joints, and the 
 metacarpal bone of the thumb moves freely on a hinge joint. 
 As stability is the leading character in the lower extremity, 
 the knee moves in one plane only, the fibula has no motion 
 upon the tibia, the joints of the tarsus do no more than 
 yield sufficiently to break the force with which the frame 
 alights upon the ground, and neither of the metatarsal 
 bones moves on its tarsal joint. 
 
 It would appear fanciful to enlarge upon the points of 
 correspondence between the head and trunk. As the ver- 
 tebral canal contains the spinal chord, the cranial cavity 
 contains the cerebrum and cerebellum ; as the main parts of 
 the respiratory organs are contained in the upper cavity of 
 the trunk, and the digestive viscera are supported by the 
 lower, so the nostrils are the cavities of the fore and upper 
 part of the cranium, and the fauces of the lower part. If 
 the chest supports the organs of prehension, the pelvis those 
 of pursuit, the orbits, the nostrils, the cavities of the temporal 
 
The Skeleton fitted for the Erect Posture. 331 
 
 bone, have points in common with the former, and the 
 fauces, which contain the tongue, have a trivial analogy with 
 the latter. 
 
 When we consider the human skeleton as designed for 
 beings distinguished by the erect posture and erect progres- 
 sion, and as a frame -work likely to be exposed to violence, 
 yet endued with strength to resist it, the following circum- 
 stances attract our notice. 
 
 1. The foramen magnum occipitis is situated nearer the 
 centre of the base of the skull in man than in quadrupeds, 
 for the evident purpose of allowing the skull to be balanced 
 with little muscular effort on the vertebral column. The 
 lower cervical and upper dorsal vertebrae are, with reference 
 to the same circumstance, deficient in man in those processes 
 to which the strong ligamentum nuchae of quadrupeds is at- 
 tached, required in the latter to give permanent support to 
 their pendent head, and economizing muscular exertion. 
 The vertebral column becomes uniformly broader towards 
 its base ; or if at one part its progressive increase seems 
 interrupted, it is but where the ribs and sternum give it 
 towards the middle of the back an adventitious strength. 
 The upper margin of the acetabulum is the deepest and the 
 strongest. The centre of gravity is situated in or but little 
 above the centre of a line connecting the axes of the two 
 acetabula, so that the head and trunk and arms of a stand- 
 ing person may be swayed to any extent forward or late- 
 rally without risking the security of the posture. 
 
 2. The lower part of the vertebral column does not rise 
 vertically from the pelvis, but is inclined obliquely for- 
 wards ; so that when the trunk is carried forwards by a sud- 
 den spring, the resistance of its inertia does not strain the 
 ligaments between the sacrum and the last lumbar vertebra, 
 or between any two vertebrae exclusively, but telling first upon 
 the inferior surface of the lowest vertebra, is then thrown 
 upon the ligamentous connections of several bones, which 
 form a column so curved as to share the strain between 
 them. The vertebral column thrown backwards in the 
 dorsal region, thus deepens the cavity of the chest, and 
 throwing the shoulders yet farther back, tends so much the 
 
332 Of the Strength of the Skeleton. 
 
 more equally to distribute the weight of the frame before 
 and behind the axis of the spine. The spine, composed of 
 twenty-four spongy bones, united by soft and elastic sub- 
 stance, is by the nature of its materials admirably qualified 
 to take off the effect of jars or concussions from the head, 
 when from a state of rapid motion the frame alights upon 
 the feet ; a purpose for which its curved form renders it all 
 the more available. The spinal column rests on an elastic 
 hoop, in the extreme circumference of which on either side 
 the deep cups are wrought, which receive the heads of 
 either thigh bone. But this elastic hoop is not disposed 
 vertically, but slants, in such a manner, that when we alight 
 upon our feet, the force of the arrested motion tells in great 
 measure on the extensor muscles of the hip. The neck of the 
 thigh bone is oblique, to disengage it from the pelvis : the 
 shaft is oblique in the opposite direction, to bring the knee 
 vertically below the hip. The numerous joints of the foot, 
 to conclude, each allowing of very trifling yielding, render 
 the entire arch the more secure ; and the astragalus, which 
 directly receives the weight of the body from the tibia itself, 
 rests immediately upon the trochlea cartilaginea, a thick and 
 strong elastic ligament, which, the more it is depressed, the 
 more tightly holds together the vaulted frame- work of the 
 foot. 
 
 3. What is most admirable as regards the strength of the 
 skeleton, does not consist in an indefinite power of resisting 
 violence, but in the surprising amount of security imparted 
 by their shape, and number, and modes of articulation, to 
 such frail materials in the equal strength of the whole in 
 its proportion to the sensibility and power of exertion and 
 endurance in the soft parts, and to the risks to which it 
 is in the common course of events exposed. In the cra- 
 nium especially, physiologists delight to notice the strength 
 derived from its arched form ; the partial thickening 
 of its most exposed and prominent parts; its texture 
 strengthened by being wrought in three layers of varying 
 density .; its sutures, which concur with the last-named pro- 
 vision in diminishing its brittleness, and their well-known 
 squamous configuration at the side of the head, enabling 
 
Of the Joints of the Atlas and Dentata. 333 
 
 the sphenoid and temporal bones to resist the pressure 
 outwards at that part, when the vertex is forcibly 
 struck *. 
 
 The physiology of the skeleton is commonly and judi- 
 ciously employed to furnish popular illustrations of the de- 
 sign evinced in the human frame. With this object in view, 
 I will mention another provision in addition to those which 
 I have already explained in treating this part of my sub- 
 ject. The five lower cervical vertebrae enjoy the same 
 kind of motion with the vertebrae below, motion equal 
 in every direction, yet extremely limited between each 
 pair of bones. But the atlas and dentata have articular 
 surfaces adapted for movements of a much more extensive 
 nature. The ligamentous structure, by means of which the 
 spinal marrow is here secured from injury, is a common 
 theme of admiration. At the same time a provision, the 
 extent of which is perhaps not equally understood, is made 
 for the safety of two great vessels of the brain, the vertebral 
 arteries. For the purpose contemplated a canal is formed, in 
 which these arteries are lodged, by perforations in the trans- 
 verse processes of the cervical vertebrae. Now the axis of 
 this canal in the five lowest vertebrae is vertical: the motion 
 between any two of these bones is inconsiderable ; the artery 
 therefore, although straight, is not in danger of being 
 strained. But above, where the atlas and dentata have a 
 wide extent of motion, the axes of their perforations are ob- 
 served to be oblique. At the same time the part of the artery 
 between the dentata and the atlas, and that between the atlas 
 and the occiput, are found to be more than twice as long as 
 the vertical height of the intervals requires. At each of these 
 intervals the artery describes a semicircle, towards which 
 figure it derives its bent, from the obliquity of the axes 
 of the bony canals. It runs, therefore, no risk of strain- 
 ing or undue extension during the utmost motions of 
 these bones with each other and with the occipital. The artery 
 is then only unbent, not stretched, in consequence of the 
 
 * I take this opportunity of recommending to the perusal of the 
 student Dr. Arnott's *' Elements of Physics." 
 
334 Of the Muscles, which move the Frame. 
 
 disposition which has been explained. But Nature delights 
 in obtaining by one contrivance more than one important 
 end. The double curves of the vertebral arteries are in 
 truth no less essential for their own preservation, than for 
 protecting the soft texture of the brain by diminishing the 
 impetus of the blood transmitted to it. 
 
 The nature of the muscular tissue has been already de- 
 scribed. That which ministers to voluntary motion does 
 not differ in its structure from the involuntary muscles : but 
 while the latter are disposed as tubular coats around the 
 hollow viscera, the voluntary muscles clothe the skeleton, 
 extending from bone to bone. 
 
 The muscles of the trunk and limbs have at least two at- 
 tachments to bone, one of which is called their origin, the 
 other their insertion. The former term is usually applied to 
 that attachment which is nearest the centre of the body, or 
 which under ordinary circumstances is the fixed point 
 during the action of the muscle. By its origin and inser- 
 tion a muscle adheres to two separate bones, which either 
 are articulated together, or have a third bone or even several 
 interposed. In the latter case a single muscle is adapted 
 to bend or extend several joints. 
 
 Muscular fibres in some instances adhere directly to the 
 periosteum of a bone, in others they are united to it by an 
 intermediate chord of the same texture with a ligament, in 
 this case termed a tendon or sinew. The greater number of 
 muscles of the class under consideration have a tendon at 
 one extremity, and commonly at both some tendinous fibres 
 are wrought into their texture. 
 
 Some have illustrated the connection between a muscle 
 and a tendon in the following manner. Each fasciculus of 
 a muscle, as it has been already remarked, has its sheath of 
 membrane ; we have but to suppose this sheath prolonged 
 beyond the termination of the fibre, as a compact thread, and 
 we have a tendon produced. On this supposition the definite 
 proportion between the strength of a muscle and that of its 
 tendon would be essentially provided for by an union of 
 threads in the texture of the latter, equal in number and 
 coarseness to the fasciculi of the muscle. The threads of which 
 
Use of Tendons illustrated. 335 
 
 a tendon is composed are never plaited and are rarely twisted : 
 they are, in almost every instance, collected into fasciculi 
 which are simply laid side by side, and strongly cohere. 
 
 The various uses which tendons serve require an elaborate 
 explanation. 
 
 The strength of a muscular fibre does not alter with its 
 length, A long and a short chord of the same texture and 
 thickness require an equal force to tear them asunder. The 
 strength of a chord is that of its weakest point. It must 
 be the same with a muscular fibre. We may suppose the 
 contraction of a muscular fibre efficient at any degree below 
 the maximum force of its weakest part ; but if the resistance 
 opposed to it exceed the strength of the latter, it is obvious 
 that the extension or rupture of the fibre at that part will 
 neutralize the force of the rest. All that the remaining 
 parts of a muscular fibre can do, is by exerting an equal 
 force with the weakest to prevent the waste of any of its 
 effect. 
 
 But the extent, to which a muscle can shorten, depends 
 upon the length of its fibres. It is ascertained, that a mus- 
 cular fibre is capable of contracting to a limited degree 
 only. When a limb has been broken, and through ill 
 management has become materially shortened, its muscles 
 are for a time rendered useless, although they subsequently 
 accommodate themselves to the altered length of the limb. 
 Let us assume, then, that a muscular fibre in action can 
 only diminish its length by one-third : it follows, that a 
 muscular fibre of three inches in length would in its utmost 
 contraction bring its points of attachment an inch nearer 
 than before, whereas a muscular fibre a foot in length would 
 be capable of reducing the distance between its points of at- 
 tachment four inches *. 
 
 Now let us suppose, that the distance between the origin 
 and insertion of a muscle be one foot, but that the neces- 
 sities of the frame never require that its attachments should 
 be brought nearer than eleven inches. It is obvious that in such 
 a case three-fourths in length of the muscular fibre would be 
 
 * A muscle can probably contract to three-fifths of the length which 
 it presents in its relaxed and elongated state. 
 
336 Use of Tendons illustrated. 
 
 useless, and that their place might as well be supplied by 
 an inextensible substance. In the wise economy of Nature, 
 this circumstance has not been overlooked : in cases similar 
 to that supposed, as in the instance of several of the muscles 
 which move the wrist, tendon is used in the place of an un- 
 necessary length of muscular fibre, and a considerable ex- 
 pense of muscular power is saved. 
 
 In the instance given of the tendon of the fore-arm a 
 provision is made for symmetry. The graceful outline of 
 the leg and ankle is produced in a similar manner, the vo- 
 lume of the limb being diminished at the lower part by the 
 substitution of tendon for muscular substance. Upon other 
 occasions the same object is attained by a different contrivance. 
 The leg, to pursue the last illustration, would certainly lose 
 its symmetry, if it had a calf on the fore part ; or in other 
 words if the muscles, which bend the ancle joint, formed a 
 short thick mass of flesh below the knee, with tendons taper- 
 ing to the instep. Instead of this arrangement, the short fibres, 
 which belong to the extensors of the toes, rise from the 
 whole length of the tibia and fibula ; and each muscle has 
 a long tendon beginning at its upper part, to which its fibres 
 are inserted in succession, so as to produce a resemblance 
 to the feathered part and stem of a quill : muscles of this 
 appearance are hence termed pennated muscles. Sometimes 
 it happens that the symmetry of a limb is best consulted by 
 interposing the muscular substance between two tendons : 
 the rectus femoris thus has a long tendinous origin as well 
 as a tendinous insertion. In this and similar cases a se- 
 cond advantage is gained : a tendinous attachment occu- 
 pies a much smaller surface of bone than a muscular at- 
 tachment. 
 
 The attachment of a muscle to bone is fleshy instead of 
 tendinous, when it is requisite that different fasciculi of the 
 same muscle should draw in different directions, as in the 
 instance of the glutaeus medius and glutaeus minimus, or 
 when the muscle through this means obtains a more conve- 
 nient form, as is the case with the obturator internus. 
 
 In the rectus femoris, the semi-membranosus, and other 
 muscles, in which a mass of muscular substance is inter- 
 
Of Antagonist Muscles. 337 
 
 posed between two tendons, each tendon forms near its at- 
 tachment a strong thick chord, but spreads out, and termi- 
 nates as a membrane towards the belly of the muscle. It is 
 to be remarked, that in these instances the two membranous 
 expansions are formed upon opposite sides of the muscle : 
 if the upper membraniform tendon is in front, the lower is 
 situated behind the belly of the muscle. The end attained 
 by this arrangement is very apparent ; it provides for the 
 equal length, and consequently for the equal action of all 
 the fibres. 
 
 In the majority of instances the direction of muscles is 
 parallel, or at least not vertical to the axis of the bone 
 which they move ; so that their action is for the most part 
 oblique. It is obvious that this application of force is at- 
 tended with a considerable loss of power : an advantage 
 however of another kind is gained by it. A muscle thus 
 disposed is capable of moving the point of its insertion 
 through a large space, while the extent, to which it shortens, 
 is very trifling. The action of the supinator radii longus 
 may serve to illustrate this position : but the action of the 
 intercostals is more obvious, and is the instance more com- 
 monly selected. 
 
 The muscles of the trunk and limbs are distributed in a 
 double series, the one as antagonists to the other : never- 
 theless those, which on one occasion are directly opposed to 
 each other, cuar-another may act in concert. Thus the pec- 
 toralis major is employed in carrying the humerus forwards, 
 the latissimus dorsi, in carrying it backwards: but both may 
 concur in simply depressing the arm. 
 
 The problem solved in the direction and place assigned 
 to different muscles is probably, in what manner should 
 they be disposed, in order that they may individually com- 
 bine in the greatest variety of actions, and that one type 
 may serve for the frame of numerous families of animals 
 with habits essentially different. It is a remark not with- 
 out the profoundest interest, that in many instances parts 
 serviceable in one animal are found to exist in others where 
 they are evidently useless, if indeed that provision be use- 
 less, which stamps the strongest evidence of an uniformity 
 
338 Instances of the different kinds of Levers. 
 
 of design in the various families of animals, by leaving ves- 
 tiges of organs in one race, which only find their physical 
 importance and development in other beings. 
 
 The plantaris is a part of this description : it is inserted 
 in man into the heel bone exclusively. But in simise this 
 muscle is attached to the plantar fascia, so as to give ten- 
 sion to that membrane, with a view to the protection of the 
 plantar vessels and nerves, when the prehensile foot of the 
 animal grasps any hard substance. 
 
 As it might be expected, various theorems in mechanics 
 find an illustration in the common frame of the bones and 
 muscles. In every movement of the body a lever of one 
 kind or another is set in motion. 
 
 A lever is supposed to be an inflexible line, which is moved 
 upon a point termed its fulcrum, that is placed either at one 
 extremity or intermediately, by a force applied at a different 
 part, so as to overcome a resistance which operates upon a 
 third point of the lever. Three sorts of levers are formed by 
 varying the relative place of the fulcrum, the power, and 
 the resistance. In the first, the fulcrum is intermediate, in 
 the second the resistance, in the third the power. 
 
 The mechanical advantage of a lever is easily estimated ; 
 the power or the resistance has the advantage in proportion 
 to its relative distance from the fulcrum, or in proportion as 
 the length of the arm on which the one operates exceeds 
 the length of the arm on which the other operates. An equi- 
 librium is produced, when the force and resistance, and the 
 distance of each from the fulcrum, are equal. 
 
 On the other hand, in proportion as power is sacrificed, 
 velocity is gained. Whenever the resistance operates upon 
 the longer arm, the weight lifted traverses in the same time 
 a greater space than the point at which the force is applied. 
 Now rapidity appears to be a more important object to be 
 attained in the movements of the animal frame than mecha- 
 nical force : accordingly in most instances the third kind of 
 lever is employed, which essentially involves a greater dis- 
 tance between the resistance and the fulcrum, than between 
 the power and the fulcrum. To such an extent is this prin- 
 ciple carried, that in order to balance a weight of one pound 
 
Strength in the Human Frame sacrificed to Velocity. 339 
 
 in the hand, the biceps flexor cubiti, if it were possible to 
 suppose it acting alone, must exert a force equal to ten 
 pounds. 
 
 On many occasions velocity again is obtained by the nu- 
 merous joints, which move in concert to one object. Thus 
 when a straight blow is struck, the hand moves forward 
 with greater velocity than is communicable by a single set 
 of muscles ; at one and the same instant the humerus is 
 raised and the fore-arm depressed ; and the fist, impelled 
 by two forces, moves in the diagonal. 
 
 The only instance, in which the second kind of lever is 
 employed in the human frame, and velocity sacrificed to 
 mechanical power, is to be found in the foot : the tendo 
 Achillis is attached to one extremity of the lever, upon an 
 intermediate point of which the weight of the body rests when 
 in stepping forward we rise upon the ball of the great toe. 
 
 The strength of muscular fibre is unknown : but it is sup- 
 posed, that a muscle, the transverse section of which would 
 present a surface an inch square, might exert a force equal to 
 five hundred pounds. It seems likely that there may be an 
 original difference in the quality of muscles ; and that some 
 of greater volume are essentially weaker than others less in 
 bulk but of more rigid fibre. Much, however, depends upon 
 the energy with which the will operates. During frenzy, a 
 slight and slender frame is often found capable of going far 
 beyond the most powerful efforts of the strongest man when 
 acting under less excitement. 
 
 The continued action of a voluntary muscle must meta- 
 physically depend upon successive impulses of the will re- 
 peated at infinitely short intervals : and a curious observa- 
 tion of Dr. Wollaston's makes it appear, that in a continued 
 muscular effort, the renewal of the muscular contractions 
 may be even appreciable by the senses *. 
 
 The body stands, when erect, on the same principle as a 
 modelled image of similar weight : its position is secure, as 
 long as a perpendicular drawn from its centre of gravity 
 would fall within its base. The muscles support the frame 
 
 * Phil. Trans, vol. c, p. 5. 
 
340 Of the Erect Posture and of Locomotion. 
 
 erect, by keeping the joints rigid in any attitude which may 
 be assumed involving the preceding condition. The securest 
 posture, that could be given to a model, would be the se- 
 curest for the human body. What renders the attitude of 
 standing practically so firm in a living person is the power 
 we have of anticipating on what side it will be necessary to 
 make resistance, and of increasing the length of the base 
 on which we rest, in the direction in which violence is 
 threatened. 
 
 If a person while standing erect be suddenly killed, 
 he drops prone on the ground : the body falls forwards, 
 because the greater part of its weight is placed be- 
 fore the column of support, which, in the supposed case, 
 suddenly gives way at every part where there is a joint. 
 The tendency of the body to fall forward seems provided 
 against accidents of a less grave character, to which we are 
 occasionally liable : we thus fall, when we lose our balance, 
 against objects which we see, and towards which our hands 
 and arms are readily advanced to break our fall. 
 
 In the more violent kinds of locomotion, in vaulting and 
 running, the body is thrown forwards by the re-action of the 
 soil, that follows the sudden pressure made upon it by a si- 
 multaneous contraction of the extensor muscles of the ankle, 
 knee, and hip. 
 
 The insecurity attending the preceding methods of pro- 
 gression is avoided in walking, in which the office of sup- 
 porting the body is alternately transferred from one leg to 
 the other, and one foot is always planted on the ground. 
 
 When we purpose to step forward in walking, we begin 
 by inclining the body to one side, till it rests upon one 
 leg. The opposite limb is then advanced, the knee being 
 at first slightly bent in order to detach the foot from the 
 ground. The hip-joint of the first limb is finally extended, 
 by which means the trunk is propelled forwards, so as to be 
 received the next instant upon the limb which was ad- 
 vanced. Each step may thus be resolved into three ele- 
 mentary movements. 
 
 The different gestures of the body, like the tones of the 
 voice, betray the presence of strong emotions. In anger 
 
Of Physiognomy. 
 
 341 
 
 the step is hurried, as the accents are; the hand is unsteady 
 when the mind is agitated, is spread abroad in wonder, is 
 clenched in agony. 
 
 Voluntary muscles are observed to take a bias towards 
 those actions which they have frequently repeated. The 
 mechanic, when he has divested himself of the dress and 
 implements of his trade, still betrays by the carriage of his 
 limbs the occupation to which his working-day labours are 
 devoted. 
 
 Individual character is formed of peculiar habits of 
 thought and feeling: now each mood of thought and 
 feeling has its corresponding sign in some change of 
 feature. But changes of feature, or changes in the ex- 
 pression of the countenance, are produced by muscular 
 action ; and the muscles of the face, like those of the 
 trunk and limbs, unconsciously take a tone from the actions 
 in which they are habitually employed : thus the prevailing 
 character of the mind becomes pourtrayed in the lineaments 
 which the countenance wears, even when the mind and 
 the features are in perfect repose. 
 
 SECTION II. 
 
 Of the Mechanism of Speech. 
 
 It has been already mentioned, that the physical cause of 
 continued sound is a succession of impulses, which, in 
 whatever way they may have originated, are transmitted by 
 the vibrations of elastic media. 
 
 The simplest example of the production of continued 
 sound is shown in an instrument invented by Cagniard de la 
 Tour, called the syren. The subjoined figure represents this 
 instrument. 
 
 B C 
 
 A 
 
 
342 Various means of producing Sound. 
 
 It is supposed, that air (or water, if the instrument be 
 placed under water) is impelled into A, so as to keep the 
 reservoir full, from which the fluid may issue by the holes 
 in the surface B. Now if the disc C, having holes exactly 
 corresponding to those in B, be pressed close to B, and be 
 made to revolve upon an axis D, it is evident that the holes 
 in B will be alternately opened and shut. Each time that 
 they are opened, there will be a jet of fluid which will 
 strike the medium without. By the velocity with which C 
 is made to revolve, the frequency of the recurrence of these 
 impulses will be regulated; the frequency necessary to 
 produce a continued sound may thus be ascertained, as well 
 as the number of impulses by which a definite pitch is pro- 
 duced. This instrument is therefore a perfect tonometer. 
 
 The vibration of a string presents an instance nearly as 
 simple as the preceding of the production of sound. If a 
 tense chord, A C, be drawn to A B C, and let go, it returns 
 
 B 
 
 A ^st " - ~ Sc 
 
 
 to A C, and through the motion it has acquired is carried 
 to A D C. It is then brought back by its elasticity towards 
 ABC, then returns towards ADC, and continues to vibrate, 
 its excursions becoming at each vibration less in extent. 
 Each excursion gives an impulse to the air, and the number 
 of excursions in a given time determines the pitch of the 
 sound. 
 
 The action of the bow of a violin upon the string may 
 equally be illustrated by the -preceding diagram; but, in 
 this case, it is the friction of the hairs of the bow that car- 
 ries to B the string, which then escapes, and flies back to D. 
 The continued pressure of the bow has the effect of sustain- 
 ing the sound at a given loudness, or even of raising it, 
 which else would die away with the diminishing excursions 
 of the string. 
 
 Suppose the string to be moved by the wind, as in the 
 
.*, Of the Production of Sound by the Lips. 343 
 
 /Eolian harp, its vibrations so produced may serve to illus- 
 trate the next instance which I have to mention. 
 
 If you blow through a tube of Indian rubber, or parch- 
 ment, or one formed of the stalk of grass, a sound may 
 be produced, as soon as you compress its sides at a part 
 near the mouth with the finger and thumb. The figure 
 subjoined represents the effect which takes place. The 
 
 narrowed part of the tube under the pressure of the air 
 blown into it becomes dilated (suppose to the dotted lines) ; 
 it then recovers itself; again yields, and is again narrowed. 
 The alternate enlargement and contraction of the aperture 
 is the source of the succession of impulses which cause the 
 sound which is heard. 
 
 Or, to bring the case still nearer home, with a little prac- 
 tice any one may produce tones by the lips. The difficulty 
 at first experienced consists in giving the lips adequate ten- 
 sion ; but when this difficulty is overcome, musical sounds 
 follow the breath, produced as it appears by the alternate 
 receding of the lips, and their recovery, in the manner shown 
 in the preceding instance, or by the adjoined diagram. 
 
 I have heard a performer, who had such perfect command 
 of the lips, that he could by their means imitate any one of 
 a variety of instruments, and thus play one part of a com- 
 
 Y 2 
 
344 
 
 The Chorda Voc.ales comparable to the Lips. 
 
 position by the lips, at the same time that with the larynx 
 he produced the higher tones belonging to another part of 
 the music. The mechanism employed in this instance is 
 different from that used in whistling, the nature of which 
 will be afterwards noticed. 
 
 Now the whole vocal mecha- 
 nism consists of the following 
 parts; Of the lungs or bel- 
 lows, capable of transmitting, 
 by means of the connecting 
 windpipe, a current of air 
 through an apparatus called 
 the larynx ; the air having sub- 
 sequently to pass through a 
 variable cavity, consisting of 
 the pharynx, mouth, and nose. 
 
 But the larynx, which is the part of the mechanism in 
 which we ascertain that the vocal sounds originate, admits 
 of being compared with the lips, when the latter are in a 
 state of adequate tension. 
 
 Variable cavity. 
 Larynx. 
 
 3 
 
 5 
 
 &- 
 
 *c 
 
 f 
 
 Lungs or bellows. 
 
 The figure here introduced represents a transverse and 
 vertical section of the larynx : the letters [E E] show the 
 parts comparable to the lips in the preceding instance. 
 They are called the chordae vocales. Their alternate vi- 
 
Of the Structure of the Larynx. 345 
 
 brations towards and from the dotted lines under the pres- 
 sure of the issuing air, are certainly the cause of those im- 
 pulses upon which the sounds of the voice depend. 
 
 Let me now proceed to explain by what means the chordae 
 vocales are placed in a condition to produce sound. 
 
 By far the most valuable account of the mechanism of the hu- 
 man larynx, which has been published, is that given by Mr. 
 Willis in the Cambridge Philosophical Transactions for 1832. 
 The description of the disposition of the muscles of the la- 
 rynx, and the analysis of their action, which this author has 
 given, appear to me equally exact and original. I shall en- 
 deavour to convey to my reader the result of his investiga- 
 tions. 
 
 The reader is aware that upon the top of the windpipe, 
 which is a pile of cartilaginous rings, serving to keep the 
 passage from the lungs always open, a stout annulus is 
 placed, called the cricoi'd cartilage : it is marked B in the 
 two figures which immediately follow. 
 
 Upon the upper surface of the back part of the cricoid, 
 are placed two small pyramidal cartilages, called the arytae- 
 noids : they are marked D, in the following figures. Their 
 bases are hollowed, and they have a sliding motion in every 
 sense upon the cricoid, to which they are tied by the strong 
 ligaments marked D. 
 
 The thyreoid or scutiform cartilage [D], bent at its 
 middle to a right angle, encloses and protects the cricoid 
 and the arytaenoi'ds. It is articulated to the sides of the 
 former by two processes upon which it is capable of being 
 moved in a rotatory motion forwards and downwards, or 
 backwards and upwards. 
 
 The chordae vocales or vocal ligaments [E E] extend from 
 the base of either arytaenoi'd cartilage to meet at a common 
 insertion in the fore part of the thyreoid. They are formed 
 of fibres possessing the highest degree of elasticity. 
 
 The opening between the chordae vocales is called the 
 rima glottidis. 
 
 A fine mucous membrane prolonged from the posterior 
 fauces is drawn over the interior of the larynx, and extends 
 from thence down the trachea into the lungs. 
 
346 Of the Structure of the Larynx. 
 
 Of the two figures upon the opposite page, the first 
 represents a side view of a dissected larynx : the upper 
 three-fourths of the left half of the thyreo'id, with the left 
 arytseno'id cartilage, and the left chorda vocalis are supposed 
 to have been removed, so as to show the flat inner surface 
 of the right arytsenoid, with its ligament and the chorda 
 vocalis attached to it. 
 
 The second figure represents the same cartilages as seen 
 from above, with the insertions of the different muscles 
 which move them. 
 
 The muscles are designated by numbers. 
 
 1. Represents the erico-thyreoideus. 
 
 2. The thyreo-arytaeno'ideus. 
 
 3. The crico-arytseno'ideus posticus. 
 
 4. The crico-arytaenoi'deus lateralis. 
 
 5. Half of the arytaenoideus transversus, and of the ob- 
 liqui. 
 
 I have not introduced into either of these diagrams the 
 cornua laryngis, or the epiglottis, or the upper vocal liga- 
 ments, or the ventricles of the larynx, inasmuch as their in- 
 fluence in producing or modifying sound is unknown. 
 
 The letters in the opposite figures represent, 
 
 A. The thyreo'id cartilage. 
 
 B. The cricoid. 
 
 C. The arytseno'id. 
 
 D. The ligament, by which the aryteenoi'd is attached to 
 the cricoid. 
 
 E. The vocal chord, or vocal ligament of either side. 
 
 K. The rinia glottidis, or passage between the vocal 
 chords. 
 
 In the next printed page I have given Mr. Willis's tabu- 
 lar view of the results produced by the action of the 
 muscles of the larynx. The direction of the fibres of these 
 muscles, which is represented in the diagrams, will enable 
 the professional reader to follow Mr. Willis's account of 
 their action, if not to satisfy himself of its correctness. 
 
Of the Structure of the Larynx:. 347 
 
348 
 
 Action of the Muscles of the Glottis. 
 
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State of the Rima Glottidis in Vocalization. 349 
 
 From this enumeration of the muscles of the larynx and 
 of their uses, it is evident that an ample provision exists 
 for enlarging or contracting the area of the rima glotticlis, 
 and for increasing or diminishing the tension of the vocal 
 ligaments. Let us proceed to inquire to what extent either 
 of these effects is employed in producing ordinary vocaliza- 
 tion. 
 
 A patient was brought into the Middlesex Hospital, who 
 in attempting suicide had cut through the larynx imme- 
 diately above the vocal ligaments. The wound was oblique, 
 and on the left side had injured the vocal ligament and 
 the arytseno'id cartilage. When the patient was tranquil, 
 and breathed gently, the rima glottidis formed a triangular 
 opening, like figure 1 of the two following. 
 
 1 2 
 
 When he attempted to vocalize (although in one only of 
 several attempts a laryngeal sound was produced), the 
 vocal ligaments were brought nearly parallel, and the aper- 
 ture of the rima glottidis became narrow and linear, as it is 
 represented in figure 2. 
 
 Another patient in the Middlesex Hospital, who lived 
 many weeks, had cut into the pharynx immediately above 
 the thyreoi'd cartilage. Upon looking into the wound, the 
 membrane covering the fore part of the arytaenoi'ds was 
 distinctly seen, and under different circumstances presented 
 the appearances shown in the following figures. 
 
 When the patient breathed gently, the sesamoid bodies 
 [FF] fig. 1 (or cornua majora laryngis, as they better de- 
 serve to be called), holding up at two points the membrane 
 which forms the posterior and upper boundary of the la- 
 rynx, showed by their remoteness the open state of the rima 
 
350 Tension of the Ligaments in Vocalization* 
 
 glottidis, and the distance from each other of the arytseno'id 
 cartilages, before and without which they are placed. 
 
 When the patient closed the glottis by an effort, the ap- 
 pearance represented in fig. 2 was produced ; the cornua 
 majora were seen to be drawn nearer to each other, and 
 the arytsenoid cartilages were visibly brought into contact. 
 When the patient uttered a laryngeal sound, the appearance 
 of these parts continued exactly the same as when the glottis 
 was closed. 
 
 The observations which have been mentioned sufficiently 
 show, that, during vocalization, the aperture of the glottis 
 is reduced to a narrow longitudinal fissure. 
 
 The difference in the pitch of vocal sounds we may pre- 
 sume to have no reference to the size of the aperture 
 between the vocal chords, or to any alteration of their 
 length, but to depend upon their tension alone. The es- 
 sential superiority of the vocal organ to any instrument 
 produced by human art, consists in the varied degrees of 
 tension, susceptible of the finest modulation, which can be 
 at will and instantaneously imparted to the vibrating chords 
 in the larynx. 
 
 Mr. Willis remarks however, that, for the production of 
 laryngeal sounds, something more is requisite than a definite 
 tension of the chordae vocales. He shows experimentally, that 
 in order that the edges of two membranes (as of leather or 
 Indian rubber) opposed to each other with a narrow interval, 
 may vibrate, the parts of the membranes near their edges 
 must be brought parallel to each other. Comparing this 
 disposition of membranes in his expe- 
 riment with the parts of the larynx, 
 he supposes that the latter will not 
 vocalize, unless some change, indepen- 
 dent of and superadded to the tension 
 of the ligaments, be produced in their 
 relative position. The adjoined figures 
 show what Mr. Willis considers the ordi- 
 nary position, and the vocalizing position, 
 of the chordaa vocaies [ E E] . The former is 
 shown by the continued line, the latter 
 by the interrupted line. 
 
Vocalizing Position of the Ligaments. 351 
 
 The following appears to be the experimental proof upon 
 which Mr. Willis founds his conclusion, that some change in 
 the relative position of the vocal chords is necessary to make 
 them speak. If the finger is placed upon the membrane 
 which intervenes between the thyreoid and cricoid carti- 
 lages, their approximation or increased remoteness may 
 readily be felt. Now their approximation being produced 
 by the action of the crico-thyreoid muscles involves an 
 increased tension of the ligaments. But it is possible by an 
 effort to keep these cartilages approximated, while some- 
 thing is still wanting in the internal arrangement of the la- 
 rynx to fit it for the production of sound. When the thy- 
 reoid and cricoid are thus approximated, and the ligaments 
 thus shown to be in a state of tension, if air is impelled 
 through the larynx, sound does not necessarily follow : 
 the ligaments have still, Mr. Willis concludes, to be placed 
 in the vocalizing position. For an account of the muscular 
 actions by which this is accomplished, I must refer the 
 reader to Mr. Willis's original paper. 
 
 It is evident, that we are now acquainted with the 
 principal elements in the production of sound in the la- 
 rynx. Much, however, remains to be explained, which can 
 only be elucidated through new series of physical experi- 
 ments. The use of the ventricles, of the upper ligaments 
 of the glottis, and of the epiglottis, are subjects of this 
 nature. 
 
 The theory of Savart converted the ventricles of the la- 
 rynx into a bird-call. He supposed, that the two pairs of 
 ligaments, with the intermediate chamber of the ventricles, 
 form an apparatus analogous to that instrument. But it 
 is evident, that the mechanism , of the chord as vocales fits 
 them for a very different purpose than forming an apparatus 
 of this description. The quality of the vocal sound, it is 
 indeed presumable, would be widely different from what it 
 is, were the theory of Savart just. It should, in that case, ap- 
 proach the character of a whistle. It is thus, at least, that 
 the lips are made to whistle, by combining them with a 
 chamber. In whistling, we form a bird-call at the mouth, 
 of which one aperture is that at the lips : the other is made 
 
352 Use of the Windpipe in Vocalization. 
 
 by the approximation of the tip of the tongue to the palate, 
 and the chamber is the space between : the shrill and pe- 
 culiar sound is owing to the construction, to which Savart 
 would find a parallel in the human larynx. 
 
 There is another part in the vocal apparatus, the influence 
 of which has probably not been sufficiently adverted to : 
 this is the trachea. Mr. Wheatstone proposes the follow- 
 ing theory of its influence. 
 
 Such a vibrating apparatus as 1 have described the li- 
 gaments of the glottis to compose, is by itself capable, from 
 the varying tension of those ligaments, of producing all 
 those sounds of which we find the voice to be susceptible. 
 But the intervention of a tube between the luno-s and the 
 
 O 
 
 larynx, must necessarily exercise an important influence on 
 the voice, though it has never yet been taken into consi- 
 deration. For, if we unite such an apparatus, or a free reed, 
 which may serve as a substitute for it, with a tube (sup- 
 posing it for the moment fixed to a determinate degree of 
 pitch), it is found, that, unless the column of air in the 
 tube is of such a length as to be separately capable of pro- 
 ducing the same number of vibrations, the sound cannot be 
 obtained in its greatest force and purity, and that when the 
 tube is half this length, the discordance between the tube and 
 the reed is so great, as to prevent the production of the 
 sound : between these limits, the sound is intermediate in 
 intensity and quality. This influence of the tube is by experi- 
 ment found to be the same, whether the tube be placed after 
 the reed, as in several wind instruments, or before it, as in 
 the vocal organ. We will now suppose the tube to be un- 
 alterable in its length, and the reed necessarily to undergo 
 all its varying modifications of pitch : the sounds, instead 
 of being of even quality, will be irregular in intensity, and 
 require different degrees of effort to produce them ; while, 
 in some parts of the scale, they will be totally extinguished. 
 All this may be prevented, and the utmost regularity ob- 
 tained, by shortening the tube, in proportion as the vibra- 
 tions of the reed increase in frequency. The trachea is ob- 
 viously incapable of changing its length within limits suffi- 
 ciently considerable to serve this purpose: butSavart's expe- 
 
Of the Compass of the Human Voice. 353 
 
 riments have shown, that a tube of constant length may be 
 made to produce a great range of sounds, by making it of 
 elastic sides susceptible of variable tension. The analogy 
 between such a tube and the trachea is perfect. 
 
 One source of giving increased tension to the windpipe is 
 the action of the transverse muscular fibres which bind the 
 ends of its cartilages together. A second is the elevation 
 of the larynx, which follows in so remarkable a degree the 
 elevation of the pitch of the voice. 
 
 We may suppose, that practice in singing improves the 
 voice, in part by giving us a more ready command over the 
 tension of the windpipe, in part by enabling us to regulate 
 and vary the opening of the glottis while we preserve the 
 tension of the vocal chords. 
 
 As the pitch of vocal sounds depends upon the frequency 
 of the vibrations of the chordae vocales, their loudness is 
 determined by the extent of the excursions which they make 
 in vibrating. The difference between the voices of men, 
 and those of women and boys, results from the smaller la- 
 rynx and shorter vocal chords of the latter. 
 
 The conditions which produce different qualities of voice 
 are not known. The falsetto voice, Mr. Willis supposes, may 
 be produced by the shortening of the chordae vocales. Mr. 
 Wheatstone supposes, that it may result from the tension 
 of the windpipe enabling it to reinforce the laryngeal sounds 
 by subdivisions. 
 
 The range of the voice seldom exceeds two octaves and a 
 half. Dr. Bennati mentions, however, that the compass of 
 his own voice extends to three octaves. He mentions as an 
 unexpected effect of removing part of the tonsils, that he 
 has found the operation to be followed by the raising of the 
 voice half an octave, without altering its compass. I sup- 
 pose that this effect results from the cicatrix stretching the 
 mucous membrane of the larynx, and thus giving increased 
 tension to its inner surface. 
 
 When vocal sounds have been formed in the larynx, they 
 have to receive articulation from the shape of the cavities 
 through which the air has yet to pass. 
 
354 Of Articulation. 
 
 The elementary articulate sounds in a language consti- 
 tute its alphabet. They are divided into vowels and conso- 
 nants. The former are produced when the passage of the 
 air through the fauces is uninterrupted, the fauces being 
 only more or less narrowed. They differ from each other 
 in requiring a different elevation of the tongue, or con- 
 traction of the lips. Consonants are produced when the 
 breath or voice in its passage through the cavities before the 
 larynx is interrupted by the narrowing of some part of the 
 channel. 
 
 M. Deleau made the following experiment, demonstrating 
 tha tthe articulation of vocal sounds takes place in the fauces. 
 He introduced through the nostrils into the pharynx a flexible 
 tube, and impelled air through it into the fauces : then closing 
 the larynx, he threw the fauces into the different positions re- 
 quisite for producing articulate sounds, when the air im- 
 pelled from the gum bottle became an audible whisper. 
 Dr. Bennati repeated this experiment, allowing at the same 
 time laryngeal sounds to pass into the fauces, when each 
 articulated letter was heard double, in a voice at once and 
 in a whisper. 
 
 Various attempts have been made to analyse and to pro- 
 duce by instruments the phenomena of articulate speech. 
 And, first, of the mechanism of vowel sounds. 
 
 Kratzenstein found, that, by using little tubes of different 
 shapes adapted to an instrument that could produce sound, 
 he could determine different vowel tones. 
 
 De Kempelin produced vowel sounds by means of an In- 
 dian-rubber bell similarly adapted, the shape and size of 
 which he altered by the hand. 
 
 But Mr. Willis's recent investigations are the most satis- 
 factory. Mr. Willis attached to an apparatus which pro- 
 duced sound, a tube, which was capable, if immediately ex- 
 cited, of producing a determinate note. By altering the 
 length of this tube, the original sound was made to lose its 
 quality, and assumed the character of different vowels ; 
 evincing, that the vowel quality added to a note is the 
 mere co-existence of a determinate musical sound. 
 
Of the Vowel Sounds. 
 
 355 
 
 The changes which take place in the human fauces, more 
 resemble those which De Kempelin employed. 
 
 The adjoined diagram dis- 
 plays the position of the fauces 
 requisite for pronouncing au 9 
 a, ee. The position for o, and 
 oo, is obtained by placing the 
 fauces in the position for au, 
 and then approximating the 
 lips. 
 
 The consonantal sounds which -we employ, admit of being 
 divided in the following manner. 
 
 There are some which may be rendered audible without a 
 vowel sound. This is the case with p, t, k, h, f, th, sh, s. 
 They may be termed aspirates. Others, again, without any 
 appreciable difference in the shape of the fauces from the 
 form required for several of the preceding to which they 
 are allied, are not heard without a vowel sound. They may 
 be termed sonants. 
 
 Again, in uttering the greater number of sounds, the soft 
 palate is raised, and the passage of the air through the nos- 
 trils obstructed. By allowing the air to pass through the 
 nostrils, a peculiar character is given to the articulation, 
 and nasal letters are produced. 
 
 Consonantal sounds, again, are divided into continuous 
 and explosive. 
 
 Continuous consonants are obtained, when the breath or 
 voice passes through this cavity, interrupted by the narrow- 
 ing of some part of the passage. 
 
 Explosive consonants are heard, when the breath or voice, 
 passing through the mouth, is suddenly impeded by the 
 entire closing of some part of the passage, or is allowed to 
 burst out by the sudden opening of the same. 
 
356 Of Consonantal Sounds. 
 
 The following scheme contains the arrangement given by 
 Mr. Wheatstone, which I have adopted. 
 Aspirates. Sonants. Nasal. 
 
 p b ni labial. 
 
 t d n dental. 
 
 k q g palatal. 
 
 Explosive sounds. 
 
 fh v 
 
 th . dh 
 
 sh f 
 
 s z 
 
 1 
 
 r 
 
 Continuous sounds. 
 
 The opposite diagrams display the 
 position of the tongue and lips in the 
 pronunciation of different consonants. 
 The reader, if he is sufficiently inte- 
 rested in the subject, may, by referring 
 to them, the more readily detect in his 
 own articulation the motions of the 
 tongue and lips by which the different 
 sounds are determined. There are se- 
 veral curious applications of this study. 
 It would not be difficult to form an 
 apparatus capable of articulating each 
 letter. De Kempelin even succeeded 
 in constructing a speaking machine, 
 which was capable of uttering entire 
 phrases ; some of which were " Vous 
 etes mon ami je vous aime de tout 
 mon cceur Leopoldus secundus Ro- 
 manorum imperator," &c. De Kempe- 
 lin published a detailed account of the 
 construction of this instrument, at Vi- 
 enna, in 1791. 
 
 The following application of the 
 study of the mechanism of. speech 
 
Of Stammering. 357 
 
 may interest some of my readers. The Italian and the 
 Spanish languages derived from the Latin are softer to the 
 ear than that language. Let me show, by an example, that 
 they are actually softer, or require less effort, in the pro- 
 nunciation. The Latin word clamare, becomes in Spanish 
 llamar, in Italian chiamare; that is to say, of the two con- 
 sonants which begin the word, the Italians drop one, the 
 Spaniards the other. In the following diagram, the conti- 
 nued line shows the double and forced elevation of the 
 root and apex of the tongue necessary for the simultaneous 
 production of c and I: the two dotted lines show, that in 
 the softer languages of Spain and Italy half the effort only 
 is required for either. Plenus, pieno, lleno, are parallel in- 
 stances. 
 
 Many persons have an imperfect articulation of different 
 letters. The letter R is sounded by several with the uvula. 
 I have no doubt that its proper articulation might be acquired 
 by any one, who understood clearly that it is to be executed 
 by raising the tip of the tongue to the roof of the mouth, 
 and allowing it to vibrate in the current of air. 
 
 One cause of stammering is doubtless a physical difficulty 
 of articulating certain letters. One means, therefore, cal- 
 culated to remove this defect is to study carefully the mode 
 of pronouncing the difficult letters, to master exactly the 
 mechanism of their articulation, and to practise their pro- 
 nunciation repeatedly, slowly, and analytically. 
 
 The other rules to be followed by stammering persons 
 are, to speak always with a full chest, to speak slowly, to 
 pause the instant the hesitation begins, and, after waiting 
 
358 Of Coughing, Hiccupping, Sneezing. 
 
 four or five seconds, to make collectedly a second attempt. 
 It must be evidently useful to acquire by the habit of com- 
 position facility and variety of expression. In the worst 
 spasm of the glottis occurring to a stammering person, he 
 will often find the difficulty yield upon attempting a simple 
 vowel sound, after which any other letter will follow easily. 
 One of the most remarkable anomalies in articulate 
 speech is, that it may take place during inspiration. In that 
 case the breath drawn through the fauces is first cut into 
 letters, and subsequently receives a tone in its passage 
 through the larynx. It appears probable, that ventrilo- 
 quists occasionally avail themselves of this artifice to diver- 
 sify the character of their voice. In general, however, ven- 
 triloquists speak during expiration ; and their art depends 
 upon the flexibility of organ, and correctness of ear, through 
 which they modulate their tones to the character which 
 they would take in the situation, from which the imaginary 
 person in the dialogue is supposed to speak. 
 
 There are other sounds, the production of which I may 
 take this opportunity of explaining. 
 
 Coughing and hiccupping are produced by the passage of air 
 through the larynx upon its being suddenly opened. But the 
 direction of the current of air is reversed in the two cases : 
 coughing is an explosive expiration, hiccup an explosive in- 
 spiration. 
 
 In coughing, as in common utterance, the soft palate is 
 raised, and the entrance into the nostrils stopped. Sneezing 
 takes place when the soft palate is lowered : it is, therefore, 
 a nasal cough. 
 
 Laughter is exactly explained by the letters in which it 
 is commonly expressed ha, ha, ha ; lie, he, he a more or 
 less broad articulation of aspirated vowels. 
 
 With snoring, the larynx has nothing to do. The prin- 
 cipal sound occurs during inspiration ; and that, as well as 
 the weaker expiratory snore, is produced by the fluttering of 
 the uvula and of the edge of the velum pendulum palati in 
 the current of air. 
 
 The mechanism which contracts the aperture of the la- 
 rynx is called into action on other occasions, besides the 
 production of vocal sounds. If the most curious use of the 
 
Of the Mechanism by which the Larynx is closed. 359 
 
 larynx is the production of the voice, its most important 
 office is the protection of the lungs. With its numerous 
 muscles and quick sensibility, the larynx is placed as a 
 guard at the summit of the windpipe, to admit indeed the 
 entrance of the salubrious air, but to obstruct the passage 
 ef every thing that would prove noxious. 
 
 The double office of the larynx is strikingly illustrated, 
 when we extend our researches into comparative anatomy. 
 
 In the cetaceous mammalia, which are dumb, we find a 
 respiratory larynx alone. The windpipe terminates in little 
 more than a contractile circular aperture : and this opens, 
 not at the root of the tongue, but is prolonged as a pipe far 
 towards the nostrils, completely out of the way of the ali- 
 ment. 
 
 In birds, on the other hand, in which the vocal function 
 is so finely perfected, there is of course a larynx for sound, 
 as well as a larynx for closing the windpipe ; but they form 
 two separate organs. The latter, an apparatus of the sim- 
 plest construction, is placed at the top of the windpipe ; 
 the former, highly complicated, is situated in the chest at 
 the bifurcation of the trachea. 
 
 Now, in man, and in animals cast in the same type, there 
 are two nerves distributed to their single larynx. One, the 
 upper laryngeal nerve, has most to do with closing the la- 
 rynx. The other, the recurrent, is found, by the experiment 
 of dividing it, to have the most influence in the production 
 of vocal sounds. The upper is given off from the pneumo- 
 gastric, close upon the larynx. The recurrent is not given 
 off' till the pneumo-gastric has reached the chest, and then 
 has to make a long course backward to the throat. This 
 lengthened and circuitous course of the recurrent is a com- 
 mon theme of wonder in the anatomy of the nerves. I think 
 its purpose is explained by referring to the vocal organ of 
 birds. In birds, there are two nerves likewise on each 
 side. The upper corresponds exactly with the upper laryn- 
 geal of man ; it is the nerve to close the larynx of degluti- 
 tion. The lower nerve corresponds with our recurrent : it 
 is given off in the chest, and then it finds at once its desti- 
 nation. It is not recurrent, for the vocal larynx is not be- 
 
 z2 
 
360 Of the Larynx in reference to Deglutition. 
 
 hind it. The human inferior laryngeal nerve is doubtless 
 given off in the chest, for the preservation of the unity of 
 type of mammalia and birds : it is recurrent only, because 
 the human vocal larynx has its situation above. 
 
 But 'by what means is the passage through the larynx 
 closed? Mr. Willis has very ingeniously conjectured, that the 
 closure takes place through the inflation of the ventricles from 
 below, when their surfaces have been brought into contact, 
 and an expiration is attempted. In the simple upper la- 
 rynx however of birds, there are no ventricles : in their 
 case, the closure of the glottis must certainly be produced 
 by the close linear, apposition of two membranous edges 
 in a state of tension, and in exact contact. An objection 
 was likewise suggested to me by Mr. Wheatstone, which 
 appears fatal to Mr. Willis's hypothesis ; we can close the 
 larynx as well during inspiration as during expiration. 
 
 In the case of a patient in the Middlesex Hospital, to 
 which I have already referred, I could look into the upper 
 part of the larynx, and observe what took place when he 
 voluntarily closed the passage through it. The appearance 
 which the parts presented is exactly that delineated in the 
 lower fig. 2, p. 349 : it was identical with that observed during 
 vocalization. The lips of the glottis, or the reflection of 
 membrane from the cornua laryngis to the epiglottis, formed 
 an open funnel as before ; but the arytseno'ids were closely 
 pressed together, and the upper ligaments of the glottis, or 
 the walls of the ventricles, seemed brought into contact. 
 
 Whatever may be the exact nature of this provision, its 
 application is no less varied than it is important. Without 
 it, the next meal would be fatal : without it, we should be 
 unable to make a single muscular effort, in which the upper 
 part of the frame takes a share. 
 
 M. Magendie, I believe, first made the observation, that 
 the epiglottis is not the protector of the larynx against the 
 passage of food into the windpipe during deglutition. He 
 found, that that part might be removed from dogs, and that 
 they retained perfectly the power of swallowing : while, on 
 the other hand, the epiglottis being left entire, if the upper 
 laryngeal nerve was divided, the attempt to swallow inva- 
 
Of Spasmodic Closure of the Glottis. 361 
 
 riably brought on fits of choaking from the food finding its 
 way down the windpipe. 
 
 In the case of attempted suicide last referred to, the epi- 
 glottis was cut through : yet the patient, in two or three 
 days after the injury, swallowed easily, and without the 
 least irritation of the larynx ; although, so free was the 
 opening in the throat, that some of the fluid swallowed al- 
 ways ran out at the wound. 
 
 In attempts at breathing, when .the medium inspired is 
 highly noxious, the effect of the closure of the larynx is no 
 less admirable and perfect. When an animal is immersed in 
 carbonic acid, it strives to inspire: but no particle of the 
 gas can it draw with the whole force of its inspiratory mus- 
 cles through the glottis, which has closed upon the contact 
 of the hurtful agent. The same happens in submersion 
 under water, or even under quicksilver. The protection, in 
 these instances, is derived from the close consent between 
 the sentient mucous surface of the larynx and its muscles. 
 
 A frequent kind of disorder in parts thus endowed is an 
 increased susceptibility of the sentient surface, and a liabi- 
 lity to spasmodic action in the adjacent muscles, whose 
 office it is to act from impressions received upon the former. 
 Thus in the urethra, a morbidly sensible state of a part of 
 the mucous membrane produces spasmodic stricture, or a 
 continued contraction of the fibres of the ejaculator. In 
 the present instance the consequences are more fatal, in pro- 
 portion as the function impaired is more immediately im- 
 portant to life. An ulcer within the larynx is therefore a 
 very serious disease. When this complaint exists, the 
 whole surface of the larynx in time is rendered acutely 
 sensible; the air passing over it is now an irritant; the 
 fibres which close the opening of the larynx forcibly con- 
 tract: the patient cannot draw his breath, and is threatened 
 with instant suffocation. In hydrophobia again the por- 
 tentous symptom, whence the name of the disease is de- 
 rived, springs from the same cause. The surface of the larynx 
 is preternaturally sensible (or is the principal seat of that 
 morbid sensibility which is generally shared by every sentient 
 organ in this disease) ; the passage of food, of liquid espe- 
 
362 Closure of the Glottis necessary for muscular Efforts. 
 
 cially, the contact of which is more perfect than that of 
 solid food, excites a spasm which threatens suffocation; and 
 even if swallowing be not attempted, a paroxysm threaten- 
 ing suffocation takes place at intervals, either from the mere 
 contact of the air passing over the sensible surface of the 
 larynx, or in consequence of some sudden impression being 
 made on another organ. 
 
 It deserves to be remarked, that whenever suffocation is 
 threatened by a spasm upon the glottis, that particular 
 symptom admits of relief by opening the windpipe ; but no 
 doubt in many instances, and hydrophobia is possibly one 
 of them, the disease would prove hardly the less rapidly 
 fatal, were the spasm upon the larynx thus remedied *. 
 
 We may wonder that muscular fasciculi so slight as those 
 of the larynx, however advantageously placed, should be 
 capable of counteracting the efforts of the diaphragm and 
 other muscles of inspiration. But they are found to be no 
 less efficient against the muscles of expiration. It was 
 shown satisfactorily, by the experiments of M. Bourdon, 
 that an animal can neither leap, nor swim, nor vomit easily, 
 if it be made to breathe through a tube introduced into the 
 trachea. In the muscular fibres, which close the larynx, 
 Nature has provided the means of rendering the pliant walls 
 of the thorax immoveable, so that the muscles which arise 
 from the ribs may have a fixed point to act from. 
 
 * In dogs affected with hydrophobia this operation is useless. I have 
 had the means of trying this experiment, as well as several others, 
 through the kindness and with the assistance of Mr. Youatt, who is 
 zealous in every inquiry which tends to throw light upon this formi- 
 dable disease. 
 
CHAPTER XV. 
 
 OF GENERATION. 
 
 GENERATION is the production of a living being. Gene- 
 ration has been divided into true and equivocal. In the 
 former, the living being is produced by separation from an- 
 other within or upon which it grew. In the latter, it is sup- 
 posed that vital existence begins during the dissolution of or- 
 ganized matter; if a part of a dead animal or vegetable body 
 be macerated for a few days in water, the water is found to 
 teem with infusorial animalculae. No decisive evidence has, 
 however, been adduced, to prove that the animalculae of 
 infusions are produced by chemical action, and are not the 
 development of germs of their kind, which were previously 
 contained in the organized texture. 
 
 True generation, again, presents several varieties. The 
 simplest form is the spontaneous division of one living be- 
 ing into two. This extraordinary process has already been 
 described as it occurs in the nai's. Plants, in general, are 
 susceptible of propagation in this manner, if one part is 
 artificially separated from the rest. 
 
 Opposed to the preceding form of reproduction, is growth 
 from seeds or eggs, or the formation of germs, which under 
 favourable circumstances are capable of gradually expand- 
 ing into the character and dimensions of the parent. Re- 
 production of this kind presents several varieties. There 
 may be one organ in the parent, by which the germ is at 
 once formed and perfected. It is supposed, that the spore 
 of fungi is thus produced. Or there may be, in one indi- 
 vidual, two organs ; one in which the seed is formed, another 
 by the influence of which the seed is fertilized. This hap- 
 pens in monoecious plants. A remarkable variety of this 
 
364 Of true and of equivocal Generation. 
 
 mode of generation is, when one individual has both or- 
 gans, yet the concurrence of two individuals is requisite 
 for impregnation, which is of course reciprocal. This sin- 
 gular phenomenon occurs in snails. 
 
 Finally, the fertilizing organ may be exclusively found in 
 one individual of the species, while the organ for producing 
 the germ is met with in another. Then the distinction of 
 sex arises, and the beings are male and female. 
 
 The extensive subject of the reproduction of the species 
 requires to be treated in three sections : the first describing 
 the difference of the sexes, and the conditions necessary to 
 impregnation ; the second, the development of the ovum ; 
 the third, the source of the nourishment of the embryo, and 
 its connection with the uterus. 
 
 SECTION I. 
 Of the difference of the Sexes, and of Impregnation. 
 
 The sexual parts, in the female, consist of the vagina, 
 which is the organ of coition ; of the ovaries, in which the 
 germ is produced ; of '. the uterus, in which it is brought to 
 maturity and by the action of which it is born; of the 
 mammse, which supply the food of the infant for a long 
 period after birth. 
 
 The sexual parts in the male are the testes, the vesiculae 
 seminales, the prostate gland, the penis. 
 
 The ovaries, which form the essential part of the female 
 organs, are two flattened oval capsules, that are lodged in the 
 fold of the peritoneum, which forms the broad ligaments of 
 the uterus. They contain a loose succulent texture, in 
 which there are several small cysts, termed Graaffian vesi- 
 cles, filled with a transparent liquid : their number is from 
 fifteen to twenty ; they vary in size, the largest being about 
 four lines in its long diameter. At an early age the surface 
 of the ovaries is smooth ; after puberty it gradually becomes 
 marked with numerous scars or cicatrices. At the same 
 
Of the Female Organs of Generation. 365 
 
 lime one or more of the cysts are often found filled with a 
 yellow curd-like substance, which is called a corpus luteum. 
 The ovaries are supplied with blood by the spermatic ar- 
 teries, with nerves by the spermatic plexuses : on their re- 
 moval the sexual passion is entirely put an end to. 
 
 The uterus is a hollow fleshy organ placed between the 
 bladder and rectum. Its texture is fibrous, but it is much firmer 
 than muscular substance. The broader portion or body of 
 the uterus contains a triangular cavity, from each of two 
 corners of which a tube termed the Fallopian tube leads 
 towards the ovaries. The Fallopian tubes are about five 
 inches in length : they become tortuous and enlarged to- 
 wards their ovarian extremity, which is open, and fringed 
 with irregular filaments or fimbrise, that are capable of at- 
 taching themselves to the ovaries. The division of the Fal- 
 lopian tubes extinguishes the sexual appetite. 
 
 The third corner of the cavity of the uterus leads by a 
 long channel called the cervix uteri into the cavity of the 
 vagina. The aperture of the uterus is called the os uteri, or 
 os tincae. 
 
 The vagina is a mucous canal surrounded by a thick vas- 
 cular membrane. At the orifice are the labia and clitoris ; 
 and in virgins a crescentic fold of membrane, termed the 
 hymen, is found, leaving a narrow aperture. 
 
 The testes, which form the organs essential to the genital 
 system in the male sex, are glandular bodies. Either testis 
 is suspended in the scrotum by a part called the spermatic 
 chord, which consists of the spermatic artery and veins, of 
 the spermatic plexuses of nerves and absorbents, and of the 
 vas deferens, or excretory duct of the testis. The testis is 
 covered with a serous membrane called the tunica vaginalis. 
 When the reflected layer of this membrane is divided, the 
 testis is found to consist of a flattened oval substance ; to 
 the upper outer and back part of which a narrow flat slip 
 of flesh adheres, called the epididymis. 
 
 The vas deferens becomes extremely tortuous as it ap- 
 proaches the testis. When this duct has been filled with 
 quicksilver injected in a retrograde direction, or towards the 
 
366 Of the Male Organs. 
 
 body of the gland, we discover that the epididymis is but a 
 continuation of the same canal now reduced to a much less 
 diameter, of enormous length therefore, though coiled upon it- 
 self into so small a compass. The upper end of the epididymis 
 again leads by six or seven convoluted tubes, called vasa 
 efferentia, to the upper part of the testis, the texture of 
 which is firmer and denser than the rest : this part is termed 
 the corpus Highmorianum, or rete testis. It consists of a 
 network of tubes continuous on the one hand with the vasa 
 efferentia, on the other with the substance of the testis, 
 which is itself wholly made up of fine convoluted tubes. 
 The connection between the veins and arteries of the testis 
 and this tubular structure is unknown. 
 
 The vas deferens is of great strength and thickness. 
 Upon dividing it near the testis in adult animals recently 
 killed, a fluid is obtained, which consists chemically of wa- 
 ter, mucus, soda, and phosphate of lime, and contains nu- 
 merous minute animalculse, which as they are seen in the 
 dog, have a head, a body, and a tail. These animalcules are 
 not found in the seminal fluid of mules *. 
 
 The division of the spermatic chord on both sides, or the 
 removal of both the testes, destroys the sexual passion, and 
 produces impotence. 
 
 The vas deferens reaches the lower opening of the pelvis by 
 a circuitous route : having passed into the abdomen through 
 the spermatic passage, it descends by the side of the bladder 
 to the under part of its cervix, where it is joined by an oblong 
 body called the vesicula seminalis : the latter part consists 
 of a long blind tube, folded upon itself, the open extremity 
 of which enters the vas deferens at an acute angle. The 
 common duct after this junction is about half an inch in 
 length : it perforates the prostate gland between the third 
 lobe and the lateral lobes, to open upon the under part of 
 the urethra by an aperture at the side of the caput galli- 
 naginis. 
 
 The prostate gland is of the size of a small chesnut, and 
 
 "I (IJOO /J 
 
 * Mageiidic, Element de Physiologic, vol. ii, p. 518. 
 
Influence of the Genital Organs on the Frame. 367 
 
 of great toughness ; its numerous ducts open in the furrow 
 at the side of the caput gallinaginis, and pour out, when 
 the gland is squeezed, an opaque whitish liquid* 
 
 The glands of Cowper seem likewise to belong to the ge- 
 nerative system : commonly extremely minute, they are 
 sometimes met with of the size of peas, one being placed on 
 each side of the membranous portion of the urethra, below 
 which they are united by an isthmus: the duct of each, 
 about three inches in length, opens by perforating the mu- 
 cous membrane lining the spongy body of the penis. 
 
 The secretions of these parts find therefore a ready pas- 
 sage into the bulb of the urethra, from whence they are ex- 
 pelled by the action of the ejaculator seminis. 
 
 As in plants the organs of reproduction grow and are 
 shed annually, in animals they are in vigour only during 
 a period of their existence. The time at which their deve- 
 lopment takes place in man is termed puberty : before this 
 arrives, the sexual organs of either sex do not participate in 
 the growth of the body, but enlarge in a much slower 
 ratio. 
 
 Antecedently to puberty, the physical character of the 
 two sexes is the same : the same delicacy of complexion, 
 and high pitch of the voice, and slightness of the figure, are 
 met with in either sex. And many striking observations go 
 to prove, that the changes in these points, which supervene 
 in puberty, are in fact as one would superficially conjec- 
 ture the direct and immediate result of the development of 
 the sexual organs mysteriously influencing the growth of 
 the rest of the frame. The facts to which I advert are the 
 following. 
 
 The removal of the testes, or the division of the spermatic 
 chords in young male animals is followed occasionally by 
 the animal attaining a larger size than it would otherwise 
 have reached. But the shape of the mutilated animal has 
 never the perfect character of a male; the neck and shoulders 
 are commonly deficient in breadth and strength, while the 
 loins are generally large and heavy. 
 
 In boys, castration prevents the enlargement of the larynx 
 and the growth of the beard, and the whole frame when 
 
368 Influence of the Genital Organs on the Frame. 
 
 grown up presents an inconsistent and effeminate character ; 
 the skin soft, the body unusually fat. 
 
 Where parts of the genital system are naturally deficient 
 the body never acquires the true character of either sex. 
 A marine aged twenty-three was admitted, in the year 1779, 
 into the Royal Hospital at Plymouth : he had been there 
 only a few days when a suspicion arose of the individual 
 being a female. He had no beard : his breasts were fully 
 as large as those of a woman at that age : he was inclined 
 to be corpulent : his skin was uncommonly soft : the hands 
 fat and short : the thighs and legs like those of a woman. 
 The penis was found to be unusually small, the testes not 
 larger than in the foetal state. 
 
 Sir Everard Home, who describes the preceding case in 
 the Philosophical Transactions, mentions likewise the fol- 
 lowing. 
 
 A female lived to the age of twenty-nine years, who was 
 of a fair florid complexion, in stature not more than four 
 feet six inches ; her breadth across the chest was fourteen 
 inches ; across the pelvis but nine : her breasts and nipples 
 had not enlarged. She had never menstruated. There was 
 no appearance of hair on the pubes, nor was there any indi- 
 cation of puberty in body or mind at twenty-nine years of 
 age. It was found on examining the body after her death, 
 that the os tincae and uterus had their usual form, but had 
 never increased beyond their size in the infant state. The 
 passage into the uterus through the cervix was of the com- 
 mon shape, and the Fallopian tubes were pervious to the 
 fimbrise. The coats of the uterus were membranous. The 
 ovaria were so indistinct as rather to show the rudiments, 
 which ought to have formed them, than any part of the na- 
 tural structure. 
 
 Mr. Hunter has described the nature of a peculiar mon- 
 strosity which occurs in black cattle, and which throws ad- 
 ditional light upon the present subject. 
 
 When twin calves are born, they may be both perfect 
 bull or perfect cow calves : when one is a bull calf, the other 
 a cow calf, the latter in general when grown up exhibits 
 no sexual propensities, and has a frame resembling the com- 
 
Of Puberty. 369 
 
 mon ox, with which animal it is generally yoked and em- 
 ployed. This animal is termed a free-martin. Upon an 
 examination of three of these animals, Mr. Hunter found in 
 them different malformations of the genital organs : each of 
 them had some rudiment of the female organs, but at the 
 same time something deficient, either in the connection of 
 the uterus with the vagina, or in the development of the 
 ovaria ; and in each some small part of the male generative 
 system was detected. In this instance therefore, as in the 
 preceding, the general character of the animal seemed to 
 follow the type of the genital organs. 
 
 The free-martin is perhaps the nearest approach in the 
 higher animals to the state of hermaphrodism, the existence 
 of which in human beings is a groundless fiction. Those 
 appearances, which are occasionally exposed to the vulgar 
 as specimens of such an occurrence, are cases in which, if 
 females, there is an habitual prolapsus of the uterus with a 
 long and narrow cervix, or an enlarged clitoris ; or in which 
 the front of the bladder and the lower part of the abdo- 
 minal parietes are deficient, so that the everted mucous sur- 
 face of the posterior half of the bladder presents the ap- 
 pearance of a glans penis above the female sexual organs; 
 in males, the want of a perforation in the penis, with a defi- 
 cient septum scroti, and the urethra opening in the peri- 
 neum, have given rise to a similar mistake. 
 
 The period of puberty differs, in the two sexes, in the in- 
 habitants of different climates, in persons of different tem- 
 peraments and habits of life. 
 
 Women reach the period of puberty one or two years be- 
 fore men ; the inhabitants of southern, before those of 
 northern climates. In the hottest regions of Africa, Asia, 
 and America, girls arrive at puberty at ten, even at nine 
 years of age ; in France not till thirteen, fourteen, or fifteen ; 
 whilst in Sweden, Russia, and Denmark, this period is not 
 attained till from two to three years later. Habits of activity 
 and bodily exertion retard the arrival of puberty. 
 
 At the time of puberty, in the male, the larynx enlarges, 
 the quality of the voice is changed, the beard grows, the 
 chest and shoulders enlarge, the generative organs are de- 
 
370 Of Menstruation. 
 
 veloped, hair grows upon the pubes, and the secretion of the 
 seminal fluid begins. 
 
 The female at the age of puberty deviates less from the 
 type of childhood ; but the breasts enlarge, the pelvis en- 
 larges, the uterine organs are developed, and a peculiar pe- 
 riodical secretion commences from the inner surface of the 
 uterus, which continues, subject to certain intermissions, as 
 long as the organ is capable of impregnation, which is on 
 an average about thirty years. 
 
 This secretion is termed the menstrual discharge or cata- 
 menia : it returns every lunar month, and consists of a fluid 
 resembling arterial blood, except that it does not coagulate : 
 the secretion amounts to six or eight ounces on an average, 
 and lasts from three to four days. But in some instances 
 the period returns regularly every third week ; and in other 
 instances, in which the common period is usually observed, 
 it occasionally happens that menstruation is put off till the 
 fifth week without any inconvenience, attending : in some 
 persons it lasts a shorter period than that above stated, and 
 is scarcely sanguineous ; in others it is more profuse, and 
 lasts at each recurrence a week. 
 
 In some instances menstruation takes place at puberty 
 without any previous or attendant indisposition, but gene- 
 rally its first appearance is preceded by uneasy feelings, by 
 pain about the back and pelvis, accompanied often by dis- 
 order of the stomach and bowels, and various hysterical 
 symptoms. These affections gradually abate, but at the 
 end of a month return with more severity, being attended 
 with colic pains, a frequent pulse, occasionally with heat of 
 skin and a desire to vomit. There now takes place from 
 the vagina a discharge of a serous fluid slightly red, but it 
 does not in general become perfectly sanguineous for several 
 periods : when the discharge flows, the preceding symptoms 
 abate, but frequently a considerable degree of weakness re- 
 mains, and the skin of the eyelids appears discoloured. In 
 a short time menstruation is performed often without any 
 other inconvenience than a slight pain in the back, though 
 sometimes a woman may suffer from many of the former 
 symptoms every time that she is unwell ; and all women at the 
 
Period at which Menstruation begins. 371 
 
 menstrual period are more liable than at other times to spas- 
 modic and hysterical complaints. 
 
 This secretion is naturally wanting during utero-gestation, 
 and some time subsequently. Yet there are instances, in 
 which menstruation takes place exactly in the usual manner 
 during the whole term of pregnancy. I have met with but 
 one case of this description : the patient informed me that 
 it had happened in each of seven pregnancies. 
 
 It is supposed that the uterus is peculiarly fitted for im- 
 pregnation immediately after the period has ceased. Yet 
 women may have children antecedently to the occurrence of 
 menstruation. Sir E. Home mentions the case of a young 
 woman, who was married before she was seventeen, and 
 having never menstruated, became pregnant : four months 
 after her delivery she became pregnant a second time ; and 
 four months after the second delivery, she was a third time 
 pregnant, but miscarried. After this she menstruated for 
 the first time, and continued to do so for several periods, 
 and again became pregnant *. 
 
 Mr. Roberton gives, in the North of England Medical 
 and Surgical Journal, the following table of the period 
 at which 326 women in the Lying-in Hospital in Manches- 
 ter began to menstruate. 
 
 At 11 years 6 
 
 12 12 
 
 13 31 
 
 14 60 
 
 15 72 
 
 16 54 
 
 17 50 
 
 18 19 
 
 19 18 
 
 20 4 
 
 Like other peculiarities of constitution, the period of pu- 
 berty in women is often found the same in members of the 
 same family. Mr. Roberton mentions five sisters who men- 
 struated at 11 j one of them was gravid and a mother at 12. 
 
 * Phil. Trans, vol. cvii,, p. 258. 
 
372 Appearance of the Ovulum, after Baer. 
 
 We have now to inquire into the conditions necessary for 
 impregnation. 
 
 For this purpose, germs are in a state of progressive for- 
 wardness in the ovaries, from the time of puberty till the 
 period of child-bearing is over. These germs were seen for 
 the first time by Baer, in the year 1827, in the ovaries of a 
 bitch. They are little specks in the Graaffian vesicles, and 
 in the bitch are from -5-6-0- to i-hr of an inch in diameter, the 
 larger being doubtless the most forward. The following 
 diagram, taken from Baer, may serve to explain his notion 
 of the structure of the Graaffian vesicle, and of the place and 
 nature of the germ. 
 
 In this figure, the meaning of the numbers is as follows. 
 
 1 . The peritoneal coat of the ovary. 
 
 2. The proper or cellular coat of the ovary. 
 
 3. The thin outermost coat of the Graaffian vesicle, 
 framed of a close filamentous tissue. 
 
 4. The internal layer, thicker, softer, more opaque than 
 the outer, from which it is after maceration readily sepa- 
 rable. Its inner surface is slightly villous. 
 
 5. The granular membrane, immediately including the 
 humour of the Graaffian vesicle. 
 
 6. The humour itself, slightly viscid, albuminous, pel- 
 lucid, but inclining to yellow in the most turgid vesicles, 
 
Production of Corpora Lutea. 373 
 
 containing numerous irregularly- shaped granules, with here 
 and there a globule of oil. 
 
 7. The discus proligerus, or germ disc, composed of 
 closely-coherent granules, which forms the bed in which 
 is placed 
 
 8. The germ or ovulum, itself a hollow sphere, the crust 
 of which consists of coherent granules. 
 
 There is every reason to believe, that Graaffian vesicles are 
 at intervals coming forward during the whole period at which 
 child-bearing is possible ; and that they burst in succession, 
 and shed the contained ovula, whether sexual connection 
 takes place or not. It is probable, however, that sexual 
 connection hastens their ripening. A principal difference 
 in the appearance of the ovary of one past the age of thirty, 
 and that of a child, is the scarred and cicatrized surface 
 of the former contrasted with the uniform smoothness of 
 the latter. The cicatrices on the former result, beyond ques- 
 tion, from the healing of numerous lacerations of the surface 
 produced by the escape of ovula. 
 
 The appearance termed a corpus luteum is the conse- 
 quence of the bursting of a Graaffian vesicle. It is formed 
 by a thickening of, or deposit in the internal coat of the 
 Graaffian vesicle. Baer mentions, that the thickening and 
 the yellow colour sometimes begin to appear before the ve- 
 sicle bursts *. 
 
 It is not known whether a state of increased vascula- 
 rity in the uterus and ovaries in women be necessary for 
 impregnation. Some change of this kind is observed in the 
 sexual parts of female animals, when they are in their pe- 
 riodical state of sexual excitement. Mr. Cruickshank thus 
 describes the appearance of the parts in the rabbit. 
 
 A female rabbit, when hot, was pithed, and the uterine sys- 
 tem was then minutely examined. The external and internal 
 parts of generation were found black with an unusual quan- 
 tity of blood : the Fallopian tubes were twisted like writhing 
 worms, and exhibited a very vivid peristaltic motion : the 
 
 * De Ovi Mammal him et Hominis Genesi. C. E. a Baer. Lipsiae, 
 1827. 
 
 2 A 
 
374 Condition essential to Impregnation. 
 
 fimbrisB embraced the ovaries, like fingers laying hold of an 
 object, so closely and so firmly as to require some force and 
 even slight laceration to disengage them : round black spots 
 somewhat .less than mustard seeds appeared below the mem- 
 brane of the ovarium. Upon injecting the vessels of the 
 pelvis with size and vermilion, the uterine organs became of 
 a bright red. 
 
 The uterine organs being disposed by these means to- 
 wards conception, we have next to inquire what conditions 
 are requisite for the fecundation of ovula? Upon this 
 subject our knowledge is extremely imperfect ; but proceed- 
 ing by the inductive method, physiologists have ascer- 
 tained, that the exclusion of one element of the usual con- 
 stitution of the uterine system essentially prevents impreg- 
 nation following sexual connection. If the canal leading 
 from the orifice of the vagina to the ovaries be interrupted, 
 conception never takes place. 
 
 Dr. Blundell found, that an interruption of the uterine 
 canal in rabbits, produced by the division of the vagina, 
 uniformly prevents conception. Yet in animals thus muti- 
 lated, which admitted the male, the uterus afterwards en- 
 larged to a considerable size, and was found to contain a 
 fluid of an albuminous nature *. 
 
 Barrenness in married women occasionally depends upon 
 an obstruction of the os uteri by viscid mucus ; the removal 
 of the obstruction by a bougie has been shortly after fol- 
 lowed by conception. 
 
 Dr. Haighton divided the Fallopian tubes on each side in 
 several female rabbits, and found that the animals inva- 
 riably lost the sexual appetite f. Upon dividing the Fallo- 
 pian tube on one side only, he found the same result gene- 
 rally ensue. In a few cases, however, the animals thus mu- 
 tilated admitted the male, and became impregnated ; but 
 the horn of the uterus on the side on which the Fallopian 
 tube had been divided never contained ova. 
 
 When we refer to analogy for an explanation of the 
 
 * Medico-Chirurgical Trans, vol. x, p. 50. 
 f Phil. Trans, vol. Ixxxv, p. 108. 
 
Place in which the Ovum is fertilized. 375 
 
 cause, why an obstruction of the uterine canal prevents 
 conception, we discover it in the fact, that in various cold- 
 blooded animals, the seminal fluid is brought into actual 
 contact with the eggs either at the time of their expulsion 
 or afterwards. We are thus led to conjecture, that in warm- 
 blooded animals likewise the seminal fluid must be directly 
 applied to the germ, in order that impregnation may take 
 place ; and that any cause which prevents this contact 
 taking place is enough to prevent conception. 
 
 If we are satisfied that this conjecture is well founded, 
 we may next inquire, whether the contact of the seminal 
 fluid and ovum takes place in the uterus, in the Fallopian 
 tube, or in the ovary. The only facts, of which we are 
 in possession, that seem to bear upon this question, are, 
 that the ovum, although in most cases developed in 
 the uterus, yet is sometimes brought to maturity in the Fal- 
 lopian tube, sometimes in the peritoneal cavity, and some- 
 times even in the ovary: it is remarkable that in the 
 three latter cases the uterus enlarges, and its inner surface 
 becomes covered with a layer of flocculent lymph, much in 
 the same manner as in cases of ordinary conception. Yet 
 curious as these facts undoubtedly are, they leave the point 
 which I have adduced them to elucidate nearly in its ori- 
 ginal uncertainty. 
 
 It has been mentioned, that Graaffian vesicles are for a 
 period continually coming forward in the ovaries. What 
 determines their fitness for fertilization is not known. But 
 as on the one hand it may frequently happen, that sexual 
 intercourse produces no conception in mature ova ; so on 
 the other does it appear certain, that sexual intercourse will 
 sometimes not only produce in a mature ovum conception, 
 but strongly influence and give a character to the immature 
 ovula, for the fecundation of which a subsequent coitus may 
 be necessary. 
 
 The remarkable instance which brought this fact into 
 notice, is the following. A seven- eighths Arabian mare be- 
 longing to the Earl of Morton, which had never been bred 
 from before, had a mule by a quagga : subsequently she 
 had three foals by a black Arabian horse. The two first of 
 
 2 A 2 
 
376 Influence on Immature Ovula. 
 
 the foals are thus described. " They have the character of 
 the Arabian breed as decidedly as can be expected, where 
 fifteen-sixteenths of the blood are Arabian ; and they are fine 
 specimens of that breed ; but both in their colour, and in 
 the hair of their manes, they have a striking resemblance 
 to the quagga. Their colour is bay, marked more or less 
 like the quagga in a darker tint. Both are distinguished 
 by the dark line along the ridge of the back, the dark 
 stripes across the fore-hand, and the dark bars across the 
 back part of the legs. Both their manes are black ; that of 
 the filly is short, stiff, and stands upright : that of the colt 
 is long, but so stiff as to arch upwards, and to hang clear 
 of the sides of the neck ; in which circumstance it resembles 
 that of the hybrid. This is the more remarkable, as the 
 manes of the Arabian breed hang lank, and closer to the 
 neck than those of most others *. 
 
 A similar occurrence to the preceding is mentioned by 
 Mr. Giles respecting a litter of pigs, which resembled in co- 
 lour a former litter by a wild boar. 
 
 Women, it is said, have borne twins by different fathers : 
 and it is certainly not physically impossible, that in those 
 cases, in which menstruation continues during pregnancy, a 
 second impregnation may take place at some interval after- 
 wards, before the expulsion of the first conception. 
 
 The cause of the production of twins is not known. Baer 
 mentions having twice seen, in the ovaries of animals, two 
 ovula in one Graaffi an vesicle : but this occurrence probably 
 gives rise, not to the birth of ordinary twins, but to the va- 
 rieties of united births. 
 
 * Phil. Trans. 1821, p. 21. 
 
377 
 
 SECTION II. 
 On the Development of the Embryo. 
 
 The detection of the ovulum in mammalia by Baer, 
 which has been mentioned in the preceding section, is a 
 point only in the extensive circle of discovery which has 
 been traced by himself and by other physiologists. Accord- 
 ing to ancient hypothesis, the development of the embryo 
 was the evolution of parts which pre-existed in the germ. 
 This opinion was first successfully attacked by 0. F. Wolff, 
 in a thesis which he published at Berlin in 1759, and in 
 which he not only described a successive production of or- 
 gans, of the pre-formation of which no trace existed ; but 
 showed, that, after parts are first formed, they undergo 
 many important changes in their structure before arriving 
 at their perfect state. The opinions of Wolff, that the parts 
 of the embryo are formed and not evolved, have been veri- 
 fied, and a vast body of knowledge ascertained upon this 
 subject, by the labours of Pander, Meek el, Oken, Blumen- 
 bach, Baer, Rathe, Cuvier, Dutrochet, Serres, Rolando, 
 Prevost, Dumas, and of many others, who have joined in 
 creating a new branch of physiological science. I shall en- 
 deavour briefly to explain the leading facts which have been 
 thus brought to light. They have an interest greatly be- 
 yond what attaches to the narration of phenomena that are 
 simply unexpected and curious. They elucidate to a won- 
 derful degree the affinities of remote families of animals ; 
 displaying how for a period their type of formation is the 
 same, and explain the seeming caprice of Nature in in- 
 stances of monstrous and defective formation, by showing 
 that what appears anomalous is not the substitution of a 
 new type, but the arrest of development, whereby a tempo- 
 rary character is rendered permanent. 
 
 The ovulum bursting from the Graaffian vesicle is re- 
 ceived by the fimbriated extremities of the Fallopian tube, 
 and conveyed towards the uterus. 
 
378 State of the Ovulum after Impregnation. 
 
 Baer detected the ovulum in 
 its passage along the Fallopian 
 tube in a bitch. Its appearance 
 is represented in the adjoined 
 figure. It was of a yellowish- 
 white colour, and consisted dis- 
 tinctly of an outer cortical mem- 
 brane, or chorion, and of a glo- 
 bule within of a granular struc- 
 ture. Its diameter was the 15th 
 part of a line. 
 
 After reaching the uterus, the 
 ovulum grows more rapidly than 
 before. Its structure may be ex- 
 amined with ease, when it is 
 about half a line in diameter. A 
 new element is then visible in it, 
 which is shown in the adjoined 
 figure from Baer. Upon the sur- 
 face of the internal globule, a 
 round, opaque, granular disc is 
 seen, with a dark spot upon its 
 centre. Dr. Allan Thompson, 
 from whose useful papers on em- 
 bryology, in the Edinburgh New 
 Philosophical Journal, I have 
 borrowed the greater part of the 
 preliminary sketch in the present 
 section, states, that he has seen 
 this spot very evident in the ova 
 of the rabbit on the sixth day 
 after impregnation. 
 
 It does not admit of a doubt, that the spot seen on or 
 through the inner membrane of the ovum corresponds ex- 
 actly with the cicatricula of the egg. This conclusion is 
 grounded, less upon their first close resemblance than on 
 the subsequent identity of the parts which replace them, 
 less upon either argument than upon both together. The 
 intermediate state to the two which I refer to, has not been 
 
Of the Germinal Membrane in the Egg. 
 
 379 
 
 as yet followed out in mammalia. I therefore shall describe 
 the cicatricula in the egg, and its first changes, as typifying 
 what analogy renders certain occurs in all vertebral ani- 
 mals. 
 
 In the unincubated egg of the 
 common fowl, the germ spot, or 
 cicatricula, lies immediately upon 
 the surface of the yolk : it is cir- 
 cular, of a whitish colour, and 
 about one-sixth of an inch in di- 
 ameter. The disc of the cicatri- 
 cula is formed of different-sized 
 granules united together, and is 
 covered by the proper membrane 
 of the yolk. The central part of 
 the disc is thinner and more 
 transparent than the rest, and 
 has been called the colliquamen- 
 tum. 
 
 Seven or eight hours after the 
 commencement of incubation, a 
 small dark line may, with the aid 
 of a magnifying glass, be disco- 
 vered on the upper part of the 
 cicatricula towards the centre of 
 the transparent area. This line 
 or primitive trace, delineated in 
 the adjoined figure, is swollen at 
 one extremity, and is placed in 
 the direction of the transverse 
 axis of the egg. The rounded 
 end is towards the left, when the 
 small end of the egg is turned 
 from us. 
 
 The cicatricula, germ spot, germinal membrane, or blas- 
 toderma, resting in immediate contact with the yolk, now 
 expands itself ; and at the same time acquiring thickness, 
 it separates, towards the 12th or 14th hour of incubation, 
 into two layers of granules. Of these, the outer, which sub- 
 
380 Division of the Germinal Membrane into Layers. 
 
 sequently gives rise to the osseous, nervous, muscular, and te- 
 gumentary systems of the body, is called by Pander the serous 
 layer. The inner, situated next to and in contact with the 
 substance of the yolk, is termed the mucous. After these two 
 layers have appeared, a third is formed in the interval be- 
 tween them : this is called the vascular layer ; it is gene- 
 rally in intimate connection with the mucous layer, and it is 
 to the changes which the two combined undergo, that the 
 intestinal, the respiratory, and the glandular systems appear 
 to owe their origin. 
 
 The primitive trace is placed in the outer or serous layer. 
 About the 18th hour, two ridges are raised from the serous 
 layer, one on either side of the primitive trace. About the 
 20th hour, the furrow between the ridges is converted into 
 a canal open at both ends by the junction of its margins 
 (the plicae primitivse of Pander, the laminae dorsales of Baer). 
 The canal soon becomes closed at the cephalic or swollen 
 extremity of the primitive trace, at which part it is of a py- 
 riform shape, being wider here than at any other part. The 
 following figures represent a longitudinal and transverse 
 section of the triple layers of the germinal membrane at 
 this period. 
 
 A represents the serous layer, B the mucous, the inter- 
 mediate dotted line C the vascular. 
 
 According to Baer and Serres, some time after the canal 
 begins to close, a semi-fluid matter is deposited in it, which, 
 on its acquiring greater consistence, becomes the rudiment 
 of the spinal chord. The pyriforrn extremity, or head, is 
 soon after this seen to be partially divided into three ve- 
 sicles, which, being also filled with a semi-fluid matter, give 
 rise to the rudimentary state of the enkephalon. Rolando, 
 
Folding of the three Layers. 381 
 
 Prevost, and Dumas, on the other hand, suppose that the 
 rudimentary state of the brain and spinal chord is consti- 
 tuted by the primitive trace itself, which they affirm exists 
 before incubation has commenced. 
 
 As the formation of the spinal canal proceeds, the parts 
 of the serous layer which surround it, especially towards the 
 head, become thicker and more solid ; and before the 24th 
 hour, we observe on each side of this canal four or five 
 small, round, opaque bodies. These bodies indicate the first 
 formation of the dorsal vertebrae : in a few hours several 
 more appear, and those first produced become quadrilateral. 
 It is about this time, or from the 20th to the 24th hour, 
 that the vascular layer appears. 
 
 Towards the 25th hour, when the layers of the germinal 
 membrane gradually expanding have covered nearly a third 
 of the yolk, they no longer retain their flat and uniform 
 position, but begin to exhibit various folds, which afterwards 
 serve for the formation of the cavities of the body. That 
 part of the germinal membrane which lies immediately be- 
 fore the cephalic extremity of the embryo is bent down into 
 a fold, so as to make a depression upon the surface of the 
 yolk ; and some time afterwards, a similar fold is formed be- 
 hind the caudal extremity. As these folds of the germinal 
 membrane increase, they gradually turn in below the foetus 
 at its head and tail ; and their margins approach one another 
 under the abdomen, which at this period always lies next to 
 the substance of the yolk. As the layers of the germinal 
 membrane are bent down in a similar manner towards the 
 sides also of the spinal canal, there is formed under each 
 end of the embryo a sac or cavity, which communicates 
 with the yolk by an opening common to both. The two 
 shut sacs thus formed indicate the rudimentary state of the 
 intestinal tube : the anterior corresponds to the resophageal 
 portion of the intestine, the posterior to the lower part of 
 the large intestine. 
 
382 
 
 Appearance of the Heart, 
 
 In the two preceding figures are given sections, corre- 
 sponding to the last, of this progressive increase. 
 
 The first rudiments of the heart appear towards the 27th 
 hour on the lower side of the oasophageal canal, at the 
 place where the layers of the germinal membrane are re- 
 flected from the edge of the anterior fluid sac which they 
 form on the embryo. In forming this fold, the mucous layer 
 [B] is reflected farthest inwards ; the serous layer advances 
 least; and the space between them, occupied by the vas- 
 cular layer, is filled up by a dilated part of this layer [H], 
 the rudiment of the heart. 
 
 About the same time that the development of these rudi- 
 mentary parts of the embryo takes place, the surrounding 
 disc of the cicatricula is also considerably changed. The 
 whole cicatricula continues to expand, and to cover more of 
 the surface of the yolk. That part of the mucous and vas- 
 cular layers which surrounds the transparent area, becomes 
 thicker and more spongy than the adjacent parts, and is 
 soon studded with numerous irregular points and marks of 
 a dark-yellow colour. As incubation proceeds, these points 
 become more apparent, and are gradually elongated into 
 small lines which are united together, first in small groups, 
 and then into one network, which is called the vascular 
 area. 
 
 The space occupied by this network is cordiform, and is 
 surrounded by a vessel gradually developed in the same 
 
Of the Vascular Area. 383 
 
 manner as those of the rest of the area. The newly-formed 
 vessels of the space become more and more distinct as incu- 
 bation advances, and the orange-coloured fluid they contain 
 acquires a darker hue : the small branches of the network 
 arrange themselves like the fibrils of a leaf on each side of 
 the embryo, and terminate towards the embryo in two ves- 
 
 sels arising from its sides, which are the omphalo-meseraic 
 arteries. Towards the circumference of the area, the smaller 
 ramifications of these vessels open into the sinus, or vena 
 terminalis, which bounds the space. 
 
 The changes in the germinal membrane of mammalia 
 have not been observed with the same detail as those in 
 birds. But the principal facts, upon which we may pre- 
 sume that these are parallel to those which have been de- 
 scribed, are the following. 
 
 The original structure of the ovum in mammalia appears 
 to be the same as that in the egg. The egg consists of two 
 membranes, the membrane of the shell and the membrane 
 of the yolk, the cicatricula within the innermost. The 
 ovum of mammalia, when half a line in diameter, consists of 
 two spherical membranes and a germ spot. 
 
 In the egg, the primitive trace is seen in the cicatricula 
 seven hours after incubation has begun. Its figure has been 
 already given. In the ovum of mammalia, Baer and Pre- 
 vost and Dumas concur in stating, that the first trace of 
 the embryo appears like a dark line near the middle of the 
 central transparent part, exactly as the primitive trace shows 
 itself in the transparent area of birds. 
 
 To complete the parallel at the period to which we have 
 
384 
 
 The Vascular Area in the Mammalia. 
 
 already brought the incubated egg, I copy the following 
 drawing from Baer. 
 
 It represents the ovum of a bitch at the third week ; in 
 which are shown, first, the outer flocculent tunic, or chorion ; 
 next, the yolk, body, or vesicula umbilicalis ; and on or be- 
 low it, the embryo, by this time as in the egg inclined upon 
 its left side, with vessels spreading from it to form the vas- 
 cular area. 
 
 In unfolding the complicated subject which now opens 
 upon the student, I shall adopt the following method. I 
 shall describe, in succession, the development of the parts 
 of the embryo. 1. Of the brain, nerves, muscles, and organs 
 of the senses ; of the bones and cartilages, and of the inte- 
 guments the produce of the serous layer. 2. Of the ali- 
 mentary canal and glands, the produce of the mucous layer. 
 3. Of the heart and blood-vessels, which grow out of the 
 vascular laydr. 
 
 The consideration of the development of the vascular layer 
 will complete the account of the embryo, leading at the same 
 time, by a natural transition, to the history of the develop- 
 ment of the remaining parts of the ovum. I shall thus finally 
 transform the ovum from the character which up to this 
 point will have been given it a double sac namely, repre- 
 senting the membranes of the egg with the germ laid upon 
 the contained yolk into that more familiar to the student, 
 of chorion and placenta and umbilical chord, and foetus sus- 
 pended by the latter, and floating in the water of the amnion. 
 
 The formation of the spinal chord and brain begins upon 
 the outer surface of the serous layer. When first seen these 
 parts arc together a line and a half in length ; the central 
 
Development of the Brain and Spinal Chord. 385 
 
 extremity is a rounded nodule. Both parts appear at once. 
 The brain does not grow from the spinal marrow, nor the 
 spinal marrow from the nodule which represents the future 
 brain. 
 
 The spinal chord is at first a membranous tube, the 
 brain three vesicles. In these a transparent fluid is con- 
 tained, from which a precipitation takes place of opaque 
 particles connected by a viscid transparent substance. The 
 precipitated matter at first adheres closely to the mem- 
 brane ; then gradually loosens itself from it. The nervous 
 substance is formed out of the primitive or elementary mat- 
 ter of the embryo antecedently to the production of those 
 vessels, by which its increase is doubtless effected. 
 
 Nervous matter, at first of the consistence of a thick fluid, 
 at the third month is evidently composed of two substances. 
 One consisting of medullary threads, which by maceration 
 in alcohol are displayed in the embryo even more easily 
 than in the adult ; the other not fibrous, or filamentous, 
 or fasciculated, being that which at a later period assumes 
 a grey or cineritious colour. 
 
 The spinal chord and brain are not originally composed 
 of symmetrical halves. This character results from the de- 
 velopment of additional matter upon their sides. 
 
 The anterior part of the spinal marrow grows more rapidly 
 than the posterior part. The sides are then developed, which 
 therefore form a groove open backward. The groove or furrow 
 is visible at the sixth week. The gradual increase of the 
 sides spreading inwards and finally meeting closes this fur- 
 row superficially, and converts it by the sixth month into a 
 canal. Afterwards the canal itself, by an extension of the 
 same process, becomes obliterated. The upper part is the 
 last to close. 
 
 The spinal chord in an embryo of three months is as long 
 as the vertebral column. Soon after this period, the growth 
 of the vertebral column gains upon that of the chord ; so 
 that at the seventh month the chord extends as low only as 
 the fifth lumbar vertebra, at the ninth to the first only. 
 
 The enkephalon consists originally in all animals of three 
 sacs, which are the rudiments of the medulla oblongata, of 
 
386 
 
 Of the Spinal Chord. 
 
 the tubercles, and of the cerebrum : these are filled with 
 transparent fluid, and have no disunion on the median 
 plane. Such is the appearance of the enkephalon in fish at 
 the earliest period, in the embryo of the chick on the se- 
 cond day, in the human embryo during the fifth week. 
 
 The two adjoined figures re- 
 present a back view and a side 
 view of the spinal chord and 
 brain in an embryo of six weeks 
 from Tiedemann. 
 
 C-- 
 
 ~A 
 
 A. Represents the spinal marrow. 
 
 B. The medulla oblongata. 
 
 C. The tubercles. 
 
 D. The cerebrum. 
 
 E. The cerebellum. 
 
 The two figures which follow represent the brain as seen 
 from behind and above, at the ninth and twelfth weeks. 
 The letters are the same as to the preceding. 
 
Of the Medulla Oblongata. 387 
 
 The enkephalon of the embryo is proportionately larger 
 than that of the adult. At the fifth month it forms one- 
 eighth, soon after birth one-tenth of the entire weight, of 
 which in adults it forms one-fortieth only. 
 
 The medulla oblongata is more developed than the rest of 
 the enkephalon. According to Tiedemann the breadth of 
 the medulla oblongata is to that of the cerebrum in the se- 
 cond month 1 : 1 .25, in the third 1 : 2 or 3, in the fourth 
 1 :3.2, in the fifth 1 :4.8, in the sixth 1:5, in the tenth 
 1 :5.63, in adults 1 :6 to 7. In the tenth month the me- 
 dulla oblongata has already half the breadth which it at- 
 tains in the adult. 
 
 In the fifth week, according to Tiedemann, the decussa- 
 tion of the pyramids may be seen : about the same time the 
 corpora olivaria appear. 
 
 The cerebellum is not an elementary part of the enke- 
 phalon. It is produced by an extension of the lateral parts 
 of the medulla oblongata or of the corpora restiformia, in 
 the egg of the common fowl on the fourth day, and in the 
 human embryo about the seventh week. The cerebellum 
 at its commencement consists of two processes, which 
 meet but do not join as yet over the medulla oblongata. 
 These two lateral processes in the human embryo coalesce 
 about the beginning of the third month, and enclose a space 
 (the future fourth ventricle) between the cross band which 
 they form and the medulla. The corpora fimbriata ap- 
 pear in the fourth month in the form of shut sacs or 
 bladders : they are rich in blood-vessels. As they increase, 
 now in the fifth month, the hemispheres of the cerebellum 
 begin to be developed, and at first towards the fore part 
 principally. Additional layers of nervous matter are now 
 produced, and the mass divides itself into the rudiments of 
 five lobes. The transverse furrows which separate the lobes 
 are first visible upon the middle part or the future vermiform 
 processes. In the sixth month more furrows are traced 
 upon the surface, and the lobes divide themselves into 
 lobules. In the seventh month the furrows become deeper 
 and more numerous : the flocks and the inferior medullary 
 velum appear at this time. In the ninth month the deve- 
 
388 Of the Cerebellum and Tubercles. 
 
 lopment of the hemispheres is nearly completed by the ad- 
 ditional growth of the posterior and inferior surfaces. In 
 the tenth month the superficial furrows, and the laminse 
 which they include, appear. The almond-like lobes are 
 finally developed, and the distinction between white and 
 grey matter is seen. 
 
 The pons Varolii appears at the beginning of the fourth 
 month. The first part developed is the posterior portion, so 
 that at first the fifth nerve has its origin before the pons. 
 
 The cerebellum does not keep pace in proportional vo- 
 lume in foetal life with the other parts of the enkephalon ; 
 and if its inward structure be earlier perfected, this must be 
 attributed to its simplicity. 
 
 The tubercles, original elements of the central organ, 
 form at first a single bladder filled with transparent fluid. 
 By the sixth to the ninth week this appearance has changed 
 into two lateral plates resting upon the crura cerebri, and di- 
 vided above and in the middle by abroad furrow. At the end 
 of the third month the two lateral plates having bent over, 
 meet in the median plane, and at the same time the upper 
 pedicles of the cerebellum stretch forward to be incorpo- 
 rated with them. In the fourth month the permanent me- 
 dian furrow shows itself. In the sixth month the tubercles 
 are covered with the cerebrum : their substance enlarges, 
 and is clad with a layer that is not fasciculated, but as yet 
 is of a grey colour. In the seventh month the transverse 
 furrow which divides the tubercles into an upper and lower 
 pair arises. The tubercles, in comparison with the brain, 
 are the larger the younger the embryo. Before birth, they 
 attain more than half their final size. 
 
 The white inferior parts or the crust of the crura cerebri grow 
 with the inferior or anterior fasciculi of the chord of which they 
 are the cerebral productions. They bear at first a large pro- 
 portion to the cerebrum. The cylindrical layer, which is 
 placed upon them, begins about the fourth month. This at 
 first consists of two lateral parts, and the furrow between 
 them leads along the infundibulum to the pituitary gland. 
 The pituitary gland contains a cavity which remains even 
 to the sixth month. This cavity may be regarded as the an- 
 
Development of the Cerebrum. 389 
 
 terior termination of the canal, which extends thence back- 
 wards the whole length of the spinal marrow. The pituitary 
 gland at four months is in length, compared with the brain, 
 as 1:9.5; at seven, as 1:16; in the adult, as 1:18; 
 showing therefore in the early human embryo a develop- 
 ment like that which it permanently retains in the lowest 
 vertebral animals. 
 
 The thalami nervorum opticorum and the corpora stri- 
 ata show themselves at the eighth week, as swellings 
 upon the crura cerebri. The thalami are of a reddish 
 hue. The posterior commissure forms in the third month ; 
 the soft commissure in the fourth. The corpora striata, 
 originally narrower and not much longer than the thalami, 
 soon outgrow them. 
 
 In the third month either hemisphere consists of a thin 
 layer, which covers the outer and fore part of the corpus 
 striatum. By the end of the third month the hemispheres 
 extend backwards over the thalami. In the fourth month 
 they reach the tubercles ; in the sixth the fore part of the 
 cerebellum. The fasciculated structure of the brain is even 
 more distinct in the foetus than in the adult. 
 
 The commissural parts of the brain begin to appear in 
 the third month. It is far from improbable that the conjec- 
 ture of the Wenzels is right, that the corpus callosum is 
 formed by the union of two processes of medullary matter 
 meeting at the raphe. The fore part of the corpus callosum 
 is the first to appear. The fore part of the fornix appears 
 at the same time, its anterior cornua stretching downwards, 
 and terminating in the thalamus. The anterior commissure 
 appears in the third month. 
 
 The convolutions of the brain are seen first in the fifth 
 month : they are at that time formed upon the inner surface 
 and upon part of the upper surface of the cerebrum. In 
 the seventh month they spread over its outer surface. 
 
 Of the ventricles of the brain, the first appearance of the 
 third, and its closure above by the formation of the soft 
 commissure, may be considered to have been already de- 
 scribed. The lateral ventricles, which when first formed are 
 open inwards and upwards, begin to be closed above at the 
 end of the third month by the corpus callosum, the comple- 
 
 2 B 
 
390 Of the Nerves. 
 
 tion of which towards the eighth month shuts them in this 
 direction. The formation of the septum lucidum begins in 
 the fifth month. The relative size of the lateral ventricles is 
 greatest at the sixth month. The central organ is originally 
 of one colour, a pearly grey. The distinction between white 
 and grey substance is first visible in the spinal marrow ; in 
 which, at the seventh month, the coloured nucleus presents a 
 deeper shade even than after birth. The pyramids and oli- 
 vary bodies become white after birth, as well as the exterior 
 fibres of the annular protuberance and of the pedicles of 
 the cerebrum. But the productions of these parts into the 
 cerebrum and cerebellum become white before birth, leaving 
 however the superficial cineritious matter of disproportion- 
 ate thickness. The medullary line which divides the cor- 
 tical matter into two layers appears after birth. 
 
 It is a question yet unresolved, whether the nerves in 
 general are formed in their entire length at once, or, if 
 not so formed, are growths from the central organ towards 
 the circumference, or the reverse. But it is certain, that 
 the optic, and auditory, and olfactory nerves are productions 
 of the cerebrum. They are originally tubes that stretch 
 from the sacs of the enkephalon. 
 
 In the instance of the optic nerves, the tractus optici are 
 seen first to grow from the enkephalon, then to meet and 
 form their commissure, and finally to push out the nerves. 
 It is therefore presumable upon analogy, that the other 
 nerves are likewise from the first in absolute continuity with 
 the chord, although the extreme delicacy of their roots may 
 elude observation. The extraordinary circumstance ob- 
 served by Magendie in the lamprey, is the only fact which 
 throws a doubt upon this conclusion. In the lamprey, while 
 the cerebral nerves distinctly rise from the enkephalon, the 
 spinal nerves cannot be traced further than to the theca. 
 I have carefully examined this point in the lamprey the in- 
 stant after it has been killed, and am certain that no visible 
 continuity of filament extends in it between the membranes 
 of the chord and the chord itself. 
 
 The muscles become visible in the human embryo at the 
 third month : they are then soft and gelatinous, transpa- 
 rent, of a light-yellow tint, and are not distinguishable from 
 
Of the Muscles. 391 
 
 their tendons. Their fibrous structure is evident after ma- 
 ceration in alcohol. In the fourth and fifth months the 
 muscular fibres become more distinct, and of a redder co- 
 lour: the tendons, on the other hand, become whiter. The 
 muscles appear in different parts at different periods. They 
 are first formed on the back and shoulders. Those of the 
 upper arm and of the thigh are formed before those of the 
 fore arm and of the leg. Each muscle is formed at once 
 in its whole length, with its attachments perfect. 
 
 There is a close relation between the development of the 
 muscles and of the nerves. In defective births, where the 
 brain, spinal marrow, and nerves are wanting, the muscles 
 likewise are wanting, and in their place a gelatinous fila- 
 mentous tissue is found. In acephalous foetuses, where part 
 only of the central organ is formed, muscles are formed in 
 particular parts only. 
 
 Among the organs of the senses, the eye is the first to 
 appear. The human embryo has not been seen without 
 eyes. Their growth is rapid. At first, as in most animals 
 so in human beings, their place is on the side of the head : 
 they subsequently move forward. The eyes, according to 
 Baer's observations, are productions of the brain; their first 
 element being a hemispherical mass on the end of the optic 
 nerve, which is the retina. The retina is at first of great 
 thickness, and folded : its subsequent increase is therefore 
 less than that of other parts. It enlarges its surface by be- 
 coming thinner, and spreading its folds. At the sixth 
 month the permanent fold in the axis of vision is distin- 
 guishable. 
 
 The humours of the eye do not grow from the retina ; for 
 they have been found where the retina was wanting. At the 
 seventh month the vitreous humour is turbid ; it gradually 
 becomes transparent. The lens is globular, originally very 
 large, soft, untransparent, milk white ; it then becomes red- 
 dish, and gradually smaller, flatter, more consistent, and 
 more transparent. The cornea is originally undistinguish- 
 able from the sclerotic,- both have an equal degree of 
 opacity. At the sixth month the cornea becomes thinner, 
 denser, prominent, and transparent. The eyelids are formed 
 by the tenth week, when their edges touch and adhere. 
 
 2 B 2 
 
392 Of the Eye. 
 
 The line of their separation is distinctly marked at the fifth 
 month, when the tarsal cartilages are formed : their separa- 
 tion is complete in the eighth month. The third eyelid is 
 larger than in adults. The caruncle is seen at the eighth 
 week, when the eyelids are beginning to be formed ; and at 
 the same time a depression is seen towards the nasal cavities 
 and mouth, marking the place of the future lachrymal duct. 
 The puncta are prominent in the fifth month. They are 
 something drawn back in the seventh. 
 
 The chorioid must be viewed as a production of the vas- 
 cular layer of the embryo. The pigment which it forms is 
 visible in human beings as early as the fourth week. It is 
 then granular and coherent, so as to appear a second mem- 
 brane* It does not acquire in the foetus the blackness it 
 has after birth. The ciliary body is formed at a later period, 
 as it has been already observed. The iris appears yet later ; 
 it is at first narrow, and not coloured : it gradually acquires 
 breadth, forms the pupil, and begins to be coloured from 
 its inner margin. At the seventh week the aperture of the 
 iris is closed, and the anterior chamber of the aqueous hu- 
 mour has no outlet. This chamber now becomes universally 
 lined with a serous membrane, the fore part of which ad- 
 heres to the cornea, the back part to the iris. The mem- 
 brana pupillaris is a production of the posterior surface of 
 the iris. It is distinguishable by the eleventh week. In the 
 fifth month it becomes replete with vessels produced from 
 those of the iris. These do not completely reach the middle 
 of the membrane. The membrane is perfected at the se- 
 venth month. In the eighth it becomes partially absorbed, 
 and disappears completely before birth. Till its absorption, 
 the lens rests against it. The aqueous humour secreted by 
 the membrane of the anterior chamber then gains admission 
 into the posterior chamber. During the foetal state, the 
 aqueous humour is reddish, and not quite transparent. 
 
 The organ of hearing, according to Baer, appears soon 
 after the first appearance of the eye. What is first seen is 
 the production of a hollow nerve from the medulla oblongata, 
 which stretches into the soft cranial wall. Upon this- the 
 vestibule is formed. By the beginning of the third month 
 the cochlea and semicircular canals are added. These parts 
 
Of the Organ of Hearing. 393 
 
 are covered with a membrane, which disappears in the se- 
 venth month. Around the labyrinth jelly is first depo- 
 sited : cartilage begins to form in the third month, which 
 is distinct from that of the petrous portion of the tem- 
 poral bone, and develops ossific points earlier than the 
 latter. It is completely ossified in the seventh or eighth 
 month, and then becomes united with the petrous portion. 
 The commencement of ossification appears at the same time 
 in the three parts of the labyrinth ; namely, at the end of the 
 third month. The ossification of the cochlea begins at the 
 circumference of the fenestra rotunda. The spiral plate is 
 the part last formed. The ossification of the vestibule com- 
 mences at the circumference of the fenestra ovalis : it is 
 completed in the fifth month. Of the semicircular canals 
 the upper vertical is the first ossified, then the lower, then the 
 horizontal, the turn of which is delayed till the fifth month. 
 The tympanum is at first proportionally small, and filled 
 with reddish, thick, gelatinous liquid. In the eighth month 
 it has acquired its full size. The Eustachian tube appears 
 at first as a wide opening from the throat ; its cartilagi- 
 nous part appears in the fifth month. The ossicula auditus 
 appear in the ninth week, and are cartilaginous at the be- 
 ginning of the third month. Shortly afterwards ossification 
 begins in the incus and malleus; later in the stapes : it is com- 
 pleted in the seventh month. The stapes ossifies first in its 
 base, last in its capitellum. The malleus, like the incus, 
 ossifies first in its head ; a second point of ossification after- 
 wards forms in the root ^>f its anterior process, of which the 
 long and pointed cartilaginous end is then absorbed. The 
 ossicula auditus are before birth as large as in the adult. 
 
 The ring of the tympanum appears in the second month : 
 it begins to ossify at the end of the third. It is incomplete 
 at its upper and fore part. It continues to increase till the 
 seventh or eighth month, becomes more elliptical, and ends 
 by coalescing at its two points with the root of the zygo- 
 matic process of the temporal bone. The membrana tympani 
 is more oblique in the embryo than in adults. 
 
 The outward aperture of the ear shows itself as a fine 
 point or slit in the sixth week, which gradually extends in- 
 wards, and reaches the membrana tympani. At the eleventh 
 
394 Of the Development of the Boms. 
 
 week it closes however temporarily by means of a mem- 
 branous plug. The outer ear commences in the eighth 
 week as a flat fold of integument, in which the cartilage 
 begins to form towards the end of the third month. At 
 first the middle parts of the helix and antitragus are 
 formed, then the tragus and antihelix ; in the fifth month 
 the concha ; in the sixth the upper part of the helix, and 
 the lobe of the ear. The ear then detaches itself more 
 from the head. At birth the cartilage does not adequately 
 fill the skin. 
 
 The organ of smell, at first a cylindrical production of the 
 cerebrum, is produced towards the anterior extremity of the 
 mucous layer, where it forms the common cavity of nose 
 and fauces. In the third month this cavity is divided into 
 two by the formation of the palate, and the nostrils are fur- 
 ther separated by a septum, in which the vomer becomes 
 ossified in the fourth month. The nose appears in the eighth 
 week. Its openings are closed by a production of integu- 
 ment, which disappears again in the fifth month. 
 
 The substance of the bones is at first an homogeneous 
 jelly, which forms itself out of the granular material of 
 which the embryo consists. The spinal column is at first 
 such a jelly inclosed in a membrane, with no distinction of 
 separate vertebrae. The bones of the limbs are in like man- 
 ner preceded by a jointless gelatinous substance. The jelly 
 gradually becomes cartilaginous, the conversion taking place 
 from the surface inwards. Cartilage is first seen in the 
 human embryo in the fifth week, when it appears in the 
 bodies of the vertebra?, and in the ribs and sternum. The first 
 rude subdivision of parts of the future skeleton now takes 
 place. One hollow cartilage forms the head ; another the 
 pelvis. Each cartilage has its covering of fibrous mem- 
 brane upon which blood-vessels are formed, which enter into 
 and ramify on its substance. The presence of red blood is a 
 condition necessary to ossification. In this process the car- 
 tilage disappears, and is replaced by threads of inflexible 
 matter, which form a network or cellular structure. This 
 change looks like a crystallization of bone earth in the inte- 
 rior of the cartilage. Two facts particularly deserve at- 
 tention in it : one is, that the ossified plate or nucleus is 
 
Of the Progress of Ossification. 395 
 
 easily separable from the cartilage which contains it ; the 
 other is, that when the bone earth has been removed by 
 chemical re-agents, the animal structure which remains dif- 
 fers from cartilage. 
 Ossification begins in the human embryo in the seventh week. 
 
 In the following instances ossification takes place from a 
 single point ; in the parietal bones, palate bones, malar 
 bones, nasal bones, lachrymal bones, turbinated bones, cla- 
 vicles, patellae, in the bones of the carpus and tarsus with 
 the exception of the os calcis. 
 
 Ossification takes place from two points, in the frontal 
 bone, the vomer, the under jaw. In these instances the two 
 points of ossification are on either side of the median plane. 
 In other instances of a double centre of ossification, one os- 
 sified point is behind or above the other : this happens in 
 the os calcis, the tarsal and carpal bones, and the pha- 
 langes. 
 
 Ossification takes place from three points, forming a 
 middle and two sides, in the vertebrae and in the ethmoid 
 bone : from three points, forming a shaft and two epiphyses 
 at the same end, in the ribs; or with an epiphysis at each end, 
 in the radius, tibia, fibula. Ossification again takes place 
 from three points in the upper jaw. 
 
 Ossification takes place from five points in the scapula, ulna, 
 femur, os innominatum, and in the second and seventh cervi- 
 cal vertebrae ; omitting in the last two instances, as in the 
 foregoing account of the other vertebrae, the rims and points 
 of bones, which ossify independently some years after birth. 
 
 Ossification takes place from seven points in the humerus, 
 from eleven in the occipital bone, from fourteen in the sphe- 
 noid, from twenty-one in the sacrum, and from an irregular 
 number in the sternum. The nuclei gradually extend, and 
 when they meet coalesce ; by which means during fcetal 
 life the eleven elements of the occipital bone are reduced to 
 seven, the fourteen of the sphenoid to three. 
 
 In the human embryo the first ossific point appears in 
 the clavicle towards the end of the second month ; the next 
 in the lower jaw, the next in the upper jaw, the next in the 
 femur. During the first half of the third month ossification 
 begins in the frontal and occipital bones, in the upper arm 
 
396 Of the Ossification of Epiphyses. 
 
 and fore-arm, leg, scapula, and ribs. During the second 
 half of the third month, in the temporal, sphenoid, malar, 
 parietal, nasal bones ; in the vertebrae, carpus, tarsus, and 
 in the third phalanges. During the fourth month in the 
 vomer, in the first and second phalanges, and in the ilium. 
 During the fifth month in the ethmoid, and lachrymal, and 
 turbinated bones. In the seventh month in the os hyoides 
 and ossa coccygis. The order in which the bones are ossi- 
 fied is not that in which their cartilages are formed : it has 
 relation to the development of the vascular system. Thus 
 at remote points parallel ossifications take place at the same 
 time : and it deserves to be remarked, that in general the 
 lateral ossifications take place the first ; as if the force of 
 vascular production were greater in the sides than towards 
 the centre of the system, which it thus seems slowest in 
 reaching. The strongest illustrations of this principle are 
 in the ossification of the true vertebrae, of which the arches 
 are the first to become bone ; and in that of the ethmoid, in 
 which the lateral parts are first ossified ; and in those in- 
 stances among the symmetrical bones, in which ossification 
 begins in pairs of nuclei on either side the median plane. 
 
 The bones of the embryo are flexible and of a reddish- 
 grey colour, from their superior quantity of animal sub- 
 stance and their greater vascularity. The periosteum is 
 thicker, more vascular, and more readily separable than in 
 the adult. 
 
 The epiphyses or marginal and terminal cartilages, which 
 ossify separately, are continually encroached upon by the 
 growth of the body or shaft of the bone, towards which 
 they present a concave surface, into which processes of this 
 central part of the bone grow. 
 
 In the long bones the medullary cavity is early visible, 
 closed only towards the ends by cancellated structure, in the 
 cells of which a reddish gelatinous marrow is formed. In the 
 flat bones there is neither marrow nor diploe during foetal life. 
 
 Before birth ossification has not begun in the upper 
 cornua of the os hyoVdes, in the patella, in the lower ossa 
 coccygis, in the four upper carpal bones, and in the trape- 
 zium and trapezoides, in the naviculare and cuneiform bones 
 of the tarsus. 
 
Of the Shape of the Embryo. 397 
 
 In parts of other bones the following ossific nuclei are 
 wanting : the vertical plate of the ethmoid ; the processes 
 of the scapula ; the upper epiphysis of the humerus, of the 
 femur, and of the digital phalanges : in the tibia, as in the 
 tarsal and metatarsal bones, the lower epiphyses : in the 
 ribs the capitellum: in the ulna, radius, and fibula, both 
 epiphyses : in the atlas, the body. 
 
 The vertebral column, according to Beclard, begins to 
 ossify in its middle : by the tenth week the bodies of twelve 
 vertebrae, from the fifth dorsal namely to the fourth lum- 
 bar, contain points of ossification : in the eleventh, seven 
 are added above, one below : in the fourth month two more 
 above, the third and fourth cervical, and below, the four up- 
 permost sacral : in the sixth month the fifth sacral ; in the 
 seventh the second cervical; in the ninth the atlas and the 
 first coccygeal bone. 
 
 The vertebral column is at first straight. By the end of 
 the second month the sacrum begins to be thrown back- 
 ward. Till the third month the sacrum projects as the coc- 
 cygeal protuberance analogous to the tail of fishes; it then 
 shrinks within the growing pelvic extremities. 
 
 The embryo at first appears to have no neck. The heart 
 is as yet, where in fish it remains permanently, in the neck. 
 As the parts of the throat are developed, the lateral processes 
 of the cervical vertebrae grow, and the heart sinks into the 
 chest. The ribs appear in the sixth week as white streaks in 
 the walls of the chest. Their ossification, which goes on ra- 
 pidly, begins at the commencement of the third month. The 
 sternum is short in the eighth week, and consists of two parts, 
 the ensiform cartilage one, the handle and body the other. 
 Ossification begins in the handle in the fifth month by two 
 nuclei, one above the other. The upper segment of the body 
 soon after ossifies, and generally from one point ; the fol- 
 lowing shortly after, and often from two points : the next in 
 the sixth to the eighth week ; the lowermost in the ninth. 
 
 The diaphragm begins to appear in the third month, as a 
 thin membrane without fibres: these are first seen in the fourth 
 month : the tendinous part for a long time is disproportionally 
 large. The parietes of the abdomen are a transparent mem- 
 brane in the sixth week ; in the seventh this membrane be- 
 
398 Of the Integuments. 
 
 comes granular and opaque. The opening of the navel, at the 
 beginning of the second month is at the lower part of the 
 trunk : it rises as the hypogastric region becomes de- 
 veloped. 
 
 ~The integument, the outermost foetal product of the serous 
 layer, does not acquire a proper strength till the middle of the 
 foetal period. The epidermis shows itself at the end of the 
 second month. The rete mucosum does not begin to appear 
 till some days after birth. At the end of the fifth month 
 the body is covered with a fine covering of short, whitish, 
 silky down, or lanugo : this begins to disappear in the se- 
 venth month. The hair of the head and of the eyebrows 
 appears in the sixth month ; at the same time the nails are 
 formed. About the fifth month there appears upon the body 
 a yellowish-white greasy substance, at first thinly spread, 
 afterwards increased to a considerable quantity. This is 
 called the vernix caseosa : it is insoluble in alcohol, oils, or 
 water ; but some alkalies dissolve a part of it, and form a 
 kind of soap : it is formed on the surface of the child alone. 
 
 The limbs are formed originally below the skin, which 
 they reach pushing out like little globular shoots in the 
 sixth week. Even when their completion is considerably 
 advanced, the upper part of the humerus and of the femur 
 has not obtained a cylindrical covering of skin, but is still 
 below it. This condition, by an arrest of development, be- 
 comes sometimes permanent in man, and it is usually 
 permanent in most mammalia. When the fingers are first 
 formed they are contained in a common mitten of skin, 
 which gradually becoming thinner between them forms a 
 web which is finally absorbed. 
 
 In vertebral animals the growth of the limbs takes place 
 in the following manner. The interior jelly, when it has at- 
 tained a certain length, divides itself into two parts; an 
 upper or cylindrical part, a lower or flat part. The cylin- 
 drical part then divides into arm and fore-arm, thigh and leg : 
 coeval with this separation is the commencement of synovial 
 membranes, capsular membranes, and ligaments. The seg- 
 ments of the limbs are thus formed by spontaneous division, 
 not by the growth of one upon another. Hence it follows, 
 that any intermediate part or segment may be left out, 
 
Of the Growth of the Limbs. 399 
 
 and the limb be deficient either in the bones of the arm, or 
 in the scapula, or in the wrist bones. 
 
 The limbs are originally very much alike, and distin- 
 guishable only by their situation. In the newly-born kan- 
 garoo the arms are as large as the legs. In batrachia the 
 abdominal limbs have the earliest growth : in fish the pec- 
 toral limbs on the other hand have the advantage, with an 
 evident reference to their importance to the animal. 
 
 In the human embryo the arms are developed earlier than 
 the legs. The swelling in the spinal marrow corresponding 
 with the origins of the brachial nerves is greater than 
 that for the crural nerves. The clavicle ossifies in the 
 seventh week, and is for some time the largest bone in 
 the body, being four times as large as the thigh. The 
 scapula ossifies soon afterwards ; the hip-bone not till the 
 fourth month. At this time the pelvis is small, while the 
 shoulders are fairly spread out. The shoulders are, at the 
 end of utero-gestation, four and a quarter to four and a 
 half inches broad ; while the breadth across from one tro- 
 chanter to the other, is but three and a quarter to three and 
 a half. The femur in the eighth week is entirely below the 
 skin, while the upper-arm is already detached. The carpus 
 ossifies earlier than the tarsus, and the fingers divide them- 
 selves and ossify earlier than the toes. Nevertheless, the 
 epiphyses at the knee and the os calcis ossify earlier than 
 the brachial epiphyses and the tarsus. At the fourth 
 month the inferior extremities are as strong as the upper, 
 and acquire by the fifth month more muscular substance 
 than the latter ; the hips enlarge, the thigh becomes more 
 fleshy, and the calves are formed. When the muscles be- 
 come developed, the limbs become bent in consequence of 
 the greater force of the flexors. The limbs originally grow 
 straight out from the trunk. The upper arm then is laid 
 against the breast, the fore-arm drawn upward : the thigh 
 is bent up to the belly, the leg drawn backwards towards the 
 thigh, and the feet turned in. The digits in the ninth week 
 are spread out, in the twelfth closed. As the hands are laid 
 upon the neck and under part of the face, so the feet are 
 crossed, with the soles turned inwards. 
 
400 Production of the Amnios. 
 
 When an ovum of any magnitude is examined, the em- 
 bryo is seen suspended by the umbilical chord, and floating 
 in a liquid contained in a loose bag, which is called the am- 
 nios. The present is perhaps the best occasion for de- 
 scribing the origin and nature of the amnios. 
 
 The amnios is a shut sac resembling a serous membrane, 
 and is the outermost product of the serous layer of the 
 germinal membrane. To form this sac a membrane is re- 
 flected from the sides and from either extremity of the em- 
 bryo, so as to enclose a space behind its frame. This 
 does not take place, according to Velpeau, till after the 
 twelfth day : up to that period, in the human embryo, the 
 amnios has no existence. Towards the eighteenth day the 
 same author found it as a bladder, three lines in diameter, 
 placed upon the back of the embryo, and continuous with 
 its ends and edges. 
 
 As the walls of the trunk close in front, the circle at 
 which the amnios is attached to the body of the embryo 
 becomes proportionally contracted. It is finally limited to 
 the edge of the umbilical opening. At this point it begins 
 abruptly where the cutis and epidermis terminate ; and 
 having invested the umbilical chord, it spreads out from the 
 placental end of the latter into that ample sac, as which its 
 appearance is familiar to every student of physiology. 
 
 The inner or mucous layer of the germinal membrane is 
 supposed, upon the analogy of its office in oviparous ani- 
 mals, to form in mammalia likewise a sac containing a yolk. 
 Now in the chick, while the inner or mucous layer of the 
 germinal membrane is on the one hand expanding over the 
 yolk, it is observed on the other to become curiously con- 
 tracted towards the body of the embryo into an oblong cham- 
 ber, which is of course open to the general vitelline sac. 
 This chamber extends the whole length of the embryo as a 
 furrow. It represents the future alimentary tube ; and hence 
 the term intestinal vesicle is given to the entire pouch out 
 of which it was taken, and of which it now forms a par- 
 tially-separated chamber. 
 
 This furrow or rudimentary alimentary canal acquires, by 
 the growth of its sides, at first the shape of a canoe or 
 
Of the Intestinal Vesicle. 401 
 
 wherry, either end being bent forward by the inclination of 
 the head and of the caudal extremity. The open furrow 
 has then its sides drawn together so as nearly to meet, ex- 
 cept in the middle, where both freely, communicate by a 
 common opening with the vitelline sac. At this point like- 
 wise, by a central elongation and projection of the canal, 
 both parts point forwards to the common opening, one part 
 representing the upper, the other the lower half of the ali- 
 mentary canal. Finally, the two canals are completed by 
 the closing of the linear furrow : they remain, however, open 
 towards the vitelline sac, as already described, and the neck 
 of communication is elongated. 
 
 In the relation of the intestinal vesicle in birds to the 
 yolk and to the alimentary canal, three points especially 
 deserve attention. 1. From the great size of the yolk the 
 mucous layer has not extended itself round it, when the 
 formation of the furrow representing the future alimen- 
 tary canal is required to begin. 2. The communication be- 
 tween the yolk and the alimentary canal does not become 
 interrupted : but, 3dly, towards the close of incubation the 
 yolk-bag is drawn into the belly of the chick, that its con- 
 tents may be used as nourishment, 
 
 Now in mammalia, in which a different provision is made 
 for the nutrition of the mature embryo, a quantity of fluid 
 equal or proportionate to the yolk is not needed. Accord- 
 ingly the ovum of mammalia is cast in the smallest mould, 
 and the primitive trace is formed in a diminutive vesicle. 
 That vesicle, however, is supposed to contain a yolk, and 
 that yolk to be enclosed within an extension of the mucous 
 layer of the germinal membrane. If this supposition be 
 just, and it is founded upon a strong analogy, the vitelline 
 sac in mammalia displays this remarkable difference from 
 that in birds it enlarges with the growth of the embryo. 
 In man it attains a diameter of six lines. 
 
 The discovery of the intestinal vesicle in mammalia was 
 made by Bojanus. He found in the ovum of the sheep a 
 sac communicating by a neck with the intestinal canal. 
 
 A second point of difference in the intestinal vesicle of 
 mammalia from that of birds is, that the tube of commu- 
 
402 Of the Fauces and Stomach. 
 
 nication between it and the intestine early becomes oblite- 
 rated. The obliteration takes place, according to Velpeau, 
 in the sixth week. Through this circumstance it was that the 
 nature of the intestinal vesicle in mammalia for a length of 
 time escaped discovery ; for i'ts existence as a small isolated 
 sac under the name of vesieula alba was well known to 
 anatomists; and Hunter had even seen it filled with the 
 same fluid as the alimentary canal, but connected to it by 
 an impervious thread. 
 
 The third and final point of distinction between the in- 
 testinal vesicle in mammalia and birds is, that the vesieula 
 alba in the former, instead of being in the end drawn into 
 the body of the embryo, as happens in the chick, remains 
 without it in the membranous appendages of the ovum, and 
 finally wastes, and disappears by the third month. 
 
 We may now trace the development of the alimentary 
 canal. The mouth becomes open in the sixth week ; the 
 anus at the seventh. The source of the imperforate anus 
 becomes thus apparent. 
 
 The mouth at first is a long transverse fissure without 
 lips : these appear in the ninth week. The tongue begins to 
 be formed in the seventh week : in the ninth week it is 
 large, broad, cylindrical, and projects out of the mouth, into 
 which it is withdrawn in the fourth month ; at the same 
 time its papillae appear. The palate is formed of three pieces 
 on each side, which unite in the twelfth week : the soft pa- 
 late is constructed in the same manner of lateral parts ; 
 hence the occasional malformation, consisting in a fissure of 
 the hard and soft palate. 
 
 The stomach, as the alimentary canal lengthens and un- 
 folds itself, is at first vertical and cylindrical, and scarcely 
 distinguishable from the oesophagus and intestine. In the 
 ninth week, however, its fund us begins to project to the 
 left side, although as yet its left edge is part of a straight 
 line continuous with the oesophagus and intestine. At the 
 end of the third month the pyloric extremity developes it- 
 self, and the viscus is disposed obliquely across the spine. 
 In the fourth month the constriction at the pylorus begins 
 to appear. 
 
Of the Intestines. 403 
 
 The small intestine is the part of the alimentary canal 
 with which in all vertebral animals the yolk sac communi- 
 cates. In general this communication takes place at the 
 middle of the small intestine ; but in mammalia it is situate 
 at a point nearer to the great intestine. The small intestine 
 is at first of the same diameter with the great : it then be- 
 comes even larger : it afterwards contracts in proportion as 
 its calibre increases in length. The small intestine is be- 
 sides originally shorter than the great, but it soon acquires 
 its proportionate length, or even exceeds it. 
 
 The great intestine becomes at first proportionally longer 
 and larger than in the adult. The caecum begins to appear 
 at the seventh month as a small projecting sac, marking the 
 distinction between great and small intestines. 
 
 The appendix caeci vermiformis appears in the seventh 
 week, at first as large as the small intestine, and propor- 
 tionally longer than in the adult. At the fourth month it 
 becomes narrower and contorted. The transverse saccula- 
 tion shows itself in the colon at the end of the fifth month. 
 
 The alimentary canal at first consists of an uniform, soft, 
 granular substance, which gradually separates into two 
 layers, the mucous and the muscular. The villi, according 
 to the observations of Meckel, are formed in the following 
 way. The inner surface of the alimentary canal is raised 
 into fine longitudinal ridges of mucous membrane : these at 
 the commencement of the third month become indented or 
 toothed at their unattached margin ; the projecting points 
 are the villi. In the fourth month they are proportionally 
 larger than in adults. Although developed both in the 
 stomach and small and great intestines, yet even in the 
 third month they are visibly lower and smaller in the latter ; 
 and by the eighth month they have disappeared. 
 
 The valvulae conniventes do not appear before the seventh 
 month, and till the time of birth they are confined to the 
 upper part of the small intestine. 
 
 In the preceding brief description of the development of 
 parts of the alimentary canal, the mucous tube has been re- 
 presented as elongating itself here and there into pouches : 
 the fundus of the stomach, the caecum, the appendix caeci, 
 
404 Of the Salivary Glands. 
 
 are parts of this nature. Now the conglomerate glands have 
 a similar origin. We are indeed in some degree prepared 
 for this by the structure of the glandulae muciparae in the 
 higher animals ; and by finding the pancreas in fish, and 
 the salivary glands and biliary organ in articulated ani- 
 mals no more than pouches communicating with the ali- 
 mentary tube. 
 
 The following is the manner in which the salivary glands 
 are developed. A small mass of primitive matter is seen 
 adherent to a part of the alimentary canal : into this one or 
 two tubes, which communicate at their origin, extend from 
 the mucous canal. The blind end of each tube is dilated 
 into a spherical pouch. From the sides of each tube other 
 tubes grow out, of similar character to the first. At first 
 there is no difference in the appearance of the tubes, and 
 their terminal bulbs ; but after a little, the latter thickening 
 become of a milk-white colour, the former a clear opal. In 
 this manner the structure of the entire gland is completed. 
 The proportionate size of the tubes and bulbs is greatest at 
 first. According to Burdach, in sheep and swine the pan- 
 creas appears the first of the salivary glands, then the sub- 
 maxillary, and afterwards the parotid : the two former appear 
 at the same time with the thyreoi'd, and something later than 
 the liver and spleen. There is this difference in the struc- 
 ture of the parotid and of the pancreas, which has an evi- 
 dent relation to the shape of each : in the latter the tubes 
 are longer, and diverge at acuter angles, than in the former. 
 
 The liver is formed in the same manner as the pan- 
 creas, by tubular productions from the upper part of the 
 small intestine. Accordingly in acephalous foetuses, in 
 which the upper part of the alimentary canal is wanting, 
 the liver is found to be wanting likewise. The liver is 
 formed upon two tubes, which originate out of the in- 
 testine. In the crab the two livers remain permanently 
 separate; and in man, at first, there is not that differ- 
 ence in the relative size of the two lobes which is visible 
 afterwards. The liver in the human embryo at the third 
 month is soft and pap-like : it shortly afterwards be- 
 comes firmer, granular, dark- red, and even more vascular 
 
Of the Liver a/id Gall-bladder. 405 
 
 than it appears to be after birth ; probably because, in addi- 
 tion to the blood of the spleen and of the bowels, it receives 
 a supply from the umbilical vein. Its size at an early period 
 is so disproportionate, that whereas in the adult it is to the 
 whole body as 1 : 36, shortly before birth it is as 1:18, and 
 at the end of the first month as 1 : 3. In the first month 
 the liver occupies the under half of the trunk, as the heart 
 the upper. In the second month it reaches to the ilium : it 
 is then gradually elevated by the increasing growth of the 
 lower part of the frame. 
 
 The gall-bladder is formed originally like the elementary 
 tubes of the liver by a tubular extension of the mucous 
 surface of the intestinal canal ; but not being received into 
 a mass of elementary matter, it enlarges into a simple sac. 
 Between the second and third month it is an empty canal. 
 It slowly changes from the cylindrical figure to that of a 
 pear. After the fourth month mucus is found in the gall- 
 bladder. Bile is found in the alimentary canal at this time ; 
 but not in the gall-bladder till the seventh month. 
 
 The reticulated folds in the gall-bladder appear in the 
 sixth month. The openings of the ductus choledochus and 
 pancreas are at first at some distance apart, and project into 
 the intestinal canal. After the fifth month they gradually 
 approximate and are drawn inwards. 
 
 The lungs may be viewed as another expansion of the 
 mucous layer of the germinal membrane : they begin to ap- 
 pear in the chick at the third day, in the human embryo 
 about the sixth week. Burdach conjectures with great 
 plausibility, that the lungs grow from the back part of the 
 ossophagus, and gradually advancing on either side of the 
 aorta, at length surround the latter. Burdach observed the 
 lungs in very young mammalia to consist of a single mass, 
 in which the rudiments of the bronchi were contained. 
 Through the middle of this mass however a spongy par- 
 tition of membrane could be traced. The separation of the 
 lungs into two begins from behind by the absorption of the 
 layer of membrane above described. A strong bridge of 
 communication is thus left in front of the lungs, which re- 
 mains for some time, and in which the divisions of the wind- 
 
 2 c 
 
406 Of the Lungs. 
 
 pipe are contained. While the lungs are being developed 
 this commissure remains spongy and membranous : it is 
 finally absorbed. The lungs are perfected first at the back 
 part. The lungs at first occupy the lower and back part 
 of the chest, being placed below the heart : they gradually 
 extend forwards and upwards, so as at length to cover the 
 heart. Their weight, according to Meckel, at the tenth 
 week, compared to that of the whole frame, is as 1 : 25 or 
 27, in the twelfth week as 1 : 43, in the seventh month 
 as 1 : 75. They grow rapidly upon their first appearance, 
 and are then specifically heavier than afterwards. 
 
 The surface of the lungs in mammalia is at first smooth, 
 but afterwards is raised into wart-like elevations. These ele- 
 vations, which mark the future lobules of the lungs, become 
 gradually less prominent. Before their appearance Meckel 
 observed the furrows to be traced by which the lungs are 
 eventually divided into lobes. In very young embryos Bur- 
 dach found the lungs to consist of a thick and homogeneous 
 jelly. In embryos something older, the same physiologist 
 found the original jelly of the lungs interspersed with small 
 firm corpuscles, with their base outwards, and their points 
 turned inwards and adhering to the branches of the wind- 
 pipe. These corpuscles soon after their first appearance be- 
 come hollowed into cells, their numbers increase, the jelly 
 which unites them becomes a close and filamentous tissue, 
 and is permeated by increasing blood-vessels. The lungs, 
 at first white, assume a shade of red in the fourth month. 
 In the sixth month they allow air to be blown into them. 
 
 The windpipe in mammalia appears originally of a soft 
 texture, and is flat. Its walls are thick in proportion to the 
 cavity. The first appearance of the windpipe in the human 
 embryo is in the sixth week. The first trace of cartilage in 
 its texture is formed, according to Fleischmann, in the 
 eighth week. Burdach remarked, that each ring of the 
 windpipe is formed of a single cartilage, and that the carti- 
 lage forms first in the middle of the future rings, and gra- 
 dually lengthens towards the ends. The bronchi are short 
 at first ; their cartilages appear something later than those of 
 the trachea. Fleischmann is of opinion that the cartilaginous 
 
Of the Wo/ffian Bodies. 407 
 
 rings of the trachea are formed of two lateral portions united 
 afterwards in front, at which part he describes the cartilage 
 as for some time thinner than at the sides. 
 
 The larynx in mammalia is at first spherical, and consists 
 of an homogeneous jelly. About the seventh week the car- 
 tilages begin to appear. The first to be seen are the thy- 
 reoid and crico'id ; and, according to Fleischmann, these are 
 each formed in two halves. The two plates of the thyreoiid 
 coalesce in the fourth month, the halves of the cricoid 
 somewhat later. At this time the horns of the thyreoi'd 
 cartilage and the arytaenoi'ds appear : the epiglottis proba- 
 bly appears a little earlier. The chordae vocales and arytse- 
 noid cartilages are developed in one thick mass of substance, 
 which at first reaches above the top of the thyreoi'd. 
 
 From the account which I have given of the origin of the 
 lungs, as well as of the liver and salivary organs, it is evi- 
 dent that to call these parts a production of the mucous 
 layer is a bold and scarcely allowable figure. They are, it 
 is true, formed in a strict relation to the mucous membrane 
 of the alimentary canal, with which their cavities are from 
 the first continuous; but they are directly developed in 
 masses which are spontaneously formed in the embryo, like 
 the original jelly from which the skeleton arises. The cor- 
 rectness of this view becomes the more apparent, when we 
 trace the history of the remaining parts of the glandular 
 system. 
 
 The kidneys are preceded in the embryo by a substance 
 first remarked by Wolff, to which the term of Wolffian 
 bodies or false kidneys was given by Rathke. 
 
 Burdach, who investigated the nature of these parts in 
 snakes, lizards, fowls, swine, sheep, and horses, found them 
 to exist at a time when the heart and alimentary canal were 
 the only other occupants of the cavity of the trunk. The 
 false kidneys form at that time a thick mass of jelly-like 
 substance, which is at first simple, but afterwards on the 
 development of the aorta becomes divided at the median 
 plane into two lateral portions. The false kidneys extend 
 originally in all other vertebral animals (like the true kid- 
 neys in fish and batrachia) the whole length of the spine, 
 
 2 c 2 
 
408 Of the Wolffian Bodies. 
 
 from the heart to the end of the intestine. They gradually 
 shorten at both ends, and at the same time acquire thick- 
 ness and breadth. This change in form takes place, both in 
 rapidity and degree, in a strict proportion to the rank of 
 the animal in the ascending scale of organization. 
 
 In mammalia the false kidneys acquire their greatest re- 
 lative thickness before the middle of foetal life ; in birds 
 about the middle ; in the higher amphibia some time before 
 that period. They then continue to grow exactly in pro- 
 portion to the rest of the body ; after a time, however, they 
 diminish by absorption, and at length entirely disappear. 
 The time of their disappearance is in proportion to the earli- 
 ness of their production. They disappear something earlier 
 in the female than in the male. They have entirely vanished 
 before birth in mammalia. In birds the right false kidney 
 begins to shrink before the left has reached its full size, and 
 has disappeared entirely at a time when the left is of con- 
 siderable magnitude. In oviparous vertebral animals a slen- 
 der tube leading to the cloaca, and termed a false ureter, is 
 temporarily found. Nothing parallel to this has been found 
 in mammalia. 
 
 The false kidneys consist originally, like the true kidneys 
 in fish and batrachia, of parallel plates alternately thick and 
 thin. In each thick plate a vessel arises, which, having 
 Coalesced with others, in birds and amphibia opens into the 
 raise ureter, and in mammalia at a later period opens into 
 the vas deferens or the Fallopian tube. The tubes them- 
 selves collect into fasciculi, and form many glandules of an 
 oval or triangular form. The false kidneys are the most 
 vascular parts in the embryo after the liver : four or five 
 branches from the aorta are distributed to each, and two 
 veins return from each to the vena cava. The upper vein 
 with an artery are converted into the emulgent vessels, the 
 lower into spermatic vessels. 
 
 The false kidneys resemble, as it has been said, the per- 
 manent kidneys of fish and batrachia. In the higher verte- 
 bral animals they are used to contribute to the development 
 both of the kidneys and of the testes and ovaries. 
 
 The true kidneys are formed upon the false. They appear 
 
Of the Kidneys, and of the Spleen. 409 
 
 in the human embryo in the seventh week. They acquire 
 considerable size in fcetal life, being at the time of birth to 
 the whole body as 1 : 80 ; whereas in the adult they are as 
 1 : 240. In the ninth week they are slender, elongated, and 
 formed of little nodules, which gradually unite together, so 
 that in the tenth week about eight lobules are observable. 
 These nodules increase in number, and at the time of birth 
 as many as fifteen are distinguishable upon the surface. 
 The ureters appear to stretch from the kidneys to the blad- 
 der, having been met with in malformations as blind tubes, 
 not having yet reached their destination. 
 
 The renal capsules appear in the chick on the twelfth 
 day. In the human embryo at the seventh week they are 
 larger than the kidneys : at the fourth month they equal the 
 latter in size : in the sixth month they become relatively 
 less, and their weight to that of the kidneys is as 1 : 25, in 
 the tenth month as 1 :3, in adults as 1 : 28. At first the 
 renal capsules touch each other : at nine weeks they be- 
 come gradually separate, and consist of granules which are 
 collected in three, or four lobuli, each of which is supported 
 on a vessel as on a stalk. In the fourth month the corpus- 
 cular structure becomes less distinct, and in the sixth the 
 renal capsules separate into an outer greyish substance su- 
 perficially furrowed, and an inner whitish or reddish sub- 
 stance containing cells in which a yellowish, brownish, or 
 reddish fluid is found. 
 
 The spleen appears later than the renal capsules. It is 
 seen first in the human embryo at the tenth week as a small 
 whitish body pointed at both ends : it gradually becomes 
 tinged with red. It is placed further forward in the embryo 
 than after birth. Its size is relatively much less than in 
 adults. According to Heusinger, the size of the spleen at 
 the tenth week to that of the liver is as 1 : 500, in the tenth 
 month as 1 : 50, in adults as 1 : 5 ; to the whole body, at the 
 tenth week, as 1 : 3000, in the adult as 1 : 180. 
 
 The thymus appears in the human embryo about the 
 tenth week as a small body in the upper part of the thorax. 
 It is formed of two lateral halves, which are subsequently 
 united by cellular membrane. It is for some time as large 
 
 

 410 Of the Bladder. 
 
 as the lungs. Sir Astley Cooper has recently shown each 
 lateral lobe of the thymus to be a congeries of hollow cor- 
 puscles, which open by single orifices into a common reser- 
 voir containing a peculiar fluid. The thyreoi'd gland appears 
 at an early period : it consists originally of two separate 
 halves, which grow together in the fourth month, and are 
 proportionally larger and more vascular than in adults. 
 
 The mammae are supposed to be produced by tubular 
 inflections of the skin, as the abdominal glands are formed 
 by tubular productions of the mucous layer. 
 
 The bladder and urethra, with the external organs of ge- 
 neration, are formed in part out of a development of the ex- 
 tremity of the intestine, in part by fissure and folding of the 
 integument. 
 
 In mammalia, as in other vertebral animals, the allantois 
 remains for a time continuous with the extremity of the ali- 
 mentary canal ; so that the last part of the bowel is thus a 
 cloaca, the common termination of the intestinal and ve- 
 sical apparatus. The sides of this cloaca gradually approach 
 each other, and two folds are thus produced, which at 
 a later period become united, and thus separate the rectum 
 from the urinary canal. The urethra is likewise formed by 
 a folding of the cloaca. The urethra is never closed, but is 
 open from the first and always. 
 
 The bladder in the seventh week is an oval corpuscle : in 
 the ninth week it is long and cylindrical, and preserves more 
 or less this form during the rest of the foetal period. It is 
 formed out of the allantois. 
 
 The vagina is proportionally longer in the embryo than in 
 the adult. In the sixth and eighth month it is wider, with 
 stronger rugae, than afterwards. The hymen appears in the 
 fifth month. The penis and clitoris appear indifferently in 
 the sixth week, like a small corpuscle before the cloaca : 
 in the seventh week the organ is spherical, with a furrow 
 channelled in it. In the tenth week it is proportionally of 
 great size. At the end of the third month the cloaca is di- 
 vided into the rectum and urinary cavity, and the difference 
 may be distinguished between the penis and clitoris. 
 
 The testes and ovaries appear in mammalia about the 
 
Of the Testes and Ovaries. 411 
 
 same time at the inner and fore part of the false kidneys, 
 attached to them by a fold of peritoneum. In the human 
 embryo at the seventh week they form slender elongated 
 bodies placed below the kidneys, with their inferior ends 
 near to each other. 
 
 The testis becomes a greyish homogeneous substance, in 
 which the tubular structure gradually developes itself. The 
 ovary is at first smooth, then nodular on its surface : this ap- 
 pearance is seen in the human embryo at the twelfth week ; 
 it vanishes again by the fourth month. The testis, at first 
 oval, is disposed obliquely ; but at the third month it is laid 
 vertically, and further apart from its fellow ; it is convex in 
 front, concave behind. The ovary, at first oblong, becomes 
 afterwards triangular : in the fourth month it becomes again 
 rounder, and then at its outer end more pointed and ovi- 
 form. 
 
 The ovaries in the tenth week are a line and a quarter in 
 length, one-third of a line in thickness : at the same time the 
 testis is a line and half in length, and three-quarters in thick- 
 ness. The proportionate length of the latter to that of the whole 
 frame in the first month is as 1 : 18 : in the ninth as 1 : 40. 
 
 The epididymis appears in the tenth week : its greatest 
 proportional size is attained at the fourth month. A corre- 
 sponding organ is formed upon the ovary, but it soon wastes 
 and disappears. 
 
 The testes and ovaries are surrounded by the peritoneum, 
 except at their posterior edge where their vessels enter. 
 From either testis and ovary there descends to the internal 
 ring a membranous process, which in the male is termed 
 the gubernaculum, in the female the round ligament. It 
 passes in either sex along the spermatic passage to the fila- 
 mentous tissue of the scrotum or labium. 
 
 The round ligament, as the ovary gradually descends into 
 the pelvis and is drawn towards the uterus, approaches and 
 finally attaches itself to the latter. 
 
 The gubernaculum, which is visible in the tenth week, is 
 originally attached to the vas deferens, and gradually fixes 
 itself to the inferior end of the testes or epididymis. The 
 preceding circumstance explains a most remarkable devia- 
 
412 Of the Testes and Ovaries. 
 
 tion which I remember to have met with in the body of an 
 adult. The left testis had not descended, and lay upon the 
 edge of the psoas muscle immediately within the internal 
 ring ; while the chord, doubled through the persistence of 
 the original attachment of the gubernaculum to it, had been 
 drawn down in a long fold into the scrotum. 
 
 The ovaries, originally attached to the loins, gradually de- 
 scend from their vicinity to the kidneys ; they remain for a 
 time placed upon the psoas muscle; they then fix them- 
 selves on the brim of the lesser chamber of the pelvis, where 
 they remain for a long period after birth. 
 
 Up to this time the progress in development and change 
 of place of the ovaries and testes is much alike, except that 
 the latter are always a little in advance of the former : in 
 the seventh month the testes reach the inner ring ; in the 
 eighth they enter the passage, in the ninth the scrotum. 
 Upon an examination of ninety-seven infants at birth, 
 Wrisberg found in sixty-seven both testes in the scrotum, in 
 seventeen one or both in the canal, in eight one testis, and 
 in three both testes in the abdomen. 
 
 It is difficult to account for the descent of the testes. The 
 gubernaculum can hardly give the first impulse, for it does 
 not become fibrous till the sixth month, and the testis is 
 then already lowered in its position. The descent is pro- 
 bably a process of growth. 
 
 The vas deferens is a production of the epididymis ; it is at 
 first directed downwards ; about the fourth month it is re- 
 flected upwards : it subsequently descends : it is already, 
 in the fifth month, convoluted. The vesiculae seminales are 
 of slow development : they are productions from the vasa 
 deferentia. 
 
 The Fallopian tubes in the higher vertebral animals, in 
 which they are in their origin and remain afterwards sepa- 
 rate from the ovaries, are supposed to be the last product of 
 the false kidneys. The Fallopian tubes gradually bend 
 themselves, and form a trumpet-like end outwards at the 
 eighth month, when they are more convoluted than in the 
 adult. By the inner extremity either Fallopian tube joins 
 its fellow at an acute angle to form the uterus. The uterus 
 
Of the Vascular Layer. 413 
 
 has thus originally two bodies ; the neck then is formed, and 
 from thence the single body of the uterus is produced. The 
 uterus is still Out of the pelvis in the sixth month. At this 
 period it descends into the pelvis. The uterus at birth is 
 proportionately much larger than during the intervening pe- 
 riod before puberty. 
 
 It has been explained that each organ begins to be de- 
 veloped without blood or blood-vessels. A force of vital at- 
 traction draws together the fitting elements in each part, 
 and it is only for the subsequent growth and perfection of 
 the organs that a circulation is established in them. The 
 heart even is formed and shaped, and its texture has ac- 
 quired some degree of consistency, and it has begun to dis- 
 play an undulatory motion, before the blood has reached it. 
 
 According to the observations of Prevost, Dumas, and 
 Von Baer upon the development of the chick, the following 
 periods are to be observed in reference to the development 
 of the vascular system. 
 
 Between the twentieth and the thirty-sixth hour appear, 
 first the vascular area, figured in a preceding page then 
 the heart then the formation of blood in the vascular area ; 
 but as yet the blood is motionless. The heart is soft, trans- 
 parent, separating itself into an oblong sac something curved, 
 and a colourless fluid ; and about the middle of the second 
 day, that is, about ten hours after its first appearance, it 
 begins to exhibit an undulatory motion, pulsating on its 
 own colourless fluid alone, while there already exists red 
 blood in the circumference of the germinal membrane, that 
 is to say, in the vascular area, which acquires motion in- 
 dependently of the heart. 
 
 By the end of the second day or by the commencement 
 of the third a simple circulation is established : the blood 
 finds its way from the vascular area by the omphalo-mesen- 
 teric veins to the heart, from which it is expelled along the 
 aorta, and from thence again to the vascular area. 
 
 Between the third and sixth day the systemic with the 
 hepatic circulation commences. The aorta distributes 
 branches to the body, and the vense cavse are formed, and 
 
414 Of the Vascular A rea. 
 
 the vena portae ; so that while part of the blood is thrown 
 through the vascular area, part circulates through the frame. 
 The aorta at the same time forms five pair of bronchial 
 branches in the neck. 
 
 During the next period the branchial branches shrink, 
 the circulation retires from the intestinal vesicle, and 
 stretches itself in a new course without the frame along the 
 allantoid. 
 
 Finally, this second extraneous circulation is drawn back, 
 and the blood prepares to flow through the lungs. 
 
 In the embryo of the chick the first vessels which appear 
 are veins which are developed in the vascular area, and ter- 
 minate in a circular vein which marks the limits of the vas- 
 cular area : this vein is called the vena terminalis or circulus 
 venosus. It is at first a simple channel in which the blood 
 is being formed with no distinguishable boundary or coat. 
 Such a vessel Cuvier saw upon the intestinal vesicle of 
 rodentia. In other mammalia it appears to be wanting, or else 
 to vanish at a very early period. The earliest branches of the 
 aorta are distributed to the intestinal vesicle, upon which 
 they radiate, and after many anastomoses terminate in the 
 roots of the veins. In mammalia there is but one omphalo- 
 mesenteric artery and one omphalo-mesenteric vein ; the lat- 
 ter is larger than the former. In the chick there are two 
 veins originally, which coalesce in a single trunk, to join the 
 posterior cavity of the heart. There is now a simple circula- 
 tion, of which the poles are the heart and the vesicula intes- 
 tinalis. The venous trunk then divides, one part forming the 
 ascending cava, the other the rudiment of the vena portae. 
 
 All the arteries take their origin from one trunk, which 
 springs from the heart. The heart in all vertebral animals 
 is originally one simple elongated sac. The single artery 
 which rises from it branches into five pair of arches, between 
 which the oasophagus lies. 
 
 The single heart and artery, with its branchial arches, 
 are permanent parts in fish : in other vertebral animals they 
 undergo a series of metamorphoses by which they are 
 brought to the characteristic type of the species. The es- 
 
Of the Heart. 415 
 
 sence of these changes in birds and mammalia is, that the 
 heart spontaneously divides into two separate chambers, 
 the artery into an aorta and pulmonary artery ; that some 
 of the arches disappear ; others becoming permanent aortic, 
 others permanent pulmonary branches. 
 
 The heart of the dog, at the twenty-first day, is a mem- 
 branous tube twisted in itself, and slightly divided into an 
 auricle, ventricle, and bulb of the aorta. The wall of the 
 ventricle soon acquires a greater thickness than the rest. 
 
 At a period which is probably between four and six weeks, 
 the rudiments of a septum begin to be perceived in the 
 heart. The septum of the ventricles is produced in two 
 ways : on the one hand it arises as a growth from the base 
 of the ventricles ; on the other it originates in the exten- 
 sion and growth of the right ventricle in such a manner as 
 to form a bifurcated extremity to the heart. This appear- 
 ance begins in the seventh week. 
 
 The external figure which the heart now assumes is per- 
 manently retained in several species of mammalia. The 
 heart of the dugong and of the manatee presents in the most 
 characteristic manner this permanent separation of the ven- 
 tricles. The same is seen in a less degree in the walrus, 
 seal, elephant, and in some of the rodentia. 
 
416 Of the Septum of the Heart. 
 
 The internal construction at present has some resem- 
 blance to the permanent character of the ventricles of the 
 alligator. But it is most strangely and strikingly preserved 
 in those human malformations, in which from this period 
 a communication remains throughout life between the two 
 ventricles. 
 
 The nature of the formation of the inter-auricular septum is 
 very obscure, and requires further investigation. The first ap- 
 pearance of an inter-auricular septum is in the direction of the 
 Eustachian valve, which at that time appears to be conti- 
 nuous with the annulus foraminis ovalis ; and thus lying 
 before the entrance 'of the vena cava inferior, causes it to 
 open into the left auricle. This is seen about the fifth week. 
 At the sixth week this septum becomes perforated by many 
 foramina, and by a process of absorption wastes into the 
 Eustachian valve. At the same time a production analo- 
 gous to the first begins to be formed in the place of the 
 permanent inter-auricular septum. It is remarkable that it 
 is at this period namely, when the inferior cava begins to 
 be shut out of direct communication with the left auricle 
 that the pulmonary veins open into it. The valvula forami- 
 nis ovalis goes on increasing till the seventh month, when 
 it is already a sufficient flap to cover the orifice of commu- 
 nication. 
 
 At this period of development it is evident that the foetus 
 becomes fit for pulmonary respiration. The oblique opening, 
 which serves if the embryo remains in utero to transmit the 
 blood from the right auricle into the otherwise empty left, 
 would it is evident become closed, if breathing and a circu- 
 lation through the lungs were now commenced, and an equal 
 stream of blood were poured into the left auricle as into the 
 right. 
 
 At the time when the aorta gives off its cervical arches, 
 the construction of the adjacent parts participates in the 
 same character, and might more readily be converted into 
 branchial organs than into a higher type. The neck is short 
 and thick, the pharyngeal portion of the intestine is of great 
 size, and its sides are penetrated by clefts. 
 
Of the Vascular Arches derived from the Aorta. 417 
 
 Four openings on each side of the oesophagus have been 
 observed in the embryo of the dog, between three and four 
 weeks old ; in that of the sheep of three weeks ; of the pig 
 at three weeks ; of the rabbit on the twelfth day ; and in the 
 human embryo of six weeks : in the embryo of the dog, 
 some little time before that mentioned above, only three 
 apertures are found. While three pairs of clefts exist in 
 the sides of the pharynx, there are in the dog, as in the 
 chick, only four pairs of vascular arches ; but before the 
 first of these becomes obliterated, a posterior or fifth pair is 
 produced, while at the same time the fourth branchial cleft 
 is formed ; so that in the mammiferous animal five pairs of 
 vascular arches and four pairs of clefts exist for some time 
 simultaneously in the sides of the neck. 
 
 A few days after the appearance of the fifth arch, the 
 neck begins to elongate, the apertures are closed gradually 
 on the outside, and the lower jaw becomes more developed ; 
 while the vascular arches undergo those changes by which 
 the permanent arterial branches arising from the heart are 
 formed. 
 
 The first and third pair of vascular arches form the ca- 
 rotid and subclavian arteries in mammalia, as in birds, and 
 the second pair seems to be wholly obliterated, or at least 
 gives only a small branch ; in mammalia, however, the arch 
 of the aorta, or permanent communicating vessel between 
 the ascending and descending aorta, is formed from the 
 fourth branchial arch on the left side of the O3sophagus ; so 
 that the order in which the vessels of the head and superior 
 extremities arise is reversed, the right innominata taking its 
 origin before the vessels of the left side. 
 
 The pulmonary vessels appear to be given off by the 
 fourth arch on the right and the fifth on the left side, the 
 fifth on the right being wholly obliterated. While, how- 
 ever, the carotid and branchial arteries become developed 
 from the anterior arches, the pulmonary arches do not con- 
 tinue to carry blood to the root of the aorta, as takes place 
 in those of the bird. The parts by which these arches com- 
 municate with the root of the descending aorta (forming in 
 
418 Transmutation of the Single Aorta 
 
 birds the ductus botalli) become gradually obliterated ; so 
 that of all the five pairs of vascular arches in the embryo 
 of the mammiferous animal, only one, the fourth of the left 
 side, remains prominent. 
 
 While these changes take place in the pulmonary arches, 
 the bulb of the aorta, from the single cavity of which the 
 pulmonary and systemic vessels arise for some time in com- 
 mon, is divided, so as to form the roots of the aorta proper 
 and pulmonary arteries. According to Meckel, the septum 
 which has separated the left ventricle entirely from the 
 right, appears to be continued onwards into the bulb of the 
 aorta, and thus separates this cavity longitudinally into two 
 compartments. The division of the bulb is, however, im- 
 perfect for a time ; it advances gradually from the part next 
 the ventricle to that from which the vascular arches rise ; 
 so that, while the posterior part is divided, the anterior yet 
 remains single, a communication being left at this part be- 
 tween the aortic and pulmonary roots, which admits of the 
 passage of the blood from the right ventricle into the aorta, 
 when the pulmonary arches are obliterated. When the di- 
 vision of the aortic bulb has just taken place, the arch and 
 descending part of the aorta appear to be a continuation of 
 the pulmonary rather than of the aortic root, the latter ap- 
 pearing to lead only into the vessels of the head and ante- 
 rior extremities. The ductus arteriosus remains for some 
 time, as at first, short and wide, and has the appearance of 
 being an opening of communication between, or a deficiency 
 in the parietes of the juxtaposed tubes; it afterwards be- 
 comes lengthened out and narrowed, and appears during a 
 short period to pass from the aorta to the pulmonary root 
 and aorta continuous with it ; but about the tenth week in 
 the human embryo this part is dilated, and forms a more di- 
 rect communication between the ascending and the de- 
 scending aorta, and the ductus botalli is now formed by 
 another part, viz. the end of the pulmonary root leading 
 into the arch of the aorta. 
 
 The following diagram from Burdach may assist in il- 
 lustrating the description which has been given of these 
 
into Aorta and Pulmonary Artery. 419 
 
 changes ; the parts of the figure left in shade represent the 
 single original artery, and those branches derived from it 
 which shrink in the progress of development : the parts 
 fully figured show the division of the primitive trunk, and 
 the persistence of some of its branches as aortic and as 
 pulmonary arteries. 
 
 The lungs of mammiferous animals do not appear to be 
 visible before the period when the branchial apertures begin 
 to close. As the lungs become larger, they receive vessels 
 from the pulmonary arches, which gradually enlarging as 
 the foetus becomes developed, divert the stream of blood 
 from the arterial duct of the aorta. This latter opening now 
 diminishes in size, and at birth, when the efflux of blood to 
 the lungs is suddenly increased, it is closed up. 
 
 Let me now recapitulate the heads which have been illus- 
 trated in the present section. 
 
 The ovum of mammalia is at first two sacs, one enclosing 
 the other : the inner containing a liquid. Upon the inner, 
 or below it, the germinal membrane is seen, with the primi- 
 tive trace. The germinal membrane expands and divides 
 
420 Of the Allanto'is. 
 
 into two layers, the outer or serous, the inner or mucous : 
 then a third is developed between the two first, which is the 
 source of the vascular system. The serous layer developes 
 in itself, the bones, joints, muscles, the brain and nerves, 
 and the organs of the senses, together with the integument, 
 and reflects from the contracting opening of the trunk of 
 the enlarging embryo the amnion, as a bladder, at first 
 covering its dorsal surface and sides, at last a capacious 
 sac, in the fluid of which the embryo hangs and floats. 
 
 The mucous layer may be supposed upon analogy to ex- 
 pand into a sac "containing the yolk; then by its contrac- 
 tion first and elongation afterwards below the body of the 
 embryo, it forms the alimentary canal, and by its tubular 
 productions contributes to originate the glandular system 
 and the lungs. The first appearance of the vascular sys- 
 tem, or the first development and expansion of the vascular 
 layer, takes place upon this membrane in the circle called 
 the area vasculosa. The second step in the development of 
 the vascular layer, is the production of the heart and aorta, 
 and the growth from the aorta of branchial branches. As 
 this second step, as well as the first, seems to have some 
 reference to a respiratory function, so has it likewise a re- 
 lation to the development of the mucous layer. The third 
 step, like the two preceding again, is an attempt to esta- 
 blish a respiratory organ, and it is again equally performed 
 through the assistance of the mucous layer. 
 
 It is this point at which we have now arrived : we have 
 seen in the human embryo how rapidly the vesicula intesti- 
 nalis shrinks and is lost ; how quickly the branchial arteries 
 are metamorphosed. We have now to trace the production 
 of the true respiratory organ of the embryo ; or, more than 
 that, of its common source of increase and breathing. 
 
 The lower end of the alimentary canal, or cloaca, shoots 
 out a sac, which is termed the allantoi's or allantoid mem- 
 brane. In the chick on the third day, the end of the ali- 
 mentary canal extends itself into a spherical bladder, which 
 by the following day is divided into a channel leading into 
 the cloaca and the proper allantoid sac. After a short 
 
Of the AlUwtois. 421 
 
 period, the terminal branches of the aorta with correspond- 
 ing veins are seen upon this sac. The sac then protrudes 
 more and more out of the body of the chick, tending to 
 the surface of the egg. It spreads from the right side of 
 the chick, first towards the pointed extremity, then towards 
 the rounded end of the egg, so as at length to form a double 
 sac laid immediately under the membrane of the shell, upon 
 which the blood-vessels are distributed with the evident, pur- 
 pose that their contents may be influenced by the atmo- 
 sphere through the porous egg-shell and its membrane, and 
 tli at thus a true respiratory organ may be established. 
 
 The allantois exists in all mammalia. It appears later 
 necessarily than the intestine which forms it, later than the 
 heart, the liver, and the Wolffian bodies. It contains from 
 the first a liquid. In the human embryo it appears in the 
 fourth week. 
 
 The allantois grows rapidly; but in man it attains a trifling- 
 size only, then wastes. In other mammalia it acquires a 
 greater amplitude. In carnivora, in solidungula, and in rumi- 
 nantia, it grows to such a magnitude as to enclose the whole 
 amnios. In rodentia and in swine it is of less extent, and 
 covers part only of the amnios. The channel of communi- 
 cation between the allantoi's and the cloaca or bladder at 
 first is short, so that the former lies directly against the 
 body of the embryo. It is afterwards much elongated, like 
 the corresponding channel of communication of the vesicula 
 intestinalis. In mammalia in general the allantois con- 
 tinues during the whole period of fetal existence : but in 
 man its duration is so short, that it has almost disappeared 
 by the sixth week. The urachus is the remains of the 
 channel of communication with the now obliterated sac. The 
 younger the embryo, the larger is the urachus. Hunter 
 traced it the whole length of the umbilical chord. Com- 
 monly the urachus at the fourth month is pervious for a 
 few lines only from the bladder, being closed towards the 
 navel, and vanishing in the chord. However it sometimes 
 happens that its origin is for a short extent permeable even 
 at birth. Burdach and Roderer concur in stating, that they 
 had met with in the mature foetus a sac containing fluid, 
 
 2 D 
 
422 Of the Navel-string, 
 
 not then communicating with the urachus, but which was 
 probably the allanto'id sac. 
 
 The origin of the navel string, or umbilical chord, may 
 be understood by referring to what has been already stated 
 of the allantois and of the amnios. The allantois stretches 
 from the cloaca to spread itself as a sac upon the outer sur- 
 face of the amnion. As it enlarges, its portion of commu- 
 nication with the cloaca shrinks to a narrow tube that 
 speedily becomes impervious. As it shrinks, the amnios 
 closes upon it, and follows it, and thus forms a cylindrical 
 tube. In the middle of this shrunk tube of communication 
 is the urachus : these parts, with the umbilical artery and 
 veins, and a connecting gelatinous tissue, form the navel- 
 string. 
 
 The navel-string , is visible in the human embryo in the 
 sixth week, as a short and straight chord. In the ninth 
 week it is longer and proportionally thinner, and no longer 
 transparent. The arteries in it are thicker and smaller 
 than the vein, which is disposed in the axis of the chord 
 with the arteries spirally wound round it. In twenty-eight 
 out of thirty-two instances, Hunter observed that the spiral 
 of the vessels turned from left to right. As the chord 
 lengthens, the vein as well as the artery, and even the 
 chord itself, becomes spirally twisted. At birth, the length 
 of the chord is on an average about two feet ; but it varies 
 from one foot to four. When very long, the umbilical 
 chord is generally twisted round the child's neck : it has 
 been known to have been so twisted four times and a half. 
 This accident does not appear to affect labour, except in 
 cases in which the child is turned. 
 
 The outer tunic of the chord, or the amnios, is a genuine 
 serous membrane with a glossy internal surface. It begins, 
 as it has been already stated, in the closed embryo abruptly 
 at the navel, contains in its tubular part the chord, and then 
 forms a loose reflected sac never tensely filled. The fluid 
 which it contains is transparent and without any sensible de- 
 gree of tenacity or ripeness ; sometimes it is foul or muddy, 
 with something of a yellowish cast. The proportion of 
 fluid is greater in the earlier months. Its actual quantity at 
 
Of the Chorion. 423 
 
 birth IB variable, averaging about two or three pints, but 
 varying from one pint to some quarts. Its composition is 
 as follows : 
 
 Water ." 98.8 
 
 Albumen, muriate of soda, soda, phosphate of lime, lime .... 1.2 
 
 100.0 
 
 The umbilical arteries and veins stretch through the chord 
 to something placed without the amnios. Their destination 
 is the outer membrane of the ovum, within the cavity of 
 which all the changes which have been hitherto described 
 take place. This outer membrane is called the chorion. 
 
 The chorion at the end of the first and during the se- 
 cond month has a villous external surface. At the end of 
 the second month, the branches of the umbilical vessels 
 penetrate and ramify in these villi, which become partially 
 or wholly intensely vascular ; the umbilical arteries ramify- 
 ing to capillary minuteness in the villi, and without inter- 
 vening cells, return their blood by the venous branches to 
 the umbilical vein. The distribution of vascularity in the 
 chorion follows three types. 
 
 In solidungula and in swine the distribution of the um- 
 bilical vessels is uniform in every part of the chorion. 
 
 In ruminants, the thickening and vascularity is confined 
 to a number of circular and spongy elevations, varying in 
 number from thirty to one hundred : they are called coty- 
 ledons. The umbilical arteries and vein send to each coty- 
 ledon branches, which winding on the surface of the cho- 
 rion only thicken and fill and develop its villi at these 
 detached points. 
 
 A third form is that which obtains in the human ovum ; 
 where the thickening and vascularity is concentrated upon one 
 part of the chorion, which is commonly on the side towards 
 the fundus of the uterus. This single thickened part is 
 called the placenta. The placenta is round but rather 
 elongated, from six to eight inches in breadth, and from 
 twelve to fifteen lines in thickness in the middle. It be- 
 comes thinner towards the edges : it occupies about a fourth 
 part of the chorion, and at birth is about a pound in weight. 
 
 2 D 2 
 
424 
 
 Of the Fatal Placenta. 
 
 On looking at its outer surface, it is evidently formed of 
 many separate lobes, or cotyledons, which being in contact 
 form one organ. 
 
 The navel-string attaches itself, not vertically and in the 
 middle, but obliquely and rather towards one edge of the 
 placenta. The texture of the placenta is a light, spongy, 
 cellular texture, in which the umbilical vessels ramify. 
 The two arteries are commonly united by a cross branch 
 before they ramify on the placenta. These branches attain 
 considerable minuteness through subdivisions on the inner 
 surface of the placenta, before they plunge into its sub- 
 stance. Each lobe of the placenta has its own divisions of 
 the umbilical vessels : they pass through to the external 
 villous surface, the villi of which are intensely vascular. 
 
 That which I have described under the name of chorion, 
 in minuter anatomy is called the exochorion : in contact 
 with it, lining it, and finally uniting with it, the vascular 
 layer of the allantois is called the endochorion. 
 
Source of the Nourishment of the Embryo. 425 
 
 SECTION III. 
 
 Of the Source of the Nourishment of the Human Embryo, 
 and of its Connection with the Uterus. . 
 
 The uterus is not necessary to the development of the 
 embryo. If the ovulum escape into the cavity of the peri- 
 toneum, it may live and attain foetal maturity, drawing its 
 source of increase through the serous membrane to which it 
 has casually adhered. The vascular foetal placenta attaches 
 itself to a vascular surface of the mother ; and although 
 there be no traceable continuity of their vessels, the matter 
 by which the embryo grows is certainly derived from the 
 maternal body through the foetal placenta. 
 
 The force of the heart of the embryo is employed at once 
 in throwing the circulating fluid through the foetal placenta 
 to imbibe fresh nutriment, and in conveying it through the 
 foetal frame to distribute it in growth. 
 
 Derived from the internal iliac arteries the umbilical arte- 
 ries ascend by the side of the bladder to the navel, wind 
 their way in the chord to the placenta, and having ramified 
 in its substance to capillary minuteness, subsequently return 
 their blood through the umbilical vein to the body of the 
 embryo. The umbilical vein distributes part of its blood to 
 the liver, and then, under the name of ductus venosus, joins 
 the inferior cava, through which the mixed blood of the 
 placenta and of the inferior part of the body is carried into 
 the right auricle of the heart. Almost all the blood intro- 
 duced into the right auricle finally reaches the aorta: part 
 passes directly from the right into the left auricle through 
 the foramen ovale ; the remainder, with the exception of the 
 small quantity transmitted to the lungs, passes from the 
 pulmonary artery through the ductus arteriosus to the aorta. 
 
 The placental circulation is commonly supposed to serve a 
 double office. It is thought to produce a change in the blood 
 equivalent in the fo3tus to the effect of breathing after birth, 
 and to introduce into the foetal system the materials of its 
 growth. Yet little is known with exactness upon either of these 
 
426 
 
 Of the Cotyledons in Ruminants. 
 
 subjects. The colour of the blood in the umbilical vein is 
 something lighter than that in the umbilical arteries. This 
 favours the idea of a placental respiration, which however 
 principally rests upon the analogy of the allantoid circula- 
 tion in the egg. And it certainly is more consistent with 
 the views of modern physiology to suppose the nutriment of 
 the foetus to be introduced by imbibition through the blood- 
 vessels than by absorption through the lymphatics. Lym- 
 phatics however there are in plenty, both in the placenta 
 and in the chord. Fohman has delineated them in rich 
 profusion extending from the placenta along the funis: 
 leaving the funis at the navel, they direct their course to 
 the groin. Fohman observes, that in new-born children the 
 iliac lymphatic glands are distinguished by their size and 
 development. 
 
 But what is the connection between the uterus and the 
 placenta? In ruminant animals, the connection between 
 the fcetal and maternal system admits of being satisfactorily 
 investigated. The cotyledons, of one of which the following 
 diagram represents a section, are organs in which extensive 
 vascular surfaces of the maternal and fcetal systems are 
 brought into contact. A cotyledon consists of a maternal 
 part and a foetal part. 
 
 In the preceding diagram, A represents the substance of 
 the uterus. B the outer or peritoneal covering of the uterus. 
 C the strong submucous coat of the uterus. D the mucous 
 coat. E the maternal cotyledon. F the fcetal. Towards 
 
Of the Decidua. 427 
 
 the side on which the letters are placed, the foetal cotyledon 
 is represented as drawn off from the maternal ; upon the 
 opposite side the two are supposed to be left in contact. 
 
 The maternal cotyledon is an oval mass, the foatal surface 
 of which is highly vascular : it is soft, and hollowed into 
 numerous tubes which lead to the submucous coat of the 
 uterus, of which the maternal cotyledon appears to be a 
 growth. The mucous coat may readily be separated from the 
 submucous : when it is detached from the adjacent surface 
 of the uterus, and followed to the edge of a cotyledon, it 
 may be traced ascending a little way along its side, when it 
 breaks off abruptly, as if it terminated before reaching the 
 upper surface of the cotyledon. The submucous coat is 
 joined to the uterus by a thick but loose stratum of fila- 
 mentous tissue. This layer of filamentous tissue is extremely 
 vascular, especially below the cotyledons, to which it trans- 
 mits a great number of small blood-vessels, that perforate 
 the submucous coat to be distributed in the substance and 
 on the surface of the maternal cotyledon. 
 
 The foetal cotyledon is of slighter, thinner, and softer 
 texture than the maternal. It consists of a number of soft 
 and vascular processes of membrane which enter into the 
 tubes of the maternal cotyledon and fill them, and adhere to- 
 them, without being directly continuous with their surface 
 through vascular anastomoses. An opaque milk-like fluid 
 is described as having been found in the tubular cells of the 
 maternal cotyledon. 
 
 The result of this arrangement is, that a very large vas- 
 cular surface of the maternal system is applied to an equally 
 extensive vascular surface of the embryo. Considering the 
 power which the ovulum displays when it first reaches the 
 uterine cavity of imbibing matter for its growth, together 
 with the facility with which according to the experiments 
 of Dutrochet fluids may be drawn through animal mem- 
 branes, it is not difficult to believe that nourishment is di- 
 rectly imbibed from the vessels of the mother by the circu- 
 lating fluid of the embryo through the fine intervening 
 membranes. 
 
 In the human embryo the relation of the maternal system 
 
428 Of the Maternal Placenta. 
 
 to the foetal system is not as satisfactorily ascertained as in 
 the preceding instance. 
 
 When impregnation has taken place, one of the first 
 effects is an increased flow of blood upon the uterus, which 
 becomes lined with an exsudation of coagulable lymph. 
 This secretion is independent of the presence of the ovum : 
 it takes place no less in extra-uterine than in uterine preg- 
 nancy. 
 
 The layer of lymph which thus is thrown out and lined 
 the cavity of the uterus is termed the decidua : as it grows, 
 it divides into two layers at every part, except where it is 
 interposed between the uterus and the foetal placenta. Of 
 these two layers, the inner and incomplete one is called the 
 decidua reflexa. The outer, or entire one, of which the portion 
 intervening between the uterus and foetal placenta is there- 
 fore a part, is called the decidua vera. When examined to- 
 wards the close of gestation, the decidua vera is thin and 
 delicate, and equally so at every part. The portion of it 
 which then intervenes between the foetal placenta and the 
 uterus, is as thin and delicate as that which lines the 
 rest of the uterus : it certainly at that time looks no more 
 than common decidua. But in the fourth and fifth 
 month it presents, according to Burdach, a different cha- 
 racter : it has at that period a thickness of four lines, and 
 extends numerous processes between the lobes of the foetal 
 placenta, so that the relation of the two parts has then a 
 striking analogy to that of the maternal and foetal cotyledons 
 in ruminants. If this account be correct, the part of the 
 decidua opposite to the foetal placenta probably deserves to 
 be distinguished from the rest of the decidua by the name 
 which Dr. Hunter gave it, of maternal placenta. Even 
 when towards the close of gestation the function of the part 
 draws to a close, and it has shrunk to membranous thinness 
 (the foetal and maternal system being now about to be sepa- 
 rated), yet to the last it distinctly gives oft' fine processes of 
 membrane which enter the interlobular spaces of the foetal 
 placenta. 
 
 Towards the close of gestation again, the relation of the 
 maternal vessels to the placenta is very ^singular : arteries 
 
Of the Maternal Placenta. 429 
 
 of the size of crow quills are found to pass through the thin 
 maternal placenta, and then to ramify tortuously upon the 
 surface of the foetal placenta, and in the interstices of the 
 latter. Mr. Hunter described them exactly, but he thought 
 that they terminated abruptly in irregular inter-placental cells. 
 It has been always however considered doubtful whether the 
 placental cells of Hunter were real, or artificial, produced on 
 the latter supposition by extravasation of the injection. 
 
 Mr. Hunter likewise observed the singular phenomenon 
 of the veins of the uterus beginning with or presenting 
 large open mouths towards the foetal placenta. " The veins 
 of the uterus appropriated to bring back the blood from the 
 placenta, commence from this spongy substance by such 
 wide beginnings as are more than equal to the size of the 
 veins themselves. These veins pass obliquely through the 
 decidua to the uterus, enter its substance obliquely, and 
 immediately communicate with the proper veins of the 
 uterus*/' 
 
 Dr. Robert Lee has recently investigated this subject. 
 His researches confirm the doubt previously entertained as 
 to the existence of inter-placental cells. Dr. R. Lee is 
 further persuaded, and his researches upon the whole are 
 confirmed by the testimony of Mr. Owen, that the mouths 
 of veins, which Mr. Hunter thought to open upon the foetal 
 placenta, really (towards the close of gestation) rest against 
 and are therefore shut by instead of perforating the decidua 
 or shrunk maternal placenta^. To throw a satisfactory 
 light, however, upon this subject, careful examinations of 
 the gravid uterus antecedently to the latest periods of gesta- 
 tion are yet wanted. 
 
 Whatever be the system of vessels by which the matter 
 of increment is introduced into the foetus, it seems not im- 
 probable that when there it may be submitted in part to a 
 new assimilative process. 
 
 It has been conjectured that the thymus gland may pos- 
 sibly contribute to this office. 
 
 * Hunter on the Animal Economy, p. \72. 
 f Phil. Trans. 1832. 
 
430 Of Fatal Digestion. 
 
 M. Magendie remarks, that the stomach of the foetus has 
 been found to contain mucus which was opaque and grey- 
 ish towards the pylorus, as if converted into chyme ; and 
 the green matter termed meconium, which is found in the 
 great intestines, has the appearance of being the refuse of a 
 kind of digestion. 
 
 In a paper by Dr. Robert Lee, in the Philosophical Trans- 
 actions for 1829, some interesting observations are made 
 upon this subject. 
 
 Dr. Lee observes, that the stomach of the foetus is usually 
 distended with a semi-transparent, ropy, mucous, and oc- 
 casionally acescent fluid, without any sensible admixture of 
 albuminous or other nutritious matter. But that in the duo- 
 denum and part of the remaining portion of the small intes- 
 tines there is uniformly present, adhering closely to the mu- 
 cous membrane, a semi-fluid matter, found on examination 
 to possess properties decidedly of an albuminous character^ 
 and to have an orange or pink colour. This matter Dr. R. 
 Lee has always found in greatest abundance around the pa- 
 pillary projection, through which the common duct of the 
 liver opens into the duodenum. 
 
 In the lower half of the small intestines the quantity of 
 this albuminous matter is considerably less, and near the 
 colon it almost entirely disappears. The colour also of the 
 contents of this lower portion of the small intestines is dif- 
 ferent from that noticed in the contents of the duodenum, 
 being of a greenish tint, and assuming more and more of 
 the character of meconium as the distance from the colon 
 diminishes. 
 
 The quality of the contents of the jejunum in the fcetus 
 was ascertained to be albuminous by Dr. Prout. Dr. R. Lee 
 conjectures, with great plausibility, that this product is a 
 secretion of the liver. 
 
 Of the freedom of communication between the blood of 
 the foatus and that of the mother, M. Magendie gives this 
 remarkable illustration. He introduced camphor into the 
 veins of a pregnant bitch, and he found that in a quarter of 
 an hour the blood of the fcetus had acquired distinctly the 
 odour of camphor. M. Magendie mentions another curious 
 
Period of Utero-gestation. 431 
 
 circumstance. The poisons which rapidly act upon the 
 brain and spinal marrow (such as strychnia) when intro- 
 duced into the serous cavities or cellular membrane of adult 
 animals, are harmless when introduced into wounds in unborn 
 animals. 
 
 The uterus grows with its enlarging contents, so as con- 
 stantly to preserve about the same thickness : it is always 
 more than sufficiently capacious, so as to be plastic, not 
 tense. 
 
 About the fifth month it rises out of the pelvis, and rests 
 against the front of the abdomen ; as it enlarges, the distinc- 
 tion between the body and cervix is lost : the os tincae is 
 flattened, and forms only a small rugous hole not readily 
 discernible : it is closed by a tough glutinous matter which 
 is fixed in the irregularities of the surface. 
 
 The fibres of the uterus exhibit something like a definite 
 disposition as pregnancy advances : viewed from within they 
 are seen to be arranged concentrically round the orifices of 
 the Fallopian tubes. The cervix has not such regular or 
 large fasciculi as the rest of the uterus : when the internal 
 stratum is removed, the fibres of the next layer, which are 
 firmer and tougher than the innermost, seem to have no re- 
 gular order. 
 
 The ordinary period of utero-gestation is forty weeks. 
 But labour frequently takes place before this term is accom- 
 plished. A child often lives that is born at eight months, 
 or seven months, or yet earlier. Labour is most likely to 
 occur at the usual expiration of forty weeks ; and within 
 that time the probability of its occurrence is directly as the 
 age of the embryo. Premature labour is brought on by any 
 cause which disturbs the system ; by fatigue, exposure to 
 excessive heat or cold, anxiety of mind, and the like. But 
 may not labour take place within the forty weeks, and yet 
 not be premature ? And, on the other hand, 'may not the 
 time of gestation be extended over this period ? 
 
 I cannot quote any better authority upon this subject 
 than Dr. Merriman, from a paper by whom, in the Medico- 
 Chirurgical Transactions, vol. xiii, I take the following 
 table: it gives an account of the births of 114 children, cal- 
 
432 .<,, Period of Gestation. 
 
 culated from, but not including, the day on which the cata- 
 menia were last distinguishable. Dr. Merriman states, that 
 he can fully vouch for its accuracy. He adds, that it seems 
 fair to infer from it that conception is effected soon after the 
 catamenial period has intermitted, more commonly than im- 
 mediately before the recurrence of that discharge. 
 
 TABLE. 
 
 At 255 days 1 
 
 256 , 1 
 
 259 . 1 
 
 3 in the 37th week, 
 
 At 262 2 
 
 263 2 
 
 264 4 
 
 265 1 
 
 266 . .4 
 
 13 in the 38th week, 
 
 At 267 1 
 
 268 1 
 
 269 4 
 
 270 1 
 
 271 2 
 
 272 2 
 
 273 . .... 3 
 
 14 in the 39th week. 
 
 At 274 4 
 
 275 2 
 
 276 4 
 
 277 8 
 
 278 3 
 
 279 3 
 
 280 . .9 
 
 33 in the 40th week. 
 
Of Labour. 433 
 
 At 281 days 5 
 
 282 2 
 
 283 6 
 
 284 1 
 
 285 4 
 
 286 3 
 
 287 1 
 
 22 in the 41st week. 
 
 At 288 5 
 
 289 2 
 
 290 2 
 
 292 4 
 
 293 2 
 
 15 in the 42d week. 
 
 At 295 1 
 
 296 2 
 
 297 2 
 
 298 4 
 
 301 ' 1 
 
 10 in the 43d week. 
 
 At 303 1 
 
 305 1 
 
 306 2 
 
 4 in the 44th week. 
 
 Labour is preceded for two or three days by a mucous 
 discharge from the vagina, and by slight pains about the 
 abdomen and loins. The external parts swell and become 
 relaxed, and even the ligaments of the pelvis lose their 
 tenseness. 
 
 The pains of labour commence with and consist in a pow- 
 erful contraction of the uterus, accompanied with contrac- 
 tion of the abdominal muscles and diaphragm ; they are re- 
 peated at intervals of half or a quarter of an hour. Impelled 
 by this pressure the membranes project at and dilate the os 
 tincse; they burst; the liquor amnii escapes, and at the 
 
434 Of the Mamma. 
 
 next pain the pressure of the uterus falls directly upon the 
 foetus. The head of the foetus gradually descends, urged 
 on by succeeding spasms, the occiput foremost, the long 
 axis of the head being disposed obliquely across the lesser 
 basin of the pelvis. The occiput, as the external parts yield, 
 glides off the inclined surface of the ischium, presenting at 
 the "orifice of the vulva, and bringing at the same time the 
 long diameter of the shoulders to correspond with the 
 greatest breadth of the pelvis. When the head is disen- 
 gaged, the trunk readily follows. The umbilical chord is 
 then tied, and divided. 
 
 After a short time fresh pains return, and the placenta 
 and membranes are detached, and come away. Labour in 
 the majority of healthy cases is completed in from four to 
 six hours. The uterus then very slowly and insensibly con- 
 tracts, so as to diminish the ample cavity, which has been 
 rendered vacant. At the same time its volume is reduced 
 by absorption. During the return of the womb to its former 
 state, a discharge, at first tinged with blood, afterwards of 
 a whitish colour, termed the lochia, ensues, which lasts for 
 several days. 
 
 At the moment after birth the infant dilates its chest, and 
 respiration commences ; at the same time the foramen ovale 
 and the ductus arteriosus contract and close. A new mode 
 of existence commences. The infant experiences sensations 
 and wants, which adhere to it through life ; it begins to re- 
 ceive impressions from the surrounding world, and tries in- 
 stinctively to gratify its newly-acquired appetites. 
 
 Yet for some time the infant continues immediately de- 
 pendent upon the maternal system for its nourishment. 
 
 The breasts form part of the generative system. The 
 gland of the mamma, remarkable for the whiteness and 
 firmness of its nodular texture, and for the mode in which 
 it is mixed up with adipose substance, consists of several 
 distinct lobes. From innumerable branches in each of these 
 a duct is formed, which, without communicating with those 
 adjoining, opens in the sulci upon the surface of the nipple. 
 The mamma has a close sympathy with the uterus, so that 
 it usually enlarges ano] becomes tender for two or three days 
 
Of the Mamma. 435 
 
 before each period. During the latter months of pregnancy 
 the mamma enlarges, and the areola surrounding the nipple 
 takes a darker shade. Towards the time of labour the breast 
 secretes a serous fluid : the secretion has generally the same 
 appearance for two or three days after labour, but at length 
 takes the well-known character of milk. The secretion of 
 milk naturally continues till the middle of the second year. 
 The milk is observed to be more abundant, thicker, and less 
 acid, when the food of the mother principally consists of 
 animal substances : opposite qualities are noticed in milk 
 produced upon a vegetable diet. No secretion indeed is 
 more readily modified by the ingesta, than that under con- 
 sideration : medicinal substances taken by the mother im- 
 part their properties to the milk, which is thus rendered 
 purgative, as the consequence of a dose of rhubarb or of 
 jalap. 
 
 The milk of women differs from that of the cow in these 
 particulars : it contains a much smaller quantity of curd, 
 and rather more sugar of milk : its oil is so intimately com- 
 bined with its curd that it does not yield butter. The 
 quantity of curd increases in proportion to the time after 
 delivery. Asses milk has a very strong resemblance to hu- 
 man milk*. 
 
 The rudiments of mammae originally exist in both sexes ; 
 and it is asserted and is probably true, that there have been 
 instances, in which the gland has been developed and has 
 secreted milk in the male sex. 
 
 * Thomson's Chemistry, vol. iv, p. 502. 
 
CHAPTER XVI. 
 
 OP GROWTH AND OF REPARATION 
 
 THE uses of the different parts of the frame have been now 
 explained ; and the wonderful series of changes has been 
 described, through which from a granular speck the embryo 
 attains foetal maturity. Where these details end, another 
 branch of physiology begins. The history of the subsequent 
 growth of parts, and of their power of restoration when in- 
 jured the progress of the frame from childhood to man- 
 hood, from manhood to decay and the study of the in- 
 fluences which promote or impair its energies are subjects 
 which have a more practical character, and therefore to 
 physicians and surgeons a stronger interest than even those 
 to which I have already adverted. A few only of these 
 topics will however be treated of in the remaining pages of 
 the present volume. I shall confine myself to describing 
 the mode of growth of the unorganized parts of the frame, 
 and the powers of restoration which exist in vascular parts. 
 
 Of the Growth of Teeth. 
 
 The rudiment of each tooth is a vascular pulp of the 
 shape of the body of the future tooth, the surface of which 
 that is most remote from the gum adheres to the substance 
 of the jaw, and gives entrance to vessels and nerves: the 
 rest of the pulp is unattached. A double membrane is re- 
 flected from the margin of the adherent surface, to form a 
 cyst or capsule over the sides and upper part of the pulp. 
 The outer layer of this membrane is soft, thick, and vascu- 
 lar ; the inner layer, which is in contact with the pulp, is 
 thin and semi-transparent ; it shows no appearance of vas- 
 
Of the Growth of Teeth. 437 
 
 cularity, when the outer layer is most successfully injected. 
 In the cavity surrounding the pulp a transparent yellowish 
 liquid is found, 
 
 The growth of the bony portion of the tooth commences 
 by the deposition of a layer of perfect tooth-bone or ivory 
 upon the cutting edge or grinding surface of a tooth. This 
 little cap of bone is therefore an exact mould of the surface 
 by which it was secreted : its adhesion is very slight to the 
 surface of the pulp, which shrinks to give room for the ex- 
 sudation of a second layer, that coheres inseparably with 
 that first formed. When the pulp shrinks, it at the same 
 time becomes elongated, but in such a manner that the 
 point where its vessels enter remains fixed, and the crown 
 of the tooth is raised towards the margin of the gum. In 
 proportion as the pulp is elongated, the capsules of bone 
 successively formed one within the other are of greater 
 length, being cast upon a longer mould : in this way the 
 whole bony portion of the tooth is produced, the pulp con- 
 tinually diminishing in thickness, but becoming elongated, 
 till it has reached the exact dimension of the future cavity 
 of the tooth. The pulp then ceases to secrete, and wastes 
 to the condition of a vascular membrane, on which however 
 the sensibility and vitality of the tooth which it lines de- 
 pend. 
 
 The preceding circumstances may be verified by examin- 
 ing human teeth at different stages of their formation, and 
 by making sections of the teeth of an animal, a growing 
 pig for instance, -with the food of which madder has been 
 mixed and discontinued during alternate periods of two or 
 three weeks. In the latter instance the bone of the tooth 
 displays alternate layers of red and white, and the innermost 
 layer is always the longest. 
 
 During the elongation of the pulp, the capsule undergoes 
 no change except in place ; it rises with the crown of the 
 tooth, to the neck of which it adheres. The enamel is not 
 formed till some time after the bone, and invests that sur- 
 face only of the tooth which is contained within the 
 capsule. 
 
 Some animals have teeth, the pulp of which never 
 
 2 E 
 
438 Influence of the Nerves. 
 
 shrinks, but continually adds to the length of the tooth : 
 this is the case with the incisors of rodentia, and with the 
 tusks of the elephant. The addition continually making to 
 the roots of the incisors of rodentia is calculated to replace 
 exactly the substance lost by attrition : these teeth are 
 constantly rising in a curve towards each other, and are 
 kept serviceable by the disposition of the enamel upon their 
 convex surface alone, which thus always presents a hard and 
 keen edge. 
 
 After the division of the fifth nerve in the cranial cavity 
 of a rabbit, I removed the crown of the incisor tooth in the 
 upper jaw of the same side, and compared the time it took 
 to grow to the level of its fellow, with the result of a simi- 
 lar experiment upon a rabbit, in which the fifth nerve 
 had not been divided. The tooth grew rather faster in the 
 former than in the latter instance. 
 
 The rudiments of the teeth in the embryo are at first con- 
 tained in a shallow groove in either jaw with thin partitions 
 between them : they adhere more strictly to the gum than 
 to the base of the socket. In an embryo of four months, 
 twelve little sacs are observed in each jaw, being the ru- 
 diments of all the temporary teeth and of the anterior per- 
 manent grinders. 
 
 The shallow grooves, in which these pulps are first lodged, 
 gradually rise and form alveolar processes : they arch over 
 the pulps of the teeth, leaving, however, an opening towards 
 the gum. 
 
 The rudiments of the earliest formed teeth of the second 
 set are at first contained in the same sockets as the tempo- 
 rary teeth, but at the period of birth they are found in se- 
 parate cells behind and without the cells or sockets of the 
 corresponding temporary teeth. The cells of the second set 
 again are not closed above, but have a narrow channel lead- 
 ing towards the gum, which contains a funnel-like process 
 of the sac, that adheres to the neck of the corresponding 
 temporary tooth. 
 
 In an embryo about the eighth month, the pulps of the 
 permanent incisors and cuspidati are found. It is not till 
 after birth that the rudiments of the remaining adult teeth 
 
Of the Temporary Teet/t. 439 
 
 make their appearance, in what order is not precisely 
 known. 
 
 The twenty temporary or milk teeth begin to appear on 
 an average about the sixth month. They generally cut the 
 gum in the following succession : the middle incisors of the 
 lower jaw, the middle incisors of the upper, the lateral inci- 
 sors of the lower jaw, the lateral incisors of the upper, at 
 intervals of three, four, or five weeks : about the twelfth or 
 fourteenth month, the anterior or small grinders of the 
 under jaw appear, and frequently about the same time those 
 of the upper : about the sixteenth or twentieth month, the 
 cuspidati appear, first in the lower jaw ; and between the 
 twentieth and thirtieth month, the posterior or large grinders 
 appeal' in the same order. 
 
 Before the teeth appear, the gums have a raised firm edge. 
 To make way for the teeth, the upper vaulted part of the 
 alveolar processes and of the gums is absorbed. During this 
 process indisposition frequently supervenes, which may be 
 allayed by cutting down to the tooth at the part where the 
 gum appears slightly swollen : the division should be made 
 anteriorly to the middle of the gum : if the incision be made 
 upon the back part of the gum, it may open the socket of 
 a tooth belonging to the second set, and spoil ijt. 
 
 The thirty-two permanent teeth begin to appear between 
 the sixth and seventh year:- at this time the term of life 
 of the milk teeth has expired ; the gums and alveoli no 
 longer adhere to them ; they become loosened, and on drop- 
 ping out, some degree of absorption is generally found .to 
 have taken place near the end of the fang. The shedding 
 of the milk teeth does not essentially depend upon the for- 
 wardness of the second set : frequently the milk teeth fall 
 out some time before the permanent teeth appear ; or the 
 permanent teeth rise, while the milk teeth continue firmly 
 attached, and require extraction to give place to the second 
 set. 
 
 The permanent teeth appear in the following order : first, 
 the middle incisors of the lower jaw ; soon after, the middle 
 incisors of the upper ; then the outer incisors of the lower 
 jaw, and at the same time the permanent anterior grinders : 
 
 2 E 2 
 
440 Of the Permanent Teeth. 
 
 then the lateral incisors of the upper jaw, after some inter- 
 val. The anterior bicuspides appear about the ninth year, 
 the posterior about the tenth or eleventh : the cuspidati and 
 middle grinders about the twelfth or fourteenth, and finally 
 the last grinders between the ages of sixteen and twenty- 
 five. 
 
 Teeth, though not sensibly vascular, have some kind of 
 life. A tooth taken from the head of a living person and 
 immediately fixed in a living part, in the comb of a cock 
 for instance, or in a socket from which another tooth has 
 been drawn, adheres to the raw surface with which it is 
 placed in contact, and becomes permanently attached to it. 
 If the same experiment be tried with a tooth that has been 
 some time removed from the living socket, it fails; the 
 tooth is dead, and contracts no adhesion with a living sur- 
 face. 
 
 The alveolar processes are formed with the teeth : in pro- 
 portion as the teeth of the infant make their appearance, 
 the branch of the lower jaw lengthens to give them room. 
 When in old age the second set of teeth drops out, the alve- 
 olar processes are absorbed ; but the same active care is not 
 then shown as during infancy in accommodating the neigh- 
 bouring parts to this alteration ; no ridge of thicker mem- 
 brane forms upon the edge of the gum to take the place and 
 office of teeth : and no adequate shortening occurs in the 
 branches of the jaw, to allow the gums to meet in exact 
 apposition, and to prevent the characteristic projection of 
 the chin. 
 
 Of the unorganized Integuments. 
 
 The unorganized integuments, the hair, the nails, the epi- 
 dermis, are formed of the same chemical elements, which in 
 animals assume the appearance of hoofs, horns, claws, and 
 feathers ; the element of which they consist exsudes in a 
 soft state upon vascular surfaces, and quickly hardens by 
 exposure. Of these substances hair and feathers grow upon 
 pulps situated below the skin, the rest are secreted from the 
 cutis. 
 
 The cuticle in human beings appears an uniform elastic 
 
Of tlie Growth of Hoofs and Horns. 441 
 
 membrane, the thickness of which is increased in proportion 
 to the pressure made upon it. No definite structure seems 
 fairly distinguishable in it : if on the one hand when form- 
 ing warts, and on some other occasions, it splits into fibres 
 vertical to the surface, in other instances the cuticle desqua- 
 mates in layers parallel to the surface, and its texture seems 
 laminated. 
 
 On examining parts in animals, with which the cuticle is 
 continuous, horns for instance, and hoofs, two types of 
 structure are apparent. Horn distinctly consists of fibres, 
 of which the greater part are inclined at an acute angle to 
 the surface on which they grow : the fibres of the tip alone 
 are vertical or nearly so. This structure is apparent on 
 making sections of variegated horns, and upon peeling 
 horns, that have been softened by maceration in diluted 
 liquor ammonise, into strips. Hoof on the other hand has 
 a porous tubular structure. The surface from which it is 
 formed gives off innumerable long and slender villi, that de- 
 scend in a vertical direction through the hoof towards its 
 under surface, which they nearly reach. The delicate tubes, 
 which render the substance of hoof porous, are the spaces 
 occupied by these villi. 
 
 It may be remarked, that the hoof is a part sustaining a 
 tolerably constant and equable pressure : horn on the other 
 hand is only occasionally employed, and that in violent 
 efforts. Now there are various instances in animals, in 
 which the cuticle naturally has a thickness of several lines, 
 and shows a definite structure. In some of these in- 
 stances again, the pressure which the cuticle sustains is 
 constant, in others occasional only : it is singular, that in 
 the former case cuticle is found to resemble hoof in struc- 
 ture, in the latter, horn. The cuticle of the whale is porous,, 
 and to the minutest points resembles the soft inferior and 
 internal part of a horse's hoof. The cuticle of the ostrich's 
 gizzard on the contrary is distinctly fibrous. 
 
 In the epidermis of the ostrich's gizzard the fibres are 
 vertical to the surface ; in a cow's horn, the fibres at the tip 
 are vertical, at the sides oblique : in each instance ono 
 principle is held in view ; the fibres are so disposed as to bo 
 
442 Of the Nails and Epidermis. 
 
 vertical to the pressure or attrition to which they are likely 
 to be exposed *. 
 
 The structure of nail appears to be fibrous. The nails 
 grow from a cutaneous surface at the back of the phalanges, 
 which is less vascular than the adjacent skin : the semi- 
 circular upper margin of this surface is seen distinctly de- 
 nned through the semi-transparent nail : the rest is hidden 
 by a fold of skin, which secretes a layer of dense cuticle 
 that adheres to and rises with the nail. 
 
 Each hair grows upon a pyramidal pulp placed beneath 
 the skin ; its central part is of less density than its crust : it 
 is uncertain how far the pulp extends into this central part 
 of a hair. In the disease termed plica polonica, the pulp 
 must extend beyond the level of the skin, if, as it has been 
 asserted, the hair ever bleeds when divided : and it is diffi- 
 cult to explain the authenticated cases of sudden change of 
 colour in hair, unless we suppose some mode of organization 
 to be prolonged into its substance. If the whiskers of a cat 
 be cut short, leaving only a third of an inch of each, they do 
 not grow, but are shed and replaced by others. 
 
 Considerable branches of the fifth nerve are distributed 
 to the whiskers of animals : in the seal, each hair of the 
 whisker receives a branch as large as a digital nerve in man. 
 In a cat which lived after the division of the fifth nerve in 
 the cranial cavity, the whiskers of the mutilated side grew 
 thin and crooked. 
 
 Of the Reparation of Parts. 
 
 When a tooth is broken across, or a hair divided, the part 
 detached has no means of becoming re-united with the rest. 
 
 * The distinction which I have pointed out between the structure of 
 hoof and horn requires some qualification. The tubular structure of 
 hoof is in effect fibrous, and even has a fibrous appearance when a sec- 
 tion is made through it parallel to the villi. The horn of the rhinoceros 
 again, though its external superficies peels into fibres, yet presents at 
 its base innumerable fine apertures of pores, which it is to be presumed 
 contain in the recent state delicate villi. It would seem that the villous 
 structure, when added to the natural fibrous character of the unorga- 
 nized integuments, is for the purpose of strengthening their adhesion 
 to the cutis. 
 
Of Re-union of Soft Parts. 443 
 
 But when a bone is broken, when a sinew, a nerve, a 
 muscle, is divided, the disjoined surfaces spontaneously re- 
 unite. Let us examine the nature of the process. 
 
 When the skin is divided by a clean incision, the blood, 
 which for a short time flows abundantly, after a minute or 
 two scarcely oozes, and at length stops. If what rests upon 
 the surface be gently washed away, a narrow red line shows 
 the edge of a thin clot of blood, by the adhesive quality of 
 which the divided surfaces are held in apposition ; but the 
 adhesion at first is slight, and the wound may easily be 
 drawn open. If the incision be superficial and of no great 
 extent, in twenty-four hours complete union appears to 
 have taken place : and when in a day or two afterwards the 
 red edge of the clot peels off, cuticle is found below it ; but 
 the linear surface remains of a darker hue for several days. 
 
 When a small portion of the body is entirely separated, 
 as, for instance, the tip of the ear, the end of a finger, if it 
 be immediately re-applied, mechanical adhesion takes place 
 in a similar way, and the circulation being restored through 
 the intervening film of fibrin, the part lives. 
 
 When large cut surfaces are brought into contact, as hap- 
 pens after the removal of a breast, or the amputation of a 
 limb, union immediately begins in the same manner. The 
 cut surfaces adhere by means of a thin film of coagulum, or 
 of colourless and fibrinous exsudation from the vessels of 
 the divided parts. In a few instances this adhesion holds 
 permanently ; no swelling, or discharge, or increase of sen- 
 sibility occurs, and in little more than a week the process of 
 organized adhesion is evidently complete. In most cases 
 however, about the fourth day, the part becomes swollen and 
 more painful ; a thin secretion takes place from a part or 
 the whole of the cut surfaces, and their union is partially or 
 wholly broken up. The discharge upon the fourth or fifth 
 day appears to be a thin pus mixed with blood ; in a day 
 or two afterwards it is pure pus, and the surface of the 
 wound is covered with a soft layer of vascular flesh, called 
 granulations, from which the pus is secreted. The granula- 
 tions rising fill the cavity of the wound, and uniting where 
 they are held in contact, close it. 
 
444 Of the Re-union of Tendons. 
 
 Union by adhesion is sure not to take place in those cases 
 in which from a return of hemorrhage a sensible quantity of 
 coagulum remains in the wound. 
 
 Pus is a viscid straw-coloured fluid, of the specific gravity 
 of 1050, it coagulates when raised to the temperature of 
 112*, or when mixed with muriate of ammonia : its colour 
 depends upon a number of circular particles, sensibly larger 
 than the particles of the blood : it appears from the re- 
 searches of Sir E. Home, that these particles are formed by 
 chemical attraction in a fluid which is limpid and colourless 
 when first secreted. 
 
 When a considerable portion of skin is removed, the cel- 
 lular membrane inflames below the blood which congeals on 
 the raw surface, and secretes pus, and forms a crop of gra- 
 nulations ; these gradually rise to the level of and higher 
 than the surrounding skin ; the secreting surface appears to 
 diminish daily, and is found to be converted at its edges 
 into a tender whitish substance, which thickening becomes 
 opaque and forms a cicatrix. On the day that a portion of 
 a cicatrix is completed, it is insensible ; about a fortnight 
 afterwards it feels if pricked with a needle. 
 
 Thus in the formation of a cicatrix after destruction of a 
 portion of skin, the material which replaces it is produced, 
 not by the neighbouring skin, but by a growth from the 
 subcutaneous texture. 
 
 When tendons, or nerves, cartilages, or bones, are divided 
 or broken across, the process of their reunion, instead of re- 
 sembling the adhesion of divided skin, has more in common 
 with the growth of a cicatrix. The injured parts are repaired 
 through the intervention of a third substance, which appears 
 to be a growth of the neighbouring cellular texture. 
 
 If the tendo Achillis be examined in a dog forty-eight 
 hours after division, upon removing the skin, the subjacent 
 cellular membrane that surrounds the tendon appears loaded 
 with coagulable lymph and extravasated blood. Upon 
 making a longitudinal section of the thickened substance, 
 the cut ends of the tendon contained within it are found to 
 be about an inch apart, but connected together by means of 
 coagulated blood and swollen cellular texture. 
 
Of the Re-union of Nerves. 445 
 
 If the tendo Achillis be examined seven days after divi- 
 sion, the ends of the divided tendon are found united by an 
 intervening substance of greater thickness than the tendon 
 itself, that is readily separable from the skin and subjacent 
 parts. Upon a longitudinal section being made, the inter- 
 vening substance appears of a dark -red colour, firm, and to 
 a certain degree elastic : it coheres, in some parts firmly, in 
 others slightly, with the cut ends of the tendon, but strongly 
 and inseparably with the cellular sheath of the tendon, which 
 is discoloured for some distance from the wound : so that 
 either end of the tendon admits without much force of being 
 displaced from a socket in the intervening substance. 
 
 At seventeen days after division, the intervening sub- 
 stance is found diminished in thickness, and to be firmer, 
 paler, and inseparably coherent with the cut ends of the 
 tendon, the nature of which it gradually assumes. 
 
 When a nerve is divided, the process by which its ends 
 are joined closely resembles the mode in which tendons 
 unite. Without detailing the appearances on dissection at 
 an earlier period, let me describe the state of the part at 
 the time when the return of its function first manifests 
 itself. 
 
 I divided the infra-orbital nerve on one side upon the 
 cheek of a cat, and removed a portion about a line in length. 
 The skin of the upper lip immediately lost sensation. The 
 wound, however, readily cicatrized ; and by the twentieth 
 day sensation appeared entirely restored. Upon examining 
 the part at this period, the nervous fibrils appeared to be 
 united by a thick knot of tough gray semi-transparent sub- 
 stance. On making a longitudinal section of this substance 
 and of the nervous fibrils which entered it, the extremities 
 of the divided filaments appeared nearly two lines asunder, 
 and firmly coherent with the intervening substance : here 
 and there a whitish fibril seemed to extend further into the 
 connecting medium, but no restoration of continuity by ner- 
 vous substance between the fibrils was observable. 
 
 When the portio dura is divided on the cheek of an ani- 
 mal, it unites in a similar manner ; but the nerve does not 
 begin under four weeks to resume the office of transmitting 
 
446 Of the Re-union of Cartilage. 
 
 the influence of the will. About this time, the eyelids, 
 which hitherto have been motionless, are observed to be 
 slowly and imperfectly drawn towards each other, whenever 
 the surface of the conjunctiva is touched. 
 
 Cruikshank and Haighton observed, that if the pneumo- 
 gastric nerve is divided, first on one side, and then on the 
 other, with an interval of three weeks between each opera- 
 tion, by the expiration of that time the nerve first divided 
 has united sufficiently to have its function restored, and the 
 division of the second is not necessarily fatal. Magendie in- 
 deed denies that this result ensues ; he found that the division 
 of the second nerve was as fatal at the expiration of several 
 weeks, as if it had been performed at the same time with the 
 division of the first. I have recently repeated the experiment, 
 dividing the second nerve a month after the first : the ani- 
 mal died in three days. On examining the parts, however, 
 I found that the nerve that had been first cut (a small por- 
 tion I should mention had been removed) had happened not 
 to unite : the upper portion retained its volume and colour, 
 and ended in a white bulb : the lower portion was shrunk 
 in size, and was greyish or semi-transparent in colour. As 
 it is not possible to doubt the correctness of Cruikshank's 
 and Haighton's experiments, I am inclined to suppose that 
 in the instances in which the experiment did not succeed 
 with Magendie, the failure was owing (as in my own 
 case) to an accidental want of union between the extremities 
 of the nerve first divided. 
 
 If the cartilage of a rib be examined in a dog forty-eight 
 hours after division, the cut surfaces of the cartilage are not 
 found to have undergone any change : they are held toge- 
 ther by a loose capsule formed by the surrounding parts. 
 Towards the seventh day this capsule has assumed a dense 
 elastic texture, and distinctly includes the adjacent cellular 
 membrane and muscular substance. The edges of the car- 
 tilage appear rounded off, and a slight exsudation of lymph 
 seems interposed between the disjoined surfaces. On the 
 seventeenth day the appearance is much the same ; the in- 
 tervening substance, which has acquired consistence, is 
 continuous with and appears derived from the capsule. 
 
Of the Re-union of Bone. 447 
 
 About the twenty-eighth day, the intervening layer of lymph 
 is found adhering to and loosely uniting the opposite carti- 
 laginous surfaces. 
 
 The changes which attend the re-union of a broken bone 
 are even more elaborate than those which occur in the pre- 
 ceding instances. The most valuable observations which 
 have been published upon this subject are by M. Du- 
 puytren. 
 
 If a fractured limb be examined within forty-eight hours 
 after the injury, the periosteum is found to have been 
 stripped irregularly from the broken ends of the bone : the 
 cancelli of the bone and the neighbouring soft parts seem in 
 a state of ecchymosis ; the quantity of blood, however, ef- 
 fused from the ruptured vessels is generally inconsiderable. 
 
 About the fourth day a change is found to have super- 
 vened ; the parts adjacent to the broken ends of the bone 
 have become condensed and indurated, and form a firm cap- 
 sule, which contains the broken extremities. The thickening 
 includes every neighbouring texture : the muscles, tendons, 
 and cellular membrane, for the extent of several lines, seem 
 condensed into one tough elastic mass. 
 
 During the next fortnight this capsule becomes of greater 
 firmness, assuming the character of cartilage : at the same 
 time lymph is frequently found to have exsuded around the 
 broken ends of the bone. 
 
 After the third week the muscles and tendons gradually 
 become again distinct, or disengaged from the thickened 
 capsule, in which ossification soon commences : so that at 
 the expiration of four or five or six weeks, the broken ends 
 of the bone are fixed in some sort of apposition by an osseous 
 case extending from the one to the other, having its adhe- 
 sion at some little distance from the fractured edge. The 
 only union between the extremities of the bones, that hitherto 
 has taken place, is by soft substance, which comprehends 
 the organized clot of blood, the lymph effused, and produc- 
 tions from the capsule, which have grown together and 
 coalesced. 
 
 During the interval between the sixth week and the fifth 
 or sixth month, the process of ossification extends from the 
 
448 Of Fracture of the Neck of the Femur. 
 
 capsule to the soft substance which directly unites the broken 
 surfaces. At the same time the capsule shrinks in propor- 
 tion as the direct union renders its continuance unneces- 
 sary. After a few months more, the capsule has disappeared, 
 the bone has shrunk to the natural size, and even its cavity 
 is gradually restored. 
 
 Thus it appears established upon a very extensive induc- 
 tion, that union of internal parts greatly depends upon 
 changes which take place in the adjacent textures, among 
 which the cellular membrane is perhaps the most important 
 agent. This conclusion derives support from, at the same 
 time that it serves to explain, the curious circumstance, that 
 fractures of a bone at a part where it is insulated from the 
 surrounding textures, most rarely unite by bone. In Sir 
 Astley Cooper's important work upon Dislocations, the fact 
 is proved by reference to a vast body of evidence, that when 
 the neck of the femur is broken within the capsular mem- 
 brane, bony union does not usually follow. 
 
 Of several instances, which I have myself had an oppor- 
 tunity of examining, let me select the following to illustrate 
 this anomaly. A woman about the age of fifty fell with 
 great violence upon the left hip. The limb was not shortened, 
 but was rendered useless : pain and swelling ensued. She 
 was confined to her bed for five months ; after which she 
 gradually regained strength in the injured hip, and became 
 enabled to walk with the assistance of a stick. Thirteen 
 months after the accident, she died suddenly of apoplexy. 
 Upon examination, the neck of the femur was found to have 
 been broken within the capsular membrane: union had 
 taken place by a layer of soft but tough substance three 
 lines in thickness, in which however not the least trace of 
 earthy matter was discovered. The preparation is in the 
 Museum in King's College, and with the details of the case 
 was given to me by my friend Mr. Sweatman : there is an 
 engraving from it in Sir Astley Cooper's work on Disloca- 
 tions. In a fracture of this description, it is obvious that 
 the broken ends of bone remain enclosed in a synovial cavity, 
 whereby they are cut off from continuity with those parts, 
 the changes in which lead to union in other cases. 
 
Of Fractures of the Cranium. 449 
 
 When the neck of the femur is broken, and the fracture 
 is half within and half without the capsular membrane, the 
 former part has been found united by ligament, the latter 
 by bone. 
 
 When the fracture is entirely within the capsular mem- 
 brane, and ligamentous union ensues, some growth of bone 
 is occasionally found to have occurred on the outside of the 
 capsule, the commencement doubtless of the process, 
 which has been already described in the ordinary reparation 
 of bone, but which in this case is prevented having any use- 
 ful effect by the intervention of the synovial membrane. 
 
 It must not, however, be denied, that union by bone, in 
 fracture of the neck of the femur within the capsule, is pos- 
 sible. I have no doubt that it occasionally takes place : but 
 I am persuaded that it is of very slow production, and that 
 it follows at a long interval a previous soft or ligamentous 
 union. The possibility of a slow process of ossification ex- 
 tending directly from bone to bone is shown by what hap- 
 pens after loss of part of a cranial bone. When the skull is 
 fractured, the membrane on either side of it undergoes no 
 change like that which leads to the reparation of other 
 bones : no thickening takes place ; no callus is formed ; and 
 for several months there is no apparent attempt at restora- 
 tion. But the edges of the broken bone are observed gra- 
 dually to become rounded, and after a time to encroach 
 upon the intervening membranous substance, the extent of 
 which in the lapse of months and years becomes less and 
 less, the bones either partially, or, if the fissure be narrow, 
 wholly uniting by a direct extension of ossification from one 
 to the other. 
 
 Let me conclude with mentioning an instance of deficient 
 union after partial division of a nerve, which is closely pa- 
 rallel to the common case of deficient bony union after frac- 
 ture of the cervix femoris. 
 
 An attempt was made to divide the fifth nerve at the side 
 of the pons Varolii in a young cat. The animal immediately 
 lost the sense of feeling in the parts supplied by the first 
 and second divisions of the fifth, and the cornea in a few 
 days became partially opaque : but the iris moved, and the 
 
450 Nerve divided in the Cranial Cavity. 
 
 animal saw distinctly with the eye, which had lost the sense 
 of touch. During eighteen months no further change ensued : 
 not the slightest return of feeling was observable in the eye, 
 the nostril, or cheek of the mutilated side. At this period 
 the animal was killed. Upon examination, the following 
 appearances presented themselves. The fifth nerve had not 
 been entirely divided ; which accounted for the continuance 
 of sensation that had been observed in the parts supplied 
 by the third division of that nerve. What remained undi- 
 vided of the fibrils of the fifth held the severed fibrils nearly 
 in apposition, and at the distance only of a line asunder : 
 they were united by a thin jilm, which seemed a clot of blood, 
 that had nearly lost its colouring matter, and gave way on 
 slight pressure. 
 
 Now a nerve when traversing the cavity of the arachnoid 
 membrane is in a position analogous to that of the neck of 
 the thigh bone : it is not in any sort of contact with the cel- 
 lular texture ; and its restoration when divided is equally 
 imperfect. 
 
 Yet in such a case every other condition favourable to re- 
 paration is present : the divided surfaces are nearly in appo- 
 sition, the supply of blood is not interrupted, and the parts 
 are kept perfectly at rest. 
 
CHAPTER XVII. 
 OF THE VARIETIES OF THE HUMAN SPECIES. 
 
 A SYSTEM of physiology, however elementary, would be 
 incomplete without some account of the diversities which 
 the human race presents in different countries. To follow 
 this subject in all its bearings, to consider it as illustrating 
 the origin and primary condition, the early habitation and 
 the distribution of our species, constitutes one of the most 
 interesting branches of speculative research. Such an in- 
 quiry demands a critical study of the traditional history of 
 nations, of their affinities in language and customs, of their 
 resemblance in mental endowments and in physical charac- 
 ter, as well as a careful examination of the analogies which 
 the natural history of other living beings presents. The 
 most important questions among those which I have enu- 
 merated, the student will find very ably treated in Dr. Pri- 
 chard's elaborate work upon the Physical History of Man : 
 he may likewise consult with advantage the Lectures of 
 Mr. Lawrence ; and in the Decades Craniorum of Blumen- 
 bach he may examine a part of the original materials upon 
 which that celebrated naturalist of the human species 
 founded his division of the families of mankind according 
 to their physical character. 
 
 It is to the last inquiry alone that I shall advert on the 
 present occasion. By extracts from the authorities col- 
 lected and quoted by Dr. Prichard, I shall attempt to 
 display the most remarkable differences in form and struc- 
 ture that are observed in different nations. They will be 
 found to be such as we may reasonably suppose to have 
 resulted from the influence of accidental causes operating 
 
452 The Human Race descended from one Stock. 
 
 upon one original species or family. Yet had we not ad- 
 ditional evidence to that which the physiological study of 
 Man presents, the opposite hypothesis would have been far 
 from untenable ; and we might with a show of reason have 
 concluded, that the earth after its last catastrophe was peo- 
 pled at different points, with beings of different physical 
 organization, appropriated to the climates in which they 
 were placed ; and that those numerous intermediate shades, 
 which now blend together and combine the whole into one 
 uninterrupted series, have resulted from a subsequent inter- 
 mixture of branches of the original tribes. 
 
 The strongest argument of a physiological nature in proof 
 of the descent of the whole human race from one family, is 
 derived from the consideration of those marked and charac- 
 teristic diversities which are found to exist between nations, 
 that are admitted at all hands to have had a common origin. 
 Take for instance the physical and moral characters of the 
 English, the Irish, and the Scotch : if in the same climate 
 and quarter of the globe, and under circumstances nearly 
 similar, so great and general a diversity should have arisen 
 in the branches of one family, is it wonderful, that in cli- 
 mates the most remote and unlike, leading to habits essen- 
 tially dissimilar, diversities yet more remarkable should have 
 been produced by the operation of similar principles ? If 
 we admit the explanation in one case, why not in all ? We 
 know that difference of climate alone will speedily produce 
 important alterations in the physical character of a race. 
 The offspring of Europeans in the West Indies are a taller 
 race than their progenitors, their cheeks are high boned, 
 and the sockets of their eyes deeper than in Europeans. 
 We know again that habits and manner of fife are causes 
 at least equally efficient. It has been observed by 
 Dr. Smith, that the negro slaves in the United States, espe- 
 cially the domestic servants, who live in houses, and are 
 protected from the hardships of labour, and of a hot climate, 
 differ very remarkably from the native Africans. They have 
 in the third generation but little remains of the depressed 
 nose ; their mouths and lips are of a moderate size, their 
 eyes lively and sparkling, and often the whole composition 
 
Of differences of Colour in different Nations. 453 
 
 of their features extremely agreeable. Their hair grows 
 sensibly longer in each succeeding generation. The field 
 slaves, who labour in the plantations, retain much more of 
 the original aspect of the race, though their features are not 
 so strongly marked as those of imported slaves. And inde- 
 pendently of these causes of diversity, the influence of 
 which is universally admitted, there exists in every race an 
 inherent tendency to change or vary within certain limits 
 from the original type ; so that, in instances where the 
 causes which I have described are apparently excluded, an 
 indigenous race frequently produces individuals, who in 
 physical character approximate nearly to other tribes of 
 men. 
 
 The characteristic differences among mankind are found 
 in the colour of the skin, in the texture of the hair, and in 
 the shape of the cranium and face. 
 
 1. The differences of colour among different nations may 
 be ranged under two classes, the melanic and the xanthous. 
 
 The melanic variety includes all individuals or races who 
 have black hair, and forms by far the most numerous part 
 of mankind. The hue of the skin varies, from a deep 
 black, which is the hue of some African nations, to a much 
 lighter or more diluted shade. The dusky hue is combined 
 in some nations with a mixture of red, in others with a 
 tinge of yellow. The former are the copper-coloured nations 
 of America and Africa, the latter the olive-coloured races of 
 Asia. In the deepness or intensity of colour, we find every 
 shade or gradation, from the black of the Senegal Negro, or 
 the deep olive and almost jet-black of the Malabars, and 
 some other nations of India, to the light olive of the 
 northern Hindoos. From that we still trace every variety 
 of shade among the Persians and other Asiatics, to the 
 complexion of the swarthy Spaniards, or European brunettes 
 in general. 
 
 The xanthous variety includes all those individuals who 
 have light brown, auburn, yellow, or red hair. With hair 
 of these colours is almost always combined a fair com- 
 plexion, which on exposure to heat acquires not a black or 
 deep brown hue, but more or less of a red tint. This 
 
 2 F 
 
454 Of Albinoes. 
 
 variety, however, passes insensibly into the others : it would 
 be difficult to determine whether some of the individuals 
 belong to it or to the melanic. 
 
 The seat of the dark-coloured families of mankind is 
 within or near the tropics; and the circumstances under 
 which the darkest shades are found, and which we are led 
 to view as productive of them, are a more completely savage 
 state, a more immediate vicinity to the equator, and a situ- 
 ation but little raised above the level of the sea. 
 
 Under opposite circumstances, the colour of the skin be- 
 comes lighter. There is something in the temperately cold 
 regions of Europe and Asia, which especially favours the 
 production of the xanthous variety ; it is in these countries 
 that it prevails, and is in some instances the general cha- 
 racter of whole tribes. Either it springs up more frequently 
 in these regions than elsewhere, or when it casually appears, 
 multiplies and is propagated more extensively. It is not 
 uncommon to find it prevailing in high hilly tracts, while 
 in the neighbouring low grounds it gives place to the melanic 
 variety. It has been observed, that the western regions of 
 North America assimilate nearly in climate to the same lati- 
 tudes in Europe. This remark applies to the country be- 
 tween the Esquimaux to the north, and the neighbourhood 
 of Port Discovery in the forty-eighth degree of latitude to 
 the south. It is extremely interesting to remark, that the 
 inhabitants of these regions, consisting of several distinct 
 races, are as white as the nations of Europe. 
 
 It appears that among the races of the darkest colour, 
 the xanthous complexion occasionally manifests itself. Pal- 
 las has minutely described a white negress seen by him in 
 London in 1761. She was born of negro parents in Jamaica, 
 and was sixteen years of age. She was of small stature, 
 fair complexion, with ruddy lips and cheeks. The iris was 
 of a brownish grey colour. Her hair, which was quite 
 woolly in texture, was of a light yellow colour, or what the 
 French call " blond." This girl had the negro features 
 strongly marked, and had every appearance of negro de- 
 scent. Such an occurrence, however, is exceedingly rare ; 
 but a deviation very slightly removed from it is by no means 
 
Of Differences in the Texture of the Hair. 4'>5 
 
 unfrequent. Persons are occasionally born, of every race of 
 mankind, who to the features of that race join a complexion 
 without colour ; not pale indeed, but rather a milk white ; 
 yet occasionally it has a uniform light tint of the faintest 
 pink. The eye has no black pigment, so that the iris and 
 pupil are of different shades of red : the hair is of a pale 
 yellowish white or cream colour ; but sometimes in European 
 people of this description, it has a pale gold colour, resem- 
 bling in texture and glossiness unwrought silk. Persons 
 with this appearance are termed albinoes. Like pied people, 
 they have not occurred in such numbers as to form a large 
 proportion of the inhabitants of particular districts. 
 
 2. The hair of the head presents three especial varieties 
 of texture : either, as in the African, it is crisp and woolly, 
 the filaments fine and short, with a peculiar spiral twist, and 
 apparently a roughness of surface, which occasions them to 
 become matted, and in some measure felted into a mass ; or 
 it is long, coarse, and lank, as in the eastern Asiatics ; or it 
 is soft and flowing, and inclined to curl, as in the inhabit- 
 ants of almost the whole of Europe. 
 
 There are three principal varieties in the form of the skull, 
 which, to borrow the terms employed by Dr. Prichard, may 
 be termed steno-bregmate, meso-bregmate, and platy-breg- 
 mate: they are thus characterized. 
 
 1. Of the steno-bregmate cranium. 
 
 " The head narrow, compressed at the sides ; the fore- 
 head very convex, vaulted; the cheek bones projecting 
 forwards: the nostrils wide; the fossae maxillares deeply 
 marked behind the infra-orbital foramen,- the jaws 
 lengthened ; the alveolar edge narrow, long, and elliptical ; 
 the front teeth of the upper jaw turned obliquely forwards ; 
 the lower jaw strong and large ; the skull in general thick 
 and heavy. 
 
 "Face narrow, projecting towards the lower part; eyes 
 projecting (a fleur de tte), nose spread and almost con- 
 founded with the cheeks; the lips, particularly the 
 upper one, very thick ; the jaws prominent, and the chin 
 retracted." 
 
 2 F 2 
 
456 Of Differences in the Shape of the Cranium. 
 
 2. Of the meso-bregmate cranium. 
 
 " The head of the most symmetrical shape, almost round ; 
 the forehead of moderate extent; the cheek bones rather 
 narrow without any projection, but having a direction 
 downwards from the malar process of the frontal bone ; the 
 alveolar edge well rounded ; the front teeth of each jaw 
 placed perpendicularly. 
 
 " The face of an oval shape, straight ; features mode- 
 rately prominent ; forehead arched ; nose narrow, slightly 
 arched, or at least- with the bridge somewhat convex ; 
 cheek bones not at all projecting; mouth small, with the 
 lips slightly turned out, particularly the lower one; chin 
 full and round." 
 
 3. Of the platy-Lregmate cranium. 
 
 " The head almost square ; the cheek bones projecting 
 outwards ; the nose flat ; the nasal bones and the space 
 between the eyebrows nearly on the same horizontal plane 
 with the cheek bones ; the superciliary arches scarcely 
 to be perceived ; the nostrils narrow : the alveolar edge 
 in some degree rounded forwards ; the chin slightly promi- 
 nent. 
 
 " Face broad and flattened, with the parts imperfectly 
 distinguished ; the space between the eyes flat and very 
 broad; nose flat; cheeks projecting, round; narrow and 
 linear aperture of the eyelids extending towards the 
 temples ; the internal angle of the eye depressed towards 
 the nose, and the superior eyelid continued at that part 
 into the inferior by a rounded sweep ; chin slightly promi- 
 nent." 
 
 The adjoined figures represent instances of the three 
 extreme diversities in the form of the head, which have 
 been described. The heads are supposed to be seen from 
 above, in which position the differences from which the 
 terms, steno-bregmate, meso-bregmate, and platy-bregmate 
 are most observable. 
 
Of Differences in the Shape of the Cranium. 457 
 
458 Distribution of the different Races of Mankind. 
 
 When we now cast our eyes over the great continents of 
 the globe, to see whether the peculiarities in colour and in 
 the shape of the head, which have been described, occur 
 indiscriminately in the same regions, or are preserved apart, 
 giving a characteristic appearance to the inhabitants of 
 different countries, we notice, that individuals may be 
 found in every nation, who, in their form, recede from 
 either extreme, and come near to the mean type of the 
 human family; but that nevertheless in different regions 
 one particular configuration is more especially affected, so 
 as to be characteristic of their inhabitants. 
 
 The natives of Africa have steno-bregmate skulls and 
 woolly hair ; the inhabitants of Europe and of the western 
 part of Asia, exhibit the meso-bregmate skull, with soft and 
 flowing hair ; the inhabitants of northern and eastern Asia 
 and of America, are characterized by the platy-bregmate 
 skull, with coarse and lank hair. 
 
 Each of these varieties contain tribes of a dark colour, 
 but the darkest shades belong to the steno-bregmate 
 variety : the fairest to the meso-bregmate ; the olive and 
 tawny colour are most prevalent in the platy-bregmate. 
 
 The people of the islands in the great Southern Ocean 
 present a physical character more diversified and capricious 
 than that of the continents of the globe ; yet its varieties 
 are referable to the three great classes which have been 
 described ; many islands contain two distinct races, one of 
 Indian, the other of Negro conformation. Others again 
 have inhabitants in which we recognize either of these 
 races separately, or which in physical character belong to 
 the meso-bregmate variety. But the great Southern Ocean 
 is bounded by continents, on the shores of which are spread 
 races of mankind having each of the three primary charac- 
 ters which have been described ; it should not therefore 
 on any hypothesis appear surprising that its islands 
 should be thus promiscuously peopled with diversified 
 races. 
 
 Let me now complete the design 1 have in view, by ex- 
 hibiting various sections of mankind, selected in such a 
 manner as to show the range of variety, or deviation from 
 
Of the ^Ethiopian Variety. 459 
 
 the three primitive or extreme types, which different races 
 of mankind present. 
 
 Of the diversities among the steno-bregmate or Ethiopian 
 variety of mankind. 
 
 1. The following is a description of the Negroes of the 
 race of Acra, by Isert the Danish traveller. 
 
 " Almost all the Negroes are of a good stature, and the 
 Acra Negroes have remarkably fine features. The contour 
 of the face, indeed, among the generality of these people is 
 different from that of Europeans: but at the same time 
 faces are found among them, which, excepting the black 
 colour, would in Europe be considered as beautiful. Com- 
 monly, however, they have something apish. The cheek 
 bones and chin project very much, and the bones of the 
 nose are smaller than in Europeans. This last circumstance 
 has probably given rise to the assertion, that the Negro 
 women flatten the noses of their children as soon as they 
 are born. But noses may be seen among them, as much 
 elevated and as regular as those of Europeans. Their hair 
 is woolly, curled, and black ; but sometimes red. When 
 continually combed, it may be brought to the length of 
 half a yard ; but it can never be kept smooth*. 
 
 2. Barbot describes Negroes upon the Gold coast, with 
 features, in which the Negro conformation was reduced to 
 an approach to European symmetry, the skin indifferent 
 black y with long curled hair sometimes reaching down to their 
 shoulders : the women for the most part having high noses 
 somewhat hookedj and long curling hair. 
 
 3. The country between the Senegal and Gambia, and 
 from Cape Verd as far as the boundaries of the Foulahs, is 
 the abode of the nation of Yoloffs, or Yaloffs, who were 
 formerly united under the dominion of the Bourb' JolofF, or 
 Yoloff Emperor, but are now divided into several states. 
 The Yoloffs are described by travellers as a very fine race of 
 people : they are tall, well made, of middle stature ; their 
 
 * P. E. Isert ; Reis na Dordrecht, 1 790. Translated in Philos. Mag. 
 vol. iii, p. 144. 
 
460 Of the Yohffs. 
 
 countenances are ingenuous and agreeable, but have in some 
 degree the flat nose and thick lips common to many Negro 
 nations, though many of them have regular features. Their 
 hair is crisp and woolly : their colour is a fine deep clear 
 black. They are cheerful and indolent. They have a 
 peculiar language, which is said to be harmonious. The 
 circumstance, that the Yoloffs at the northern extremity of 
 Negroland are of a deep black colour, has drawn the follow- 
 ing remark from a traveller well acquainted with the nations 
 of Africa. 
 
 "This race of Negroes, the most handsome and the 
 finest black of all those dependent upon the government of 
 the Senegal, proves that the deepest colour does not arise 
 solely from the heat of the climate, nor the being more sub- 
 jected to the vertical rays of the sun, but results from other 
 causes. For the Joloffs are to the north of Nigritia ; and 
 the further you recede from them and approach towards the 
 line, the black colour of the Negroes becomes less and less 
 strong and unmingled*." 
 
 3. The Tibboo are divided into six tribes, who occupy 
 the country east of Fezzan, and between Fezzan and 
 Borneo. The following account of them is by Captain 
 Lyon. 
 
 " The Tibboo females are light and elegant in form, and 
 their graceful costume, quite different from that of the 
 Fezzaners, is well put on. They have aquiline noses, fine 
 teeth, and lips formed like those of Europeans ; their eyes 
 are expressive, and their colour is of the brightest black. 
 There is something in their walk and erect manner of carry- 
 ing themselves which is very striking. Their feet and 
 ancles are delicately formed, and are not loaded with a 
 mass of brass or iron, but have merely a light anklet of 
 polished silver or copper, sufficient to show their jetty skin 
 to more advantage : they also wear red slippers. Their 
 hair is plaited on each side, in such a manner as to hang- 
 crown on the cheeks like a fan, or rather in the form of a 
 large dog's ear. 
 
 * Golberry, i, p. 75. 
 
OftheTibboo. 461 
 
 " The Tibboo of Bergoo seem to approach the Negroes in 
 their physical character. They conceal themselves from 
 the Arab hunters by kneeling on the ground, which is of 
 the same colour as their skin, being black basalt. They 
 are however of lighter complexions than other Negroes, 
 and are handsomer people. The females wear their hair, 
 which is not very woolly, in long plaits." 
 
 5. "The people of Berber," says Burckhardt, "are a 
 very handsome race. The native colour seems to be a dark 
 red browrij which, if the mother is a slave from Abyssinia, 
 becomes a light brown in the children, and if from the 
 Negro countries, extremely dark. The men are somewhat 
 taller than the Egyptians, and are much stronger and 
 longer limbed. Their features are not at all those of the 
 Negro, the face being oval, the nose often perfectly Grecian, 
 and the cheek bones not prominent. The upper lip is, 
 however, generally somewhat thicker than is considered 
 beautiful among northern nations, though it is still far from 
 the Negro lip. Their legs and feet are well formed, which 
 is seldom the case with Negroes. They have a short beard; 
 their hair is bushy and strong, but not woolly : it lies in 
 close curls when short, and when permitted to grow, forms 
 itself into broad high tufts." 
 
 6. The term Nouba is given to all the blacks coming 
 from the slave countries to the south of Sennaar. Speak- 
 ing of these, Burckhardt observes, that their noses are less 
 flat than those of the Negroes ; their lips are less thick, and 
 their cheek bones not so prominent. Their hair is generally 
 similar to that of Europeans, but stronger and always 
 curled ; sometimes it is woolly. Their colour is less dark 
 than that of Negroes, and has a coppery tinge*. 
 
 7. The Copts are well known to be the descendants of the 
 old Egyptians. Many travellers have remarked among 
 them a certain approximation to the Negro. Volney says, 
 that they have a yellowish dusky complexion, with a puffed 
 visage, swollen eyes, flat noses, and thick lips, bearing 
 much resemblance to Mulattoes. M. Denon says he was 
 
 *. Burckliardt's Travels, p. 312. 
 
462 Of the Copts. 
 
 much struck with the resemblance of the Copts to the old 
 Egyptian sculptures, characterized by " flat foreheads, eyes 
 half closed and raised up at the angles, high cheek bones, 
 a broad flat nose, very short, a flattened mouth, placed at a 
 considerable distance from the nose, thick lips, little beard, 
 a shapeless body, crooked legs, without any expression in 
 the contour, and long flat toes/' 
 
 Mr. Ledyard, whose testimony is of the more value, as 
 he had no theory to support, says, " I suspect the Copts to 
 have been the origin of the Negro race ; the nose and lips 
 correspond with those of the Negroes. The hair, whenever 
 I can see it among the people here (the Copts), is curled : 
 not like that of the Negroes, but like the Mulattoes." 
 
 It seems that the complexion of the Copts is liable to 
 considerable variations. Though it must be true, as 
 M. Volney asserts in the passage above cited, that the 
 Copts are generally of a dusky and yellowish colour, like 
 the Abyssinians : yet we are assured by M. Belzoni, that 
 some of them are nearly as fair as Europeans. 
 
 8. The complexion of the Hottentots is like that of the 
 palest Negro, but still more dilute. Mr. Barrow observes, 
 that it is of a yellowish brown, or of the hue of a faded 
 leaf. The hair is of a very singular nature: it does not 
 cover the whole surface of the scalp, but grows in small 
 tufts at certain distances from each other, and when clipt 
 short, has the appearance and feel of a hard shoe-brush, 
 except that it is curled and twisted into small round lumps, 
 about the size of a marrowfat pea. When suffered to 
 grow, it hangs on the neck in hard twisted tassels like 
 fringe. 
 
 " The Hottentots are well-proportioned, erect, of a deli- 
 cate and effeminate make; not muscular; their joints and 
 extremities small ; the face generally ugly, but different in 
 different families ; some having the nose remarkably flat, 
 others considerably raised. Their eyes are of a deep 
 chesnut colour, long and narrow, distant from each other ; 
 the inner angle being rounded as in the Chinese, to whom 
 the Hottentot bears a striking resemblance. The cheek bones 
 are high and prominent, and, with the narrow pointed chin, 
 
Of the Hottentots. 463 
 
 form nearly a triangle. Their teeth are very white. The 
 women when young are graceful and well made ; the nipple 
 is unusually large, and the areola much elevated ; but im- 
 mediately after the birth of the first child, the breast becomes 
 flaccid and pendent, and in old age becomes greatly dis- 
 tended. The belly becomes protuberant, and the posteriors 
 are covered with a huge mass of pure fat. That elongation 
 of the nymphse, which is well known to characterize the 
 Hottentot women, has been falsely ascribed to art. It is a 
 natural variety of conformation. 
 
 Mr. Burchell states the following characters as peculiar 
 to the Hottentots. Hands and feet little ; eyes so oblique, 
 that lines drawn through the corners of each, would not 
 coincide as being in the same plane, but would intersect as 
 low down as the middle of the nose ; end of nose wide and 
 depressed ; nostrils squeezed out of shape ; chin long and 
 forward ; narrowness of the lower part of the face, a 
 character of the race. 
 
 9. All the physical characters of the Hottentots are re- 
 cognized in the Bushman. In the latter people all the 
 deformities of the race are seen in an exaggerated degree ; 
 they are extremely ugly and diminutive ; the middle size of 
 the men being four feet six inches, and that of the women 
 four feet. 
 
 Cuvier has given some valuable information on the 
 anatomical peculiarities of this race, in his account of the 
 dissection of the Bosjesman woman, well known under the 
 name of the Hottentot Venus. In this individual, the skull 
 and the bones of the face presented a striking combination 
 of the traits of the Negro with those of the Calmuck, the 
 jaws projecting more than in the Negro, the face being 
 wider than in the Calmuck, and the nose flatter than in 
 either, and in this respect approximating more to the monkey. 
 
 The characters of the ^Ethiopian variety are met with 
 again in many of the inhabitants of the islands of the 
 Indian and Pacific Oceans. In some instances, people of 
 this description are the exclusive inhabitants ; in others 
 they are mixed with a totally different population ; in 
 others they are wholly wanting. They are termed in the 
 
464 Of the Papuas of New Guinea. 
 
 islands of the Indian Archipelago, by the other inhabitants, 
 Pua-pua, or blacks, in allusion to their complexion ; and 
 thence by Europeans they are denominated Papuas. The 
 principal residence of the Papuas, strictly so called, is in 
 the great islands of New Guinea and New Britain, of which 
 they are almost the only inhabitants. 
 
 M. de Bougainville says, " the men of New Guinea are 
 black, with frizzled woolly hair." Captain Forrest, " that 
 the Papua Caffres of New Guinea are as black as the Caffres 
 of Africa." They wore their frizzling hair so much bushed 
 out round their heads 'that its circumference measured about 
 three feet, and when least two feet and a half. 
 
 Dampier informs us, that the country of New Britain is 
 " very well inhabited with strong well-limbed Negroes." 
 And at Pulo Sabuda, between Ceram and New Guinea, 
 " the people," he observes, " are very tawny Indians, with 
 long black hair, who differ but little from the Mindanayans 
 and others of the Indian islands." These, he adds, seems 
 to be the chief, but besides these we also saw shock, curl- 
 pated New Guinea Negroes. 
 
 The skin of a Papua, from Sir. E. Home's description 
 of one brought home by Sir Stamford Raffles, is of a light 
 colour, the woolly hair grows in small tufts, and each hair 
 has a spiral twist. The forehead rises higher, and the 
 hind head is not so much cut off. The nose projects more 
 from the face ; the upper lip is longer and more prominent ; 
 the lower lip projects forward from the lower jaw, to such 
 an extent, that the chin forms no part of the face, the 
 lower part of which is formed by the mouth. The buttocks 
 are so much lower than in the Negro as to form a striking 
 mark of distinction ; but the calf of the leg is as high as in 
 the Negro. 
 
 Besides the Papuas, who are characterized by black com- 
 plexions and woolly hair, there are tribes in many of the 
 Indian islands, chiefly those in the eastern and more re- 
 mote parts of the Archipelago, who are as black as the 
 Papuas, or nearly so, but have instead of woolly, straight 
 and wiry hair. 
 
 The principal seat of people of this description, however, 
 
Of the New Hollanders. 
 
 465 
 
 is in New Holland. The complexion of a New Hollander 
 is of the colour of woad-root, or what is commonly called a 
 chocolate colour. The shape of the head resembles that of 
 the African Negro, but its harsher features are softened ; 
 the alveolar edge of the upper jaw projects perhaps in the 
 same degree, but the bones are not so heavy and massive, 
 the head rises to a greater height at the coronal suture, and 
 the chin does not recede as in the Negro. Dampier de- 
 scribes them as having great bottle noses, pretty full lips, 
 and wide mouths. The first of these features appears a 
 frequent characteristic of the inhabitants of the Indian 
 islands. The New Hollanders appear to be the most 
 wretched of mankind ; and in their habits, the least re- 
 moved above the brute creation. What has struck me 
 most in the skulls of New Hollanders, after their general 
 but softened resemblance of the Negro cranium, is the re- 
 markable projection of the superciliary ridges, which gives 
 a scowling expression to the vacant orbit. The left-hand 
 figure of the two following is drawn very accurately from 
 the skull of a native brought from Sydney. The other 
 figure, not so faithfully drawn, is from a Negro cranium. 
 In this skull the coronal suture terminated on the temporal, 
 not the sphenoid bone. I have noticed the same in the 
 opposite extreme, in the Calmuck skull. It is very singu- 
 lar that a similar difference is found in the skulls of the 
 higher and lower 
 
466 Of the Inhabitants of Van Dieman's Land. 
 
 The inhabitants of Van Dieman's Land are a woolly-haired 
 race. They are thus described by Anderson. " Their 
 colour is a dull black, not quite so deep as that of the 
 African Negroes. Their hair is perfectly woolly. Their 
 noses, though not flat, are broad and full. The lower part 
 of the face projects a good deal, as is the case of most 
 Indians I have seen, so that a line let fall from the forehead 
 would cut off a much larger portion than it would in an 
 European. Their eyes are of a middling size, with the 
 white less clear than in us. Their teeth are broad, but not 
 equal nor well set. Their mouths are rather wide ; but this 
 appearance seems heightened by wearing their beards long 
 and clotted with paint, in the same manner as the hair on 
 their heads. In other respects they are well-proportioned, 
 though the belly seems rather projecting. Their manners, 
 he adds, resemble those of the New Hollanders in most 
 particulars. They make huts of a similar kind, though 
 their chief habitation is in hollow trees. They are without 
 clothes, and cover their skins with dirt." 
 
 When we look eastward for traces of the derivation of 
 the Papua race from the coast of Africa, we meet with here 
 and there circumstances which seem to favour this sup- 
 position. 
 
 In the Andaman islands in the sea of Bengal an aborigi- 
 nal race is still found. In stature they seldom exceed five 
 feet; their limbs are ill-formed and slender, their bellies 
 protuberant ; they have high shoulders and large heads ; 
 and like the Africans they have woolly hair, flat noses, and 
 thick lips ; their eyes are small and red ; their skin of a 
 deep sooty black, while their countenances exhibit the ex- 
 treme of wretchedness and ferocity. 
 
 In Madagascar, on the other hand, two races are found, 
 the one distinctly African, the other joining a dark skin to 
 straight black hair, and features nearly European. The 
 dialects of these people, observes Dr. Pritchard, bear an 
 undoubted resemblance to the language of the black and 
 the tawny races of the Philippines. 
 
Of the Inhabitants of Europe. 467 
 
 II. Of the meso-bregmate or Caucasian variety. 
 
 1. It is unnecessary to adduce authorities to prove the 
 general resemblance that exists among the inhabitants of 
 Europe. The points in which one nation differs from 
 another, are the following. Towards the north of Europe, 
 a lighter complexion, with light hair, and high and large 
 features, prevail ; towards the south, a darker complexion, 
 dark hair and eyes, and a more marked and expressive coun- 
 tenance. 
 
 2. The Circassians who inhabit the heights of Mount 
 Caucasus, and the Georgians who dwell at its feet, admit 
 of being similarly contrasted. Both are the choicest speci- 
 mens of the meso-bregmate variety; the former fair; the 
 latter a dark-complexioned race, but superior to the former 
 in' symmetry and beauty. 
 
 The Ossites on Mount Caucasus have a fine sanguine 
 complexion. In external appearance, according to the de- 
 scription of Pallas, they exactly resemble the peasants in 
 the north of Russia ; they have in general, like them, 
 either brown or light hair, occasionally also red beards. 
 
 3. The Afghans occupy a great part of the Persian em- 
 pire. They approximate on the one hand to the northern 
 Persians and Europeans, on the other to the Hindoos. 
 " The Afghan women," says Mr. Elphinstone, " are de- 
 scribed as large, compared to those of India, and very fair 
 and handsome. The men are all of a robust make, and 
 are generally lean, though bony and muscular. They have 
 high noses, high cheek bones, and long faces. Their hair 
 and beards are generally black, sometimes brown, and rarely 
 red ; their hair is always coarse and strong. They shave 
 the middle part of their head, but wear the rest of their 
 hair. The tribes near towns wear it short, but the rest 
 have long and large locks hanging down on each side of 
 the head. They wear long and thick beards." 
 
 In the northern parts of Persia the complexion of the 
 people is fair. A writer who had travelled in the countries 
 between Caucasus and Persia, and who was acquainted 
 with the people of this frontier, mentions a slender form 
 and blue eyes as characteristic of the female Persians. 
 
468 Of the Arabs. 
 
 The Kinos are remarked to have a white complexion with 
 animated features. 
 
 4. Mr. Frazer thus describes the people of Muscat, on 
 the eastern coast of Arabia, below the Persian Gulf, and 
 more particularly the natives of the celebrated Ormus. 
 " The Arabs in colour resemble Mulattoes, are of a sickly 
 yellow hue, with a deeper brownish tinge about the eyes, 
 neck, and joints : some are very dark. The genuine Arabs, 
 with some exceptions, are rather spare and active than 
 athletic men. Those of the superior orders, who came 
 under our observation, as the Shieks and their families, 
 bore a strong characteristic resemblance to each other in 
 features. The countenance was generally long and thin ; 
 the forehead moderately high, with a rounded protuberance 
 near its top ; the nose prominent and aquiline ; the mouth 
 and chin receding, giving to the line of profile a circular 
 rather than a straight character ; the eye deep set under 
 the brow, dark and bright; thin and spare, deficient in 
 muscle, their limbs were small, particularly their hands, 
 which were sometimes even of feminine delicacy; their 
 beards were almost always of a deep black artificially co- 
 loured, if not naturally so ; a few wore them grizzled, and 
 we observed an old man, whose beard of a milk white colour 
 he had dyed yellow, which, contrasted with a singular pair 
 of blue eyes, had a very extraordinary effect. 
 
 " Les princesses, et les autres dames Arabes," says 
 M. de la Roque, " qu'on m'a montre par le coin d'une 
 tente, m'ont paru fort belles et bien faites. On peut juger 
 par cellesci, et par ce qu'on m'en a dit, que les autres ne 
 le sont gures moins : elles sont fort blanches, parce qu'elles 
 sont toujours a convert du soleil. Les femmes du commun 
 sont extrmement halees, outre la couleur brune et basanee 
 qu 'elles ont naturellement ; je les ai trouve fort laides dans 
 toute leur figure, et je n'ai rien vu en elles que les 
 agremens ordinaires, qui accompagnent une grande jeu- 
 nesse." 
 
 The variety of complexion above described, seems to be 
 a natural deviation, and is not referable to any mixture of 
 breeds. A brown or tawny yellow is the natural colour of 
 the Arabs in some places. But there are races of Bedouins 
 
Of the Hindoos. 469 
 
 and other tribes of a still darker complexion, and even 
 black or nearly so. 
 
 6. The form of the skull in the natives of Hindoostan and 
 the Deccan presents no decided difference from the shape 
 common among Europeans. The only character in the 
 osteology of the Hindoo, which has drawn the attention of 
 anatomists, is the length of the legs, which is said to be 
 greater in proportion to the trunk than that of other na- 
 tions. 
 
 The people of the northern provinces of India are of 
 lighter complexion than those of the south. Those of in- 
 ferior caste are generally of darker complexion than the 
 superior Hindoos. The people of Malabar are said to be 
 darker than the natives of other provinces, and approach 
 to, if not equal, the blackness of the natives of Guinea. 
 The Mahrattas are of a yellow tint of complexion, and the 
 natives of the mountainous tracts in the north are of very 
 light colour, and approach to the complexion of Europeans. 
 The Kattees, a race of high caste, are supposed to descend 
 from a tribe on the banks of the Indus. The stature of 
 the Kattee, according to Lieutenant M'Murdo, is larger 
 than common, often exceeding six feet; he is sometimes 
 seen with light hair, and blue-coloured eyes. His frame is 
 athletic and bony. 
 
 The following extract from Dr. Prichard will serve to 
 show, that a physical character like that of the Caucasian 
 variety appears again in the islands of the Southern Ocean. 
 
 The people of New Zealand and the Sandwich Isles, 
 those of the Tonga Isles, and again the inhabitants of the 
 Society Isles, Otaheite, and the Marquesas, display a re- 
 gular gradation from a very dark to a light complexion. The 
 complexion of the New Zealanders varies from a pretty deep 
 black to an olive colour, or yellowish tinge ; and the Sand- 
 wich Islanders are often of a very dark brown colour. In 
 the Tonga Islands the general complexion is of a cast deeper 
 than the copper-brown, though some have a true olive com- 
 plexion, and individuals, principally females, are much 
 fairer. In Otaheite, and the adjacent isles of the same 
 groupe, the most beautiful, and at the same time the most 
 variable, tribe of the whole race is found. " There," says 
 
470 Of the South Sea Islanders. 
 
 Forster, t( nature seems in the human species to follow that 
 richness, luxuriance, and variety, which we have observed 
 in the vegetable kingdom : she is not confined to a single 
 type or model. The common people are of a dark colour, 
 and degenerate towards the appearance of the natives of the 
 New Hebrides; but the better sort have a complexion, which 
 is less tawny than that of a Spaniard, and lighter than the 
 fairest inhabitants of the East India Islands : in a word it 
 is white, tinctured with a brownish yellow ; however, not so 
 strongly mixed, but that on the cheeks of the fairest of their 
 women you may easily distinguish a spreading blush. From 
 this complexion we find all the intermediate hues down to a 
 brown, bordering the swarthy complexion of the race found 
 in the New Hebrides. Their hair is commonly black and 
 strong, flowing in beautiful ringlets. I saw but few with 
 yellowish- brown or sandy hair. But in some instances the 
 decided characters of the true sanguine complexion display 
 themselves even here." Dr. Foster adds, that a single man 
 in Otaha had perfectly red hair, a fairer complexion than 
 the rest, and was sprinkled all over with freckles. Captain 
 Wallis says, that " the hair was in some brown, in some 
 red, and in others flaxen ; but that in the children of both 
 sexes it is generally flaxen." These marks of the fair, or 
 sanguine complexion, which in Otaheite are occasionally 
 seen, appear to be almost general in the Marquesas, the in- 
 habitants of which were thought by Captain Cook to be the 
 finest race of people in the South Sea. " The women and 
 children," he says, " in general terms, are as fair as some 
 Europeans. Their hair like ours is of many colours, except 
 red, of which I saw none." In the accounts, however, of 
 Mendana's voyage, who discovered these islands, it is ex- 
 pressly said, that many of the people had red hair. It is 
 observed, that the general colour among them was almost 
 white, and that they had in person greatly the advantage of 
 the Spaniards. 
 
 The texture of the hair is in general like that of the Ja- 
 vanese, but in some instances it varies. In some of the New 
 Zealanders it is curling ; the Tonga and Sandwich Islanders 
 have occasionally bushy and frizzled hair. 
 
 The features of the Otaheitans are more soft and delicate, 
 
OJ the Kalmucks. 471 
 
 but appear to have a general resemblance to those of the 
 islanders near the Indian continent. The face of these 
 people is said to be handsome, but their noses somewhat 
 flat. In the Tonga Isles, there are hundreds of truly Eu- 
 ropean faces with aquiline noses. The most general trait in 
 the whole race is a fulness of the nostrils, which reminds us 
 of the bottle noses of the New Guinea Negroes. 
 
 III. Of the platy-bregmate or Mongolian variety. 
 
 1. Dr. Clarke has drawn in very strong terms the de- 
 scription of the Kalmucks. " We saw a horde of these 
 people, who were all quite naked, with their skins perfectly 
 black. Their hair is coarse and black, their language gut- 
 tural and harsh. Nothing is more hideous than a Kalmuck. 
 High, prominent, and broad cheek bones ; very little eyes, 
 widely separated from each other ; a flat and broad nose ; 
 coarse, greasy, jet-black hair, scarcely any eyebrows, and 
 enormous prominent ears, compose no very inviting por- 
 trait." 
 
 The following is from a description given by Pallas. 
 " Les traits caracteristiques de tous les visages Kalmouks 
 sont, des yeux dont le grand angle place obliquement en 
 descendant vers le nez est peu ouvert et charnu ; des sour- 
 cils noirs, peu garnis et formans un arc rabaisse ; une con- 
 formation particuliere du nez, qui est ordinairement camus, 
 et ecrase vers le front; les os de la joue saillans, la tete et 
 le visage fort ronds. Us ont aussi la prunelle fort brune, 
 les levres grosses et charnues, le menton court, les dents 
 tres blanches; ils les conservent belles et saines jusques 
 dans la vieillesse. Ils ont tous les oreilles d'une grosseur 
 enorme et detachees de la tete. Les Kalmouks ont Todorat 
 tres subtil, Touie tres fine, et la vue tres pergante. Un grand 
 nombre entre eux disent, en mettant le nez a 1'ouverture 
 d'un terrier, de renard, ou autre bete, si Panimal s'y trouve 
 ou non." 
 
 2. Mr. Frazer thus describes the Tuckehs, one of the 
 Turkoman races in the desert northward of the Elbero-h 
 
 o 
 
 range of mountains and the Steppe of Khaurezm. 
 
 " The Tuckehs have a great deal of the Mongolian phy- 
 
 2 G 
 
472 Of the Tungmiam. 
 
 siognomy; many of the men were tall, stout, and well made; 
 with scanty beards, eyes small, and drawn up at the cor- 
 ners ; high cheek bones and small flat noses. Some on the 
 contrary had handsome features, more resembling those of 
 Europeans than Asiatics." 
 
 3. The persons of the Tungusians are thus described by 
 Gmelin : " Les Tongouses ont le visage conforme a peu 
 pres comme les Kalmouckes ; cependant ils Pont un peu 
 moins large ; il m'a semble qu'en general leur taille etait 
 peu elevee. Leurs cheveux sont noirs, et la plupart les por- 
 tent tresses comme les Chinois." 
 
 4. Pallas thus describes the Northern Chinese. " Ils 
 sont tres bien formes dans leur jeunesse ; on en voit beau- 
 coup qui ont des figures tres agreable, un beau teint, de pe- 
 tits yeux noirs qui forment Tangle, et des cheveux du plus 
 beau noir. Cependant ils preferent ceux qui ont une figure 
 mandshoure, c'est-a-dire, le visage large, de hautes ma- 
 choires, un nez tres large et d'enormes oreilles. Cette der- 
 niere conformation est propre aux Chinois, et presque gene- 
 rale parmi eux. Ils ont la barbe noire, et clair semee ; les 
 gens ages sont les seuls qui la laissent croitre." 
 
 Mr. Barrow informs us, that the Chinese are somewhat 
 taller and more slender than the Mantschoo Tartars. He 
 adds, that " the small eye, elliptical at the end next the 
 nose, is a predominant feature in both the Mantchoo and 
 Chinese countenance, and they have both the same high 
 cheek bones and pointed chins." 
 
 " We saw," observes Mr. Barrow, " women in China, 
 though very few, that might pass for beauties even in Eu- 
 rope. The Malay features prevail in most : a small black 
 or dark-brown eye ; a short rounded nose, generally a little 
 flattened ; lips considerably thicker than in Europeans, and 
 black hair is universal. 
 
 5. Mr. Turner has described the physical character othe 
 Bhoteans, and his description may probably be regarded as 
 referring to the Tibetans in general. 
 
 " The Bhoteans have invariably black hair, which it is 
 the fashion to cut close to the head. The eye is a very re- 
 markable feature of the face ; small, black, with long pointed 
 
Of the Japanese. 473 
 
 corners, as though stretched and extended by artificial 
 means. Their eyelashes are so thin as to be scarcely per- 
 ceptible, and the eyebrow is but slightly shaded. Below 
 the eyes is the broadest part of the face, which is rather 
 flat, and narrows from the cheek bone to the chin ; a cha- 
 racter of countenance first appearing to take its rise among 
 the Tartar tribes, but which is far more strongly marked in 
 the Chinese. Their skins are remarkably smooth, and most 
 of them arrive at a very advanced age, before they can boast 
 even the rudiments of a beard." He adds, " many of these 
 mountaineers are more than six feet high. Taken altoge- 
 ther, they have a complexion not so dark by several shades 
 as that of the European Portugueze." In describing the 
 people of the mountainous districts to the northward of 
 Bhotan, he observes, " I never beheld a more florid picture 
 of health than was exhibited in the complexion of the 
 mountaineers we met to-day ; the women in particular, with 
 their jet black hair, and clear, brisk, black eyes, had a rud- 
 diness, which the most florid English rustic would in vain 
 attempt to rival." 
 
 6. The physical character of the Japanese bears a strong 
 resemblance to that of the Chinese : " they are well made 
 (according to the description of Thunberg), active, free and 
 easy in their motions, with stout limbs, although their 
 strength is not to be compared with that of the northern in- 
 habitants of Europe. The men are of the middling size, 
 and in general not very corpulent ; yet I have seen some 
 that were fat. They are of a yellowish colour all over, 
 sometimes bordering on brown, and sometimes on white. 
 The lower class of people, who in summer, when at work, 
 lay bare the upper part of their bodies, are sunburnt, and 
 consequently brown. Ladies of distinction, who seldom go 
 out into the open air without being covered, are perfectly 
 white. It is by their eyes, that, like the Chinese, these 
 people are distinguishable. These organs have not that ro- 
 tundity, which those of other nations exhibit, but are ob- 
 long, small, and are much deeper in the head, in conse- 
 quence of which these people have almost the appearance 
 of being pink-eyed. Their eyes are dark brown, or rather 
 
474 Of the Inhabitants 
 
 black, and the eyelids form in the great angle of the eye a 
 deep furrow, which makes the Japanese look as if they were 
 sharper sighted, and discriminates them from other nations. 
 The eyebrows are also placed somewhat higher. Their 
 heads are in general large, and their necks short; their 
 hair black, thick, and shining, from the use they make of 
 oils. Their noses, although not flat, are yet rather thick 
 and short." 
 
 7. The inhabitants of Transgangetic India, and of the 
 peninsula of Malacca, exhibit a marked physical affinity to 
 the Chinese. The same character again is strikingly ob- 
 servable in the inhabitants of many of the Indian islands. 
 " The forehead of the Javanese," says Sir T. S. Raffles, " is 
 high, the eyebrows well marked and distant from the eyes, 
 which are somewhat Chinese or rather Tartar in the forma- 
 tion of the inner angle. The colour of the eye is dark ; the 
 nose small and somewhat flat. The beard very scanty ; the 
 hair of the head generally lank and black." 
 
 Let us now pass to the American continent. 
 
 The inhabitants of America are in stature generally supe- 
 rior to the nations of Europe, Asia, and Africa, though to 
 this remark there exist some notable exceptions. Their 
 bodies are remarkably smooth, and devoid of pilar hair, 
 while that of their heads is generally lank, though in some 
 few instances curled, but in none crisp or woolly. Their 
 colour, though not uniform, some being white with a florid 
 complexion, and even with red or yellow hair, while others 
 are nearly black, is yet subject to fewer varieties than we 
 might expect from the diversity of the climates they in- 
 habit, and a coppery hue prevails more extensively among 
 them than in any other department of the human species. 
 
 " The Indians of New Spain," observes Humboldt, 
 " bear a general resemblance to those who inhabit Canada, 
 Florida, Peru, and Brazil. They have the same swarthy 
 and copper colour, straight and smooth hair, small beard, 
 squat body, long eye, with the corner directed upwards 
 towards the temples, expressions of gentleness in the mouth 
 strongly contrasted with a gloomy and severe look." " Over 
 a million and a half of square leagues, from Tierra del Fuego 
 
of the Continent of America. 475 
 
 to the river St. Lawrence and Behring's Straits, we are 
 struck at the first glance with the general resemblance in 
 the features of the inhabitants. We think that we perceive 
 them all to be descended from the same stock, notwith- 
 standing the prodigious diversity of languages which sepa- 
 rates them from one another." " In the faithful portrait 
 which an excellent observer, M. Volney, has drawn of the 
 Canada Indians, we undoubtedly recognize the tribes scat- 
 tered in the Savannahs of the Rio Apuro and the Corones. 
 The same style of features exists in both Americas." 
 
 It has been remarked by several writers, that the cheek 
 bones of the Americans are almost as prominent as those of 
 the Mongoles. In other respects the physical characters of 
 these races are said to resemble each other. " The analogy 
 between them," says Humboldt, " is particularly evident 
 in the colour of the skin and hair, in the want of beard, the 
 shape of the cheek bones, and the direction of the eyes. 
 We cannot refuse," he adds, " to admit, that the human 
 species does not contain races resembling one another more 
 nearly than the Americans, the Mongoles, the Mantchoos, 
 and the Malays." 
 
 The opinion of Von Humboldt has been confirmed by the 
 distinguished naturalists, Von Spix and Von Marius, who 
 were lately sent by the king of Bavaria into South America. 
 These writers have made the following remarks upon the 
 resemblance between the native Americans and the Chinese 
 colonists settled in the Brazils. " The physiognomy of the 
 Chinese was particularly interesting to us, and was in the 
 sequel still more so, because we thought we could perceive 
 in them the fundamental lines which are remarked in the 
 Indians. The figure of the Chinese is, indeed, rather more 
 slender, the forehead broader, the lips thinner and more 
 alike, and the features in general more delicate and mild, 
 than those of the American who lives in woods ; yet the 
 small not oblong but roundish angular rather pointed head, 
 the broad crown, the prominent sinus frontales, the low 
 forehead, the pointed and projecting cheek bones, the 
 oblique position of the small narrow eyes, the blunt, propor- 
 tionately small, broad flat nose, the thinness of the hair on 
 
476 Tendency to heighten artificially Physical Peculiarities. 
 
 iht chin and the other parts of the body, the long smooth 
 black hair of the head, the yellowish or bright reddish tint 
 of the skin, are all characteristics common to the physio- 
 gnomy of both races. The mistrustful, cunning, and as it is 
 said often thievish character, and the expression of a mean 
 way of thinking, and mechanical disposition, appear in both 
 in the same manner. In comparing the Mongole physio- 
 gnomy with the American, the observer has opportunity 
 enough to find traces of the series of developments, through 
 which the Eastern Asiatic had to pass under the influence of 
 the climate, in order at length to be transformed into an 
 American." 
 
 It is among the American races that we meet with the 
 extreme degree of flattening and compression of the head : 
 the instances in which this peculiarity is most marked are 
 some nations of North American Indians, and the Caribs. 
 In these countries an attempt is made artificially to exagge- 
 rate the natural configuration. It is thus that men in all 
 ages have been pleased with the physical peculiarities with 
 which Nature has endowed them. Thus the Mongole and 
 the American, with a rare and late growth of beard, arti- 
 ficially remove the little they possess ; while among various 
 Caucasian nations, the beard, naturally copious, has been 
 at different times carefully preserved and nourished, and 
 associated with the possession of rank, or wisdom, or sanc- 
 tity. It was doubtless in some measure under the uncon- 
 scious operation of a similar feeling that the Grecian artists 
 invented, that ideal form, the characteristic points in which 
 the distinct and regular features thrown below the expanded 
 brow and forehead beautiful as they appear to us, are but 
 the exaggeration of a national contour. 
 
CONCLUSION. 
 
 IN looking over the preceding pages, which I have put 
 together as a compendium of Physiology for the use of 
 students, although little satisfied with the manner in which 
 the different subjects that I have touched upon are treated, 
 I am still less so with the narrow scope which this book 
 embraces: and I am mortified that I have not leisure 
 at present for those comprehensive inquiries which may be 
 said to constitute a higher Physiology. I must content my- 
 self with simply enumerating in what the inquiries to which 
 I refer consist. To several of them it will be evident, that 
 the ordinary course of a professional life is continually con- 
 tributing materials; but that I shall ever have time and 
 knowledge qualifying me to treat the whole in any degree 
 adequately to their importance, I do not venture to anti- 
 cipate. 
 
 I. In the chapter upon embryology, I have mentioned the 
 principal steps which are observed in the development of 
 the human ovum ; and have shown by a few examples the 
 relation of this study to comparative anatomy, and to the 
 history of malformations. In such a work as that which I 
 profess my inability to write at present, one division would 
 consist of a complete exposition of the laws of foetal deve- 
 lopment ; comprising an account of what is common to 
 every instance of reproduction by ova; of the gradual 
 complication and superaddition of changes which are met 
 with in the improving economy observed in the ascending 
 scale of animals; of the reciprocal relations of these im- 
 provements; of the establishment upon these principles 
 of different families of animals, as steps in the march of a 
 loftier organization; and finally of the disturbance or ar- 
 rest of development which may take place in the natural 
 order of mutations which the higher animals exhibit a 
 magnificent series of illustrations of the unity of Nature. 
 
478 Conclusion. 
 
 II. Another head would comprise an account of the 
 alterations which take place in the frame after birth, 
 and are analogous to the changes described in the embryo 
 which precede birth : the history of the successive muta- 
 tions in each elementary tissue and organ of the frame, 
 which attend the growth of the infant to boyhood, to 
 manhood, to old age, closing with decay and dissolution. 
 
 III. A third head in such a work as I am supposing, 
 would comprehend an account of those varieties of struc- 
 ture which casually supervene, either from original weakness 
 of parts, or from circumstances prejudicial to health ; the 
 laws of morbid productions, the conditions under which 
 degenerations of structure present themselves, and the 
 course which they have a tendency to run. 
 
 IV. Under a fourth head would be included the history 
 of those influences, by means of which the growth and 
 health of the frame is modified : the effects of climate, 
 temperature, food, exercise, mental occupation : the agency 
 of these influences when variously modified upon different 
 organs of the body primarily, and by sympathy upon the 
 rest. 
 
 When I began preparing this third edition of my Outlines 
 of Human Physiology for the press, I calculated upon add- 
 ing to it an exposition of some parts of the subjects which 
 I have enumerated. As it is, the improvements which I 
 have made in this volume are much more limited : they will 
 be found in the chapters which treat of the history of the 
 mental phenomena and of the brain ; of the organ of vision ; 
 of the mechanism of speech ; and of embryology. 
 
 FINIS. 
 
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