CIHM Microfiche Series (Monographs) ICIMH Collection de microfiches (monographles) Canadian Inatituta for Historical Microraproductions / institut Canadian da microraproductions hittoriquas Tachnical and Bibliographic Notas/Notas tachniquas at bibliographiquas The Instituta haa attampted to obtain tha bast original copy available for filming. Faaturas of this copy which may ba bibliographically unique, which may altar any of tha images in tha reproduction, or which may significantly change the usual method of filming, are checked below. L'Institut a microfilma la meilleur axamplaire qu'il tui a at^ possible de se procurer Las details de cet exemplaire qui sont peut-Atre uniques du point de vue bibliographique, qui peuvent modifier una image reproduite. ou qui peuvent exiger une modification dans la mAthoda normala de filmaga sont indiquAs ci-dessous. D Coloured covers/ Couverture da eouleur □ Coloured pages/ Pages de eouleur D D Covers damaged/ Couverture endommagie Covers restored and/or laminated/ Couverture restaurAa et/ou pelliculAe 1/ n Pages damaged/ Pages endommag^as Pages restored and/or laiv' Pages restaurees et/ou p ^..-«rl n Cover title missing/ Le litre de couverture manque Pages discoloured, stained 311' a/ Pages dAcolorees, tachetAes &■ ^/ quuas D D Coloured maps/ Cartes gAographiques en eouleur Coloured ink (i.e. other than blue or black)/ Encre de eouleur (i.e. autre que bleue ou noire) a Pages detached/ Pages d^tachees Showthrough/ Transparence ryi Coloured plates and/or illustrations/ \v I Planches et/ou illustrations en eouleur a Bound with other material/ Relii avac d'autras documents n Quality of print varies/ Qualita inAgale de I'imprassion Includes supplementary material/ Comprend du material supplementaire D n Tight binding may cause shadows or distortion along interior margin/ Lareliure serree peut causer de I'ombre ou de la distorsion le long da la marge intirieure Blank leaves added during restoration may appear within the text. Whenever possible, these have been omitted from filming/ II se peut que certaines pages blanches ajout^es lors dune restauration apparaissent dans le texte, mais. lorsque eela Atait possible, ces pages n'ont pas M filmAas. D D Only edition available/ Seule signifie "A SUiVRE". le symboie Y signifie "FIN". Mope, platoa. charts, etc.. may bo filmed at different reduction retios. Those too lerge to be entirely included in one exposure are filmed beginning in the upper left hand comer, left to right end top to bottom, as many frames ss required. The following diagrams illustrate the method: Los cartaa. planches, tableeux. etc.. peuvent Atre filmis i doe taux da rOduction diffOrents. Lorsque le document est trop grend pour Atre roproduit en un soul clichO, il est films a pertir do rengie supArieur geuche. do gauche i droite. et do haut en baa. en prenent le nombre d'imeges nOcessaire. Las diagremmes suivants illustrent la mOthode. 1 2 3 1 2 3 4 5 6 1.0 I.I Li|28 i2.5 tit iU 1^ 136 Hi ■u IL25 III 1.4 tSi I 12.0 1.8 1.6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI and ISO TEST CHART No. 2) PHYSI()L()(a FOR DENTAL STCDKNTS WJy PHYSIOLOGY FOR (g) DEN lAL STUDENTS BY R.G.PEARCE, B.A.,M.D., Associatt' in Physiology, Western .'epcrve University AND J. J. R. MACLEOD, M. B., D. P. H., Professor of PhysioloRy. Western Reserve University HyDNlNh Il.l.LSTKATIUSS, ISCI.UDIS'G TEN COLOR HI.ATES ST. LOUIS >"l ('. V. MOSEY COMPANY 1915 Copyright. 1915. by C. V. Mosby Company PreHH uf St. Louis PREFACE. A knowledge of the fundaniontuls of huiiiHii pliysioloKy in t'sscntiHl in tlu' training of the dental student, beeause phvHioioffy eonstitutes, along with anatomy, the basie seienee upon wiiieli ail medical and snrgieal knowledge ih founded: and dentistry is a highly speeiali/cd department of snrgieal praetiee. To oper- ate on the teeth without knowing something about the physi- ology of the body as u whole, would reduce the dentist to tlw h'vcl of a craftsman who, although perhaps very hijrhly skilled in his technical work, was yet ijuitc ignorant of the nature of th«' machine upon a part of which his work had to be done. Hut there are also practical reasons why the dentist should be familiar with physiology, for good health, and not good looks alone, depends very largely on sound teeth. The neglect of this fact may cause disturbances in bodily functions to which, at first sight, the teeth may apparently bear very h.tle relation- ship; thus, extreme emaciation, with its cons(M|uent lowering of the normal resistance of the bmly towards disease arid infection, is well-known to be fre(|uently due to no other cause than som-- abnormal or ; Mujlogical condition affecting the teeth; and, on the other hand, this ver.v condition itself nia.v bci ome intract- able to the mo.st skilled dental treatment and hygiene, if meas- ures are not taken at the same time to impi'ove the geii.ral health. Although it is obviously beyond the i)rovince of the dentist to undertake the treatment of the.se general conditions, yet it is most important that he should be sufficiently familiar with the normal functioning of the human body to bo able 1c recognize what is really at fault. A knowledge of tlic laws of nutrition and dietetics must therefore form a mo.st important part of every course in dentistry, and these have received particul.ir attention in this book. The physiology of the digestive system, of the cii.'ulation of the blood and of tlie nervous system is sciircely less iniporfant. The pain and shwk i)roduce(i by a denial openslion nuiy cause considerable disturbance in the action of the heart or in the dis- tribution of blood in the bodv, and this di- iirbance, especially V HV VI PBEPACE. ill viiHvH ill whi(*li tho )i<-art and tlii- hlixMi vi'HM'Ih arc digcafU'd, may iM-r-oiiKf HO prnnoiiiict'd aN to render u eertaiii luiiouiit of medical Nki'.l iieeewMiry. Or if, ti» avoid such pain, it Ih> deemed advisublc to adniiniHter aiicHtheMia, then must the dentiHt Im' eoiiHtaiitly on his iniai'd that no more than the proper amount of anesthetic is given, whieli he can do intelligently only hy observing the condition of the nervous ami circulatory systems. Mesides knowing something about the physiology of the body as a whole, the dentist must l)e pnrtieularly familiar with the local physiology of the mouth, such as the finely coordinated nervous mechanisms involved in the acts of mastication and swallowing and the secretion of saliva. He must understand the nature of the sensations of the teeth and Ituecal mucosa, and be on the lookout for any lesions of the cranial nerves that siip- ]>ly the muscles ami other tissues adjacent to the mouth cavity. The chemistry of the saliva has demand* d special attention because of the verv interesting scientific investigations which are Ix'ing prosecutrd ,,'garding the nature of the undoubted relationship that c.xisis between changes in the salivn and the in- cidence of dental caries. To adeipiattly describe tlie present status of this work we have found it neces.sary to devote some space (in the second chapter) to a I'cview of the main i)hysico- cheinical principles which may regidate the reaction and neu- tralizing power of .saliva. Whenever the occasion presented itself to do .so. we hj;ve given a brief deseription of the general nature of the diseases in which dental involvement is possible. A few simple, but very instructive, laboratory demonstrations ai'c described in an appendix at tlic close of the b(K)k. We have found that such demonstrations furni.sh an invaluable aid in the teaching of the subject. To facilitate a clear understanding of the subject, diagrams have been used whenever neces.sary, ami many of these have been .specially drawn for the work. To Prof. T. Wiiigate Todd and Mr ^' if. Spurney, the authors are deeply indebted for the valual issistance which they gave in the prejiaration of these. H. O. I'EARCE. J. J. II. M.\CLE()1). CONTENTS. INTRODUCTOIIY: THi;: CHEMICAL BASIS OK THK CKl.L. Cii.uTEB I. Page The Scope of PhysloloKy— The Physlcachemlcal IteBlB of Ufe- The Chemical Basis of Anlm- ' Tissues— Wat r— Protelns- Lipoids — Carbohydrates 17 ClIAPTRH II THE INFLUENCE OF PHYSICO-CI' ^MICAL LAWS ON PHYSIOLOGICAL ''MCKSSHIF^ iiNZYMES. Propertl' of Crystalloids— Osmotic Phenomena in Cells Hi-ac- tion of Body Fluids— Colloids— General Nature of Enzymes or Ferments ' -♦» ClIAPTKR III. DIGESTION: NECESSITY AND GENERAL NATURE. Digestion in the Mouth— The Salivary Glands— The Nerve Supply of the Salivary Glands — The Reflex Nerve Control of the Sali- vary Secretion— The Normal Stimulus for Salivary Secretion (Direct and Psychological) — General ' unctions of Saliva ;!7 ClIAITEK IV. DIGESTION: THE CHEMISTRY OF SALIVA AND THE RELATIONSHIP OF SALIVA TO DENTAL CARIKS. Organic and Inorganic Constituents — The Reaction of Saliva— The Method of Measurement of Neutralizing Power of Saliva— The Deposition of Tartar and Calculi 46 ClIAITKR V. DIGESTION. Mastication— Deglutition or Swallowing— Vomiting. vii 53 Vlll CONTENTS. Page ClIAITKIl VI. DIGESTION: IN THE STOMACH. Mechanism of Secretion of Gastric Juice— The Active Constituents of Gastric Juice— The Movements of the Stomach— The Open- i.ig of the Pyloric Sphincter — Rate of Discharge of Food from the Stomach KO Chapter VII. DIGESTION: IN THE INTESTINE. Secretion of Bile and Pancreatic Juice — Functions and Composi- tion of Pancreatic Juice and Bile — Chemical Changes Produced by Intestinal Digestion — Bacterial Digestion in the Intestine — Products of Bacterial Digestion — Protection of Mucous Mem- brane of Intestine Against Autodigestion — Movements of the Intestines — The Absorption of Food — Resume of Actions of Digestive Enzymes 71 Chai'tkh VIII. METABOLISM: ENERGY BALANCI-:. Introductory— General and Special Metabolism— Energy Balance - Caloric Value ot Foods — Basal Heat Production — Influence of Food, Muscular Work, Atmosphere, and Size of Body 8;i CtlAPTEK IX. METABOLISM: THE MATERIAL BALANCE OF THE BODY. Starvation-Nitrogen Balance — Protein Sparers — The Irreducible Protein Minimum — Varying Nutritive Values of Different Proteins i»l ClIAl'TKK X. THE SCIENCE OF DIETETICS. The Proper Amount of Nitrogen — Chittenden's Experiments — The Most Suitable Diet for Efficiency —Chemical Composition of the Common Foodstuffs 99 CONTENTS. I CllAI-TKU XI. SPECIAL MKTAROLISM. Special Metabolism of Proteins — Urea— Ammonia— Creatinin — Purin Bodies— Relative Importance of Proteins. Kats and Carbohydrates in Metabolism ix 'age 108 115 U'l i:;i 14(1 147 • CllAlTKIt XII. SPECIAL METABOLISM. Metabolism of Kats— Metabolism of Carbohydrates -Metabolism of Inorganic Salts— Vitamines ClIAI'TKK XIII. THE DUCTLESS GLANOS. Introduction— Thyroid and Parathyroid Glands Adrenal Glands- Pituitary Gland- Spleen— Thymus Gland CilAITKH XIV. ANIMAL HEAT AND FEVEU. Animal Heat— Normal Temperature — Factors Concerned in Main- taining the Body Temperature— Regulation of Body Tempera- ture—Fever CliAITKIi XV. THE BLOOD. Introduction— Physical Properties— The Corpuscles— Erythrocytes —HfBmoglobin— Enumeration of Blood Cells— The Origin of the p:rythroeytes— The White Cells— Leucocytes— Lympho- cytes— Functions of the White Cells— The Blood Platelets— The Blood Plasma CllAlTKIt XVI. THE BLOOD. The Defen.sive Mechanism oi the Blood Coagulation of the Blood — Antibodies in the Blood -^ The Process of Inflammation Toxins— Antitoxins -Ehrlieh's Side Chain Theory— Anaphy- laxis— Phagocytosis— Opsonins # CONTENTS. ClIAPTKR XVII. THE LYMPH. Page Lymph Formation — Lymphagogues — Lymph Reabsorption — The Movement of Lymph 155 Chai'teb XVIII. THE CIRCULATION. Introduction — The Heart — Anatomical Considerations — Physiologi- cal Properties of Heart Muscle — Character of Cardiac Con- traction — The Sequence of the Heart Beat— The Action of Inorganic Salts on the Heart — The Vascular Mechanism of the Heart — Definition of Terms — Events of the Cardiac Cycle — The Heart Sounds — Diseases of the Cardiac Valves 159 Chaitkk XIX. THE CIRCULATION. The Blood Flow Through the Vessels — The Part the Heart Plays— The Part the Vessels Play — Arterial Blood Pressure — p-actors That Maintain the Blood Pressure — Velocity of Blood Flow — The Return of the Blood to the Heart— Circulation Time — The Effect of the Circulation of the Blood Itself— The Pulsa- tile Acceleration of the Blood Flow — The Pulse — The Circula- tion in the Lungs 171 Chapter XX. THE CIRCULATION. The Influence of the Nervous System on the Circulation of the Blood— The Nervous Control of the Heart— The Cardiac Nerves — Accelerator Nerves — Inhibitory Nerves — Interrelation of Inhibitory and Accelerator Nerves— The Cardiac Center — The Cardiac Depressor Nerves— The Nervous Control of the Blood Vessels — Vasomotor Nerves — Vasoconstrictor Nerves — Vasodilator Nerves — Vasomotor Reflexes — The Effect of Grav- ity on the Circulation — Haemorrhage —Chemical Control of Circulation— Asphyxia— Nitrous Oxide— Cocain 184 CONTENTS. XI Chapter XXI. Page THE RESPIRATION. Introduction — The Internal Respiration— Oxidation in the Tissues — Relation of Oxidative Process to Muscular Activity — Physi- cal Laws Governing Solution of Gases — HaBmoglobin — Rela- tion of Oxygen to Haemoglobin — The Mechanism of the Res- piratory Exchange — The Effect of Carbon Dioxide on Oxy- haemoglobin — The Exchange of Carbon Dioxide 197 Chapter XXII. THE RESPIRATION. The External Respiration — Structure of the Lungs — The Mechan- ism of the Respiratory Movements — The Part the Diaphragm Plays — The Part the Thorax Plays — The Movements of the Lungs — Respiratory Sounds — Effects of Respiration on the Circulation — Artificial Respiration — Volumes of Air Respired — Mechanism of Gaseous Exchange in Lungs 207 Chaptkr XXIII. THE RESPIRATION. The Nervous Control of the Respiration — Reflex Respiratory Move- ments — Chemical Control of the Respiration— The Effect of Changes in the Respired Air on the Respiration — Mountain Sickness— Ventilation — The Voice — Mechanism of the Voice — Speech 219 Chapter XXIV. THE FLUID EXCRETIONS. The Excretion of Urine — Composition of Urine— Organic Constitu- ents — Urea — Ammonia — Uric Acid— Creatinin — Inorganic Con- stituents — Abnormal Constituents— The Organs of Excretion — The Blood Supply of the Kidney— Nature of Urine Excretion —Micturition— The Secretions of the Skin— The Swe; Glands — The Sebaceous Glands — The Mammary Glands 229 Xll C(JNTENTS. ClIAiTKB XXV. THE NERVOUS SYSTEM. Page General Nature and Structure of the Nervous System in Different Groups of Animals — Fundamental Elements of the Reflex Arc — Integration of the Nervous System 23!t ClIAlTKH XXVI. THE NERVOUS SYSTEM. Reflex Action — Tha Nerve Structures Involved in the Reflexes of the Higher Animals — The Receptors of Pain. Touch, Tempera- ture — Local Anesthesia and Analgesia — The Afferent F'iber — Choice of Paths on Entering Spinal Cord — The Nerve Center — The Efferent Neurone^Types of Reflexes — Spinal Shock — The Essential Characteristics of Reflex Action — Muscular Tone and Reciprocal Action of Muscles — Symptoms Due to Lesions Affecting the Reflexes -44 ClIAPTKU XXVII. THE NERVOUS SYSTEM. The Brain Stem — The General Course and Functions of the Cranial Nerves, Particularly of the Fifth and Seventli— Relationship of the Fifth Nerve to the Teeth and to Neuralgia— Referred Pain Through this Nerve— Sensitiveness of the Tooth — Tri- facial Neuralgia — Relationship of the Seventh Nerve to Bell's Paralysis 256 Cll.U'TKK XXVIII. THE NERVOUS SYSTEM: THE BRAIN. Influence of the Brain on the Reflex Functions of the Spinal Cord — Functions of the Cerebrum — Cerebral Localization — Experi- mental and Clinical Observations — The Sensory Centers -The Mental Process — Aphasia — The Cerebellum — Relationship to Body Equilibrium— The Semicircular Canals — The Sympa- thetic Nervous System — General Characteristics -The Course of Some of the Most Important Pathways 267 C( )XTKNTS. Mil CllAITKR XXIX. THK SPKCIAL SENSES: VISION. Page Optical Apparatus of the Eye— Formation of I{etinal Image — ( hanges in the Eye During Accommodation from Near Vision —The Function of the Pupil— Imperfections in the Optical System of the Eye— Long and Shortsightedness— Astigma- tism, etc.— The Sensory Apparatus of the Eye— The Functions of the Retina- Blind Spot— Fovea Centralis— The Movements of the Eyeballs— Diplopia— Judgments of Vision -Color Vision — Color Blindness 27H Cll.\l'TKK XXX. THE SPECIAL SENSES. Hearing— The Cochlea— How Sound Waves are Transmitted to Ihi.s by Tympanic Membrane and Auditory Os.sicles— Causes of Deafness-Taste— Nature of Heceptor^ for Taste— The Location of the Four Fundamental Taste Sensations— Rela- tionship Between Chemical Structure and Taste— Association Between Taste, Common Sensation of Touch, and Smell- Action of Certain Drugs on Taste— Smell— Nature of the Re- ceptors of Smell (the Olfactory Epithelium) — Nature of Stimulus III! Cll.\ITKK XXXI. THE MUSCULAR SYSTEM. The General Properties of Muscular Tissues— Contractability— Irritability— The Simple Muscular Contraction -Tetanic Con- traction—Effect of Load— Elaoticity of Muscle — Chemical Changes Accompanying Contraction— Rigor Mortit- :!im CiCAl'TKH XXXII. REPRODUCTION. Fertilization — The Accessory Phenomena of Reproduction in Man— Female Organs— Male Organs— Impregni'tion— Ovulation — Pregnancy — Birth :!().■; APPENDIX. Fundamental Demonstratiou In Physiology ;itiit Pig 1. 2. 3. 4. 6. 8. !t. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. ILLISTHATIONS. I'age Dlalysor 27 Cells of parotid gland showing zymogen granules 40 The nerve supply of the submaxillary gland 41 The changes which take place in the position of the root of the tongue, the soft palate, the epiglottis and the larynx during the second stage of swallowing 53 Diagrams of outline and position of stomach as indicated by skiagrams taken on man In erect position at intervals after swallowing food 61 Diagram of stomach showing miniature stomach separated from main stomach by a double layer of mucous membrane 62 Diagram of time it takes for a capsule containing- bismuth to reach the various parta of the large intestine 80 Diagram of Atwater-Benedict Respiration Calorimeter 86 Dietetic chart (colored plate) 104 Cretin, 19 years old 126 Case of myxoedema 127 Photographs showing before and after onset of acromegalia symptoms 1,'52 Thomas-Zeiss HsBmocytometer 142 Diagram of circulation (colored plate) 158 Position of the heart in the thorax 160 Generalized view of the vertebrate heart 161 Diagram of valves of heart 162 Dissection of heart to show auriculo-ventricular bundle 165 Diagram showing relative pressure in auricle, ventricle and aorta 168 Diagram of experiment to show how a pulse comes to disap- pear when fluid flows through an elastic tube when there is resistance to the outflow 173 Apparatus for taking tracing of the blood pressure 174 Apparatus for measuring the arterial blood pressure in man.. 176 Jacquet Sphygmocardiograph 181 Pulse tracing made by sphygmograph 182 Effect of stimulating vagus and sympathetic nerves on the frog's heart 185 Tracings of arterial blood pressure 186 Curve chart 203 Diagram of structure of lungs, showing larynx, bronchi, bronchioles and alveoli , . , 207 XV XVI Kig. 2!t. :{(). :n. •■!:•. .'!:!. :'.4. r.b. ,-.8. nit. 40. 41. 4J. 4:!. 44. 4."). 46. 47. 48. 4ii. r>(t. oi. 54. 55. 56. 57. 5S. 59. nAA'STR.\TiOSii. Page Thf poHition of the IiinRs in the thorax I'dit llering'B apcaratiiH tor deiiionHtraiiiiK the attion of the respir- atory pump 210 Diagram to «how nioveiiient of diaphragm during respiration L'll Position to be adopted for effecting artificial respiration 215 Diagram of laryngoscope 225 Position of tlie glottis preliminary to the utterance of sound. . 226 Position of open glottis , 226 The position of the tongue and lips during the utterance ot the letters indicated 228 Diagram of the uriniferous tubules, the arteries and the veins of the Itidney (colored plate) 2:!2 Diagram of urinary system 2'i6 Schema of simple reflex arc 240 Diagi. m of nervous systeu; of segmented invertebrate 242 The simplest reflex arc in the spinal cord 244 Diagram of section of spinal cord, hhowing tracts 247 Reflex arc through the spinal cord, in which an intermediary neurone exists between the afferent and efferent neurones (colored plate) 247 Course of the pyramidal fibers from the cerebral cortex to the spinal cord (colored plate) 248 Under aspect of human brain 257 Vertical transverse section of human brain 258 Diagram of the dorsal aspect of the medulla and pons, show- ing the floor of the fourth ventricle with the nuclei of origin of the cranial nerves (colored plate) 260 Diagram to show areas of referred pain in distribution of fifth nerve due to affections of the various teeth (front view) (colored plate) 262 Diagram to show areas of referred pain in distribution of fifth nerve due to affections of the various teeth (side view) (colored plate) 264 Cortical centers in man 270 The semicircular canals of the ear, showing their arrange- ment in the three planes of space 276 Formation of image on ret'"". 281 Section through the anterior portion of the eye 282 A, spherical aberration: B, chromatic aberration 285 Errors in refraction 286 Semidiagrammatic section through the right ear 292 Diagrammatic view of the organ of Corti (colored plate) 292 Tympanum of right side with the auditory ossicles in place. . 2!i4 Schema to show the course ot the taste fibers from tongue to brain 296 Page 1'0!« 'Bpir- 21(» ation 211 215 22.". iid. . 22« 22« •e ot 228 reiiiR 2:!2 2.!6 240 242 .... 244 247 to 247 248 257 258 261) 262 264 270 276 281 282 285 286 292 292 204 296 PHYSIOLOGY FOR DENTAL STUDENTS CHAPTEK I. IXTRODICTOHY: TIIK CHK.MICAL HAvSIS OF THE CELL. The Scope of Physiology.— Pliy.siology i.s tlio study of tli.' Iiliciioiiieiia ot" living things, just jis auatomy or morphology is a study of tlit'ii- structuiv. Tlie study of auatomy is most logically pursued by starting with the simplest oi-Kanisms and frradually proccediiifj through the mon- complex f^vrms until nmn is reached. E.xcept for certain fundamental functions, such as nutrition, which are common to all cells, this methcMl is not the most suitable one to pursue in physiology, because in the low- est oiganisms all of the functions are crowded together in a lim- ited number of cells— indeed, it may be in one single cell. It is easier to study a function when it is performed by a tissue or org II that has been set apart for this particular purpose than wiien it is performed by cells tiiat do many oX\. v things. Another reason for i)aying more attention to the functions of higiier rather than lower animals is that the knowledge which we ac(|uire may be more directly applicable in explaining the functions of man, and therefore in enabling us more readily to detect and rectify any abnormalities. During the embryonic development of one of the higher ani- mals, a single cell, the ovum, j)roduees numerous other cells, which become more and more collected into groups, in many of which the cells undergo very marked changes in sha|)e and structure, or produce materials, such as the skeleton or teeth, which show no cell structure whatsoever. Thus we have formed the tissues and organs, each having some particular function of 17 I 18 PIIYSIOLCKiY FOR DKNTAI. STl'DKNTH. itH own, althouRh rertaiii fuiu'tions rt'inaiii whicli arc i-oimuon to all. Ill other words, as tin- organism Im'coiucs iiioit! aiul iiiorc conipli'X, tlurc eoiiics to 1k> a division of labor on tli« part of the cells that eoiiipriso it. The eoiulitions are exactly like those which obtain in the development of a community of men. In primeval communities there is little division of labor, every indi- vidual makes his own clothes, hunts his own foml, manufactures and uses his own implements of war. but as civilization b«'giii8 to appear, certain individuals specialize as hunters and fighters, others as makers of clothing, others as artisans. Although, in its first stages, this division of labor may be far from absolute, for every member of the community must still fight and take part in the building of his hut. yet it soon tends to become more and more so, until, as in the civilized communities of this twentieth century of ours, specialization has become the order of the day. A good example of a (me-celletl animal is the amaba, which is often found floating in stagnant water, and which consists of nothing more than a mass of tissue, or protoplasm, as it is called, and yet this apparently simple structure can move from place to place, it can pick up and incorporate with its one substance par- ticles of food with which it comes in contact, it can store up as granules certain of these foodstuffs, and get rid of others that it does not recjuire ; it grows as a result of this incorporation, until at last it splits in two and each half repeats the cycle. In other words, this single cell shows all of the so-called attributes of lii'e : movement, digestion and assimilation of food, growth and repro- duction. No one of these properties is necessarily confined to living structures alone, for some perfectly inanimate bodies may exhibit one or other of them, yet when all occur together, we consider the structure to be living. In the higher animals, these functions are performed by the so-called systems, such as the digestive, the circulatory, the res- piratory, the excretory, the motor, the nervous and the reproduc- tive, each system being composed of certain organs and tissues which are designed for the special purpose of carrying out some particular function or functions. One function, however, is com- mon to all of tiie organs and tissues, namely, that of nutrition, TIIK CIIKMICAI, BASIS (iK TIIK (KM,. 19 wliidi iiifliiilt's the pioct-sN by wliicli tlio ili^fstcd I"(mh1 is Imilt up into the ])rot()|)lasiii of tlic cells, or assimilation, ami tlmt by which the rcsultiiiK Hiibstaiic<>s an- broken down a^ain, or difuiH- siniilution. It is by these pnM-esses that the energy of life is set free; the enorj?y hy which the tissues jiert'orm their fi ■•etions, and which appears as bmly heat. Every cell in the animal luMly is therefore a seat of energy production, and at the sanit! time each is a machine for converting this energy into some definite form of work. In this regard the animal machine is quite unlike a steam engine, where energy liberation occurs in the furnace, but conversion of this to niovenumt occurs in the pistons. The furnace and the machinery of the animal body are part and par- eel of the same structures, and the digestive, circulatory, respira- tory and excretory systems arc moi-e highly speciali/cnl for tlio.purpos«? of transporting fuel, the oxygen to burn it and the gasra j)roduced by its combu.stion to and from tiie Hying cell. These processes of as.similation and disa.ssimilation constitute the study of metabolism, the i)raetical side of wiiich is included in the .science of nutrition. The Physico-chemical Basis of Life. "With tlie object of ascertaining to what extent the known laws of i)hysics and chemistry can explain the fundamental proce.ss«>s that are common to all cells, we must make ourselves familiar, first of all, with the chemical and ph" < ture of the constitu- ents of the cell, and secondly with i.ysieo-chemieal laws which govern tin- reactions that take [tiace betwwn these con- stituents. The same laws will control the reactions which take place in the juices secreted by cells: for example, in the ;;'>od and in the secretions, such as the saliva. The Chemical Basis of Animal Tissues.— Certain substances are found in every living cell and in approximately e(iual quan- tities; hence these may be considered the primary constituents of protoplasm. In general they consist of the proteins, lipoids, in- organic salts, water, and probably the carbohydrates. Protoplasm is the substance composed of these primary constituents. By its 20 PIIVSIOLOOY FOR DENTAL STfDENTS. ai'tivity the protoplasm prtMluccs thi- .s^vomlnnj constituents of the cell, which arc not the same in all ccIIm. aiul which include the Krnnulcs of pigment or other matrrial, the mass«'s of nflycogi-n, the kIoIiuIcm of fat or the vesicles of fluid which are fouml em- lM'«l(led in the j)rotoplasni. ]iy what«'ver prwess we 'ittempt to isolate itn constituentH, we of course kill the cell, ho that we r THE CKl.U. 21 later in connoption with ioiii?.atinn. Wator has hIho a vrry (front surface toiiHlon. It is this which ilctcrniiiics the hci^lit to which it will Hsu in plants and in the soil, and which no doubt plays a role in tho prooessps of absorption Ko'iug on i'l various parts of the animal boensable in- Rredients of food. An animal fed on food containiiiK no protein will die nearly as soon as if foo PHYSIOLOGY FOB DENTAL STUDENTS. molecules, which can be further resolved into simple crystalline substances. These have boon callod the building stones of the protein molecule, and altliough llioy differ from one another in many respects, they have one feature in common, namely, that each consists of an organic acid liaving one or more of its hydro- gen atoms* substituted by the radicle, NIL. Such substances are called amino bodus. For example, the formula of acetic acid is CILCDOn. If for one of the 11 atoms there is substituted the NIL group, wo luivc CII,NILCOOII, which is amiini acetic acid, or glycine. Tlie same sort of substitution may take place, not alone in the simple organic acids containing one acid group, but also in those containing two acid groups, as in amino-succinic acid, coon. CIL (NIL) coon, or in acids containing the aro- matic or benzene ring group, as in the case of tyrosine, C,.,H40H. C,H,. NIIoCOOII, or again there may be two amino acid groups present, as in the diamino acid, ornithin or diamino- valeric acid, C,IL(NlL)X"OOII. That the large aiid complex protein molecule is really built up out of these amino bodies lias boon very conclusively shown by Eniil Fischer, wlio suecoodod in causing two or more of tiiem to become united to form a body called a j^oh/pcptid. When sevoral amino bodies were thus synthesized, the polypeptid was found to possess many of the pi-<)i)ortios of peptones, which we have just stated are the earliest decomposition products of protein. Proteins differ from one another, not only in the nature of the amino bodies of which tlit y are composed (although certain of these are common to all proteins), but also in the manner in which the amino bodies are linke!M. The proteins of the cell are classified into two groups. The first includes the simple i)roteins, such as egg and serum albumin ; and the second, the compound proteins, from which non-protein groups can bo split off. As i)riiiijiry coll oonstituonts, the follow- ing siiiii>lo ami compound protoins are important : albumin, globulin, nuoleoprotoin, ami tlu; glycoproteins. They are all of the nature of colloidal substances (see p. .'52), and therefore are THE CHEMICAL BASIS OP THE CELL. 23 either precipitated or coagulated when solutions containing them are boiled or have inorganic sjilts dissolved in them. Albumins are characterized chiefly by their great solubility in water. Three forms are of importance : egg albumin, lactal- bumin of milk, and serum albumin. Globulins occur principally in the muscle proteins, and arc insoluble in water, but soluble in dilute neutral salt solutions. Jlany consider that the albumins and globulins are only nutri- tive materials from which the protoplasm manufactures the compound proteins which are the essential cellular proteins. Xuclcoprotcins, both in (juantity and in relation to their activ- ity, are probably the most important constituents of the cell. They have a very comi)le.x structure, and occur in many varieties. They consist of a combination between protein and a substance called nucleic acid, which, on being broken up by chemical means, yields phosphoric acid, a simple sugar called pentose, and nitrogenous substances known as purine bases, and pyrimidines. The purine bases are of great interest, because they are the ante- cedents in tile body of uric acid, which, being relatively insolubh'. may become deposited from the bwly fluids and cause gout or gravel. That it is possible to have an enormous variety of nucleo- proteins can be imagined wlien we consider that there exist differ- ent sorts of purine ba.s(»s, of carbohydrates, and of amino bodies. The nucleus of the cell contains a nucleoprotein which is particu- larly rich in purin bases and is often called nuclein. Phosphoproteins are compounds of phosphoric acid and simple proteins, without any nucleic acid. An example is the casein of milk {.see j). 105). Gli/coprufi'ins are compound of carbohydrates with proteins. The mucin of saliva is an example (see p. -46). Insolubh proteins resemble the coagulated proteins, and are left behind after tlie extraction of the other proteins from the cell. •liii>()M)s. — These include all tlie substances composing a cell whicli are soluble in fat solvents. Hesides fats anhoric acid, and a nitrogenous base called cholin. Choli alirol is another widel.v distributed lipoid. It is not in reality a fatty body, but i'ath«'r resembles the terpcues. Leeitliin anil cholesterol are abundant in brain tissue, in the envelopes of erythrocytes, and in bile. Th< fats exist mainly as secondary con.stituents of the cell, being dei)osited in very large amounts in certain of the connective tissue cells of the bmly. in bone nuirrow and in the omental tis- sues. Chemicall.v. the tissue fats are of three kinds: olein. pal- mitin, and stearin, each having a distinctive melting point. They are compounds of the tri-valent alcohol, glycerine, and one of the higher fatty acids, oleic, palmitic, or stearic acid. Besides those that arc present in the animal tissues, fats made up of glycerine coiJibined with various lower members of the fatty acid scries occur in such secretions as milk. In order to understand the influence which fats have on general metabolism, it is important to remember that they differ from the carboiiydrates in contain- ing a very low |)ercentag»> of oxygen and a relatively high ])er- centage of hydrogen and carbon. Thus, the empirical formula of palmitin is <'o,II,,..0,, or r,n.((',eH.n( ).").;. that of dextrose C«H,,0„. and of protein r,,H,,„X,sO,„S. The Carbohydrates are also mainly secondary cell constitti- ents. although it is becoming more and more evident that they are also neces.sary as primary constituents. In general they ma.v l>e defined chemically as consisting of the elements (_', II, and <>, the latter two being present in the molecule in the same proj)or- tion as in water; thus, the fornuila for dextrose is C,,!!,^.!),;. The basic carbohydrates arc the simple sugars or motiosat- charidis, .such as grape sugar or dextrose. When two molecules of monosaccharide become fused together with the elimination of a molecule of water (tliiis giving the formula <\_,ir,_.(),,), a secondary sugar or disaccharide lesulls. ("ane sugar, lactose (or milk sugar) aiul maltose (or malt sugar) are <'xamples. If sev- eral nonsaccharide molecules similarly fuse together, polysav- THK CHEMICAL HASIS OK TIIK CKI.L. 25 c^ iirkhs liHviiig the formula (C,iIT,„0.)„ arc forint-il. Those in- I'lude the dcxtrincs or gums, glycogon or animal stai-ch, the ordi- nary starches, and cellulose. Since so many molecules are fused together, it is not to be wondered at that there should be so nmny varieties of «'ach of these classes of polysaccharides, for, as in th(( case of proteins, not only may the actual ''building stones" of the molecule be diffei-ent, but tiiey may be built together in very diverse ways. The polysaccharides may lu' hydrolyzed ( i. e., caused to take up water and split up) into disaccharides, and these into monosacchariilcs by boiling witli acids or by tiie action of diastatic and inversive ferments (see [). -Hi). CHAPTER II. THE INFLUENCE OV PHYSICO-CHEMICAL LAWS ON PHYSIOLOGICAL PROCESSES: ENZYJIES. Having Icaniod of wliat niatorials tlio ecll is coinposod, wo may proceed to cn(|uire into the clioniical and physical reactions by wliich it performs its functions. Tiie cell, eitiier of plants or of animals, i' v be considered as a ciieinical laboratory, in which definite reac iis are constantly jjoing on, being guided, as to their direction and scope, by the piiysical conditions under which they occur. A study of the material outconit; of tluse reactions constitutes the study of metabolism, to which special chapters are devoted further on. At ])resent, however, we must briefly examine the j)hysico-ehemical conditions exi.sting in the cell vvhieh may give tiie directive influence to the reactions. Wiiy should certain cells, like those which line tiie intestine, absorb digested food and pass it on to the bloo( physical chemistry, the cell may be considered as a collection of two classes of chemical substances, CRYSTALLOIDS. 27 called crystalloids and colloids, dissolved in water, in the lipoids, or in each other, and surrounded by a membrane which is per- meable towards certain substances but not towards others (semi- permeable, as it is called). On a larger scale, the same general conditions exist in all of the animal fluids, such as the blood, the lymph, the secretions and the excretions, so that we may stu«ly the laws with a view to applying thorn to both cells and body fluids. Properties of Crystalloids.— As their name implies, these form crystals under suitable conditions. When i)resent in solu- tion they diffuse quickly tlirougiiout the solution, and can readily Kit;. I. — Kiiilyscr mailc nf tul>c of imrohnu'iit paiicr suspfiulcii in a vfs.scl iif distilled wattT. The fluid to be dialyscd is rilaced In the tul)e, and the distillfd water must be fiequ- ntly changed. pass t^'-ough membranes, such as a piece of parchment, placed hoU le solution containing thtm and another solution. This prot , called diaf • •, and tiie apparatus used for observing it, a iimujarr (see Fig. 1). Dialysis differs from filtration, tiie latter process consisting in the pa,s.sage of fluids, and the sub- stances dissolved in them, thi'ough more or less pervious mem- branes as a result of differences of pressure on tlie two sides of the membrane. If instead of using a simple membrane, such as l>archment, we choose one which does not i)ermit the crystalloid itself 1o diffuse, but permits the solvent to do .so — a simiix rmcnhir mnnhrtinc, as it is called, — a very interesting property of dis- solved cry.stalloids comes to light, namely, their teudem^y to ex- L'8 lMIVsl(»l,»XiY FOR DENTAL STUDENTS. jmiid in the solvci'.t, that is, to take up morp room by attracting the solvent through the membrane. Cell membranes are semi- permeable, but they are too small and delicate for experimental jturposes, for which we use one compoH<'d of a precipitate of copper ferrocyanidc supported in tlie pores of an unglazcd clay vessel. If a solution of a crystalloid — say. cane sugar — be placed in such a vessel and tins then submerged in water, it will be found that the cane sugar solution (|uickly increases in volume, or, if tliis be preventtnl by closing uj) the vessel and connecting a pres- sure gauge with it. a remarkably high pressure will become devel- oped. Tills is called osmotic prfssun, and it is a measure of the tendency of dissolved crystalloids to expand in the solvent. It has been found that the laws which govern osmotic pressure are identical with those governing the behavior of gases. Therefore, the osmotic pressui-e would be expected to be proportional to the iuunber of molecules of tiissolved crystalloid and such is the case for the sugars, but it is not .so for the saline crystalloids, such as the alkaline chlorides, nitrates, etc. These cause a greater osmotic pressure tiiaii we should expect from their molecular weights. Why is this? The answer to the ((uestion is revealed by olwerving the behavioi- of the two classes of crystalloids towards tln' electric current. Solutions of sugars or urea do not conduct the current any better than water, whereas .solutions of saline crystalloids conduct very readily. The former are therefoi-e called tion-fhclrohjf(s and the latter dectroh/tfs. The reason for these differences has been found to be that molecules of electro- lytes when they are dissolved break into parts called "ions," and each ion carries a charge of electricity of a certain sign, i. e., positive or negative. Whenever an electric current is passe«l througti the .solution, the ions, hitherto distributed througimut tile solution in pairs carrying charges of opposite signs, now line themselves up so that the ions with one kind of electrical charge form a chain across the solution along wiiicli that kind of elec- tricity r<'adily pas.ses, and in so doing carries the ions with it. This .splitting of ebvirolytes into ions is called (lissorintioii or iotnzation. The ions which carry a charge of positive electricity and which tiierefore travel towards the kathode or negative jiole CRVSTAM.(ims. 29 (since uiilik»; t'li'ctricitii'S attract caeli other) are eall<>tl kalhions, ami the nepitively eliarjjed ions tliat travel to tl»e ano swdlinjf. to its diffusion in; tiiat is to say, in the former ease the osniotie pressure of the surrounY KI.I 1I>S. 31 proi'OSKt's piocffd, tliat drpciul on llic coiu'ciitnitioii of Il-ioiis. The convci-sioii of cane supar into invert sii^jar is a wood priM-esM to employ for measuring tlie speed of reaction. But even this refinement in teelini(pie dws not enable us to measure the II -ion concentration — for now we must use tins ex- pression when speakinp of aeidity or alkalinity — of such impor- tant fluids as blood and salini, in whieh there is an extremely low H-ion concentration. If either of these fluids be jdacwl on litmus papers, the red litmus turns blue, but all that this sifjnifies is that the litmus is a stronjjer acid than those present in blood or saliva, so that it decomposes the bases with which tht-y were combined and changes the color. If we emi)loy i)henolphthalein, which is a much fwbler acid, then blood serum reacts neutral and saliva often acid. There are two methods open to us for measuring the Il-ion concentration in such cases: 1. The Iljjdrojjot Ehitrode. — Place the fluid (e. g., blood serum or saliva) in a snuiU closed vessel filltMl with hydrogen ami with a platinum electrode dipping into it. Connect this hydro- gen electrode with a standard calomel eleetro«le by wires in the course of which are suitably arranged electrical instruments for the measurement of electromotive force. From the ditferencc in the electromotive force which is found to exist between the hydro- gen and the calomel electrodes, we can calculate the H-ion con- centration. This method is being employed for measuring the reaction of saliva in relationship to its influence on caries of the teeth. 2. The Use of Standanlized Indicators. — It has been found that different indicators change color at different H-ion concen- trations. Hy taking solutions with variable known proportions of acid and alkaline salts such as NhIIoPO^ and NaoIIP04 or NallCOj and measuring their actual acidity in terms of the H-ion concentration — by the electi'ical method — and then observ- ing their behavior with different indicators, it has been possible to e\'aluate the different indicatoi*s in terms of the H-ion concen- tration at which they change color. Expressing the results as the fraction of a normal solution of H-ion at which this change 32 •IIVsKIMMiy KilR DKNTAI, STCDENTS. I (M-eiirs. it has lictii foiiiul that iiaiaiiitro-iilit'iiol turns at about .000.001 (or 1 X 10 " I, which is the ll-ioii foiicfiit ration of [lurc water, and is thcrcfoii- the most |»nictical |)oint to chooso as iinli- catiiiR neutrality. .Methyl red and rosolie aeid also change color about this ])oiiit. Phenolpiitlialeiii. on the other hand, changes color at a 11-ion concentration of 1 .\ 10 ', i. e., its is very sensitive towards acids, and methyl orange, at 1 .\ 10-^, i. e., it is relatively insensitive towards acids. The indicators wliich ciiange color at about the Il-ion concen- trations found in animal fluids are rosolie acid, paranitrophcnol and methyl red. \\y comi)arinR the color prwluccd by adding one of these indicators to the unknown fluid with those obtained by adding the same indicator to a series of .solutions containing varying but known Il-ion concentrations, we can accurately tell the Il-ion concentration of the unknown solution, for the Il-ion concentration of the solution whose tint matches with that of the unknown is the Il-ion concentration of the latter. The series of .standard solutions is nuulc by mixing varying proportions of acid and alkaline phosphates. Before leaving this sub.ject. it is important to point out that the blootl lias an Il-ion concentration wliich is jiractically the .same as that of water, i. e., is as nearly neutral as it could be. It also has the power of maintaining this neutrality practically con- stant even when large amounts of acid or alkali are added to it. Although saliva and .some other Ixxly fluids sire not .so nearly neutral as blood, yet they can also lock away much acid or alkali without materially changing the Il-ion concentration. This property is due to the fact that the body fluids contain such salts as phosphates and carbonate's, which exi.st as neutral and aeid salts, and can change from the one state to tlie other without greatly altering the Il-ion concentration, and yet. in so changing, can lock away or liberate II- or Oll-ions. This has been called the "buffer" action, and is a iiip.st important factor in maintain- ing constant the neutrality of the animal body. Colloids. — These are substances which do not diffuse through membranes when they are dissolved. Thus if bloml scrum be placed in a dialyser which is surrounded by distilled water, all rot,M»ins. 33 tlic prystalloiils will (litTuHt- out of it. Ifiivinn tin- <'ollt)i(ls, wliicli (•onsist iiiHiiily of prott-iiis. The physicjil rciisoii for this failure to (lifTiiMt* is tli<> larK*' ^i/-*' <>f tin' inolfciilcs, in coinparison with till' small si/c of those of thf crystalloids. My caiisiiiu a hfaiii of liffht to jmss through a colloitlal solution and holding a iiiicro- scopc at rifjlil an^jlcs to this licain. the i-olloidal partii'h-s Im-comm' <'vi«lt'nt, just as particlis '•♦" dust hi'conit' evident in Uw air of a room in a beam of daylight. In eontirmation of this view of the cause of the indilfusihility of colloiils is the fact that filters can Im' made of un^la/.cd porcelain impregnated with (;elatin. in which the pores are then-fore very minute, through which col- loids cannot pass, though water and inorganic salts do so. When l»l(H)d .serum is filtered through such a filter, tln' filtrat*- contains no trace of protein. The colloidal molecules can also very readily be caused to fuse together, thus forming aRgrejiates of molecules which become so larjjc that they either confer an opacity on the solution or actually form a precii>itate. This fusinjr together of colloidal particles can be brought about either by adding certain neutral salts or by mi.xing with certain other colloids. The ex])lanation of these results is as follows: colloidal molecules carry either a positive or a ne(^..tive electrical charge, and when this is neutralized, the colloidal molecules fuse together, i. e., become aggregated. This neutralization of elec- trical charge can be brought about either by adding an t'lectro- '.vte. one of whose ions will supply the proper electrical chui'ge, or by a colloid having an opposite charge. Tlnus the SO4 anion of Xa;S(J^, in virtue of charges of negative electricity which it carrier ill very readily i)reeipitate such a colloid as eolloidal iron (lerrum dialysatum, V. S. P.), which is charged with posi- tive electricity; or again, this colloid itself will readily preci|»itate arsenious sulphide, another colloid carrying a negative charge. The physiological importance of the.se reactions lies in th<' fact that they probably explain many of the peculiarities of behavior of mixture« of different animal fluid.s. such as toxins and anti- toxins (see p. 149). A property of colloids winch is closely related to the above is that of adsurpfion. This means the tendency for dis.solved sub- M l'IIYsIOl,K\'r.\I< STrPF.NT!*. HtuiiCPN to Im'coiih' pomlt'imcd or coiiceiit rated at the surlacc of colloidHl inoli-ciilcH. An fXHinph* '\n the wt'U known action of chan-oal wlu-n Nhakt-n with colorftl solutions, [t nMiiovcs the piif- inent by adsorbinK it. Atlsorption is duo to xurfarr ti imion, which is the tciiHioii croatt'd at th»> surface In'twccn a solid and a liijuid, or Iwtwccn a li(|uid and a gas. It is in virtue of siirfacc tension that a raindrop assumes more or less spherical shape. Since colloids exist as particles, there must be an enormous num- ber of surfaces throughout the solution, tl'a, is. an lMiohi .>."< sur- face tension. Now many substances, when in solution, have the power of decreasing the surface tension, and in doing so it has been found that they accumulate at the surface, that is to say, in a colloidal solution, at the surface of the eolloidal molecules. The practical application of this is that it helps to explain the p' vsical ci.cmistry of the cell, the protoplasm of which is a eol- loi.i j) solution containing among other things proteins and liptflds. The latter depress the surface tension and therefore collect on the surface of the cell and form its supposed mem- brane, whilst the proteins exist in colloidal .solution inside. It is possibly by their solvent action on lipoids that ether and chloro- form 80 disturb the condition of the rerve cells as to cause anes- thesia. General Nature of Enzymes or Ferments. To decompose proteins, fats or carbohydrates into siinjile mole- cules in the laboratory necessitates the use of powerful chemical or physico-chemical agencies. Thus, to decompose the protein molecule into amino bodies retiuires strong mineral acid and a high temperature. In the animal body similar processes occur readily at a comi>aratively low temi)erature and without the use of strong chemicals in the ordinary sense. The agencies which bring this about are the enzymes or ferments. These are all col- loidal substances (see p. ;}2). so that they are readily destroyed by heat and are precipitated by the same reagents as proteins. They are capable of acting in extremely small quantities. Thus, a few drops of saliva can convert large quantities of starch solu- tion into sugar. During their action, the enzymes do not them- l \ ENZYMK8. 35 srlvi'H iiikIitko jiiiv pfmiaiH'iit cliaiiKt'. for <'Vfii afti-r tln-y have IwfH actiiiK for a lonn time, tlioy fan still k<» <»" i"K thoir work if fn'Hli Tiiati'i-ial Im- Hiip|)lit'to|>lasin is incfssary to bring the suhstrat in contact witii thcni. On this aico\n)t enzymes used to he dassitietl into orf/uiiUi d and nii(>ry variouis routi-s: those to the submaxillary and suit- lingual glands in the chorda tympani. and those to the jtartoid l)y way of the tympanic branch of the <;losso-pliaryngeal. The ganglion cells connected with tl.e cerebral fibers are situated more or less jteripherally ; in the case of the subnuixillary they are embedded in the substance of the gland; in the case of the sublingual gland, in the connective tissue of the so-called submaxillary triangle, and in the case of the jtarotid, in the otic ganglion (Fig. ;i). In both cerebral and sympathetic nerves there are two vari- eties of fibers, the one nisotnotur, the other s< cnforii. The for- Kij;. ;{, The in-ivi- siipiily of tln' sul'iiiiixilhiiy kI;iiii1 : l.i. !iii«unl iici\e: r. t., chorda t> inpaiii : ;/. Kb'iid Whaiton'.s duct is liKatcd and it wiU In- 'noticed that the chorda leaves tile linKUal nerve. Just Itefore tills criiss.s the duct, thus foinniig the .subniaxillaiv liianKle, ((Maude Bernard.) mer. in the cas.' of the cerebral nerves, are dilator in their action, but in the sympathetic they are constrictor. On account of the association of secretory and vasodilator fibers, in the cerebral nerves, stinndation leads to the secretion of large (|uantitie.s of saliva, the amount of which, as well as its percentage of organic and inorganic constituents, varies within certain limits, with the strength of the stimulus. Althougli .secretory activities also be- eomo excited when the sympatlietic nerve is sfimulaled. as is 42 PMYSIOLiXJV FOB DKNTAL STUDENTS. revealed by histolopioal exainination of the gland, there is only a slight flow of saliva from the duct beeause of the eonconiitant eurtailment of the blood supply. In so far as actual secretion of saliva is concerned, the net result of stimulation of either nerve is therefore dependent tlpon whether dilatation or constriction of the blood vessels of the gland occurs, and this might lead us to conclude that the secretion is secondarj' to changes in the blood supply ; in other words, that it is unnecessary to assume the independent existence of specific secretory nerve impulses. That such secretory fibers do exist, however, is established by many facts. Two of these are: (1) The vessels still dilate but no secretion o<'Curs after a certain amount of atropin has been allowe'd to act on the gland. This alkaloid paralyzes the secre- tory nerve fibers, but has no action on those concerned in vaso- dilation. (2) If the secretions were merely the result ot in- creased blooil sui)ply, in other words, were a filtrate from the blood, the pressure in the duct would at all times be less than that in the blootl ve.s.sels, but this is not the case, for dui-ing stim- ulation of the cerebral nerves the duct pressure may rise far above that of the blood vessels. But it must never be lo.st sight of that although both kinds of fibers do exist, thry are very closely associated in their action. The Reflex Nervous Control of Salivary Secretion.— The structural differences between the parotid and submaxillary glands suggest that their functions may not be the same; that their respective secretions nuist be rei|uired for different pur- poses. To put this suppf)sition to the test, it becomes Jiec«'.ssary to adopt some means by which the conditions calling forth the secretion of each gland may be .separately studied. This can be accomplished by a small surgical operation in which the ducts are transplanted so as to discharge tlirough fistula; in the cheek, the secretion being easily collected, by allowing it to flow into a funnel which is tied in place. In general, two distinct types of stimuli may call forth secretion of one or other gland, immely: (1) dinct sfimulnlion of semory nerve endings in the mouth, and (2) psifiholoyual stimuli in- volving more or less of an association of ideas. SALIVARY SECUfcTION. 43 Of the stinmli which eauso socretion by acting on sensory nerve endings in the moutli. some influence the parotid, others the sub- maxillary gland, and different stimuli produce different effects. Even for pure mechanical stimulation of the buccal mucosa, u marked degree of discrimination is shown; thus, sihooth clean I)ebbles may be rolled around in the mouth and yet cause no .saliva to be secreted, whereas dry sand will immediately cause the parotid to discharge enormous (luantities of thin watery juice. Similarly dry bread crumbs invoke copious parotid secre- tion, bread itself having little effect; water, ice, etc., are ine- but if they contain a trace of acid an abundant secretion is i stantly poured out. It is plain in all these cases that the pui- l)ose of the secretion is to assist in the removal or neutralization of the substance which is present in the mouth. The thick mucous secretion of the submaxillary and sublingual glands seems to depend more on the chemical nature of the food than on its mechanical state, boiled potato«'S, hard boiled eggs, meat, etc.. causing the secretion of a thick slimy saliva, which by coating the food a.ssists swallowing. The relish for the food seems to be of little account in influencing the secretion of sidiva, for noxious substances, or those that arc acid, or very salty, call forth much more secretion than do savory morsels. Although mere mechani- cal stimulation is not in it.self an ade(|uate stinuilus, yet move- ment of the lower jaw is (piite effective, as for example in chew- ing, or when the mouth is kept open, as by a gag in a dental oi)eration. The stimulus does not, however. re<(uire to be applied to the biN'cal mucosa itself; it may be /w.i/c/i »• or associationnl. and here again a remarkable (iiscrimiiiation is evident, althougli the response is not so predictable as when the stimulus is local. Thus, when dry bread or sand is sliown to a dog to whom previ- ously these substances have been given by mouth, salivation fol- lows, but this is not the case when moist bread or pebbles are offered. Appetite plays an in>-)ortant part in this psychic reflex, for when dry food is shown to a fasting animal, salivation is marked, but may cause no secretion when it is offered to a well- fed animal. It is possible in this case, however, that there may \ 44 PiiY!?10L0GY FOB UENTAI. STUDENTS. J be inhibition of the Kbuulular activities on iiceount of tlie j)n's- cnce of foot! proiliu-ts in the blood. Porhaps tlu' most intt'ivsting fact of all i.s that even a fa.stinp animal will after a time fail to .salivate if lie be repeatt-dly shown fomi which causes a secretion, but which he is not permitted to ffet. The resjionse is immedi- ately established again, however, if some food, or indeed some other object, be placed in the mouth. A hungry animal will even .salivate when he hears some sound which by previous experience he has learned to a.ssociate with feeding time. The psychic reflexes are evidently dependent u[)on an asswiation of ideas (a nervous integration, see p. 242) ; they are conditioned reflexes, and are therefore the residt of a certain degree of education. They are easily rendered ineffective by confusing the u.sual as.so- ciations. General Functions of Saliva.— Th.-se observations indicate that a very important function of the saliva is what we may call a mrchnniail one. namely, either to flood the mouth cavity with Muid and so to wash away objectionable objects in it, or to lubri- cate the food with mucin and .so facilitate .swallowing. The sol- vent action of saliva is also important for the act of tasting (see p. 2!»5). Its chnniail activities in many animals seem to be lim- ited to the neutralizing })roperties of the alkali which is present in it, but in man and the herbivora it also contains a certain amount of a diasiatic enzyme, ptyalin. which can ((uickly con- vert cooked starches into dextrines and maltose. Even when this action is most pronounced, however— for it varies consitlerably in different individuals — it cannot proceed to any extent in the mouth cavity, partly on account of the .short time food renuiins here, and partly becau.se many starches, as in biscuits, are taken more or less in a raw state. In some animals, such as the dog. the .saliva has no diastatic action whatever. Although there can therefore be little diastatic digestion in the mouth, a good deal may go on in the stomach, for the saliva that is swallowed along with the fooii ;.\MV.\RY SKCKKTIDX. 45 ity. aiiotluT exists wbicli is of v<'ry Krcat iinportiiiict' for proper (liKestion; this is the stimuhition of the taste nerve eiuliii>;s. and, for fooj the st-eretion of the Kastrie juiee. Without any relish for food, digestion as a whole materially suffers, and for this reason unpalataltle food is always more or less indigestihle. '1 CHAPTER IV. DICJKSTIOX (Cont'd). The 0heini5tr7 of Saliva and the Relationship of Saliva to Dental Caries. A knowlfxlge of tlip composition and chomical proportios of saliva is of ^reat iniportancp because of the undoubted etiologi- cal relationship wliieh exists between this secretion and dental caries. Mixed saliva wlien freshly secreted is a watery, more or less opalescent and sticky fluid, often containing small masses of mucin, but on standing it becomes cloudy because of precipi- tation of calcium carbonate. Its specific gravity is 1002-1006, and it contains about 0.05 per cent of solids. The saliva from the sublingual and submaxillary glands is very much richer in solids than that from the parotid. The parotid saliva also differs from that of the other glands in containing no mucin, although it is often rich in ferment. Th(! solid constituents, with some of their properties, are as follows: ' (ilycoprotein (mucin) : precipitated by acid. Other proteins: coagulated by heat. Organic. . .■{ Ptyalin : a starch-splitting enzyme. Potassium sulphocyanide : gives ji red color witli ferric chloride. Sodium chloride: Potassium chloride : Calcium bicarbonate Calciinn carbonate : Inorganic, ^l standing. Calcium and magnesium phosphates : SoH appi'ur in the saliva, as a n-siilt of ])aotcrial action in the inoutii, and bo rcspon- sibh- for caries of the teeth. Tlie anionnt is, liowevcr, so very .small in comparison with the iiiKcsti-d carboliydrates that it can be entirely disre^anUHl. phiolin. — This belonjfs to tlie class of diastatic or am.vlolytic enzymes, convertinK starch into siinar. It is not so powerful as tile similar enzyme in pancreatic .jnice (.see p. 74), for it has no action on uncooketl starch, which the latter has. It acts best in neutral reaction and in the presence of .siMlium chloride, but is little atTected by a small dcj^ree of akalinity. On the other hand, it is readily destroyed by acids and by higher deRrees of alkalinity. These facts are of importance in connection with the continuance of action of .saliva after it has Im-cii swallowed, for although the food remains in the mouth for nuich too brief a period to permit of more than a trace of sugar iK'ing formed here, yet, after the stomach is reached, i)t.valin may continue to act for about half an hour. The ptyalin content, however, varies very considerably in different individuals. Ptyalin convi-rts starch into the sugar maltose, so called be- cause it is also formed by the action of the diastase of nudt. As intermediate substances are formed the ilextrins. two of which are distinguishable on account of their l«>havior towards iodine ; the first dextrin, called erythrodextrin, gives a brown color, while the next gives no color and is called achrcH)dextrin. It has been suggested that a deficiency of ptyalin may pre- dispose to caries of the teeth becauw. under such circumstances, a large amount of dextrin is formed, which being very sticky in character adheres to the teeth and becomes u suitable nidus for l)acterial growth. Potassium Stdphocyanidr {sulphotiiinuili). — This salt has the formula KCNS, and is usually present in human saliva to the extent of about 0.01 per cent. It is produced in the blooKNT\I, STIDKSTS. Well as the sjiliva. In contrast to cyanidt's it is non-poisonnuH. ho Y\ that it r(']in'>M'nts the inociioiis form into vvliicli tln-sc milwtanciM / ari' convt'rtfil. The cht-niiral tt-st uscil for its detect ion is tlie red color which it Kives with a solution of ferric i-hlori«le (FeCI,). Soinetiines, however, the reaction is not very detinite, in whieli case the method of Uuntinj; shoidd he employed. ThiN is pcrforme«l ns follows: Slowly evaporate 5 c. c. of saliva in a watch {rlass and while stirring with a kI«ss rod ad. saliva, some of this fluid is diluted about ten times with ..i.stilled water, which has been boiled and cooled so as to free it of carbon dioxide, ami 0.5 c. c. of paranitrophenol solution is added. The resulting tint is then pomjiared with that obtained by adding 0.") c. c. of the same indicator to each of a series of test tubes containing vary- ing jn-oportions of acid and alkaline pho.sphate solutions {^/,^ normal). The tint of this series which matches with that of the .saliva indicates the H-ion concentration of the latter k-cause this is known in the standard from the proportion of the two phosphates present. TiiK Method ok Mk-vsirlnc the Neutr-MJ/ixo Power of Sa- i.iVA. — Interi'sting thouKh Il-ion results may be, they do not aj)- pear to be of any practical value in connection with the relation- ship between the saliva and caries of the teeth. To study this ([uestion it has been found to l)e of more value to determine fhi IK ntmlaing power of saliva ; that is, to find out how much stand- ard acid or alkali we nnist add to a measured quantity of saliva in order to get a chancre with one or more of the above indicators. In doing this, however, we are immediately struck with the fact that the reaction does not change in ]>roporti()n to the amount of acid or alkali added, but that the saliva under .such conditions p()s.sc.sses the property of changing very slowly in reaction. This same property also exists in the blooil, and it depends on a series of changes which tho phosphates and carbonatirs ia:i undergo, when acids itr alkalies are added to solutions ontaining them, I ii 50 PHYSIOLOGY FOR DKNTAI- STIDKNTS. witliout causing any coiisidcinbl.' aiiiomit of fm- H- or Oll-ioii to be set fm'. This has Ihmmi calh-d Uw "biiffrr aclioii" of such salts. It endows tin- saliva with the power of locking away con- siderable (juaiitities of acid or alkali. Tn actually measuring the neutralizing power of saliva, it i.s best first of all to bring the saliva to a definite Il-ion concentra- tion by adding standard acid an"»<»H 1.S employed in the acidity titration becaus.. phenolphthalein cannot be u«ed with ammonia. 2Cf. J. A. Marshall, Amer. Jour, of Physiology, 191.''i, XXXVI. p 260. CHEMISTRY OP SALIVA. 51 that tho neutralizing power of siiliva, eoUeeted without any ef- fort or artificial stinmhttion of the nioutli (resting saliva), is very distinctly less than that of sjiliva collected whilst chewing on a i)iece of paraitin (activated saliva), ai\d that this difference becomes virtf much ](.ss in thosi with rarioKs hilh. Marshall has suggested that we shoidd express the ratio of the neutraliz- ing power of resting saliva to that of activated saliva as a per- centage ratio, which he calls the sdlirarj/ factor. In persons im- mune from caries this factor amounted to 4:{-S0; in those with caries it varied from H0-l;{2. The following examples will illus- trate these points: NOBMAI. RESTING SALIVA ACTIVATED SALIVA Case c. e. N 200 HCI c. c. N/200 NaOH Neutral- izinr Power c. c. ~ N 200 HCI c. c. N,200 NaOH N.iitral- Power Salivary Factor No. 22.22 7.60 29.82 57.55 0.90 58.45 51 canes Carious Without 18.50 7.00 25.50 22.80 2.13 24.93 102 care If those interesting (>l>sei'vations should prove to be confirmed by other observers, it will supply us with a comparatively simple method for -olving what has hitherto been a most i)uzzliiig ques- tion and which has i)rompted several observers, particularly Hunting and Price, to employ the very delicate physico-chemical methods of the concentration cell (p. M ) anil electrical conduc- tivity to its elucidation. Before leaving the subject of the relationship between the character of the saliva and the occurrence of dental caries, it may be well to point out that other factois besides the neutral- izing power of the saliva must be taken into con.sideration, name- ly, its amount and the presence of phosphates. A large and free flow of saliva, besides mechanically cleansing the teeth, will offer more neutralizing fluid. An e.xcess of phosphates, on the other hand, will encourage fermentation of any carbohydrate which may be adherent to the teeth and, by forming acids, thus tend to erode the t4»eth and predispose to caries. ! f 52 PHYSIOLOGY FOR DENTAL STUDENTS. Tartar Fonnation and Salivary Calculi.— Under certain con- ditions a precipitate, varying in color from pale yellow to almost black, collects on the teeth, particularly on the lower incisors and molars. This precipitate is called tartar, and it may be either hard (as on the incisors) or soft (as on the molars).' Its chemical composition varies considerably, but may be given as follows : T II Water and organic matter 32.24 per cent 31.48 per cent Magnesium phospliate o.98 per cent 4.91 per cent Calcium phosphate 63.08 per cent 72.73 per cent Calcium carbonate 3.7 per cent (Talbot) The organic matter consists of epithelial scales, other extran- eous matter and leptothrix chains. The place and manner of deposition shows clearly that the tartar is largely derived from the .saliva, the chemical explanation of the precipitation being probably as follows : Saliva, as it is produced in the gland, con- tains calcium bicarbonate, which is soluble in water, and is pre- vented from changing into the insoluble carbonate by the pres- ence of free carbon dioxide in solution. When the saliva is di.«i- charged into the mouth some of the carbon dioxide escapes from it 80 that the bicarbonate changes to carbonate and becomes pre- cipitated. The precipitate carries down with it phosphates as well as any organic debris or mico-organisms that may be present. The precipitation of calcium carbonate may even take place in the salivary ducts (Wharton's), thus forming salivary calculi, which may reach the size of a pea or larger. Such calculi may contain as much as 3.8 per cent of organic .natter, the remainder being largely calcium carbonate. The following table gives the composition of three such calculi : r. , . ' " I" Calcium carbonate 81.2 per cent 79.4 per cent 80.7 per cent Calcium phosphate 4.1 per cent 5.0 per cent 4.2 per cent Magnesium phosphate ... . present Organic matter and other soluble solids 13.3 per cent 13.3 per cent 13.4 percent ^*'®'' 1.3 per cent 2.3 per cent 1.7 ,er cent (T«lbot) CHAPTER V. DIGESTION (Cont'd). Mastication: Deglutition: Vomiting. Mastication. — By the movpmonts of the lower jaw on the ujiper, the two rows of teeth come together so as to serve for bit- ing or crushing the food. The resulting eomipinution of the food forms the first step in digestion. The manner of occlusion of the cusps of the teeth in the performance of this act is not a problem of Physiology, but rather of Anatomy and r)rthodontics ; never- theless, the other factors whicii '-ontribute to the efficiency of the process and the condition into which tlie food is brought by it are subjects to which we must devote some attention. The up and down motion of the low»'r jaw results in biting by the in- cisors, and after the mouthful has been taken, the side to side movements enable the grinding teeth to crush and break it up into fragments of tlie j)roper size for swallowing. Tlie most suit- able size of the mouthful is about five cubic centimetres, but this varies greatly with habit. After mastication, tlie mass weighs from 3.2 to 6.5 grammes, about one-fourth of this weight being due to saliva. The footl is now a semi-fluid nnish containing par- ticles which are usually less than 2 millimetres in diameter. Some, however, may measure 7 and even 12 millimetres. Determination of the proper degree of fineness of the food is a function of the tongue, gums and cheeks, for which purpose the mucous membrane covering them is supplied with vei-y sensitive touch nerve endings (see p. 244). The .sensitiveness of the tongue, etc., in this regard exi>lains why an object which can scarcely be felt by the fingers seems to be <|uite large in the mouth. If some particles of food that are too large fnr swallow- ing happen to be carried backward in the mouth, the tongue re- turns them for further mastication. The .saliva assists in mastication in several ways: (1) by mass of food so that it is nioro ivadily crushed; (4) by covering the holus with mucus so as to make it more readily transferabh- from place to place. The secretion of saliva is therefore stimulated by the chewing movements, and its composition varies according to the nature of the food (p. i'l). In some animals, such as the cat and dog, there is no mastication, coating of the food with saliva being the only change which it undergoes in the mouth. In man the ability thus to bolt the food can readily be ac<|uired. not however without .some detriment tc t';e efficiency of digestion as a whole. Soft starchy food is little chewed, the length of time required for the n.a.stication of other foods depending mainly on their imture, but also to a certain degree on the appetite and on the size >f the mouthfid. The crushing foire of the molai-s. as measured by a dyna- mometi-r. has been found to rise as high as 270 pounds, which is far in excess of the force re<(uired to crush the ordinary foot! .stuff.s. Thus cooked meats have a crushing point which varies between 1.") and SO i)ounds on direct thrust, but is considerably less when there is a side to side movement, as there is in chewing. Candies have a crushing point of AO to 110 pounds, and inits .").") to 170 pounds. Admixture of the foo. (iO). Thus it lias been ob.stTved in cliil- divn with ga.stric fi.stuhe that the chewing of agreeable l,M)d caused the ga.stric juice to be actively seereted, which, however, was not the case when tasteless material was chewed. DEOLITITION. 55 Tbo benefit to digestion as a whole of a large secretion of sa- liv . brought about by persistent ehewing. has been assumed by some to be mueh greater tiian it really is. and tliere has existed, and indeed may still exist, a sehool of faddists who. by deliber- ately ehewing far beyond tlie neeessary time. imagiiM' themselves to thrive better on less food than tiiose who oeeupy their time with other more profitable pursuits. Deglutition or Swallowing. — After being masticated tiie food is rolled up by the tongue acting against the palate into a bolus, and this, after being lubricated by saliva, is moved, by elevation I f ■ Kijf. 4, — 'Phf ihiinms which tiikc iilaii in the iiDSitiiiii of tlif niut of tlic tciiiguc, th»" .soft puliitf. the f|iiKli>ttis and tlic Imivmx duriiiK: thi> seiond statfi' of swallowiMK. The thick dotted line indicates the |)re the cardiac sphincter, ordinarily contrar > ;1. relaxes for a moment .so that the bolus pa.sses into the stomach. The peristaltic wave travels much more rai)idly in the upper portion of the oesophagus than lower down because of differences in tlic nature of the muscular coat, this being of the striated variety above, and of the non-striated, be- low. The purpose of more rapid movement in the upper portion is no doubt that the bolus may be hurried past the regions, where, by distending the o'sophagus, it might inttn-fere with the function of neighboring structures, such as the heart. The peris- taltic wave of the o'Sophagus. unlike that of the intestines (see \). 7!)), is transmitted by nerves, namely, by the oesophageal branches of tiie vagus. ]f these be severed, but the muscular it- self left intact, tlie (esophagus becomes dilated above the level of the section and contracted below, and no peri.staltic wave can pass along it ; on tiie other hand, the muscular coat may bo sev- ered (by cru.siiing, etc.) but the peristaltic wave will jump the breach provitled no damage has been doJic to the nerves. The propagation of the wave by nerves indicates that the sec- ond and third stages of deglutition must be rehearsed, as it were, in the medullary nerve centers from which arise the fibers to the pharynx and the different levels of the oesophagus. The afferent stinudi which initiate this process proceed from the pharynx by the fifth, superior laryngeal and vagus nerves and not at all from the o'sophagus it.self ; thus, a foreign body placed directly in the (esophagus remains stationary, but innuediately begins to move if the pharynx be stimulated, as by touching it. The af- ferent fibers in the glossopliaryngeal nerve exercise a powerful iiilnbitonj influence on the deglutition center as well as on that of respiration. Thus, if swallowing movements be exeited by stinudatiug the central end of tlie superior laryngeal nerve, they can be instantly inhibited by simultaneously stinuilating the oS I'llYslOUKiV FOK DKNTAI, STI DKNTS i I'i Klossopl.a,..vn«..al. an.l the ,vspir„to,y ,„ov,.„u.„ts stop i„ wl.at ever position th.-y ,„ay ha v. h....„ i„ „t the ti,„e This inh.hition of the .esopha^nis is i.„i....,, « „„„t important art ot the p,.„ees. when li.ni.i or snui-IU^ui food is swiuowed I > the eontraet.on of the n.yh.hyoi.l mnsele. tJui.ls are ..uick •shot down the .liste.ul. sopha^ns. at the h,we,. en of w.ie on aeeonnt of the eardiae sphineter hei,.,, elosed. they 1 -Lnu ht e" ""t.I t e „,.rival of the peHstaltie wave whieh l^ili:::; >-" set up by stnnnlation of the pharynx. If the swallow I ■'"""'diately .vpeate.l. as is „s„ally the ease in drinkin.! t," -opha,..s remains dilated beean.- peristalsis is inhibite.r „i 1 These faets have been revealed by listenin.r with a stetheseo,,e i^ the sounds pro*- '-.-o,.- The Act of Vomiting.-Tl.is is usually pre..ed..d bv a IVeling of sickness or uausc. and i.s i.u.iated by a very activ'c scretidn VOMlTlNti. 59 of saliva. The saliva, mixed with air, accumulates to a consider- able extent at the lower end of the (psophagus and thus distends it. A forced inspiration is now made, during the first stage of which the glottis is open so that the air enters the lungs, but later the glottis closes so that the in- spireil air is sucked into the (esophagus, which, already somewhat distended by saliva, now becomes markedly so. The abdominal muscles then contract so as to compress the stomacli against the diaphragm and, simultaneously, the cardiac sphincter relaxes, the head is held forward and the contents of the stonmch are ejected through the i)reviously distended n'sophagus. The compression of the stonmch by the contracting abdominal mus- cles is assisted by an actual contraction of the stonmch its«>lf, as has been clearly demonstrated by the X-ray method. (See p. 58.) After the contents of the stomach itself have been evac- uated, the pyloric sphincter may also relax and thus permit the contents (bile, etc.) of the duodenum to be vomited. The act of vonuting is controlled by a center located in the medidla, and the affcrriit fibers to this center may come from many different regions of the Iwdy. Perhai)s the most potent of them come from the .sensory nerve endings of the fauces and j)harynx. This explains the tendency to vomit when the mucosa of this region is mechanically .stimulated. Other atferent im- pulses come from the mucosa of the stonmch itself, and these are stimulated by swallowing certain drugs called emetics, import- ant among which an- strong salt solution, mustard water, zinc sulphate, etc. When some poisonous s\ibstance has been swal- lowed, the immediate treatment is to give one of these emetics and thus cause the poison to be vomited. Certain other emetics, particularly tartar emetic and apomorphine, act on the vomiting center itself, and can thei-efore act when given subc\itaneously. Afferent vomiting imj)uls«'s also arise from the abdominal vis- cera, thus explaining the vomiting which occurs in strangulated hernia, and in other irritative lesions involving this region. CHAPTER VI. DIGESTION (Cont'd). Digestion in the Stomach. The Secretion of Oaatric Juice.— After nass„no. «!.,. i .>hi.^, ..e foo., eo„.t. i„ the ^.n.nZ TZ:l 'tZ \lo\7! '"-""f «•"'•>' it l.H.ome.s dispo..cl in definite layers center. W hen, as ,h usual in n.an, the food is more or • . fluid th.s ayer formation is less evident and it eolleets in f alst pendent part of the body of the stomach (see Fig. 5) vSi a few m.„ut.s of the entry of the first portion of Ll the ghl,: of the gastrie mucosa begin to seerete their digestive juiees The unn.ed,a e exc.ting cause of this secretion is Lt the o, act o ioo.l w^h the mucosa-although this acts later-but i a .. r vous st.n.ulus trans„.itte.l to the ston.aeh through tl vag. s" iK-rve. and c.„„ng fron. a nerve center situated in the medX The ac^v^Uc, of th,s ,j„stru- center are called into operation h, afferent „„p„,,,,. , ,,, „,,,.^^. ,,^^, ,^^^^^.^^^^^ .^ th tast^M. ond o factor, epukclU.n. The process of gastric secretion therefore H„t,ated in the mouth, and the stimulus that i r sponsible for U ,s the good taste and the flavor of the fo^ ,Zt as in the case of the salivary glands, the foosophag„s ■ ^Arter outtln. th. v.,, this .....u.n „r .a.tric Jui.. au.« not occu. 60 DIGESTION IN THE STOMACH. Gl ln' had to ]h' fed tliroiiKli tli<» f^astrii; fistula, but vvlicii ln> was al- lowed to <'how food for \vhi«'li lit* had a rolish and tlu'ii spit it out. (i^astric socretion ot-curn-d. Tills obwrvation s>igK«'''tt'd to I'aw- low the establisliment of analogous conditions in dogs, with tlic modification that, besides the fistula in the stomach, one was made of the oesophagus in the neck in s\ich a way that swalloAved food escape skla- Kianis taken on man in the erect position at intervals after swallowing food impregnated with liismuth subnltrate. A, moderately full ; li. practieally empty. The clear space at the upper end of the stomach is due to ga.i. and it will lie noticed that this "stomach bladder" lies close to the heart. (T. Wingate Todd.) tliat when it did so, gastric juice flowed, provided this "sham feeding" wa.s with appetizing food. Stones, bread, acid or irri- tating substances, although they might cause much saliva to be seereteil and swallowed (see p. 4'?), had no influence whatso- ever on the fiow of gastric juice. The only adequate stimulu!^ was gratification of the appetite. «2 I'MV-lul " \ r. ,i{ 1)1 xT^,, sTIDKNTs. In f.assih^f. „ M«y Im m-II to rail i.ff.Mtion t„ th.- pra.h.al inipuifi.n..,. of tlM.s,- olw, . .41, „.s i„ -.,iMM-.-tioii with the f.-.-dinu «l /W<7, ju,,,, ainl It lasts sonu'tini.-s for n.arlv iw.. hours aft.-r sham fWdin^ h ■< Ix-n .l.scontiiMi.Ml. V.-t this is ..nh ahoiit on. half as lon^ as th- tun.' .lunnK which KHstri,- juic,- is ..cictcl when tiic f.XMl is ac FiK. fi._i)iaK,aii from till' iniiiii stm .... •' "'"marh shi.winK miiiiai Ktom: h (S) «..pa ...I th.. ma.M .si„„,a,.h . l) by a ,l.,ul.I.. lav.-r ..f .,.j.-, the oi).ninK ..I th.- i>.,uch on th.- abdominal wall .)us iH<-ml>nin. t 1 awlow I tiially i)crmittc(l to • ut-r the stomach tfii vaii.sf of fht <'iea V s iiecessa- to u- -n-.-ted. I, ^lyf -ss, Ha\ do illd be as ill '» .'Oiili! 'Uch w ■etin^' I, inj-.- was b\ ning i h.. ature OS of IH«iK>T" N i\ .'il i iiM \< II. nil til tilt' ■ rt.T M. ' 111 till >toiii. ll llHN Idcll .li\ - . In wlow Kiu (!'). III- iilliiiM oii>. ctllcctiii!,' till net iiDiii I' niiiiii stoMiii iiul til' iiiliijit i-fstiilii ll iifli • slwllii I'ljiin; \v;is fitniul til.: tllt'.v i.iii si -icli |iMl'iil' vitli ' ■ iiiinthcr. ill itiiiit as well s iu ■ti-i'iiirfli " !«MTctHii Th. M'ci-ftioii ill tl. ininiatiii-i' stm lacli lln'ivf<" .■ ■iir;ii '\ iiiiri'dr^ •Iii' si'ci'ctioi. inM-iii-rinir 'm th.- ;;in >l(tnifi( aii.l s< • riiiits lis to stinlv this ,> Ihmi I'ikkI is ;, luall' Iwiiijr iti>ri"*'t'' 'h , Wittes peptone) was phK-en It was i.r olisifved. when meat was (inectly jilacrd in the stomach ■■ it the juice which collected in the pouch increased, both ill qu.iitity and in streiijrth. after tl first hour, ai I that it continued to flow even after four h ii- us indicatiii}? that til. primary stimulus had come from t la -tives in the meat, iuit that, as the protein of the meat , .uiie diKt'stci. further stiniuJatioii o<'curred on account of the proteose and jieptones liberated. This local sliiiiiiliifioii is imlependeiit of flic iiMiinJIarv nerve center that controls secretion of the appetite juice, for • stili (m-- curred after both vapi liad beei divi ''d or even after destruc- tion of the .symiiathetic nerve pei-.uw's m the .ilMlomen. It (iiiglit, however, .still be a n. vvous reti- \ i- > mi.' the jncal nerve struc- tures (plexus of Aucrbach i i- he v\., , of th. .stomach. althouKh this is not so probahlr a- „T t i.-, depriid.-i.t upon > cie clicmicai o.xeitation of tlie gland cells by substances appearintr u the blmxl ■feas a marked II ■■xtract, or ■> <>- ,,( ptic (lines- he main stomach. If' 64 PHYSIOLOGY FOR DENTAL STUDENTS. jl ! as a ivsult of iihsorptioii from tli.; stoiuadi. Tliis '•honiioiic" (st'e p. 124) is not iiumvIv absoilK-d food, for no jrastric si'cretioii occurred when solutions of meat extract, or of peptone were in- .jected nitraveuously. It must therefore be some substance that IS absorbed into tlie blood from the mucous mend)rane of the stomach, and which is produced in this as a result of tlie action of the gastric contents on its cells. In confirmation of this view it^has been .shown that boiled extracts of the mucous membrane of the pyloric region of the stomach (made with water or weak acid or solutions of peptone or dextrin) eause some gastric juiee to be secreted when they are injected in small quantities everv ten minutes into a vein, similar injections of the extracting fluids themselves being without effect. We are now provided with the necessary facts upon which to draw a completed picture of th.' medianism of gastric secetion The satisfaction of taking food causes appetite juice to How and this soon digests some of the protein. The i)roducts of this diges- tion, along with the extractive substances of the food, after some time (which is probably quite short in the case of man), gain the pylorus, where they act on the mucosa to produce some hormone which becomes absorbed into the blood and stimulates further secretion of the juice. As digestion proceeds juice therefore con- tinues to be secreted. The appetite juice sets the process agoing • It Ignites gastric digestion. The Active Constituents of Gastric Juice.— When there is no fooil 111 the stomach, a certain amount of the mucous secretion IS present in it, and most of the gland cells are filled with zymo- gen granules (see j). 40). An extract (made with glvcerine) of the muco.sa in this resting condition exhibits no digestive powers; but if the muco.sa be first of all macerated with weak hydrochloric acid, the extract becomes highly active, because it contains large amounts of the proteolytic ferment pepsin. Other cells in the stomach produce the necessary hydrochlork acid It may be concluded therefore that during the process of secre- tion the zymogen granules in the cells are acted on bv hvdro- chloric acid and converted to pepsin. In conformitv witii'this It has been found that the secretion of a pouch of stomach pre- ll: DKiESTKtN IN Till'. STOMACH. G5 pnrcd from tlio pyloric region pos.s('ssf'S no difjcstivp activity, for in this rctrioii no hydrochloric ncid is secreted. The activation of this pepsinogen can also be accoinj)lisheicked out of the blood and secreted as IICl. Little as we know about the cause and mechanism of the secre- tion of hydrochloric acid, we do know something regarding its value and use in the i)roccss of digestion, and in general we may stat«' that this is partly regulatory and partly digestive. It is rryiihitory in tiiat it serves as the exciting cause of subsey trypsin alone, and crcpsin will cause no dijiestioii at all unless the native protein is first of all aeted om either by pepsin or trypsin. lint peptic digestion is not essenltal for life, for sev- eral cases are now on record in which individuals liave thrived after the stomach has been removed. The milk curdling action of gastric juice is due partly to the Vydroehloric acid and partly to pepsin. Curiously enough the curdled milk underg(H>s little further change until the food has got to tlic small intestine. The lipa.se in gastric juice can act oidy on emulsified fat and in neutral or alkaline reaction. Fat digestion cannot therefoi'c be an important gastric process. It has been supi)osed that there is a certain specific adaptation between the chemical nature of the food and the amount and strength of the gastric sei-retion. For exami)le, it has been found, by observations on the juice flowing from a miniature stomach, that feeding in the ordinary way with bread causes a maximal secretion during the fir.st hour, whereas with an eipiiva- lent amount of flesh the maximum occurs during the first and „ , > si hours, and with milk it is delayed till the third or fourth. ■ : pi teolytic i)0wer the bread juice is much the strongest of the ti. -, but it contains a lower i)ercentage of acid than the others. The Movements of the Stomach.— Solid food after being swalloweil accumulates in the body of the stonuich, where on ac- count of an absence of movements it is not uniformly acted on by the gastric juice, its outer layers only becoming digested. In the case of the man, however, some of the food, because of its semi-fluid nature, i)as.ses beyond the so-called transverse band and into the pyloric region, in which waves of contraction nnike their appearance. Starting very faintly at this point, these waves travel towards the pylorus and become gradually more marked until they may become so ileep as practically to cut olT a portion of the pyloric region from the rest of the stomach. This last portion of the pylorus, sometimes culled the pyloric canal, Jii m PIIYSI0IX10Y FOR DEXTAL STUDENTS. gradually contrafts on the food which has been foreed into it, thus tending to ejeet it through the pvlorie sphincter, or, if this is elo.sed, to cause it to pass back again as an axial stream intle, no food may i)ass the sphincter, although during this time there may have been well over a hun dred peristaltic waves. Nor is it the con.sistency of the food which controls the oi>e!iing. It must therefore be some chemical pr.>perty which the food aci|uii-es during its stay in the stomach. This has definitely been shown by Cannon to be the presence of free acid. By measuring the length of the skiagram shadow in the intestines after feeding cats with bisnnith-impregnated foods rendered acid or alkaline, it could be clearly shown that acid liastened the initial discharge, whereas alkalies retarded it, and observations through a fistula in the vestibule showed that any delay in the appearance of acid in the contents was associated with a delay in the opening of the sphincter. liut the sphincter does not remain open ; it (juickly close.'? after a little ehym(>, as the half |uate stimulus for the oi)en- ing of the pyloric sphincter, and consequently the rate at which the different food stuffs leave the stomach is to a large extent jiroportional to their power of combination with the acid. Pro- teins, combine with large amounts of acid, so that their initial discharge is delayed and their subse(|uent i)assage slow. Car- bohydrates absorb but little acid, so that they begin to leave early and the stomach is soon emptied of them. The pa.ssage of fats is peculiar; when taken alone, which, however, is scarcel.v ever the ca.se, they seem to bring about a partial relaxation of the pyloric sphincter, so that bile and pancreatic juice regurgitate into the .stonmch and some fat may pa.ss out, but the subse(|uent dis- charge into the intestines is ver.v slow, so slow indeed that each discharged portion seems to become completel.v absorbed before any further discharge occurs. When fats are mixed with other foods, the.v materially delay the discharge. These effects are no doubt due in part to the inhibitor.v influei'"e which fats have on gastric secretion; and in j>art to the liberatioii of fatty acid in the duodenum by the action of pancreatic lipase. This fatty acid seems to be liberated more IOLCXJy FOK DKNTAL STUDKXTS. Wjitcr aloiio begins to It-avo the stomach almost iinnu'diatt'ly after it is taken, beeause tlie sphincter opens before an acid reaction has been acquired, and remains open on account of there being no acid in the duo(h'num to effect its closure. Water stays for too sliort a time in the stomach to excite any gastric s<'cretion, and conseipiently it readily carries infection into the intestine. The discliarge of raw egg albumin is peculiar. Like water it Ijcgins to i)a.ss the j)ylorus immediately after ingestion, its reaction for some time being alkaline; it becomes acid later, .so that the discharge becomes int«'rmittent because of the duo- denal reflex. The consistency of food itself does not affect the rate of discharg.^ niiless hard jiarticles are present in it, when a marked retardation occurs. It is well known that the gastric contents are but .slowly dis- charged into the duodenum when there is excessive gas accu- mulation. This is due to the atony of tile .stomach which accom- panies pathological gas accumulation. CHAPTER VII. DKiKSTION (Coufil). Intestinal Digestion: The Movements of the Intestines: Absorption. The Secretion of Bile and Pancreatic Juice.— Hcsidt's eaus iiig ivflt'x closurt' of the pyloric spliiiictfr, the coiitiu-t of tht- chiftue, whif'h is the iiaiiu- jiivt-ii to tlif sfiui-difrfstcd food as it leaves the stomaeli. witli the diioih'iial mucosa inaugurates the l)rocesses of intestinal digestion by exciting tiie secretion of bile and pancreatic juice. Neither of tiiese juices is secreted into the intestine (hiring fasting; l»ut both begin to How very soon after taking food, and they gradually increase in anunmt for about three hours, and then rapidly decline. The bile at Hrst conies mainly from the gall bladder, in which it has accumulated dur- ing fasting. When the gall bladder sup|ily is exhausted, the bile comes directly from the liver without entering the gall bladder, and this secretion becomes more and more marketl as digestion proceeds. The storage of bile which occurs during fasting is necessitat.'d by the fact tliat although it is not re.|uin'd in the intestine, bile is nevertheless being constantly ]iroduced by the liver, because it is an excretory produe as well as a digestive fluid. It must, therefore. Ih- got rid of from the blood, but. !)«•- ing also useful for dige.stion. it is stored until it is reciuired to a.ssist in this process. The sudden discharge of iiile from the gall bladder is depen- dent upon a nerve reflex .'Xciled by tiie contact of the acid clivme with the duodenum. The increa^'d secretion of bile from the liver, like th<' secretion of pancreatic juice, is however, inde- pendent of nerves, for it has been fountl that the application of weak hydrochloric acid to tlie duodenum causes the juices to flow after all the nerves, but not the blood vessels of the duodeiinm have been cut. The only way by which such a result can be ex- plained is by assuming that the acid causes some chemical sub- 71 l'IIYSIOI,(MiY FDU DKNT.Xr, tJTfDKNTS. stance to I)f iiddfd to tlu- blood, whidi tlicn carrit's it to tlic i)aii- crcas and liver, ui)on the cells of which it exercises a stinmlatinj,' influence. That this is the correct explanation was shown by studyinjf the effect which is pnxluced on the secretion of i)an- creatic juice and bile by intravenous injections of decoctions of intestinal mucosa made witii weak acid and subse(|uently neu- tralized. An immediate secretion resulted. The acid extract evi- dently contained so hormone whose production, in the normal process of digestion, is evidently occasioned by the contact of the acid chyme with th- duodenal mucosa. This hormone is called sivrdin but we know very little of its e.vact chemical nature. It is not a ferment, for it withstands heat: it is not a protein, for it can be extracted by lioilintr the mucous memb?-ane with weak acids after tr.-atment with alcohol. It is readily oxidized in the l»resenci' of alkalies, and is of the .same nature in ; 11 animals. It is useless to jfive .secretin as a druf? with the hope that it will stinuilate i)ancre;itic secretion, for it is not absorbed from the lumen of the intestine. Although most abundant in the muosa of the duodenum and jejunum, secretin is also present in the mucosa of the lower end of the small, anrfstit)ii aiitl iib- sorptiiiii of fat; for. in the altsi-ncf of citluT stcrftion. larui- aniouiits of unal)st)rlu' is a sulficient concentration of sodium cailnmate to neu- tralize the acid in an ei|ual vulume of gastric juice. The action of pepsin disapjiears whenevei- the chyme becomes alkaline aiitl eonditioiis thus become suitable for the activities of the i)an- ereatic enzymes. Hesides its neutrali/iuK action, tlie bile causes the chyme to assume a somewhat jjrcater consisteiiey. by pre- eipitntinn incojnpletely ])eptt)ni/etl protein, as well as pejjsin. The j)rccipitate becomes rcdissolveii when excess of bile has be- come mi.\ed with it. and the sifrniticance of the precipitation may be that it causes a temporary delay in thi' movement of the cliyme along the d\ioilenum. thus allowinerly mixetl with jtancreatic juice before it moves furth-r along tiie intes- tine Composition, Properties and Functions of the Bile.— Water ^^-i' Total St>litls l-ll of which : ( )rg'aiiic ■< I'.ih' Salts !».U Lecithin ami ("hole.sterol 1.10 Mucitioitl Sid)stance ) Pigment ) Inorganic Salts D.TS The bile is a grcenisli-yellow tluitl of sticky consistency antl bitter taste. Its most interesting constituents arc the bile salts. which are complex organic substances, having an important func- tion to perform in as.sisting the lipas" and amyloi)sin of pan- creatic juice in their digestive activities. (tt}«*rwise the bile con- tains no digestive enzymes. The cholesterol is not a readily soluble substance, so that i' is apt to become i)reciiiitated in the 74 I PIIY.sIUUKJV FOB DKNTAL STUDENTS. I)il.' ;i,il stones or by inflaniiiiatory sw-.-llin^ of tlu- mucous membrane, the ,o,/t u I ^^\f^j, .'"''*>« •»" P'-oteiu). Although the bile contains no enzymes, it T^ IS. as we have seen, a most imj.ortant accelerator of the activities of the lij.ase and amylopsin of the pancreatic .juice. Bib- has no action on trypsinog..n. which is nevertheless without any action until it has become changed into trDpsin. This does not occur until the pancreatic .juic- has i-eached the intestine, when the activation is brou>?ht about by a fennent j)resent in the intes- tinal .juice (.secretion of I.ieberkiihn's follicles), called cnliro- liiiasf. The int.-stinal .juice contains this activator only when it is rey tli.- varying .|iiaiiti- tifs ..f aci.l cliym.' .•<.min« in conta.-t with th.' .lu.ul.'nal imn'osa. Chemical Changes Produced by Intestinal Digestion.— In the lou'fr portion of th< duothinim n>imfs of Ih, pinirr, alir jiiia mi on th, food in fnll intrnsitif. Th.' trypsin rapi.Uy hy,lf..iyz»"s th." prot.'ins to p.-pton.'. whii-h if it is not inimediatciy ahsoih.-.l may h.'c(nn.' tnrtli.'i- brok.'ii .lown to amino bon in .'X- traets of the intestinal muc.isa than in suc.-us enterieus, so that, like the inverting enzym.'s. it possibly .lisplays its action while the protein is b.'ing ab.sorbed as proteoses an.l peptont>s. It s.'rves as the last barri.-r again.st the entry into the bloo.l of prot.-in in any other form than as a mixture of amino bodies. Less om- pletely digested i.roteiu is poisonous wli.-n added to tlie bl.K).l (p. 152). 70 l'liy.sI«i|,ri> are on.' or two furth.-r digentiv.- changeM that wr nmst con- tiiilcr. The Digestive Function of Intestinal Bacteria.-()n acci.unt ot the antiM.ptic action of fi. hv.lro.'hh)ric a.'i.l. th.-n- is. onli- iiiinly. no baftorial jrrowth in th.> stomach, but th.- n.-utrali/.a- tion of acieeial provision is made to eneourage baeterial growth by the greiit length of the large intestine, for without baet.M-ia, digestion of <-ellu!ose is impossible. Thus if n.-wly-halehed ehieks Iw fed with .sterilized jtraiii they sueeiinib in about two we.-ks. but if a small amount of the exeivinent of the fowl be mixe.l with the grain, they thrive, as ordinarily. On the ..ther hand, if th<' foml contains no cellulose, animals may .levelo|) and grow with sterile intestinal contents; thus guinea j.igs have been re- moved from th>- uterus under a.sej.tic conditions and kept in a sterile i)lace on sterilize.l milk and have thrive.l and grown as normal guinea pigs. The organisms in the intestine of man are probably much more useful than harmful. No doubt they are parasites, but tliey are u.seful (>arasites: th.-y work for th.-iV liv- ing, not only by assisting when necessary in th.- digestion of food but also by destroying certain substances which, if absorlx-d would have a toxic action on the hcst. Thus cholin. a substanet" produced by the digestion of lecithin, is distinctiv poi.sonous but It really never gets into the blocnl becau.se the bacteria d.-stroy it. In the ca.se of man bacterial digestion occure both in the small and large intestines, and there are varieties of bacteria capable of acting,,,, all the food stuffs. They may break up th.' sugars into lactic acid or evn further so as to form CO., and II Ii has been claimed that this formation of lactic acid in the intestine is INTF^TINAI. PKlKSTIiiS. t t of bonofit to tho health of man brcnuso wlu-ii it ooo\irs other bar- trria which arc nion- haniifiil than usofiil hfconic (IcHtroycd, To cncouniKc this growth of lactic acid bacteria, it has b.( ii rcconi- nicnih'il that larjrc (|uantitics of sour milk slioubl be taken. It is untloubtedly true that sucli treatment is of benefit in numy per sons who fiuffer from excessive intestinal putrefaction, but thai Rucli treatment shouhl jirolouK the life of otherwise healthy indi- viduals is visionary. Ah in lu-rbivora. there are also bacteria in man which break up cellulose, pro«lucinj? methane and ("().,. After d, ts eontainin» much v i,Me matter, therefore. « lame anu.int of gas is likely tc tu'i lin*" in the intestines. From fats, the intestinal bactenu juedie-. .iwer fatty acitls, which teiul to cause the contents in ii • 1' -A.r jmrtion of the small in- testines to become acid in i ■ r-nri Although capable of bydrolyzintt native protein from the very start, bacteria act more readily on protein that has been partially digested by the proteolytic enzymes of tiie stomacii and intes- tines. The pnxhicts of this action are more or less characteristic becaus*' of the peciUiar manner in which the aromatic groui)s of the i»ri)tein molecule are attacked, producing from it such sub- stance- as phenol, skatol, indol, etc., to which the characteristic odor ()! the fa-ces is due. When protein has been adeciuately .U- gt-sted in the stomach, it is so rai)idly acted on by the trypsin (and erepsin") of the small gut and is so quickly absorbed that bacteria have mo chance to act on it. When protein has been in- adeiiuately digested in the stomach, however, the trypsin fails to digest it (|uickly enough, so that bacterial putrefaction sets in which may be quite marke • in the small intestine, although much more so in the colon. Even when they do not find a suitable sub- strat in the food, the bacteria attack the proteins of the intes- tinal .secretions them.selves, which accounts for the well-known occurrence of this process during starvation. The Immunity of the N&Oa of the Digestive Organs Toward the Enzymes Which Act within Them.— The immunity of tiie mucosa of the stomach and intestines seems to be due in main to the presence in the cells of the mucosa of anti-enzymes, that is of substances which can inhibit the action of the various enzymes 78 PIIYSIOI/WY FOR DENTAI, STUDENTS. (aiitipopsin, antitrypsin, etc.). As w.- should pxpeet. very strong anti-enzymes can h.- prepared from tapeworms and otiier intes- tinal worms. It is in virtue of posst-ssing tliese, that the worms are r t digested. The immunity of the gland eells and duets, as qf the panereas, to the proteolytic enzymes whieli th<>y produee is possibly to be e.xi)lained in another way, namely, by tlie ex- istence of the enzyme as an inactive i)recursor (e. g., trypsino- gen) until after the secretion has bwn carried to a regioii whose walls contain the specific anti-body. A certain degree of im- nninity to a possible destructive action of the intestinal bacteria may be conferred by the nnicin. whicli is quite abundant, at least in the empty stomacii and in the large intestine. The relatively poor growth of bacteria which occurs on inoculating fiecial mat- ter in culture media— although many bacteria can be seen by microscopic examination to be j)resent— is probably to be ex- plained by their having been killed by the nuicin. The Movements of the Intestines. The luovfmnils of the suiall inlrstiiH have two functions: (1) to macerate and mix u]) the food and (2) to move it along to- wards the lower end of the gut. These two functions are sub- served by two different types of movement, the .so-called pendular and the peristaltic. The ju tiduhir moi; mints are rendered evi- dent by allowing tiie intestine to float out in a bath of isotonic saline, when the various loops sway from side to side like a pen- dulum. By clo.ser examination it can be .seen that the movements are protluced b\ faint waves of contraction of both muscular eoats which sweep with considerable rapidity along the gut. When the waves arrive at a part of tlie intestine containing any solid substance, they become accentuated, and this becomes most marked at the middle of the solid ma.ss of food, thus tending, on account of the contraction of the circular fibers, to divide the ma.ss into two. They are therefore sometimes called scijmrt,tins are absorbed in solution, which woultl lead us to ex- pect that, because of the water absorbed along with. them, the contents of the small intestine would Im- more solid at its lower end than at its upper end; but this is not the case, for the diges- tive juices which have been secreted make up for the loss of water. It is in the large intestine that the water is finally ab- sorbed. Attempts have been maih' to explain the pi'ocess of absorption in terms of the known laws of filtration, o.snmsis, surface tension, and ind»ibition, but little further |)rogress has been made than to establish the fact that although these i)rocesses may play a role, they do not e.\i)lain the whole thing, for if blood serinn be placed in an isolated loop of intestine, it will become entirely absorbed even although identical in all the above i)ropeities witli the blood of the animal. That osmosis does have some influence, however, is evidenced by the well-known effect of a strong saline solution in the intestine: it attracts water from the blood, tbus diluting the intestinal contents and stimulating peristaltic contractions. It is in this way that saline cathartics ai't. Regarding the absorption of fats, it is now definitely kn«wn that these first of all split into fatty acid and glycerin.- b\ th»- action of the lipa.sc of i)aucreatie .juice The fatty awid then unites with alkali to form a soap, or with bile salts to forw a s«»l- uble comi>ouiid. Jn either ca.se. the dissolved fatty acid f^Mwes into till' intestinal epithelium, into which is also af)sort*--(1 the glycerine, the two re-uniling after their absorption so as to* form neutral fat again, which then pas-ses into the .-entral lact»«l »f the villus, whenei' it is transported h> the abdominal lymphatics to the thoracic duct, which discharges it into the sulx-lavian veiii on the left side of the root of the neck. Ifuuifir SI iisiitiiitis coincide with stomach contractions which difl'er from those oceui'i mg fluring ns«8 ami pep- tsees. «C' Clots millf. di Produces met^iroteins. (2) Acts as antiseptic. i(3) Stops action .« ptyalin. • Acts on emulsifleti fats. ■ Inactive until actwi on by ent^rokinase. Splits neutral fai titto fatty acid and glyrerfae. . Conv#-rt8 all Marches into maitose. . (1) Helps to neutralize HCl of chyme. (2) Combines with fatty aeid t© form soaps. . n Augmeai: 'tie action ni lipase and and asyioiHBn. (i) Precipitate pHpstn and peptoaet^ in chyme. I (31 Combines wrA fatty iKdds. ■ (1) HidpH to ueuttKlize SIM of chyme 1(2) Cjambineu with tatr- acid to rorni iMSPS. Converts trypsinogeii into trypsin. which splits proteins into amino UcKlieB. 'nn verts caseiiiuicen and peptones into simple amino bodies. (Jne for each disaccharide. splittinR them into monosaccharides. (Both the last two enzymes are more plentiful in (he epithelium than in the intestinal juice.) (1) Digest cellulose. (-) Splits monosaccharides into lactic and lower acids. Split higher, into lower fatty acids. Split off aromatic groups, as phenol, cre-iol, et?. (Besides these specific actions, bacteria : may perform many of the diges- j tive functions of the juicei i m^. CHAPTER VITT. METABOLISM. The Energy Balance. Introductory.— The objcet of digestion, iis wo have seen, is to render the food capable of absorption into the eireuhitory fluids, the blood and lymph. Tlie absorbed food pnKlnets are then transported to the various organs and tissues of the bo may l)e eith. r usid or stored away against future requireft*ents. Afte>- bein^; used, certain su>»stanees are prmlueed as waste products, and these pass l)aek into the bltKKl to be <'ar- ried to the orjfans of excretion, by which they are expelled from th- h«Hay. IJy eomparison of the amount of tiiew t-xeretory pi'od- ucts with that of the constituents of food, we can tell how much of the latter lias been retained in ihe l>ody. or lost from it. This constitutes the subject of ijrut nit mftdholisfii. (hi the other haml, we may direct our attention, not to ihe baiaiire betw -n intake ajid output, but to the cheiiiical i-lian>res tiiroush winch each fooiistuflfs miust pas.s between its alworption and excretion. This is the subject of sptcial m'taboUsui. In the one case we content oui's«'lves with a conipar»t4(n of the raw material which is ac(|uired and tlie tinished prof'si.i.-> oxy gen. the proteins, fats ami c.irbohydrates. and th.' output, carbon dioxide, water and the various nitrogenous constituents of urine. This dissimilarity in chemical stnnture ijctweeu the substances ingest, d and those excreted lindts us, in bulaneing the one 84 PIiySIOLOGY FOR DEXTAL STl'DENTS. Jiifiiiiist tile otli.T, to a coniiiarison of the siiuillcst frajriiifiits into wiiicli cacli can he l)mkfii. Thi-sc arc tlic elements and of them carbon and nifrop-ii aiv the only ones wliicli it is possildc to nieasuro with accuracy in both intake and output. From bal- ance shtM'ts of intake and outi)ut of carlmii and nitrogen and from information obtained by observinjj the i-atio between the amounts of oxygen consumed by the animal and of carbonic acid (CO.) exci-eted. we can draw far-reacliing conclusions regaru ^ the relative amounts of protein, fat and carbohydrate which liave been involved in the metabolism. As lias already been stated, the essential nature of the metaboli<' process in animals is one of oxidation, that is to say. one by which large unstable mole- cules are broken down to those that are simple and stable. Dur- ing this ])rocess of katabolism, as it is called, the potential energy which is locked away in the large molecules beccmies lilx-rated as actual or kinetic energy, that is to say, as movement and heat. It therefore becomes of importance to conij)are the actual energy which an animal expends in a given time with the energy which has nieanwiiile been rendered available by metabolism. This is called the » n< rtjii balanc, . We .shall first of all consider this and then proceed to examine somewhat more in detail the mutt rial hdhnia of the bodif. « Energy Balance. The unit of energy is the large calorie (written C). which is the amount of heat reipiin d to raise the temjH-rature of one kilo- gramme of water tiirongli one degree (Centigrade) of tempera- ture.' We can determine the calorie value by allowing a meas- ured i|uantity of a sub.stance to burn in comj)res.ser clearly uiiii.r.Mtiiiiil. Th.- fumifi- ...xpit !-s.'.m iiinnilili/ of mtuiil hciit .■iicrKv • tlif iHlter merely tells u.h llie iiiteii.-dty iit which the heat eneigv is Wing Kivcn THE ENEUiOV BALANCE. 85 callfd, it lias bt'cii fouiul that thi- number of caloiii-M lilicrattil by buriiiiip one gramiiR' of each of tlic proximate priiicipk-s of food is as follows : ,.,,,, \ Staroli 4.1 ( arhonvdratt'S ■' , , ,, / Sufrar 4.0 Protein .'>.() Fat 0.:{ Tile same number of calories will be liberated at whatever rate tiie eombustion i)ro<'eeds, i)r()vide(i it n'sults in tlie same end l)roi,\ of oxygen t.i the animal. Aiii}>iii! 'fhtr itiiiton dioxide (and water) 'li»eli r,,red ami of oxygen afiwiHM- hy tin animal during the «l)st i \,-- . >n. Su<"h respiration calm ■»« ters iiave been oiade lor ail sorts of mi- ?nals. the most iwrft***! t'i*r hw on man having lt<-"ii i-i«iisi nieti'd in Anierieii (see K« Si As ill list rating the extreme !ie«'Uracy of even the iaTTfcsl .»!• rln-s*' i- .s iileresrtH^ to note tli.-'t tin act ual iieat give (lut xkwu ii ikauite amount of alcohol or ether is 86 PHYSIOLOGY FOB DENTAL STIOENTS. burned in one of them exactly corresponds to tli<' amount as meas- ured by the smaller bomb calorimeter. All of the enerRy liber- ated in the body does not, however, take tiie form of heat. A variable amount appears as mechanical work, so that to measure in calories all of the energy which an animal .expends, one must add to the actual calorifs nivcn out. the caloric ci|uivalcnt of T □ m KiS- S. — Diagram of Atwater-Bcni'dirt I'esiiiiiilion CiiIdi imtlrr. .\y ;hi' animal u.sps up tlip <>-, the total volumi* of air Hliiinlc.s. Tliis .shrlnkaKi' is liuli- cated by thf metiT, uml a lorrfspoiiiiiiiK uinoutit of i >.. i.s il is the product of the load in iciiograiunu s l)y the dis- tiou-i- In nielre.s throuKh which it is lifted. TlIK KNKRUY BAI.ANCK. 87 inal; tlius, a man (loiii^ work on a bicyclf crfjoiiu'tcr in tin- l>A'-i'> <" H.v drawing np a balance sheet of his intake and output of food material ut while lie is still resting in bed in the morning, and fifton hours after the last meal. When the results thus obtained on a nund)er of individuals are calcu- lated so as to repr«icnt the calorie output i)er kilogranune of lH)dy wt ight i'l each case, it will be found that 1 C. per kilo per hoTir is di.scharged. That is to say. the total ent rgy expen«liture in 24 hours in a man !,f 70 kilos, which is a good average weight, will be 70X24 = 1,()80 (". When food is taken the heat production rises, the increase over the basal heat production amounting for an oidiniry diet to about ten i)er cent. Besides being the ultinmte source of all the body heat, food is therefoic a direct stinudant of heat pnMluction. This specific dynamic action, as it is called, is not, however, tiie same for all groups of foodstuffs, being greatest for prott-ins an< liouis .or sb'cp a-u! 1»; hours for work, we can thus accotint lor 2.1«S (',. tiie remaining :{()() odd ('. Mhich is reiiuind to bring the total to that which we know, from statisticMl tables of the diets (»f such workers, to b.' the actual (iaiiy ex|M'nditure. In-iiig due to the exercise of walking If the exer.'is-' be more strenuous, .still more calories will Ik- ex- pended: thus, to ascend a bill of l.ti.jO feet at the rate of 'J.7 miles an hour reipiires 407 e.xtra calories. Field workers may e.xjiend, in 24 hours, almost twice as nuiny calories as those en- gaged in sedentary occupations. .\nother factor which controls the energy output is the cool- ing influ(u<( of (h, atmosiihtn. When this is marked more heat must be liberated in order to maintain the body t. mp -rature (see p. 135). In otiier words, the necessary heat loss must be compensated by an increa.sed heat i>roductioii, just as we nuist burn more coal to keep the house at a given temperature on a cold, lliau on a warm. day. This ad.ju.stment of energy liberation to the rate of cooling at the surface of the body explains, among other things, wiiy it should be that small animals give out mudi more energy, per unit of ImkIn weight, than thus.- thai are larger. The small aninud has relatively the great, i- surface area, just as twoctd)es of (Mjual weight when brought together have a com- bined weight which is double that of tither cuiie. but a surface TIIK K.NKUliV BAr.AVCK. S!> area which is Ichs tliaii iloiihh' (twn siirfiUfs hiivin>» hiiii Itrou^ht toKftlicr). Its Kft'iitcr tfiKimi'v ti» fool cxithiiiis why siiiitll iitii- iiuiIh witw i M HO much more quickly sucoumh to cold thau tlioHc that arc lar^cf. ainl why slim persons bIhhiW led the cold more keenly than those that are stout. Other thinjTs. sucli as diet, external tem|ieratiu'e. etc. bein^ the same, it is therefore siirftin unn ami iiul h<»hf ivrif/ht wh'hh (li trrmiiii s Ihi i ik rt/n jiroilm lion, a tact wliicli is clearly deiii- onstratef to square metre of surface tin- dif fereiices practically vanish. These facts, however, do not apply when the dilTcrences in size arc due to a^e. This fai-t has been imwt strikiiiRly dtMuonstrated in the case of man. for it has been found that the calorie requirenient per unit of surface is very ry ilischarfje. the followin-; results have been obtained from indi vif .iiirfiiif ,inil li'Mir (uraiiinii-s) 2».!t 26.5 23.5 21.8 18.5 I6.!t !«.:{ 14.2 26.6 20.1 16.0 14.8 16.3 17.!t \\i'l'iii:t' iiui' .\\iTiii:i' »fi«lil ( \i';irs) Ikiliiur.'iiiiiiii'si Mtllrx !t 2 :■. 28 12 1 2 34 1.1 1 2 51 lit 1 2 fiO 25 68 36 68 45 77 58 85 h'liiml'S 8 22 12 36 1.-. 4!t 17 2 :; 54 30 54 45 67 Ui |2B tii itt 1^ l£ ^ 1^ lEg Ibl 1.4 il.6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI and ISO TEST CHART No. 2) 90 PHYSIOLOOY FOB DENTAL STUDENTS. TJiis table shows us clearly that over and above the greater combustion necessary on account of their relatively greater sur- face, children require calories for growth. They must be fed more liberally than adults, otherwise they starve. The table further shows that boy. must be more liberally fed than girls of ecjual age and body weight, probably because of their greater restlessness. It is on account of these greater food requirements that children are the first to die in famine. CHAPTER IX. ■ METABOLISM (Cont'd). The Material Balance of the Body. We must distinguish .between the balances of the organic and the inorganic foodstuffs. From a study of the former we shall gain information regarding the sources of the energy production whose behavior under various conditions we liave just studied. From a study of the inorganic balance, although we shall learn nothing regarding energy exchange— for such substances can yield no energy— we shall become acossiblf bi'iiif? (Icrivt'tl from pi'otciii. This {y\tv of iiu'tabolisiii yj' ^j[j^ liists until a ll liif available rcsourct's of fat have Ik-coiiic i-x- hausted, wlivii a iiion' cxtoiisivt- iiictabolisni of protfiii sets in with the coii8t'<|Ui'iiec that the iiitro}?eii cxcrt'tion rises. This is really the harbinger of death — it is often ealled the prouurtnl I'ine in uUrugen tsvntion. It means that all the ordinary fuel of the animal economy has been used up. and that it has become necessary to burn the very tissues themselves in order to obtain sufficient energy to maintain life. Working capital being all exhausted, an attempt is made to keep things going for a little longer time by li(|uidation of pernmnent assets, liut the.se as.sets, as rei)resented by protein, are of little real value in yielding the desired energy because, as we have seen, oidy 4.1 calories are available against f)..'{, obtainable froi fats. These facts exj)lain why during starvation a fat man excretes daily less nitrogen than a lean man, and why the fat man can .stand the starvation for a longer time. Not only is there this general saving of protein during .star- vation, but tliere is also a discriminate utilization of what has to be used by the ditferent organs according to their relative activities. This i^ very clearly shown by comparison of the loss of weight which each organ undergoes during starvation. The heart and brain, which nuist be active if life is to be maintained, lose only about Ji per cent of their original weight, whereas the voluntary nniscles, the liver and the spleen lose lU. 'A and 67 l)er cent, respectively. No doubt some of tliis loss is to be ac- counted for as due to the disapi)earancc of fat, but a sufficient remainder represents protein to make it plain that tiiere mu.st have been a mobilization of this substance from tissues where it was not absolutely necessary, such as the liver and voluntai-y muscles, to organs, such as the heart, in whicii energy transfor- mation is sine qua non of life. The vital organs live at the ex- pense of those whose functions are accessory. When "e compare the excretion of carbon dioxide from day to day during starvation, it will be fount! to remain practically constant when calculated for eacl- ' 'logram of body wi irht. The same is rue for the calorie outpui Certain unusual substances , I r )4 ly**' * PHYSIOLOGY FOR DENTAL STUDENTS. such as crcatiii also make tlieir appearance in tlie urine, anil there is an increase in the excretion of ammonia, indicating that larger rjuantities of free acid are heing 8«'t free in the organism. Starvation ends in death in an adult man in somewhat over four weeks, but much sooner in children, because of their more active metabolism. At the time of death the body weight may be reduced by 50 per cent. The body temperature does not change until within a few days of death, when it begins to fall, and it is undoubtedly true that if means be taken to prevent cool- ing of the animal at this stage, life will be prolonged. Normal Metabolism. — Apart from the practical importance of knowing something about the behavior of an animal during starvation, such knowledge is of great value since it furnishes a standard with which to compare the metabolism of animals tmdcr normal conditions. Taking again the nitrogen balance as indi- cating the extent of protein tear and wear in the body, let us consider first of all the conditions under which equilibrium may be regained. It would be quite natural to suppose that if an amount of protein containing the same amount of nitrogen as is excreted during starvation were given to a starving animal, the intake and output of nitrogen would balance. We are led to make this assumption because we know that any business bal- ance sheet showing an excess of expenditure over income could be met by such an adjustment. But it is a very different matter with the nilfogen balance sheet of the body; for, if we give the starving animal just enough protein to cover the nitrogen loss, we shall cause the excretion to rise to a total which is practically e(iual to the starvation amount plus all that we have given as food, and although by daily giving this amount of protein there may be a slight decline in the excretion, it will never come near to being the same as that of the intake. The only effect of such feeding will be to prolong life for a few days. To strike equilibrium we must give an amount of protein whose nitrogen content is at least two and one-half ti-.es that of the starvation level. For a few days following the establishment of this more liberal diet, the nitrogen excretion will be far in ex- cess of the income, but it will gradually decline until it corre- NORMAL MKTABOMSM. 95 spoiids to the intake. Having once gaine/ p)-ofci)is shoidd vtn-n so )HU(h in //»,/> )iii(rifii'c vitlut, we must examine their ultinuite structure very closely. When the ])rotein molecule is disintegrated, as by diges- tion, it yields a great iminber of nitrogen-containing acid.s, the amino acids, as well as several bases and aromatic substances. The most important of these acids are glyein. alanin, serin, valin. leuciii, prolin, aspartic and glutamic acids, the bases being lysin. histidin and arginin and the aromatic bodies, phenylalanin, tyro- sin and tryptophan. These substances constitute the available NOKMAI. MKTAI'OI.ISM. 97 "units" or "btiiltHiiK stoiifs" of protein niolt'ciilcs, but in no two proteins an- the inaterials used exactly in the same propor- tions, some proteins liaviuK a preponderanee of one or more and an absenee of otiiers. just as in a row of houses there may be no two that are exaetly alike, allhouph for all of them the same building materials were available. Albumin and globulin are the most important i)roteins of bloml and tissues, so that th" food m\i.st contain the necessary units for their construction. If it fails in this regard, even to the extent of lacking only one of them, the organism will either be unable to construct that pro- tein, and will therefore suffer from partial starvation, or it will have to construct for itself this mi.ssing unit, a process which it can accomplish for some but not all of the above list. It is therefore api»arcnt that tho««» proteins are most valu- able as foods that contain an array of units which can be reunited to form all the varieties of protein entering into the structure of the body i)roteins. Naturally, the protein which most nearly meets the re(|uirem«'nt is meat prot<'in, so that wc arc not sur- pris«'d to fiiid tliat less of it than of any other jirotein has to 1m? taken to gain nitrogen equilibrium. ('as«'in. tne protein of milk, although it does not contain one of the most important units, namely, glycin, is almost as good as meat protein, because tlit organism is itself able to manufacture glycin. When, on the contrary, proteins such as zein from corn are given, in which cer- tain units are missing, starvation inevitably ensues. liut it does not do so if the missing unit, which in the case of zein is trypto- phan, is added to the diet. These n)ost important facts have been ascertained by experi- ments carried out in New Haven by O.sborne and Mendel. Young albino rats, just weaned, were fed on a basal diet con- sisting of the sugar, fat and salts of milk to which was added the protein whose nutrition value it was desired to study. The rats were weighwl frc a day to day. and the results plotted as a curve — the nirvc of growth. A gradually rising curve was obtained when casein or the albumin of milk or eggs, or the edestin of hemp se:>d, or the glutenin of wheat was fed, but this was not the case with the gliadin of wheat or, a.s 98 I'llVSlOtXWY P(»B PENTAf, HTl'DENTS. above mentioned, with zein of corn. It will be wen, there- fore, that of the two proteins in wheat one, gluteiiin, contains all t le .("cessary units for building up the growing tissues, but that in the other protein, gliadin. some essential unit is absent; by analysis this was found to be lysin. By adding lysin to glifldin a normal curve of growtli resulted, thus showing that this was really the missing unit. The result was made even more spectacular by feeding a batch of young rats on gliadin alone, so that they remained undeveloped and stunted, and then adding lysin to their diet, when they very <|uiekly made up for lost time, and soon reached, if not (juite, yet aim ♦ as gooil a developm^int as their more fortunate brothers who h i b«>en fed on glutenin or casein from the very start. The animal economy itself can therefore protluce certain of the amino bodies — thus, as we liave seen, it can pros of proti'iii niul carbohydrnto ill the diets wliieli the people are aceiiHtoiiUMl to live nii, and aver- affiiiK the reHultM. (hie reimirkahh- oi'teome of siieh NtatiNtieal work haH iH-eii to Hhow that for |H-ople.s living under approxi- mately the same eonditions as rejraivlH elimate and aiiioiint of daily museiilar work, the aveni^e daily rei|iiiremeiit of ealories. carbon and nitrogen works out pretty much the same. altiiou(;li there may Ik' some diversity in the proportions of protein aiuj carbohydrate. The following table shows this: Type of individualB. Pi Average workman in Germany, 20 years age. Oerman soldier in the Held British soldier in peace... UuBsian soldier in war (Man- rhurian campaign ) . . . . Professional man Such fipures can be compiled with tolerable accuracy because the diet is under control. It is of course more difficult to collect sufficiently accurate data rej^ardiiiR the diets of civilians, but it is safe to say that the average city dweller in temperate zones derives his daily requirement of 15 gr. nitrogen in 95 grammes of protein, which also yields 60 gr. of the reipiired 2.'»0 gr. car- bon. This deficit he might supply either from fats or earbohy- di'iates, the actual proportion dejM'ndiiig on availability and price. It should be particuliirly noted that the |)roporti()n of j)rotein is very much increased whenever strenuoiJs muscular work has to Ix' performed. Now the (|uestion is. do such .statistical studies substantiate Chittenden "s claim that the protein which we are accustomed to consume could profitably biiKii1. wlio howcviT Im'Ioiik to tlio SHiiie rnct' ns \hv Idwci' Ilfii KiiHs, l»nt (lifft-r from them in taking iiion' prott'iii in tlifir f«M)«l Not only this, but tl m' people arc in every wnw of the word half starved, and tiuy are very prone tt> diseas*-, espeeially of the kidneys, the very type of dis«'as«' whieh we are toli!ic(,. " have returned to their old dietetic habits. f..;aclly co ■ .'dant results have been obtained when attempts h ' been made to reduce the protein in the dietaries of [)ublic institutions such as prisons, alms houses, etc There has invari- ably been a di-stinct increase in the sick list, especially of such diseases as inieumonia. tulM-rculosis, etc. And if wc .seek for evidence of an oi)posit«' nat'iie. wc do not find that excess've protein ingestion is fraught with any evil consei|Uences to the community. Thus the Kskinm takes five times more protein tiian the Jicngali and two and one-half times more than the Kuroi)ean. and yet he is peculiarly free from "uric acid ' diseases; and his l)hysical endurance and his power of withstanding cold arc ex- traordinary, and there is no i|uarre!ingl Tliere are a great man.v .st'condar;. factors, sucli as nvailabilily. ta.stc, etc., that determine the average diet of a conununity, l)ut the main determining factors arc instinct and experience. In the struggle for existence between human races, we ma.v a.ssnme that adequacy of diet has played a role ami that the average which is taken rcj)resents that which conduces to the greatest efficiency. We have dealt at some length on those (piestions because of their great ractical imi)ortancc, and because they .show us that in the matter of the protein content of our diet, as in that of all other animal functions, there comes into pluy the princij)l(' of 102 PHYSIOLOGY FOB DENTAL STUDENTS. If ' i'i the "factor of safety." We have two lungs, although it is quite possible to live with one only, two kidneys, although one will usually suffice, and so with protein in food, we could get alon^' for some time with about half of wiiat we take, but at the con- stant risk of a deficiency, for should physical exhaustion occui-. a reserve of building stones ouglit 1o be available to restore the tissue which has been consumed. Instead of the excess of pro- tein throwing a strain on the organism, the contrary is the casi', for it is indisputably a greater strain for the tissues to have to construct new building stones than to us(> these supplied ready made in the food. Another deduction which we may «lraw from these observa- tions is that more protein should be taken when its source is mainly vegetable food than wh.n it is animal. On the other hand, there is nothing to indicate that one kind of animal pro- tein possesses any advantages over another; fiesh protein, milk protein, egg protein are practically of eijual dietetic value, and with regard to what varieties of meats— whether light or d;ii-k— are most luitritious, all we can say is that any ditferences that may be thought to exist are not due to differences in the chemical nature of the proteins which they contain, but depend on their flavor and digestibility. There are more fads and fancies about what meats are nutritious and what are not so than would fill a volume, but after all the whole question is one of flavor. ^Man digests best what he likes best, and he thrives best when digestion is good. Doctors and dentists must be i-eady to discuss ([uestions of diet, for the public likes to be treated with something more than the hard facts of science; he demands something mystical and mysterious besides: if he agrees to be fed according to calorie and protein values, he demands besides that he be told fairy tales about some peculiar virtiies which this or that vai-iety of foodstuff possesses. Very practical conclusions may be drawn from tlies«> observa- itons regarding the most suiluhlr du t {or 1h< resent in the flour. 1(1 21) 3(1 4" r>(p fi" "" *>" " 1SS5 :ui(i (I iiiii ~n Wluilc milk "j Skim mil ( Mn'csc. r.utlir. \vci;in«' mill' ' ("i» ). AviiiiKf million (raw). AvciMKi' P'lik ( niw). l-'isli — lloiiinlir (liiw). Hncon. Whciit Ixi'Mil. Ash iiiid water. mm variou."* proximat.- prin.ipl. s ( in.li.atr. .y the shadfil aivas) an.l th.- calori ( imli- rat. .■ah.ri.. yalu.s an.l Hi.' nain.s t.. th.' m li. th.- food in (iU(>»lion. DlETfVnCS. 105 Wh-ii tlu" voast has bocn allow.-d to act Un- sonu- time, or if bakiii« i)owar souj.s aro mainly dilute solutions of moat »'X- tractivc-s, but in beef t.-a. .if properly mai\ livci. urea is foinu-d. (2) If this organ th' seriously tlainajftMl. citht'r experimentally or by disease, less urea and more ammonia ai)l)ear8 in the urine. We see therefore that urea is formed in order to prevent the poisonous action of ammonia. But the am- monia may be more usefully employt'd; instead of iM-inj? com- bined with carbonic acid in order that it may be got rid of, it may be employed to neutralize, and thus render harmless, any other acids that make their ap|)earance. Thus, it nmy be em- ployed to neutralize the acids which sometimes result during the metabolism of fat, as in the disease, diabetes; or the lactic acid that ar)pears in the muscles during strenuous nuiscular exercise ; or the acids prmluced on account of inadequate oxygenation. Taking acids by the mouth has a similar effect; thus the am- monia excretion rises after drinking solutions containing weak mineral acids. Ammonia is. of course, not the only alkali which is available in the organism for the purpose of neutralizing acids. The fixed alkalies, sodium and potassium are also used. Thus. whei. we greatly increase the proportion of these, as by taking alkaline drinks, or by eating vegetable foods, the ammonia excretion diminishes. Urea is an inert substance, capable of uniting with acids to form unstable >a!i> (urea nitrate and oxalate), and like other amino bodies, being decomposed by nitrous acid so as to yield free nitrogen This latter reaction is used for the ((uantitative estimation of urea, the evolved nitrogen being proportioiml to the amount of urea, thus : CO + 2 UNO, = 2. CO. + 2 N, + 2 ILO \ NIL (Vrtain bacteria are capable of causing urea to take up 2 mole- cules of water so as to form aniiuouium carbonate, a process no I'llYHIOliOflY FOR PKNTAIi STl'DKNTS. really tlip roverso of that which weun in the orKanism and rep- rt'SiMited by the above forinul«>. This chanRe oeeui-s in urine a:i(l aeconnts for the anunoniaeal (nlor which develojw when thin fluid Ih allowed to stand. Creatinin.— This is very clow-ly related to creatin, which is the most abundant extractive substance in muscle, and which yields urea when it is boiled with weak alkali. Thew chemical facts would lead us to expect that scmie relationship nm.st exist be- tween the creatin of muscle and the creatinin and urea of urine, but, so far, it has been impossible to show what this relationship is. One very important fact has. however, Iwen brought to light, namely, that creatin makes its appearance in the urine when carbohydrate substances are not being oxidized in the body, as in starvation, and in the disease diabetes. This is one reason for the growing belief that carbohydrates are something more than mere energy materials (see p. li:}). The excretion of creatinin is so remarkably independent of the amount of i)rot«'i»i in the food that it is believed to represent more especially the end prod- uct of the protein break-down of the ti.s.sues themselves, in con- trast to urea, which partly represents the cast-off nitrogen of the protein of the food. PiRiN HoDiES. — These are of particular interest because they include uric acid, about which more nonsen.se has been written than about any other product of animal metabolism. The so- called uric acid diathesis is very largely a medical myth — a cloak for ignorance. Trie acid is the end oxidation product of the I)urin bodies, which include the hypoxanthin and xanthin of muscle and their amino derivatives, the adenin and guanin of nuclein. These relationships are .seen in the following fornuilie : ^ • f 1 f Hvpoxanthin CJl4N^0 Oxv punns of muscle } • * , . r, it xw^ ' ^ \ Xanthin CJI^N^O, . , , . ( Adenin C5II4N4NH Amino punns of nuclein . . ) ^"'^" " r. jt ^r rlx-tr (Guanin C5H4N4OMI Uric acid CsH.N.O, There are therefore two sources for uric acid in the animal TIIK MKTAHllMSM <»F I'ROTKINS. Ill bmly, naiiu'ly. th.- inusolos aiul the nudci of the e.lls. ThiH ex- plains why tin- uric acid excretion increnHcM after strenuous mus- cular work. anI<>l,(NiV KOH t>H.NTM. sTII>K,\TS. from till' (iiftary s\icli foudstiiirs hs mt-als ami sWfctbii'atlH. wh'u'li yield ('X<»Kiii(»u« |>uriiis. As wi- liavi' saiil. tlurc is no reason to iM'lifVf tliat any otiitr diseases Insides i^oiit are due to excess of uric acid in the )il*H)d. Ilesides the above there are traces of nllnr iiitrot/t mmx siih- sttnirfs in tlie urine, such as: 1. Hijipuric acid, whieli. as its name si^Miifies. is very alnin- dnnt in the urine of the liorse and other herhivora. and which is the excretory product of the aronuitic sul»staiiees whicli the fond of these ainiiials contains. 2. Cystin. an amino acid containing sulphur. :{. I'i(;ments and inuciii. The exact si;iiiili(iitiii iif llu rtiil firoihu Is of nilroiii iioiis mi I- iiholism has heeii very lieautifully demon.strated liy Folin. of Harvard. The nbservations vere mad*' on several men who lived for .s'MMc wliicli was very poor in protein. The ]H'ohlein was to see how each o'" the nitrdp-noiis constituents Itehaved duiinjr the two periods, both absolutely and in relation to the total amount of idtroncii "xcreted. In or- der to sliow the latter relationship the results are jrivcn, as in the following; table, not as urea, etc.. but as ureii-iiitro>rcn. etc: On tlif protein-rich On the protrlii- diet poor diet Quantity of urine 1170 c. c. 385 c. c. Total nitrogen 16.8 gr. :!.« gr. Urea-nitrogen 14.7 gr. (87 5) 2.2 gr. (61.7) Ammonia-nitrogen 0.4!t gr. (:?.(•) 0,42 gr. (11..!) Uric acid-nitrogen 0.18 gr. (1.1) (».()!» gr. (2.r)) ("reatininnitrogen (».58 gr. (:!.6) 0.60 gr. (17 2) Undetermined nitrogen ... i>.85 gr. (4.9) 0.27 gr. (7.;!) Th(! tij?urcs in i)arenthe.si's repre.senl the jieie ntatje which the nitrogen of eacii substance furnishes of the total amount of nitro- {ren excreted. It will be seen that urea decrea.ses on the poor dirt relatively more than total nitrDgio. thus indicating that it comes partly from proteins in the food (exogenous) and partly TIIK MKTM«H.I>M i »K I'KUTKI.NS. 1i:J fniiii fill' oru'iiiiiiHiit it*l>' (••rMlo«;ortaiit of these eiidojieiious bodies is evidently Cnitlinin, for, as will be seen from the above table, this substance is excreted in the same absolute amount during' both the starvation and the protein-rieh periods. Direct eviilence t . t this conclusion is correct has been ob- tained by e\aiiiinatioii of the blood and muscles for amino botlies, ammonia and urea. Tiie results have shown that the amino bodies altsoibed from tlie intestine arc carried through the liver into the .systemic blood, which transports them to thi' muscb'S, > here those that arc not recjuired for building up the tissues arc l)roken down into ammonia and a carbonaceous residue, which Is then burned just exactly as if it were carbohytlrate or fat. The ast'less aniinonia becomes converted into urea in the manner already described, either in the muscles themselves, or by beinj; carried to the liver, which, as we have seen, possesses to a Very hi^h decree the jjower of i)roduc'iiif; urea. The Relative Importance of Proteins, Pats a »2). Carbohydrates are very readily depos- ited as a stareh-like snl)stanee. called jjlycogen. and this reserve is tlie first to l)e called on. not only in starvation, l)ut also when muscular work is perfornn'd. It nuiy be considered as the most immediately available material for eond)Ustion in tlie organism, but the limits of its storage are restricted in man to some hun- dreds of grammes, which, as we have .seen, .soon becomes used lip in starvatioji. Fat is i)re-eminently the .storage material, and the supply may serve in man to furnish, along with a little pro- tein, enough fuel for several weeks" existence. The relative importance of the tliree foodstuiVs is shown in the extent to which each is used in the wdaholism ilurinij nuisnilnr /.rrrcisr. When tliere is an abundant store of glycogen, the energy is entirely derived from this source: when there is little glycogen but mucli fat. it is fat that is burned, and when neither of these is abundant but much jirotein is being taken with the food, or the animal is reduced to living on its own tissues, as in starvation, it is protein. In other words, the type of metabolism occurring during muscular work is the same as that which imme- diately preceded it ; the only change is in the extent of the com- bustion, not in the nature of the fuel employed. ifisn CHAPTER XII. SPECIAL .METABOLISM (ContM). Metabolism of Fats. — Fats are absorl)od into the lacteals and (list'liarged into tho blood of the left subclavian vein through the thoracic duct. They arc carried to various i)arts of the body and gain entry into the cells, in the i)rotoplasin of which they become deposited. This process occurs extensively in the sub- cutaneous connective tissues, iH'tweeii the muscles, and retroperi- toneally around the kidney (the suet). The fat which is thus deposited pos.sesses more or less tln^ .same ((ualities as the fat of the food. Thus, when the oidy fat taken over a long jx'riod of time is one with a very low melting-i)oint, such an oil, the fat deposited in the tis.sues is likely to be oily in characti-r, whereas it is stitl' after feeding with a high melting-point fat, .such as nnitton fat. This similarity between the tissue fat and that of the fiKHl beconu's very striking when the animal has been sub- jected to a preliminai-y i)eriod of starvation and then fed for some weeks with a large excess of the jiarticular fat and as little cai'bohydrate and i)rotein as possible. Fat in the IVmmI is of course not the only source of the fat in the tissues. It also be- comes formed out of carbohydi'ates, a fact wiiieh is well known to farmers, who fatten their stock by feeding them with maize and other starchy grains, and to i)hysicians, who reduce their cor])ulent patients by restricting carbohydrate foods. The fat thus deposited has the chemical characteristics of the fat which is peculiar to that animal. It is alinost certain that there is ordi- narily no formation of fat out of protein in the higher animals. The fat thus deposited in the tissues may remain for a long time, but ultin\ati'ly it is again taken up by the blood and car- ried to whatever active tissue rei|uires it as fuel. Before being thus burnt, it si)lits into glycerine and fat acid (see j). 7.")). Tlie fat acid possibly undergoes some preliminary change in the 115 ifrn^ 116 PHYSIOLOGY POH DKNTAL STl'DENTS. 'ivci'; ill any ciisc. Ilic loiijf cliaiii (if ciirlHiii atoms of which we have seen fat acid iiiolcciiic to be composed (sec p. 24,, liccoiucs oxidized (burnt), not all at once but iiiece by piece, two carbon atoms beiiif,' split ofT at a time. If the fat acid chain orijiinally contained an even number of carbon atoms, the oxidation process may stop short when there are yet four carbon atoms in tlie chain, thus producing o.xybutryic acid ({.'II;,('II()II<'IL("()OII). This imperfect metabolism of fat oc- curs in severe cases of iliabetes and often causes death. It also occurs in carbohydrate starvation, and indicates, more clearly than any thing else, tliat even caibohydrates are essential for life. Metabolism of Carbohydrates. — It will be remembered that these include the starches and the sugars, and that during diges- tion they are all hydrolyzed to dextrose or hevulose, as which they are absorbed into the blood of the portal vein. This ab- sorption is rapid, so that a striking increase in the percentage of sugar occurs in the blood of the portal vein shortly after the food has been taken. :Most of this excess of sugar does not imme- diately gain entry to the blood of the systemic circulation, how- ever, because it is retained by the liver. For this purpose the liver cells convert the sugar into the starch-like substance, (jlyco- (jot, which becomes deposited in their protoplasm as irregular colloidal mas.ses, which stain with iodine and carmine. The liver does not manage in this way to remove all of the excess of sugar from the portal blood, so that, even in a healthy animal, there is a distinct postprandial increase of sugar, or hyperglyciemia. as it is called, in the systemic l)lood. If too nuich sugar passes the liver it causes so marked a postprandial hyperglyca'mia that some sugar escapes into the uriiii'. thus causing (jlycnsiiria, which is one of the early symptoms of diabetes, and whose occurrence furnishes us with a warning that less carbohv : tes should be given in the food. If the warning be heedeu. the severer foi-m of the disease will very i)robably be staved otY. The glycogen deposited in the liver stays there until the per- centage of sugar in the systemic blood begins to fall below its proper level (which in man is about 0.1 jier cent), when it becomes reconverted into sugar, which is added to the blood. THE METABOLISM OP CARBOHYDRATES. 117 The reason why the sugar in the systemio bhwid tends to fall is that the tissues, espeeially the nniseh's. are usiiip it up as fuel. If so mueh sugar is taken tliat tlie storage eapaeity of the liver is overstepped, the e.veess of sugar is carried Ity the .sy.stenne blood to the tissues, where mueh of it may be changed into fat. The (jltfcogcnic fiinctian of the liver, as the above pnteess is called, is analogous to the stai'cli-forining fuiuMion of inany plants, such as potatoes, of the sugar which is formed in the green leaves, some is immediately used for buihling up other substances, the remainder being converted into starch, which 1m>- pomes dei)osited in the roots, etc.. until it is rccjuired (as during the second yeai''s growth i. wiien it is gradually reconverted into sugar. Besides carboh.si rates it is known that proteins form glyco- gen; fats, however, eaiuiot form it. In severe caws uf diabetes it is therefore usual to tind that althougli earbohyei'ccntage of sugar in the systemic blood is effecteil partly through the nervous system and partly by means of substances called chemical mes- sengers or hormones (see j). 124) seci'eted into the blood from tlie ductless glands, such as tln> i>anereas and the adrenals. Tln' very first syvtptoms of mia becomes more and more marked and takes longer to disappear, so that there comes to be a permanent increase in the percentage of sugar in the blood. This persistent excess of sugar acts as a poison and causes deterioration of many of tiie tissues, and if unchecked will lead to severe diabetr It is for tliese reasons that diabetes is relatively c. amongst locomotive engineers and ship captains; it is -lo said to be distinctly on the increase amongst business men. A most important element in the treatment of diabetes is tlierefore removal of the possible causes of nerve strain. Rest and M"i*'t and freedom from worry, cmii.le.l with removal of sufficient auKmnts of carbohydrates fi'om the 1 !i1(.M.- tho boat soon stops, with excess of potas-siuni an inunc.liat.' paralysis ocenrs. and witli excess of calcium an iniine.liate rifior or permanent contraction. Analogous results are obtainetl with other muscles. Salts in cci'tain projiortions may ev(>ii cause .j.roccsscs of ceil division to start in tli.' ova of sonn' of the lower animals. In other words, a process of .•mhryo (h'velojjnn'nt may whidi is usually indued by impregnation by Die male dements. Vitamines. Tvpially remarkabb' as adjinicts of diet is a class of bodies calb'd vitamines. Without tliem metabolism becomes upset, and serious symptoms make their ai.pearance with per- haps death as the ultimate r-snlt : and this happens even altlioU','h the protein, fat, carbohydrate and inorganic salts of the diet be in proper proportion. The first indication of the imi)ortance of vitamines was furnished by observations on a disease calleil liiri-liiri, which occurs anion*,' peoples of tropical countri«'S. and is characterized by severe neural<,'ie pains, muscular weakness and paralysis: symi>toms which are due to inflanunation of the ncrv.'S (neuritis). It was note.l that it occurred most frequently in the cas(( of people whose main article of diet was polished rice, but was infre(iuent in the ease of tliose usin^' the unpol- islied grain. The difference between these two grades of rice is that the on.- (the unpolished) still contains .some of tho brown- ish husk ; the otlier is free of it. This observation suggested tho experimont of adding some of the ground-up rice husks to tho polished vice diet of those suffering from the disease, with the result that the symptoms soon disappeai-ed. :Moreover, when unpolished rice was supplied, in place of polished rice, to natives among whom l',eri-P.eri was very prevalent, the disease disap- peared entirely. Other foodstuff's contain this vitamine, so that Beri-Bcri does not occur with mixed diets. In order to learn something more about these remarkable sub- stances it wa.s necessary to seek for some animal in which .symp- toms similar to those of I'.eri-lh-ri coidd be indii 1 by feeding with polished I'ice. Pigeons were foi nd most suitable. When these birds are kept exclusively on such a diet, they dcveloi> the U'^ 122 PIIVSIOKOOY FtiR DENTAIi STl'DENTS. most alarming symptoms of neuritis (paralysis, weakness, etc.), which however disappear in a few houis. not only when unpol- ished riee or riee polishinjrs (or husks) are given, hut also when meat, or heans, or a small pie<'e of yeast is mixed with the rice. Attempts have naturally bi'en made to isolate the substance which is responsible for this i-emarkable action, and indeed some success can already be reported. For exampU". it lias been pos- sible to separate from riee polishings and from yeast snudl traces of crystalline substances having a most powerful action in pre- venting Jieuritis. Even such success in investigating the ca\ise of IJeri-Bcri in rice-feeders would scarcely warrant us in asserting that vita- mines are essential constituents of our own varied diets. To show that they are. however, iias been mo very difficult task. Tiius, it is known that although young rats thrive admirably on milk diet, they fail to do so on one of artificial milk, that is. of milk made in the laboratory by mixing together, in proi)er proportions, the same proteins, fats, carbohydrates and salts that occur in milk. In this chemical mixture, .something is wanting wliich exists oidy when the ingredients of milk are compounded by the mannnary glands. The addition to synthetic milk of desiccated milk from which most of the proteins had been removed bestowed on it full nutritive value. The practical importance of this observation in tlie feeding of infants, we lu'ed not insist on. Suffice it to say tiiat it is quite po.ssible that i)rolonged boiling of milk, as for its .sterilization, nuiy deprive it of vitamines and tlius render the child liaiile to such diseases as rickets and infantile scurvy, or at least interfere materially with its proper development and growtii. Among the symptoms th\is ])roduced, esi)ecially in the ca.se of infautili! .scurvy, ulcers may develop on the gums, or the teeth may become loaseneil. Change of diet may in a few days restore perfect health, or even the addition of a few teaspoonfuls of orange or lemon ,iuice to liie original diet may sutlice. It is often miracu- lous how <|uiekly such ti'eatnient may change a fretful, pain- stricken ciiild to one of perfect health and cheerfulness. InnuiuerabK' other exanipUs uf llie wundirful infiuciicc of VITAMINKS. 123 tlu'se nivHteriouH vitniniii.'s in nutrition nuKlit l)e fitt-d. Tlif practieal point to bear in n.iiul is that, howcvor convctly our ilict may Iw coniposwl with roRanl to calorie and ch.Mnical r.M|unv- mcnts, it is likely to W unsviitable unless it eoiitains a eertain, thouRh perhaps extremely minut.". amount of the drug-like sub- stance called vitamines. i CHAPTER XIII. THK DL'CTLESS (JLANDS. Introductory. — We have no more than toiiclicd Ihe very l'iin(?e of the subjeet of metabolism, ami yi-t we liavc li-ariicd enough to imi)ress us with the faet that ..1th' Utfli it is extremely eomplieated, it is ncvfrtlieh'ss undt-r pi-rftct eontrol. Jt renuiiiis for us to learn soncthinK regardinj? the nature of this eontrol. If we take sueh a metabolic process as that which carbohy- drates undergo, we should expect that the conditions which deter- mine whether glycogen shall be formed or broken down would be chemical in nature. We should expect, in other words, that some change in the chemical composition of the blood — either its reaction or the amount of sugar in it, or the appearance in it of some decomposition product of sugar — woidd determine whetlier or not glycogen .should be mobilized a-s sugar. In muscnlai- work, fm- example, sugar is re(|uir(Hl by the contracting nniscles. and we find that the gbcogen stores in the liver become very quickly dei)leted to meet the denmnd. The (jue.stion is, how do the mus- cles transmit their re(|uiremeiits to the liver so as to cause this organ to mobilize the dextro.se? Our natural assumption would be that the active muscles cause some change to occui "u the blood and that it is this change which excites the liver cells. Such a control of the metabolic activities of one tissue by prod- ucts of the activity of another, transmitted between them In way of the blood, is known as hormone control. We have already become ac(iuainted with it in connection with the control of cer- tain of the digestive glands, particularly the pancreas (see p. 72), and it is no doubt very largely by sueh a mechanism that a given metabolic i>rocess becomes active or supre.ssed, as occasion demands. The hormones in sueli eases are in part tiie intermediary \u-m\- nets of metabolism, but besides these hormones others must exist 124 TIIK. THYKOin CI.ANO. 125 tt. rail fortli •»!• ivnnlatr tlir aclivitifs of tissihs wliicli arv not iiniiir.liattiy coiiciiu'd in ^r.•M»•l■al ni.'tal.nliHni Will ratli.T witli HiM'«-iul proc'ssfs, siH-h as tli." i-Xfitubility of the n.rvous syst.-ni (»'. >?., adivnalin"). tli.' iM-havior of tli.- ivpn)sf toK.-tli.T. liowcv. r. that it is v.-iy ditli- cult to study th«'ir scparat.- functions. Th.- iinportaiicf of tii.' Klnnds is indicated by the relatively large hlmxl supply. Fip. 10.— Cretin. Ift years old. The treatment with tli.vrold extract was started too late to lie of benetil. (Talient of I >r. S. J. Wel.ster.) "When the tiiyroid is not properly developed in children, the condition is known as entiiiism (Fif?. 10). The child fails to grow in height, although its bones may thicken. It cranial bones soon fuse together, so that the growth of the brain is hindered Tin; TliVKHll) (il,\M). r. iithl till- iiii'iitiil |M»\virs r.iil to ilivilitp. It thus h.coiius iMiolir. :iiiil iiltliiiimli it niiiv live lor Vfjiis. it will niiiiiiii tvin at lliirt.v \ in noiim' wa.v witli thf ilcticicncy of tlif thy- roid, for if thf fntiii hi' >;ivtn ixtract of this kIiiikI. itn comiition will iiiiiiitMliatfly iiiiprovc, ami imli'iMJ. if tai<.n early enough, it may quickly iiiaki- up for lost time aiitl yrow hotli phyHically and iiii'iitally as it ou^ht to. Atrophy of the thyroid tfland in older persons causes nii/rn- ill mil 1 l*"i«. lit. The syiiiptoins of this arc wvy characteris- ( Tigerstedt. ) tic. lieiu^ iixist coniiiionly seen in women. The skin is dry and often of a yellowish color, the hair falls out. the suhcutaueoiis tissues yrow excessively, so that th( hands, the feet ainl the face become large and j)un'y. and the speech indistinct. Iiecause of the thickening' of the lips. The nietaholism .il-o becomes very slu^;- flish, so that the intake of food and tl e \cretioii of nitrogen in the urine become diminislied, and tlie teniperalurc siibuormal. If 128 IMIYSloLOiiY KOU UKNTAI. STIDKNTS. li U ' tit-- i t ^ „„,,i...-k,..l. n,..nl.l syn.ptoM.s Ium-omu. Mpi.ania. hrst ol , 1 a ,,inn. o,- th. iut..ll....t .1,1. sl,..,.ln..ss ana '.■^'-•K>. -^ ^^-; n,us..ulnr twlt.-l.iM.s and t-vnors. Just as m '•"■^' -" '^ ' X to disappear, so that in a nn-ntl. or so th. patuM.t luay has ■ r"tunu..l to his or her uunnal ..on.litlon, to nuuntau. winch, ho.- ,.vor tl... thvroi.l extract must continue to be given. When the", lan.l is removed surgically, either m lower annnaK „r in nun., verv aeut. syn.pton.s ending in death usually su.e,- " , These include a peculiar form of muscular tremor cal d :;,, passing into actual convulsions, which, by .nvoWn.g th respiitorv >uusclcs. ultimately cause dyspna-a and death is, Loweve;. probable that these nervous p-.nptoms - ;^- ^^ „ .avoidable removal of the parathyr...d gland Ihe bt.i ...oved by giving -alciun. salts. T'''"-, ^-'ij' ^y" ' with deficiency of the thyroid are grouped together as h>ji>oliu, "Ei^;;-in healthy individuals thyroid extract taken by mouth ..xeites a n.ore active metabolisn., and may cai.se increased lu . ac itv One result of this increased metabolism is disappeai- .c of subcutaneous fat and increased appetite thus rendering Ur^^ninistration of moderate doses of thyroid ex^ra^ a no uncommon method of treatment tor obesity. ^^ ^^^fT'^ should never be attempted except under ^^^^^^^^ ,^^f^^, eian, for it is very .-asy to take t..o much of the ext.act and (aus. iialnitation and lu'i'vous excitement. ' Iv en the thvroid (and parathyroid) glands become exc-ss- iv^r tive in imui. the condition is called km>n-^U,roul..U and :!-s;., ptoms are very like those above described as p roc need ;. tiking thyroid extract. To be exact, tl.y are p.ilp at n wasting of the muscles an.l conscMuent weakness, '-tu . ■ousneL and pr<,trusion of the eyeballs. On "-"-^^^^ ^^ nK-ntioned svmi,tom the condition is usually called ,xophlh„hnu ; Thi; a nte and often fatal disease is to be distinguished ? m"^,v,>uc noUr.:, in which there are very few gem-ra symp- us, but greal enlargement of the thyroid ^^^^^^^^ largJment which may be so pronounced as practically to obUtci ^<3^S^^ Tin; ADUI.NAI. (il.ANDS 12t) Mti' tilt' neck iiiid siMiictiincs so compress the tniclicii iis to iiitcr- fm" witli liri'iitliiii'r. Tlic cnscs of clironic jroitn- occur in tin- siiiiic l)taiiu'r,m>,i>,, mlroin or rpinrphri,,. It is a eompa.'atively simple chemical body, having the formula ; (11 (II())(' iClKIIiOlIjriL — MICH, (1I())C iCII (•II and .-xisting in two vari.'ties which diffe." from one another ae- coi'ding to the din-ction to which the plane of polarized light is rotated. The vai'iety rotating to the left is. by many t.nies. stronger in its physiological actions than that which rotates to the right. The discovery of its eh.'mical structure has made it l)ossible for chemists to prepare suj.rarenin synthetically, and al«o to prepare a ser.es of ivlated substances having less n.arked l.roperties of a similar kind. These are closely r..late„ the other hand, the posterior lobe can be removed with un- punitv. althouRh .-xtracts of it have profoun.l physioloK.cal ,,tf,.i.ts when they are injected into normal animals. ■DiiifBiilis symp- Aflei KiK U -A. To s.,..w th.. appeKrano.. Uefo.v the onset ..t "-^r,u-^.U. .: „.,U «. T.,.. ..ppearan... aft.-r .ev.ntoen years of ...e disease. (. CiimpbeU (ieddes. ) The Spleen.-Notwithstandintr the fact that this is the larg- est of the ductless glands, it is the one whos,- functions are the least well und.'rsto.xl. It can be ex.ise.l without causing any .videiit disturbance, an.l extracts of it when injected mtraven- ouslv do not have any characteristic etTects. It beconu.s wry much enlarge,! in certain .liseases. namely: (D n. leucocythe- „na. a form of aiuemia, which is characterized by a great increase in the leuco<-ytes of the blood (see p. 145) ; (2) in typhoid U^vv (enteric fevc-r) : (3) in malaria. It becomes contracted after TIIK TIlVMrs til. AM). i:{:{ liikiiifj i|uiiiiii('. T'mlcr tlic niieroscoix' it is seen to he (•(iiiipiisiMJ of a spoil",'!' of fibrous tissue, tlic sfmccs iM'injr tiili'd witli blood, whicli flows frt'fiy into them from artcriolfs in wliosc walls lyiiiplioid tissue is abundant. Here and liiere. tiiis lymphoid tissue l)eeomes collected in nodules, wliieli are larp' eiioujili to be .seen l)y tlie naked eye and are called .Malpijrhiaii corpuscles. In tlie blocul of the spleen, partly broken down erythrocytes are often visible. Soinctimes. also, cells like those found in red bone marrow and having; to do with the manufacture of new red corpuscles make their api)earance. Taking all these facts togethi'r, it is believed that the spleen has the following functions: (1) manufacture of leucocytes; (2) inamifacture of erythrocytes; (;5) destruction of erythro- cytes; (4) removal from the blood of certain poisons. The Thymus Gland. — The thymus gland, situated at the root of the neck, is (|uite large at birth, but its si/e gradually dimin- ishes as the animal grows. I>y the time that puberty is reached, it has almost di.sappeared. It is composed of peculiarly arranged lymphoid ti.ssuo, having nt'sts of epithelial cells embedded in it. It .seems to bear some relationship to the generative glands, for its removal in young male animals hastens the growth of the testes. 1 n Vm (IIAPTKH XIV. ANLMAI. HEAT AND FEVEU. 1„ c-onsLl.Tin^ tlu- ,.n.bl.-n, of aninw.l iu-at. it is .ss.ntial t-. ,„,,r c-lcarlv in nu.ul th. .listinctiou In-tw.-.M. anu.unt a.ul int.. - sitv of heat. Tlu- for.nn- is nu-asun-l in caloru-s (s.-. p. K4 , ,, ,, , „,a„ a n.axin.al tiu.rn.oMu.t.- w.th the ^>^^ .r V.ut\^VH,W seal., is placul in soni. prot.-.-t.-a part of ti.e l.o.l>. as the mouth, the axiUa or the .v.-tun.. It is foun.l by suc-h n.eas „,,nH.nt that the tenu-rature varies aeeor.l,n« to the s.t^e oi ob- servation an.l the tin.e ..f day. It vanes between .{b.O^ ( . (%8^' V ) ar-.l :n.8 C (100.0 K. i in th.- reetuni; l.etween .i(,..5 (• ;!,73' F.) and :{T.5 C. {^^ F.) in the axilla; ami between :J6 ' C' (96.8^ F.) an.1 :n.25 C. (!H).:r F.; in the mouth. These variations in.lieate that the ten.perature is higher ,n tl^' deeper than in the snpertieial parts of the body; ^n other wonls H at t,H. visceral blood is warn.er tl>an tiu.t of the snrtaee ot the bod> The variations of ten.perature. due to the tune ot day are n.ost evident when it is taken in the reetnn.. and they anumn m health ,., , Httle ov..r 1 C or a little below 2 F.. the h.ghest ten.pe. ^ ture oceurri),g about :? p. m.. an.l the lowest about 3 a. m. This is called the iUurnol rarialion an.l it n.ay b.-.-om.- ...u.-l, ^tvat.-i in febrile diseast^s. i i ..^> Anin.als whos.- ten.p.-rature b.-haves as above described are called warm-bloodai in contrast to ..ther anm.als. .-alh-.l ro/. - l^loodecl, in wh.>m it is only a d..gree ..r two above hat ot 1 . air with which it runs parallel. Such annuals n.clu.l.. hsl • s an.phibians. snak.-s, etc. U.^w.-en the eol.l an.l the warm-bloo. ed ani nals is a gr.mp in whi.-h the aninud is warm-blo..de,l nt sum- ;;:: an.l col.l bl.>o.l.-,l in winter. These are tl... Jul. r.aln,, 'on- ,„„ls, such as the luMl«eh.>j;, the marmot, th.- bat. et.-. In tins coni-ectiou it is interesting to note that th.> human u.fant be- 134 AXIMAI- IIKAT AND FIAT.U. i:?.') hav.'s more or Irss lik.' a cold-hlofxlcl aiiiiii.il for some time ini- in.'diatcly following birtli. .luiin« wliicli jH-riod it must tlu-n-- fore be carefully protected from cooling', for. if its temperature he allowed to fidl to any considerable extent, it is not likely to survive. It tak.'s sev.'ral moiitlis before the heat rejmlatin>; mechanism bec(mies so .leveloped that the infant can withstand anv considerable dejrree of cold. Factors Concerned in Maintaining the Body Temperature.— The body temi)erature is a balance between heat production and heat loss. Heat is prixhical by combustion of the orjranic food- stuffs in the muscles, the amoun which each foodstutf thus pro- duces being the same as when is burnerotein. where allowance must be made for the incomplete condaistion of this substance in the animal body (see 1). S.">). The nuisdes are tli<-refore the furnaces of the ani- mal body, the fuel bein}? the organic foodstuffs. Heat is lost from the body nnvwW from the skin, but partly also fi'om the lungs and in excreta. Heat loss from the skin is brought abmit by the utilization of several physical proces.ses, namely: (1) by conduction along objects which are in contact with the skin ()r through the air; (2) by convei-tion. that is. by being carried away in currents of air which move about the body; (M) by radi- atioii; (4) by evaporation of sweat. This last is the means by which most heat can be lo.st. because it takes a large amount of latent heat to vai)ori/.e the sweat (see p. 20). Heat loss from the lungs is mainly due to vaporization of water, with which the exi)ired air is saturated. .\ small anu)unt is also alworbed in warming the air itself. The heat lost in the urine and fu'ces is almost negligible. The Regulation of the Body Temperature.— It is i)lain that a very .sensitive rcgiilatory mt-ehanism must exist in order that the production and loss of lieat may be so ad.justed as to keep the body tempi-ratur.' practically constant. When lieat loss becomes excessive, then must heat i)ro(luetion be increased to imiintain the balance, and rln n rso when heat loss is slight. The conditions are to a certain extent comparable with those obtaining in a house heated bv a furnace and railiator.s and provided with a i:!(; I'llYMOl.d'.V KOK DKATAl. STIOKNTS. t,...,,„o-r..Kulator. wln.lu lu-in, a.-tivat.-.l l-y U.-U-unu-vMnv. of tlu- n.oins. acts .... tlu- fuma.M- s., as to ....s.- ...■ I..vv.t .ts ,at.. ut 1„ tl..- a..imal l.o.lv tl.- 1lu..-...o-.v-ulato.- ,s tl.. ur^um. s s- t..,„ \Vl.H..-v.'.- 11..' t.i..iM..'atu.v of tl.. I.I00.I .-haop's l.-oin tl..- „„,;„,,. . ......v.. ......tn. .-all..! tl..- //nmo,,./.. l..-o,„.-s a.-t.-, on with tl..- .vs..lt that it t,-a..s...i1s i>,.imls,-s t.. tl..- .....s.-h-s. Nvh..li. ,,, i„,n.asi..^' ..r .lin.inishi.,n th.-i.- to...- (s.-.- ,.2..:$.. .-aos.. a ./n-at.-r or a h-ss h.-at-i..-o.lu.-ti.>... I'-.t th- .-.-..t.v . lo.-s umv tl.a.. ^l... th..rn,o.r.-jj,.lato.. of a l.o,.s... f...- it .•.mt.-..ls th- a,.-...-..-s ot h.-at-loss Thus. wl..-.. tl..- I.I00.I t,-...p.-rat,..v t.-...ls t.. r.s.-. tl..- t„..,„H>,....i.- c..-..t.-.- -aUM-s .....n- h..at t.= 1..- Inst f...... th.- sk... a... ,,„.,. i,. tl... followi..,' ways : (1 . It a.-ts o.. th- h 00. v.-ss. s , f ,h.. ski... .....sin, th-,.. to .lilat.. so that ...on- hlo.-l .s hr..u,ht t th.. s,.rfac-- of th- h...ly to 1.- ..x.l-.l otT. (2) It .-x.-.t.-s th- ,s«-at .lan.ls. so that ...o.-.- h.-at has to h.- ,.tili/,.-.l t.. .-vaporat.- th.- sw.-at. (15) It .ii.i.-k-ns th.- n-spiratio-.s. so that ...o.v a..- has t.. l..- wan...-.l a..a saturat-.l with n.ois,.,,--. Th.- .l-.n-.- to wh.-h th.s- ,.,„,i„^ pm-SH-s a.-.- ,.s.-.l va.-i-s i.. .iitV-n-..t a...n.als lh,.s the dojj. si,.- th-,v an- ..o svv.-al ^'la„.is ov.-,- th- su.-ta-.- ot h. iKxlv (th-v ar- -oi.fi.UMl to th.- na.ls ..f th- paws), .„.-n-as.- .„ th.- ,-..spi,-atiou is th. chi-f ,...-tho.l ..f -ooli,.«. l.-> tl..- pa..ti,.^' 0,1 warm .lays. ; , ti . 1„ th.- -as,> of ,..a>.. civili/ati..,. has st-pp.-l .„ to ass.st t „ ,vt1.-x -o,.t,-ol of h-at loss, as by th.- .-hoi.-.- of H.-thn,,' a,..i th- artiti-ial h-ati..^ of .•oo„.s. D-si.-ahh- tl...u..h th.s vol,„.ta,-y ......trol of h-at-l«ss f,-.„.. th.- h...ly -aay h.-. tl-,v -a,, h- 1> *• .lo.iht that it is oft.-., ov-nl..,.- to th- .l.-t,-n.,-..t ot «ooss f.-.m. th- hody in,.! th-n-hv 1..W.-.-S th- to..- a,..l h.-at pn..l,.-tio,. of th- ,.,us-,.lar svst-n, Th- foo.i is th.-n-hy i..-..„.pl.-t.-ly ,..-tal...l,/.-.l a,..l ,s stored away as fat ; th- s„p..,-fi-ial .-ai.iUa.-i.-s a,-.- ......stn.^.-.l a... th- ski.. h.-c-..,.i-s l.loo,ll-ss. r.ut it is ,.ot l..oks alo,,.- that snt .- , b.,t h..alth.as w.-U, fo.-. hy havi..^' s., littl- 1.. .lo. ti„- h.-at-,v-u at- \uyr ,...-ha,.is„. n-ts out of f..-ar so that wl.-.. it ,s .--..u.,--.! o a.; as wh-,1 Ih- p-rson go., uutsitl-. it .nay ,.„t do so p,-o,.,ptly AMMM. in;\l' AM' KIAI.U. VM wliat. ana ..ata.Tl.s...t.-.. an. tlH., vM.lt. TI....V ..an h. h,t ,■ .1,.,. t that nuM-h of tl„. l..-n..tit nf .M-'M-air sl....,..n^ ,s . n. "' 1'- ;' - stant stinn.lation of th- n.-tal-.h,. ,.r ss-s wln.-l. .t h,.n>;s "'"It iniiM.rtan... nl- ,1.. ,.va,M..alion nl' su..at in l.rin^in^ alM ,.,s.s ..f h..at in nnn. partly .xplains wl,v ,ll.,al, sln.nM In.v. su .„„,,„„,„ inHu.n.... nn l.is w,.ll-l...inv'. it is ..ut s., nu,..!. tlw ,.,,;,,,,,,,,, ..Ml., air. as its n.lativ.. Innniai.y. lliat .s n u.M.".- „„,',, that is. tl... .h.,Mv... ..M.n.ss,..! i.. p..m.nta,.-. K. whu-h th. .,n- issatnn.t...l with n.nistnn. at th. t,.>n|nTatn.v ot „l.s..rvatmn Thus, a ivlativ.. h.nnnlitv of T-". l-.-r .-nt at L". C n.-ans hat th. air .Mmtains T-'. p.r ....nt of tl... total anu.unt of n.o.stur.. xvh..-l. it w.ul.l .-ontain if it w..r.. saturat...! with n.oistnr.. at a t.. al...v.. th,. nor.nal limits ,-onstitut..s f..v.r. ^\\u^u ..f sli^'ht rh.'r in in- fants and youiijr chihlrfu than in aihilts. As to th' Kins, s of f( VI r, two possihiliti.-s .'.\ist : citli.T ( 1 ) that h.-at ].ro:oin<,' '>n m the bodv (see J). SSi. (•ertain drugs called antipyretics lower the temperature in fever Tlio most important of these arc aeetanilidc. salicylates (aspirin). phena<-etin. and .|uinine. The first three menti.med act on the thermofrcnic centre, whereas .piinine seems to act directlv on the combustion processes in the muscles. The body temperature is raisi-.l by cocaine and by the toxic pro.lucts of bacterial growth. Hveii cultures which have 1 n att.-miated by keeping them for s-ime time at high temi.eratuivs have this eff.'ct. and it is believe.l by nmny that fev.'r is of the nature (.f ii j>rotective mechanism to destroy or attenuate the invadiii',' bacteria. There is bacteriological as well as KKVKK. 139 t,K..u...us Of ..rvsip.-las^ oaM.u.t livo at a iHnp.-.at.uv ahoo 41 !;:, Hw,l..nM>..tiH.ts an. nm..lMnon. liU.ly to survm. .t th,. .l.s. ..„se iH. a.-.-on.|.anu-.l by a n.o.l.rat. .l.-«n-.' of f.-vr. p..^:;^:. is abovoth. limits of saf..t>. Wh..n sw..at>n« a,..l otla.r ,.nu...sH..s l,v wl.iH, l...at is lost fr..n. ,l- boMy a.v aH- ' nro,u- Iv it is .v.narkabl.. bow bi«b an a.r t..n.,.-a1u.v u,a> ri,n'wm..ntMan...r:for..xanM.b..in.lry,n^ L son., n.inut.s in an ov..n at 100 (^ wb.b. lus ann.r ...^^^^ ,,..si.l.. bin. (l.'onanl llillK H'.t if anyth,n« shonM .ntnt.. . will, boat loss, or if b.-at ,.n..luHion 1 x.-.-ss.v.- as .lnnn« "U.s- ,.„,,,. .xen-iso. tb.Mv is Mhvays dan...- of boat strok.-. b n- n.ov.- ,„,„t „f ,1,, air is probably tb. n.ost in„.ortant way t..r sat.- .uanlin, against .l..H.-i.-..t b..at b.ss. I, is almost n-lam y on a.-.-onnt of tin. abson.-.. of sn-b air n.ov..>n..nt. .-oupb..! ^^.tl a l.inh .vlativ.. bun,i,iity. tlu.t .lis.-on.foH is ..xp-.n.-nn. .n bot. stuffv atn>osplu.n.s. for lb., fa.illy b.at b.ss .-ans-s a sl.jibt nsr i„ hiuly t..n.,H.ratun.. Tbis sli«bt .b'^-n-.. of byporpyraxn, low- ers iht' n.sistanc.' of tb.- ortranisni to inf..ction. CIIAI'TKIJ XV. TIIK liLOOl), Introduction.— The iiulividiml .'.lis formiiiu tlif most sin.j.l.' tvpcs of liff arc iiounshcd l».v suliHtaiics wliidi tlu'.v ol.liiiii (li(vctly from tlif wat.r in which the aiiiniiil lives. In cxchaiiRc f()r this food, they cxcr.tc into the water tiie waste uiateriais of their iiietaholisni. As the orKanisni l.eeoiiies more and more complex this direct interciiantfc of materials hcfomes impossil)h'. un{uU-k\y from pla<'e to jdaee. Th( refori' alJ th.' elements fouml in tin- tissues and all the waste materials produced by the body are presei.t at some time or another in the bl(M)d. The bhxMl may in- deed be eom|>ared to the wholcsal.'r of commerce, who handles all the materials for the support of life, and the lymph to the retailer, who distributes to the tissue cells the nmterials which th.-y need. In short, it may be said that the bUnxl replenishes the lymph for the loss«-s which it incurs in supplying the ti.ssues. Physical Properties.— Ordinary mammalian blood is an opa.|\ie. somev.hat viscid fluid, varying in color from a bright red in arterial blood to a dark re.l in venous Idootl. Contact with air changes venous IiIcmxI to arterial bliMxl. Microscopical exami- nation shows thai the bloo.l is not perfectly homogenous, but consists of a clear fluid in wliicli cells called cori.uscles are sus- li'-'uled. The Corpuscles. Tiin-.. are three varieti.-s of thes.-: the ml lorjHisrhs (to which the c.ioi'of blood is duel, the irhilr corinisch.t and the hlooil pliilihts. 140 •^mi^^ ^sfs=^^^m^ Tin: Hi.fHin cnui'ixi.K.s 141 Erythrocytes. Th. n,l ,o,;»>s,l's, ..>• , n,ihn„„i.s. as tL-y an. ...11..I, H.V by far th. most nuMH.nn.s. th...y l..-.n« hv- nnl^ li.,M of th...u in a rul.... Mulli.-Ht.v of ....r.nal I.I.hhI. Kxanm....l >,„.l.,,. ,h.. .ni.Tas...,,..-. th..y a.v s.-n t.. 1m- tlatt.M....l. 1,,-o.M-av.-. „ou.Mm-l..at.Ml disrs i. .nan: l.ut in tl n.hryo, as w-ll as .n hinis an.l .vptiLs. tiny hav a nu-l.-ns. Kach .•..r,.ns..i. ..ons.sts „f an rnv.l..|M- an.l a trannw<.rk oC |.rot.-in an.l l.p..Hl n.at-nai contaiiiinj? a snl.stanc' known as liH'ino«lol>in. U KMo..i,oH.N is a v.-ry .-on.pl.-x horofins .s.- p. 21 >• lla-n.o«lol.M. has th- „l,ilitv to .-;•. with larjfr amounts of oxy>f.-n. thus ..nahlin-i th.' bi(K)a " .-. n • the oxy,r.-n «ath.Mv.i in th.' Innjrs. to th.- .i.s- t.,„t tissu.s It consists of a ronihination of a snnph' prot.-.n. ^lol,in. an.l a i-iKMunt. ha-n.atin. Il, n,„h,n,smuK svhu-h is tvsponsibU- f..r th.- ability of oxy^.!. to unit.- with th.- ha-n.o- irl„bin ,Mol.-.-ul... Th.- .-on.bination <.f ha-n.onlob.n with oxy^.-n is not v.-rv stabl.-. a.ul .-an b.- r.-a.lily brok.n with th.- l.b.-ration of oxvu.-n" It is for this n-ason that this n...l.-.-ul.. is a.lai.t.-.! to ..nn-v ..xvp-n to th.- tissu.s. Th.- .p.antity ..f ha-n...Klob.n h.-l.l ),v tlH- .-orpusH.- may vary an.l in son..- .lis.-as.-s, as n. .-hl...-..- ana-mia. f..r instan.-.-. it niay b.- «n-atly .liminish.-.l. so ...u.-h s.. that tin- tissu.'s nmy b.- unabl.- to ..btain th.- prop.-r am.mnt ot oxvK'."n The amount of ha-mo^clobin a.-tually pr.-s.-nt in a samph- of'bloo.1 may b,- .-stimat.-.l by th.- int.-nsity of th.- ml cm> or it eivfs t<. tin- hhMMl To ,-stimat.- this int.-nsity a .Irop of bloo. is m-.-iv.-.l on bl..1tins pap.-r. th.- stain b.-inK th.-n compar.-.i ,.ith.-r with that p.-.Hlu(-.-cl by normal blo.).l in vari.uis .lilutions „„ th.- sam.- pap.r, or with a stan.lar.liz...! .-hart. From tlu- con- ,.,.ntrati..n of normal bloo.l whos.- stain most noarly match.-s that of th.- unkn.>wii sampl.'. w.- can ,l.-tcrmin.- tlu- p.-rccntag.- ol ha-mo-lobin in th.- latter, .>r wc can rca.l this .lin-ctly from tli.- ' '*Enimek\ti..n ..f TiiK BI..X.I) CoRi-t s(i,Ks.— The numb.r .)f rc.l or white cells pr.-s.-nt in a cubic millimetre of blood may b.- esti- n.ateil bv th.- us.- ..f a ba-macytoinet.-r or blood-.-oimt.r. This consists i.f two mixiiiK capillary tubes, in one of which th.- blo.>.l ,s .lilui.-.l ..ne huh =rcd iin.es with salin^- solution, and m th.- m^^mm. 142 I'llYSIorifKlY FOR DKXTAIj .STUDENTS. Other, tiMi times with 0.'.V.i~'/, Heetie aeid. Tlie former dilution is for counting red, and tlie latter, for eountinsr white eorpuse]e.s. A drop of the diluted blood is then i»laeed on a speeial glass slide whieh eontains a (•ountiii'': ehamber of sueli a de|)th that when a eover .slij) is ])ut over a drop of Huid in the ehamber, a polumn of fluid one-tenth of a millimetre deep is obtaineil (Fig. 13). The chamber is graduated with cross lines, so that each s<|uare rej)resents a known fraction of a millimetre. The average number of corpuscles found in a nu'nber of s(|uares. by actual count with a microscope, is multiplied by the factors of dilution employed, the product being the number of cells in a cubic niilli- 0.100mm. C. Zeiss Jena. KiK. 13.— Thoma-Zoi.ss Haemocytoni.'ter ; .\r. mnutlipieoi' of tube (O). by wliich lilood iM Kuiki'd into .v.- H. bead for mixiriK; n. view of slide frimi ulM)ve ; h. in section; r. xijuares in niiddl<> of H. as sieii under niieroscoiie. nu'tre of blootl. The erythrocytes, whieh in health number about five million in a cubic millimetre, may decrease to less than a million in disease, such as ixrnicious anaMuia. or after hasnior- rhage. On the other hand, they may nund)er six or seven million in people who live at high altituch's. The oxygen-carrying power of the blood is ijrojjortional to the jjercentage of haemoglobin, so that by estimating this and the number of corpuscles, a fair idea of the eonditi(m of the blood is obtained. The Origin of Krvtiikocvtes. — It is interesting to incpiire into the source of the blood cells, but although this has been the subject of many researches, it is by no means definitely settled ani Till-; lu.ooi) rui{i'rs('ij;s. 143 just vvliat tlic i)nx'i'is.s is or in wliat i)art()f tliobody the eolls orifji- iiatc. Nor is it definitely known just wiiere tlie worn out eells are dealt with. Jn the embryo certain cells are set ai)art to develop the vascular systei;;. Some of these form the blood ves- sels and some the red eor])uscles. but later in fo'tal life, the latter come from eells in the spleen, liver and red bone-marrow. At first the red cori)Uscies are nucleated, but towards the end of fo'tal life they begin to lose their luiclei. so that at birth there are very few nucleated red corpuscles reinainiiifi in the blood. After birth, the red corpuscles are formed in the retl bone-mar- row of the flat bones. In these i)laees s])e('ial luicleated eells arc found, which are called erythroblasts, and from these the ery- throcytes develop. After severe hiemorrhage nucleated red cells may api)ear in the bl(R«i for a siu)rt time; the same is true in some forms of ana'mia in which there occurs a very rapid destruc- tion accompaiued with a very rapid formation of red cells. Since the life of a i rj/llirvcijlr is necessarily limitetl, provision must be made for the y the bile. It is. on the contrary, stored U]) by the liver to be used again in tile formation of fresh ha-moglobin. Some have thought that the function of the spleen is to destroy the nd blood alls, the waste i)roilucts of which are sent to the liver through the .splenic vein. The evidence for this is the [)resence of pigment and iron- containing substances in the blootl of this vein. Iron is an essential constituent in the ha'moglobin molecule, and it is n(>ee.ssjiry that sonu> be constantly supi)lied to the body in the food. But this amount need not be large, since the iron- containing substance can be used time and again in the manu- facture of new ha'moglobin, and once the body has the re(piisite amount, little more need be added (see p. 120). Indeed, it is 144 l'IIVSI(lI,()(iV KOK DKNTAI, STIIIKNTS. quostioiiabit' if tlic iiiortraiiic forms of iron can be utilized by the body, tlif iron in our bl(MHl bciiii; probably derived from a con- jugated protein known as lucmatofreii. found in small (|iiantities in the food. The White Blood Cells.— In normal liunian blood tlien- are about ten thousand cells in a cubic millimetre of blood, or about one to every five hundred val cells. In many ways they resemble the luiicellular amu'ba. for like it they have the power of makinjr indei)endcnt movement by extendinj; tiny |)rocesses called pseu- dopodia in one direction and by retracting' them in another. In virtue of this peculiai' movement they are able to flow, as it were, between the ener cent of the total whiti lis. They are -terized by a lobed n\icleus. the parts of which are connected by strands of chroniatin nuiterial. To this class belong several sub-rise about !>(> per cent of the leucocytes. Another type are known as eosinophyles. since they have granules with a marked afTtinity for acid stains. Thr L\imph(n!iU s. — The second variety are so-called, since they are sui)posed to be formed in the lym]ih h<)( ijlis, which contain a rather abun- dant cytoi)lasin about the nucleus, and the snuill monoiniilinr himphonjifs, in which the anumnt of cytoi)lasm is very small. The former comprise about 4 |»er cent, and the latter about :{() per cent, of the white ci'lls. EsTlM.\Ti(tN OK TiiK WiiiTK ( 'km.s. — Tile number of white cells found in the l)lood is estimated by the sanu' jtriiu-iple that is em- ployed in the counting of the red cells (see p. 142). In certain k mm THE BLOOD PLASMA. 14.-, diseases tlieir iiuiiiImt iiwiy vary greatly. Tli(> nunibi'r is also in- creased after meals. A marked inerease over normal is known as a loueccytosis. The FiNCTioN of the LEtTocVTES. — In aeute iiifeetions. as in appendicitis, pneumonia, and Iwalized or jjeneral sej)tie con- ditions in wliicli jms is formed, there is usually a great inerea.se ill the number of the polymori)lionuclear leucocytes. In more clironic infections, as in tuberculosis, the lymphocytes are found ill greater numb -r. In the parasitic diseases of animal origin, as tapeworm and hookworm, in some skin diseases, and in scarlet fever, tlie e()sino})hile leucocytes are more abundant. In the disease leuccK'ytha'inia tlie lymphocytes may be present in such great numbers that they impede the movement of blood by iu- creasiig its viscosit.\ or thickness. The above observations sug- gest that leucocytes ])lay an important role in the protection of the body from infective processes. This function will be dis- cussed later. Another important function they may have is the preparation of the peculiar i)roteiiis which are found in the blood i)lasma. Tih: ]?L(«)d Platpxet.-^.— -These bodies are smaller than the erythrocytes, and nund)er about :}00.000 in a cubic millimetre "f bl(K)d When blood is slied they disintegrate very rapidly, and s«'t free a sub.stance which plays a part in the coagulation of the blood. Little is known concerning their dieiiiical constitution or their physiological function. The Blood Plasma. The blood jilasma is a very complex Huid containing all the va- ried substances associated with tlie function of the blood. Water composes f)0 per cent of the plasma. The plasiii;i proteins consti- tute the largest solid constituent (7 per cent), and inclmle ^^.nnn idnlilllin. smu" all^"'")"' and fibrinogeii. There are a number of bodies which contain nitrdgen which are not proteins. These mny be grouped into two cla.s.ses. the first, represented by the amino acids and other nitrogenous bodies derived from the pro- tein of the food and from which the tissue cells are built, and tiie second group, represented by waste materials given off by the 146 IMiySIOLCKiY KOR OENTAI. STIDENTS. tissue colls. Tht'so includt' substaiipt-s sncli as iiroa. uric acid, crcatiiiiu, ami ainiiionia. The iioii-nitrnp-uoiis orfjaiiic bodif^- arc dextrose, of which 0.1 percent is present in normal i)lasina. and a small t|uaiitity of fat. About 1 l>er cent or inorganic salts are found, the chi«'f of which is sodium chloride, which constitutes fiO per cent of tiie ash. So. 149 tho other liaiul— such as nyphilis, Tiialaria. slocpiniu' si«'kiifss ami tliost' caused by aimi'ba in the mouth aii«l alimentary traet— tind rehitively little resistance offered to the ingrowth in the body, and their destruction therefore must be for the most part brought about by drugs. The Process of Inflammation, wincii in a general way is known by tho common symptoms of fever, pain, swelling and redness, is a sign of an increased activity on tlic part of tiie tis- sues in an effort to destroy sonie foreign body which is poisonous to tho cells. Microseoj)ical cxannnation of a st'ction of inflamed tissue will show that the blood vessels arc dilated, and tliat the tissue spaces are infiltrated with leucocytes. It suggests that the blood elements must have a very important part in the process. The study of this function of the body is one of the most inter- esting cliapters of physiological science, and includes the ques- tions of immunity from disease and the cure of infectious pro- cesses. Many pathogenic organisms can be cultivated on artificial media and the products of their metabolism can then be studied. It has been found that they nuiy be divided into two groups; the one group producing the soluble poisons, or true toxins, which are excreted from the cell ; and the other group producing toxic substances, tiie endo-toxins, which are not excreted from the cell. We will first take up the nummr in which the body deals with the toxins. Toxins.— If a culture of diphtheria or tetanus bacilli be fil- tered through a porcelain filter, the bodies of the bacilli are re- moved and the filtrate contains the soluble toxic principles which the bacilli have produced and excreted into the nutrient fluid. Injections of a small amount of this filtrate into an animal will l)roduce the same symjitoms as are produced when a pure culture of the bacilli is injected. Kach bacilhis produces a specific kind of toxin. Diphtheria toxin acts i)rimarily on the vasc\dar sys- tem ; tetanus toxin, on the central nervous system. The chemical luvture of the toxin molecule is unknown, since it has been impos- sible to sepai'ate it in pure form. It is i)robably closely related to the protein mok-c-ulo, and ou the other hand resembles the 150 I'llYSIOMKiY FOR DENTAL STIDENTS. t'cniu'iits ill many of its aetioiis (sw p. ;{4). A pfciiliaiity in the action of the toxins is tiiat a relatively long period elapses between the injection of tiie toxin and the reaction of the body, whereas in the ease of the alkaloids or vegetable poisons, the re- action appears very <|iiickly. Antitoxin. —In spite of the very poisonous character of tlie toxin molecule, the body is provided with a means of defense against it, and is able to make itself still further immune to the action of the toxin. Thus, if somewhat less than the fatal dose .)f diphtheria or tetanus toxin be in,jected into the body, certain symptoms will follow, and tlie animal will react to the toxin in such a way that a subsecjueiit injection can be made larger with- out proving fatal. If successively increasing doses are given, the animal after some weeks will be able to withstand very large doses of the toxin. In other words, the body develops an im- nuinity towards the toxic agent; it i)roduces an antibody which ne\itrali/es the poison of the toxin. To this body we give the name of antitoxin. Since these antibodies are found in solution in the l)looi)hitiv ki-oui) of the tetanus toxin, and also suhstanees that are readily attacked by the toxophore Uroiip of the toxin. The antitoxins are supposed to act by com- bining with the haptophore jrroui). thus preventiuK the toxin from uniting with the cell. Accordint,' to this theory the formation of antitoxins may be accounted for as follows; When a rrcrpfor, as we nniy term tlu- portion of the <'ell which unites with ha|)tophore ^'roup. is united to the toxin, the cell endeavors to ada|)t itself to the loss of this radicle by the prodiu-tion of another similar one. Since the gen- eral rule of nature is to resi)ond to an action with an over-reac- tion, many more receptors are made than are actually needed to luiite with the hai)toi)hore Kroui>s of the toxin present. The re- ceptors produced in such «reat number break away from the liarent cell. These accordinifly are stored up in the blood, and whenever any of the partieular toxin for which they are adapted is present in the circulation, they unite with it and thus prevent the toxin from uniting with the tissiie cells. A body which pos- sesses a store of such antibodies i^ said tlu'refore to be immune. Toxins are not the only substances which will produce specific antibodies. This property is a general characteristic of proteins. Any sub.stance producing an antibody is known as an antigen. For example, if liunuin blood be in.jt'cted into a rabbit, and after several days some of the rabbit's blooil serum is mixed with hu- niaii blood serum, a precipitate will form, whereas the blood of a normal rabbit will produce no such precipitate. The first in- jection of hviman blood serves to stimulate the rabbit cells to form some substance which precipitates any human blmnl sub- sei|Hently added. The reaction is specific, for the blood of any other species of animal will not be precipitated by blood from a rabbit sensitized with human blood, and the reaction otfers a very accurate method of differentiating Ix'twceii hunuin blood and othei- blood in medico-legal cases. The body t.ius formed is known as a pnripilin. Anaphylaxis.— Again, if a rabbit be injected with some liu- 152 I'lIV ilOLOUY KOR DENTAIj STl'DENTS. iiiiui .sciniiu two or tliroc wt'cks aftci- a previous iiijtM'tioii, tin- aiiiinal will go into a vt'i-y profouii*! stati- of sliork. The IiIo(m1 pressure will be lowered, the heart's action weal Iish iinixiitaiit than that i>l' thi- l>ha^()c\ tf. Ill very siiii|>h' I'ortiis of life the cells of tlic aliiiu-ntai'v tiact hoth iiip'st iiti<| digest the food inatcriiil. In hi<;hi r fui-iiis the cells of the iilinicntary tract secrete the llniils wliieh difjest the food. In the one case tlie digestion is intra-cellnlar. and in the latter, extra-ceiluliir. In tlic same way we find the hlood leu- cocytes ahle hoth to (hstro\' and to dijfcst snhstaiiees liy intra- (.•ellnlar action, and also sjiiirinj; with other cells of the hods the power to secrete siihstiinces into the hlood plasma which have the power of destroyiiijr the ori^anisms or toxic mati'rial. Opsonins. — Norma! hlood serum has a very strong,' destrnc- ivc infliience on most sj)ccies of hactcria. whether they arc patho- ireiiic or not. This ahility is not possessed to the same extent li\' the hlood plasma. The ditrereiice is exjiliiined l)y the fact that ill the procc.ss of eoafjulation the white hlood cells are hroken down and lihcratc tin'ir hactericidal bodies. lOxtraets in.ide of leucocytes have this saiiie elVict. but the n'aetion is much more rapid in the pri'sonce of bhxtd jilasma or s.'riim. The co-oper- ation on the part of tlic plasma or serum is explaiiud by the presence of sonic substance in solution which eiialijcs tlic leu- cocytes the more readily tle to at- tack only one or two bacteria ; later in tiie disease, however, when the opsonic power has }>een increased for the infective ajreiit. the leucocytes may be aiile to iiij.rest a much I,ir;rcr number without in.jury to themselves. The opsonic index is a ti^iire cx|)ri'ssinI.IKi\ KUK uKNTAt. ST^!>K^T^ piit'ciil who is stifffriiiK from flu mf.itivc ajfi'iit A !iitfli op H:i;.ic iiul. \ tlu-rt't'on' indicati-s h rflativt- iniiimnity or liifth r ^int ancf 1o tht' iliscasc in i|vitstion. The hjii-tfricidal (towt-r "i the leu»'o«'yt«'H for many hacti-ria i-ari he >jri>atly incrcawtl In th' in- joctiuii of (Icii'l h-.M'U lia iiilo flic hoily. This fart In ^.inli- uw- "f in thi' inHMiifa<'tur' of hai'tfrial vaci'in«-s. whirh con^iHt of i> pensions (»f dt-ad haciiria in salint ClIAITKi X\ II TFIK h^ MIMI Tlif 1iI(mmI cinuliitcs in fli)>«u tiiln wliicli is supplifd 111!' tissues suit from llifir jicti\ \' iii'is' M'Is. Thf rttliil 'lU'li > ti-i. siiitouimIs the «, .Is o' serves as the iiiediuin |)iiisiiiii. It is the mid the tissues. Lympli is h. reseliibliiitf the hlooi the earryiiij; itff o\' cial system of vcssi walled caiiill ti hules li-Jiij to ••• ulaiid aloii",' th( sel, tile tlioi-aeic .i !•! " ii^t the liolll'isllllli'iit he In : oduets whieli » i iiiolUfh walls of the m^ from the pdlaries and which V known .IS the lyinpli, and ween the cells and tli-' hlood iiiije hetweeii the hkuxl and transparent fluid, closely h it is derive ! ,>h. there is piovided a s(»e- ied 1. I niphatics. which are very thin- ! icd with endothelial cells. These tu- vhich, after passinj; through a 'ymidi i , tinallv empty into a lar>je vcindike vcs- lyinjr alongside of the o-sophaKUs in the thorax, and emptyinff into tlie left suhclavi.in vein. A smaller lymphatic vesse' the liirht thofacic duct, empties into the rifiht subclavian \ in The lynipi nl I'd from the thoracic duct hy mrans of a tine tube in.scrte. • the vcs.scl v; lic- somewhat in nature. After a meal the fluid is like ndlk. heeanse of the preschcc of droplets of fat which have Ineii alt-or])ed from th" intestines. The lymphatics of the viscera appear as white lines in th^ mesentery and on thi.s account are called lacteaK The h inph whic is collected dnrin^r a fast is vt'-y much like the Idood plasma. It^ spe4-itic uiavity u less thtui tliat of blood, s'lice it oiitains less protein ina;( rial, hut on the athi^^ hand its salt content is the same and it • ot.i in much th'- vinii iui-r as lood. On microscopic examinatioii there ai' !oun m jiiuseles ace hii in 1 vvitimi I;ie lyiiiph 156 g !,-)(; I'IIYSIOI,Otiy FOR DENTAL STIDKNTS. glands throufjli which tlic lymph vcssols pass on their way to tiic subclavian vein. Lymph Formation. —Many physiologists have allcniptcd to discover the j)reeise mechanism by which the plasma passes tiirough the capillary walls into the lyinpii spaces, but the com- l»lete knowledfje of the process is not yet at hand. The relatively high blood pres.sure within the capillaries provides filtration l)re.ssure by which a fluid might be filtered through the cai)illary walls, and there is no doubt that such a j)rocess does occur, as, for I'xample, after the capillary pressure has been increased by con- striction of the veins by a bandage, etc. Filtration, howevei', cannot explain all the known phenomena of lymph formation. Osmosis (p. 27) also plays a part as follows: The tissues use up the initritional elements brought to them by the lymph. The diffusion pressure of the substances in the lymph is now reduced so that it becomes less than that present in the blootl. Therefore substances within the blood must pass out through the papillary walls into the lymph, thus keeping the concentration of the fluid more or less constant. The waste products of the tissue pass into the lymi>h and, by increasing the molecular concentration of the lymph, draw water from the blood. Again, the breaking down of the large protein molecules into smaller ones, in the processes of ti.ssue metaboli.sm. will cause the molecular concentration of the tissues to rise, increasing the osmotic pressure. This causes water to be abstracted from the lymph, which in turn draws on the blood for water. Lymphagogues. — There are certain substances which afTect the rate of lymph formation in a very peculiar way. These are called lyniphagogues, and include extractvS from many shell fish, leich extract, peptones, etc. When such substances are injected into the blood of an aninud, there follows a great increase in the rate of lynsph formation and lymph flow. Indeed some people are very su.sceptible to this action, and eating sh<'!l fish, oysters, and some fruits will cause their tis.sues to become swollen be- cause of an increased lym|>h formation. How these substances can etVect the change by altering the physico-chemical con.stitu- tion of the blood plasma is not clear. Some investigators believe ii THE LYMPH. 157 thiit tlit'V liavc a stimiilatiiifj action on tlic cndotliclial cells linintr Die cai)illarics and tlnis jjrotlucc an actnal secretion of lynipii. It is more jn-olmble, however, that they i)oison these cells in a way which increases their i)enneal)ility and tlius jn'rinits a freer filtration of lymph from the blood i)lasma. There arc other facts nevertheless which sui)port the theory of an actual secretins mechanism within the cells of the capillary walls, but they are t(Ki technical to considei- here. They suggest that although the j)liysico-chemi('al laws of dilTusion, osmosis, filtration, etc.. i>lay the most impoitant role in lynij)!! formation, the cells of the capillary walls may them.selvcs have an active i)art in the pro- cess. Lymph Reabsorption. — Within the tissue spaces, and within the cells of the tissues, chancres are continually taking place which alter the character of the lymph. ().\yj?en and food substances are I'emoved from the lymph by the tissue cells, and waste sub- stances, the result of the ti.s.sue metabolism, are added to it. In the case of o.xygen and carbon dioxide, the exchange is so reg- ulated as to keep constant the supply of thcst; bodies in the lymph. The loss of any substance is (|uickly compensated for by the addition of new material from the blood. The solid waste jnat...r excreted by the cell can also find its way directly from the cell through the lymph and into the blood plasnui. It is probable that during i)eriods of rest or of slight activity the lymi)hatics are of little importance in the exchange of the lymph. However, when the exudation of lyiui>h becomes increased, as during exercise or following the use of some lymphagogue. or when there are substances in the lymph which the capillaries cannot absorb into the blood, the lymphatics become very im- portant in helping to renu)ve the excess of lymph formed. The Movement of the Lymph. — The mechanism by which the lymph of the tissues is collected l).v the capillaries of the lymph- atic system is not understood any better than the mechanism of lymph fornuition, but no doubt the same laws apply to both pro- cesses. The movement of the lymph along the lymphatic vessels is ])o.ssible because of the presence of valves along the course of the vessels. 158 PHYSIOUXSY FOB DENTAL STIDEXTS. Tlu" prot'oss <»f lyinpli absorption is ratlici- slow except wlioii it IS anlt'd by tii,- !iiassiij;f produced Uy tli.- iiioveineiits of tlie siir- roundini; parts. Tlie rapid action of poisons, or .Irugs intro- duced by a hypodermic syringe, is due to their absorption from the intra-cellular or lymph spaces directly into the blood. Col- ored solutions as india ink are absorbe.l by the lymphatics, and by using a substance like this it is i)ossible to trace the lymphat- ics of a portion of the body. Micro-organisms, such as the strep- tococcus, which causes one of the familiar forms of what is known as blood i)oisoning. are taken up by the lymphatics, and it is ••asy to ti-ace the channels traversed by the organism by the in- flamed lymphatic wails which appear as red lines under 'the skin. Since all these vessels pa.ss through a lymphatic gland on their way to the subclavian vein, these glaiuls are often very much swollen, and may even l)e destroyed as the result of the infection. It is probable that one of th,- functions of the lymph gland is to catch an(] render non-to.\ic. poi.sons which are being carried into the circ .:; ion by way of tiie lymphatics. One of the most dreailed diseases, carcinoma, is carried by the lymphatic svsteni to other parts of the body. For this reason we most often see the metastatic growths of canc-r in the region of the lymph glands which have caught the straying cancer cell and have been infect- ed by it. The increased exudation (f lym{)h in the tissu. ■ . !i -h occurs in inflammatory conditions is n;. doubt of great ad, lage to the tissues, since, by this mean.s. a gr.'ater sui)ply of nourishment is provided for the repair of the damaged celLs, and the defensive substances (antibodies, etc.) are brought into play. 11*5 KIk. 14. — DiuKram of ("iroulatioii. Tlip l>loo(l ciiculatps iis follows: V.C. y.C. (VfTiiP cava"), K.A. < ilifht auricli-). It.V. (liBht Vfntiiclc). /'. .1. (pul- monary artery ), I,. A. (left auiiclf). /,.r. (left vt-ntrlcli' ), .1..1. and D.A. lascenJinK and drscendinK aorta). //. l". and /*. (caiiillariis of head, visc.-ra and lK)dy Benerally). I'.V. (portal vein). I.i. (liver). The small blai'k ves- sels an- the azyj;iis veins. '■ CHAPTER XVllI. THE cniCrLATOKV SYSTEM. Introduction. — Tlic circulHtory systom provides for the trans- ])ortation of blood through the tissues, thus euabling eaeli indi- vidual cell to obtain nourishment and to rid itself of the waste produets of its activity. The system includes the heart, the blood ves-sels, and the lymphatics. From a mechanical standpoint, we may say that the heart con- sists of a pair of pumps; each pump consi.sting of two parts, an upper dmmber, the aiiriclr, and the lower one, t!ie rnitriclr. Tiiin. nuMubranous valves, called aurieido-ventricuiar. .separate the upper and lower chambers and prevent the blood from flow- ing back into Hie auricle when the ventricle contracts. Connect- ed with the ventricles are the nrtcrua, which conduct the blood away from the heart, to which it is returned by the great veins leading into the auricles. At the point where the arteries emerge from the heart are cup-shaped valves, called 8(Mnilunar, which ])revent the passage of blood from the arteries into the ventricles, while the latter are relaxing. As will be seen from the accompanying diagram (Fig. 14) the blood pumped from the two sides of the heart circulates through two distinct and separate systems of blood vessels. From the right ventricle the blooil goes through the pulmonary artery to tht> lungs and is returned to the left auricle by the pulmonary veins, then to the left ventricle, whence it is sent over the body through the aorta and its branches, to the <'apillaries imbedded in the tissues. From these it is returned through the veins to the venjB cavae, which discharge it into the right auricle. We may .say, therefore, that the circulatory system consists of two circles of tubing interposed in which are two force pumps, the valves of which are so disposed as to allow the blood to flow in one direc- tion only. 150 KiO l'IIYs|nI,0(iY Filli OKNTAt; STIOIATS. I. The Heart. Anatomical Considerations. —Tin- licart is suspciKicd at its base by tlic lar<;c arti'i-ics. and lies practically free in a sac of toiiffli fibrous tissue called tlic />< riitinliinn. On cadi side arc the lun. — Thi' iM.sitii.ii i>r t:.c hcail in !V,i' t!..iriix. i T. WiriRMlf TmlcM tion diminishes the size of the cavities and empties the heart of bi(Mid. From the study of the eiid)ryonic heart, and from comparative studies in the lower animals. ( Kiir. 16) we know that the h"art has develo|ied from a sinj^le tube, the division of the auricles and the ventricles Inmu^j a rather lat. stap!neiit of the auricles from the proximal, and r» — - - .' —i^ . .^- i-"^'_wi I ^TTT^Bi!* ANATOMY (IK Till: IlKAKT. Kil of till' ventricles from the distal end of tiie |)rimitive eardiic tube. The fibers of the auricles run transversely, hetriiniinji; and end- ing in the fibrous tissue which separates the aui'icles from the ventricles. The musculat\ire of the veiitriclcs is somewhat hard- er to trace. There are layers that run transversely around the ventricles, and also layers which describe more or less of a spiral course from the base of the ventricles to the a|)ex and then are reflected back in transverse layers, until they finally end in the papillary nniscles, which are connected with fibrinous threads. yifi, ifi._A K'lniializiii \ iiw cif tlir viMtcliiiitf licait (Kt-ith) sliowinn: ((. the sitniw mmiipsus; Ii.i-., tin- iiuiiclf ; .!.(. the auiiculo-VHiitiiculiir niilkc and valVfM-, (/. tiK rinlrich- : c. thi> IwRinninp of tlit- aof.ii with the sciniluiiai- valves at .'.. The valves lietweeii < anil / nut exist in the heart of inati. (Kicini liMWell's I'h.v«lol(i'iiiii'iit. iiiul is cxjdiiiiHMl by tlu- fact that the blood, when it is forced from • ventricle during the cardiac contraction, exerts its force on tlic apex as well as on t'.'f blood in the arteries. This serves to fix the apex in the vertical ])ositioii and to bi-ing the base of the ventricles downwards during their contraction. In some individuals there is a vi.sible pulsation at about the level of the fifth rib on the left side. This is called the apir huif, and is caused by the rotation of the apex in the transverse diamet«'r and by the sudden chaiiK*' (tf the ventricle from a soft flabbv condition into a firm one. i4.~ 1 Fin. 1". — KiuKram of Valve.s (if tbe Hf.i ' The valves are .mipiio.seil to l>e viewed from above, the aurieleK havinir l«en iiaitiall.v leinoveil. A. aorta with semilunar valve: H. pulmonar.v artery anil valve; (\ trii iisplil, and T>. mitral valve; A'. riKht. and F, left coronary artery; (r, wall oi liKht. and //. oi left aurii'le : /. wall of right, and •/, i.. left ventriele. ( Kroni .Stewarts rhysiology. ) 11 The walls of the auricles are relatively thin, as they are not reijuired to do heavy work. The ventricular muscles, on the other hand, are well develoj)e(l. that of the left ventricle being very strong and adapted to the heavv work it must perform. The valves guarding the opening between the "iricies and ventricles are eomposed of thin membranes of fil»rous tissue, cov- ered with endothelial cells similar to the lining of the heart and the blood vessels (Fig. 17). In acute rheumatism and tonsil- litis, the endothelial covering of the interior of the heart and of the valves is often inllamed, and permanent changes may take TIIK lll'.AKT HKAT 163 |»lac»' wliicli iii,j\irp tlu' valves aiul jirodnt't' what is known as val- vular dist-asc of tlic heart. The chorda' tendinea' connect the free nnir>?iiis of the valves with the i>a|)illary muscles, which ariso from tin- musculature of the ventricle like little knobs of tissue. This arrangement jjpevents the valves from being everti'd into the auricle during the contraction of the ventricle. The valves on the left side consist of two flaps and are called the uiitnil rolffs; those on the right side have three flaps and hence are called tricuspid valve.s. The valves guarding the arterial orifices consist of three cup-shaped niend)ranes and are known as the s( mil(it\itr vdlrrs, because of their crescent-shape when they are closed. Whenever the i)ressure in the arteries is greatei- than that in the ventricles, these valves are tigiitly closed, and i)revent any blocxl entering the ventricle from the arteries. The Physiologic Properties of Heart Muscle. The Character of Cardiac Contraction.— The contraction of our voluntary nniscjes is not due to a single stimulus sent from the brain through the nerves, but rather to a series of such stim- uli, which ])roduce a nu)re or less continued or tonic contraction of the muscle. If this were not the case, our movements would l)e very (piick and .jerky, similar to those nuule by <■ son suf- fering with St. Vitus dance. In the case of the lit.... nuisde, however, each l)cat consists of a single complete muscular con- traction, and it is impassible to prwluco a tonic or continued con- traction in the lieai't such as can be produced in voluntary mus- cle by rapid successive stimuli. Another peculiarity of heart nuiscle is that each time it contracts it does so with all the force that it has at the moment. Skeletal mu.scle contracts with great- er or less intensity according to the strciigth of the stimulus it receives. Heart muscle, and in a lesser degree some other muscles, such as those of the intestinal tract and splwn. have the power of making autonuitic rh\ thmic contractions which follow each other in a definite senuence. Thi.s phencmienon in the case of cardiac muscle is not dependent on the influence of the nerves, as can be sLawu bv the fact that the heart removed from the body will con- ■^,-. .«*'■ .:;,'■- Trrr^^'fsmm 1(14 i'iivsr(ir,iMiv K(ii{ i)i;\T\i, stidknts. tiniif to Ix'Ht for sonif time if it is |»ro|Mrly iiourislicd hy perfus- ing' hlooil Ihroiif,'!) it uihIiT iucshuic. TIh' cause of this piop- •Tty of aiitoniiitieity is still unsettleil. ami there have hi eii some very iiiterestinjr (iiseiissioiis iiixi arjfumeiits amoiiff physiologists eoneeriiiiiff it. Some iH'lieve that tiie heart miisele has this prop- erty inherent in itself, and that it ori>rinates the impulse which causes the contraction of the heart; while others think that there are pres«'nt in the In an -muscle cells of a nervous character whose special function it is to orifjinate the heat. Kxperimeiital facts can 1m' found in siip|)ort of «'ither theory, hut the (|uestion is still in dispute. Heart muscle dirt'ers from nthi-r mu.scle in that each Hher consi.sts ttf a single cell containing striated |H'otoplasm. It imiy (|uite well be that this kind of muscle pos.se.s.ses some char- acteristics usually a.scrihed to nervous ti.ssue, and that it does orijrinate the stimuli which produce automatic movements. The Sequence of the Heart Beat. — Inspection of the heatini; heart of a recently killed turtle or frojf shows that the heart heat hejjins hy a contraction in the lartre veins where the.v .join the auricles. From these vessels the heat spreads, as it were, to the auricles and then to the ventricles, iM-jjinniiiff at the base and ending at the apex. It is possible to stop the contraction of the ventricles by drawiufj a threatl tightly around the heart between the aurich's and the ventricles. The aur -les will contiiuie to beat as before, and the ventricles can lie mad to beat rhythmical- ly again by artificially stimulating them. In this case, how- ever, they will contract without any reference to the aiiricidar Ihat. Likewise the base of the large veins, or the sinus venosus as this is known iu the aini)hibian heart, ma.v be separated from the auricles hy a tight thread. The auricles now continue to beat, but at ;i much slower rate, whereas the beat of the sinus is not changed. Tin' tissues of the sinus mu.st pos.sess to a marked d'gree the power of making individual or automatic movements ; they are thus able to control the rate of the heart. For this reason the sinus has been called the tnrdittc piuemitkrr. The great muscular development of tlie human heart has caused it to lose some of its })rimitive characteristics. Xeverthe- k'ss, there still exist in the musculature of the heart some strands aS" Till-: IIKAItT HKAT 163 of tissue wllicll ns* lulitc tln' tissue of the ievs ilevclopetl tir more piiinitivi- lieait. We (iiid in the Wiills of the aiirieies siiiHii nodes iiiid islets of tissue, whieli no iloiilit represent the sinus tissui's found in the frojjs heart. These nodes of tissue are really the pacemakers of the heart, for it is in them that the impiils • stimidus arises whieh sets anoin>.' tlu' contraction of the auricles and the ventricles. These nodes are connected In fibers with the musculature of the auiides and ventricles, those runiiinjr from Vijr. IS.— Dissfilioii i.r tifuit ti( xliow nuilful.)-v sioloK.v. ) the auricles to the veiiti'icMS lu'lnj.' •rathered into a hundle of ti.s- siu- which has been named the hinulli of Ilix (!''!>.'. H). Numerous eases have been recorded of iiulividuals liavinjr a very irregular or a very slow heart In-at in whom post-mortem examination of the heart showed a diseased condition of the bundle of His. The conditions oliserved in man have been re- l)roduced in the case of animals by cuttinj; or clamping the tis- sue about this binidle. The result is much the same as that ob- served ill the turtle's heart when the striii}.' is tied between the auricle and the ventricle. The ventricle may continue to Iteat. hut it does so without reference to the aiu-icles. Such a condi- tion is known as luarl block. 166 I'UVSIOUKIV Ft»B IlKNTAL STtDENTH. It is of iiifcrcHf to know tluit tlitTc )ih.s hccii <|iiit(' iiii ailvaiicc n-cfiitl.v ill tlu' kiiowlctlK*' of the foiMluctioii of tlic cardiac iiii- pulst' from the auridcM on to the ventricles. It has been known for a hniff timi' that when a imiscic contniets. a small but definite el. 'trie current is set up iK-tweeii the relaxed and the contraet- injf portions of the muscles. New methods of detecting and rc- eordiiiK the direction of the flow of .such currents produced in the heart in man have shown that cases of heart block are by no means rare. The instrument used for this puipos*- is a 'lighly sensitized galvanom. ler. and the tracinjrs arc known as r/. Iru- (iinlioi/rattis. \\y this method it can br shown that in certain eases of iieart disease the auricles beat twice to the ventricles once, or a^ain that the auricles may boat very fast vhile th<' ventricles arc beating very irrcfrulariy and slowly. The Action of Inorganic Baits on the Heart Beat.— A very interestinp theory has recently been advanced concerning the cause of the heart beat. It will lie remembered that the niood contains salts of .scxlium. pota.ssium and calcium in solution. If these salts are replaced by other non-poi.sonous .salts in the same concentration as the .salts removed, the heart will not beat. If the heart is perfu.sed with a .solution of sodium chloride aloiic. the beat becomes very weak and finally stojjs. If. however, a small amount of calcium' and potassium salts is aibh-d to the sodium chloride solution, the heart will again begin to beat, but it stops after a while in a state of rela.xation. or diastole, if calcium chloride is removed from the solutiun, or in systole, or contrac- tion, if the potassium .salts are removed. These experiments sug- gest that the salts of the blood otr.-r a solution to the problem of the eau.se of the heart beat, the potas,sium favoring relaxation, and the calcium contraction. If the proper balance of tlie.se salts is present in the blood, it is conceivable that a regular se- (juence of contraction and relaxation of cardiac muscle will take place because of the action of the .salts. The Vascular Mechanism of the Heart. Definition of Terms.— A definition of the terms !ii»plied to the different phases of the heart's activity will help in the tie- Tin. (.\1C0IA<- CYCIJ lf)7 s<'ri|ifi((ii lit" tl vnits wliidi dciMir ilui-in>^' tin.' <-iim|.|.ti' li.art l)ciit. The iMTidd ol' ai'lunl cuntnictiini c>t' tli<' Ikjii-I is ti-r li st/sloh . This is tlividnl into mirli idtir inn! ii ulni nhir siixlith . The term sfilnii/mli jii rioil is itpplicd t(» that |)art ot' vriitriciilar svstolf (luriiitf which thf IiIinmI is ac-ttially h-aviiij? tlir vcntiifl^s. Th<' iM'i'iod of n-laxatioii ami n-st ot" the i-anliac imis<'h-s is callfl iliustiilr. Thf iiirdiiii ( i/ili iiii'lii.h's tin- tiim- of systole an. I ilias tolf of the licart. The Events of the Cardiac Cycle. -During iliastoh tiir 1>Ioim1 f. ies :,,'(• the veiitrieles. the aniii'uhi vent ricnhir valves hi-iin: ,,| ; ., \\1h-\ the Veiitrieles are as full as the wriyht im! the pres- s-.r ( ( I). ■ hlooil eaii make theiii. aiirieiilar :-.- 'ole liejrins. The . ; ; :u \ .iitrieiilar valves at this instant are Hoatiiitf in the hlonc'i which has colle<-te(l in the ventricles, and are almost in the jiosition of elosiirc. hnt a narrow chiiiK still remains hetweeii them, and throujrh this, anriciilar svstole fon-'/s blood under pressure into the ventricle, thus fillin>r tin ventricles eompletely. At the tlead stop of aiirieulnr systole the le are currents of Mood rcHcctcd back alonj? the sides of the ventricles which strike the i.inder surface of the valves and comi)li-tely clos.- them. Ven- tricular systole now iM^ins. The closed valves prevent tlx' pass- ajre of blood back into the auricles, and the entire force of the ventricles is expeixled in forcing: the blood out through the ar- terial o|)eiiiiiKs. Whenever the pressure in the ventricles cxcceiis that ill the arteries, the .semilunar valves open and remain ojicn till the force of the ventricle falls below the pressure of blood in the arteries. The time between the dosing of the auriculo-veii tricular valves and the openinj.' of the semilunar valves is calhM' the period of l,(MiY K(l|{ DKNTAI, STIDKNTS. ll' S<'llliluiliir Villv the clastic recoil of tlic iirtcrics on tlic hlood. the wiiiiiuiiar valves arc dosed tifflitly by backward cddyiiifr currents in tlic arteries. Their closure j)revents any return of blood into the ventricles. The bloml, having attained a certain inonieiituin (lurinj? the sphyjjniic period, is carried ou by its inertia for a fraction of a second after the ventricle cea.ses to exert i)ressMre on it. thus pro- ducing a partially relaxed artery just beyond the sniilunar valves. This nionientuni beiuff lo.st, the blooiiiK.iiiii Nhc.wiiiK ivliitive p: cssur.- in tiuiiclc. vi'iitri.-l.. iiii.l udrhi l)lo()d. is forced back on to the semilunar valv.'s and into the par- tially ivlaxed base of the aorta. The blood, beiiifr thus prevent- ed from returnin't to the heart, n.u.sl contiiuie to How on into the capillaries, and this onward How never cea.s<'s. because tin next cardiac systole occurs before the arteries have ceas-d to exert all of their recoil pressure on the blood (see also p. ITlii. After the arterial valves close, the ventricles eontiniie to relax, and the pressure within quickly falls below that whieh obtain.s XT TIIK iii;ai!t SOr.NDS Hi!) ill the partially filled auricles. At this nioiiieiit tlie weifjlit (if the lilood whieh has aceiiiiiulateii in the auricles diiriii}; the systole, forces the valves of the auriciilo-veiitriciilar orifice oiieii, and the ventricle apiiii hcirins to fill. The pei'iod between the closure of tlie seiiiiluiiar valves and the opeiiinjjr of the aiiricirio-vciitricular valves is known as the />a\7-.v/>/i//.7>*(/r in ri.xl, and is the hej^in niiifi of the diastole of the ventricles. The aliove events com- prise tliose takiiif? jilacc in a coinplete cardiac cycle. The Heart Sounds.— If one applies his ear to the front of the chest, or lietter still uses a stethoscope, which physicians use to e.xaniiiie the .sounds of the luiifrs and heart, two sounds will lie heard duriiifj each cardiac cycle. Tlu' lir^i somid is dull, low pitched, and loiifr; the second sharp. Iiifrh ami short. l<'ollowint? the second sound is a short pause. It has lieeii di'tcriniiied ex- pcriiiieiitallv that the first sound is caused partly by the closure and sudden tension of the auriculo-veiiti'icular valves at the iiio- nient of eardiac .systole and parll.v liy the inuseiilar contr:ietion f the ventricle. Anythiiifr which interferes with the closure of the valves causes an alteration in tin sound; for instance, if the valves are diseased there will lie a leakinjr of blood back into the auricles dui'injr systoh'. and this will cause a distinct niuriiiur to take the place of the sound. If the musculature of the heart is \veakeiieouiid is eliaiii^ed in character and is a useful iliatrnostic siirn. iJy iisiiitf these heart sounds as sijrnals of the events (M-currin^ within the heart, it is pnssibh^ to calculate the lime relations of the various phases of the i-,ii'(liai- cyeii'. The heart in th" ordinary individual \x-nU alimit seven1\' times a iiiinii'''. su that we mav 170 PHYSIOLOGY FOR DENTAL STUDENTS. t ' say that tin- pardiat' cycle is completed in about ono-tcnth of a second. Systole of the auricles takes about one-tenth of a second, systole of the ventricle thri'e-tenths of a second, and diastole al)out four-tenths of a second. Diseases of Cardiac Valves. — If the mitral valve is diseased, tlie blood may be retarded from tlowing from the auricle into the ventricle. This condition is called mitral stenosis. If the valves cannot close ti>rhtly and thereby permit the blood to regurgitate into the auricle during ventricular sy.stole, the condition is called mifrnl intiuffkinici/. Disea.se of the semilunar valves is likewise divided into aortic .stenosis and insufficiency, dejx'iuling on the ciiaracter of the fuiu-tionai change in the valves. 11^ ('HAPTKU XIX. TIIK CIWcri.ATION (C.Hi! .1 The Blood Flow Through the Vessels. Introduction. — A rlciircr iilc.i of ihc prin. iplis ndvicniwir tin' circulation of hlood tln'oiifjii tin- vi-sscis can he luul it' tht laws ffovcniiiif? tile How of watci- in a cit>- watc- -ivstcm arc callcti lo iiiiiid. For c.\aiii|)lc. a water works system ^> ari-aiiu<'ii hy iiieans of cither special pumps or a staiiii|tipt to tiirnisli a sti'cam of water at constant rate and |)ri'ssnre into tin city water mains. The water is first forced into one large pi]>e and from this de livcrcd to the consumer hy means of niiicii smaller pipes. \\y simple mathematical calculation it can li»' slumwu that the total cross-soction area of the smalh-r pipes is iii;ni\ limes that of the main pi|)e: for the sake of arjrument. let us sa.\' N(}() times uy;h one half of them. In otlt^-i- *»-tkr>'i*. it takes X I'orce to ovci'comc the resistance offered l»y Y. th'-'M'ore X ei|Unls V. When X re- mairiK constant and Y is halved, fh^'ii X -V 2 e or the level of water in the stand pi|>e. the amount of pressure of water d»'li^''''<'*l »'> i'l*«* xaried in the same direction. 17! 17l' I'llVSlOI.MIiV K(IH KHNTAI, STIDKNTS. i Th<- pvHiips (ir thf stiiii(!|.i|)c corn-spoiK] t.> tlic licart and tlic lartrc iirT.rics. tli.' disti-ihiiti.nj: Iii|><'s to the Miiallcr aHcri.-s aiul «r*apillarr!'s. Wifli rlii'sc idcits in m,»i(i let us consider tin- i)art the iH'Mrt iiii.i bioiMJ vessels |il;i\ in iiiaintainint; the eifeidation. The ^rt the HMUt Hiys.— At each systole (id t.. !»o c. c. ot' Wwxl aif force., into r-hr aoHa. Cardiac systole lasts about ().:! ♦rf a -«.co».l. fhe diiwtwJe ()..". second. Therefore the heart is rest- vm. about (iO per cent of the time. |!y .'xpcriiiient it has been demonstrated that th.- left vent ride forces the i)l<)od out into the aorta with a presH«:-e e.|uivaieht to the weji.'h'^ of i Iiimii of mercury from IW) n, l!t(» mm. in heifrht. Th.' heart alone, Innv- ever. actually propels the IiUhmI through the arteries for only the t:me of its sysjoie ; dnrin>r th- diastole, as alrea.jy explained, the Mood wouM c^Hse t<. flow .■ntirely if it were not foi iie part wliich the lara?- artern-s plav in r\^^. mainiaininyr of the circula- tion. Tfe Part tke ansnes Ray. - if 't^ti >■ r. .,f waiii- are t..reed even O.S seciwid iwo an oniiriury uieral pipe, in :; second. iDd c. c mast flow ,mt irmn rh»- opposir.- en.i in the siime period. For ()..'> M-itmni no wat»-r will he tlowini.' ni the Tut«e. Let us iu»w re- place ti=,^ im'taJ Tul)t- w,Ti! ail eia.stie nibliee rube, riie end of which is fittei;i«r.mi "!' '-xp* rim»'Tit lo stinw how ;i iiiilsi- i |ii'imIii<-<-i1 lt\ i-uin- IiicKsiti*; '111- hiilli /■' I .(iiiiHS til ll-^iiiiiii'iir vvlnii lluid lliiws thrniiKli mi liMstn mill' I /•' 1 wliiii thiTi- IS ii'sist . ' !■ 1(1) '■ ihi' iiiilflow. .1, linslii of wiit.'f ; 11. Inilli s\ i-iiiiii- : '' :munipin observed that each In-at of the heart and each res|nratur\ movement affected the pressure of the blood. The |)ressure exerti'd b\ the blood on the vessel wall at the heiffht iif the systole of the vent rich is knou n as the siislvlii- hhitiil pnssitn. and that exerted by ilie elastic ncoil of the arterb'S on the blooil during the diastole of tin heart is known 174 IMIYSIOI,(MiY K each systole of the heart, is of greatest amplitu ir. th. pf.-s<«n- in the air sac or compress inj^ band etpials the lowest pieSMU ' present in the vessel hi IWeell the pulses. Recently improvements have Iteeii .iiade in the ii.etho«l of jiulir- mg ihe point uf obliterittion of lh« i.rtery. and also the \h^uX of tmixitinnn |iu!sation. by lislentJig to the sounds prcvjuced at ea -ii ftnt^xk WHM' wh-n tl:e arttrv i> iM'ing eoTii|H-i-s.sed ■fV systolic blood pressure iu the artery ol the arm in health v jm^mE^KI* 17(J l'IIV,«.|(i|,(HiV Kitlt KKNTM, STIDIATS. youiifr men vai-i.s from 110 to l:i() mm. oi m.ivury wlicn it is ilclcrmiiicd in tiir sittiii^r postiiiT. When ii p.-rsnii is lyinij down the |ii-fssniv is ii little less, iind after hard exi-rcise a little hi-jher. The blood pressure under ordinary conditions i- relatively con- stant, and is dependent on a delicati- adjustment !• tl.e relation- ship existinjr between the force of the heart, the amount of bUxtd Vin. 22. — .\|i|iai;itiis fni iniii.^uriim tin- :irli ii:i; I.I i jncsKurc in w.ni. Thi- |if.-sHUi'. in 111. .ufi is i-ai..^iil i.y in. ,iiis ..I' il.> syiinK.' until III.' piilsi- ..in II.. Iiiiin.i I..- r. It at thf wrist Tliis iii-rss..i. . r.a.l ..IT .111 tli,. m.-i.-my iii;iiiiiiii.-I.'i .s>.^t..(if pfcssur.- 1. liumjMMl at ea.-h Ixiit. the resi.stane. which the walls of the blood vessels olfer to the tlow (d' till- iiiiiod. the si/e of f|ie vascular svs- teiii. and the aiiioiinl of IiIimmI in tin body. Since tin- am. -nut of blood in the boily i« relatively coiistaiif. we may >,!i\ ilial the factors which cjiaiii;e aiv the heart and the blood vc^w-ls. How T!iK VKi.itriTY OF TiiK nrxM»n 177 llii'sc fiH'liii's iiiHiii'iii'f till' liloitil |>i'fssun' may lie sci'ii if we iij,'aiii conipiii" till' system to tli' city wati-r supply. Factors Which Maintain Blood Pressure. -Wii.n the most Wiitci- is ht'iiifr piimpi'd into the mains, tlifii tlit' water has tlie jjn'iitest velocity and pressure. Likewise, when the heart is puinpinfj most Idotwl into the aorta, the vel )eity ami the pressure of hlood in the vessels are the jrreatest. If the amount of water remains constant, a uniform outflow throuj^h all the outlet tubes will he maintained, hut if the number of outlet tubes be diiuin- ished. then more water will have to How. |> r minute of time, throuffh the renuiininu' tubes; hem-e the velocity and the pres- sure must be increased. The .same conditions are present in the bcxly. A narrowing of the arterioles throu},diout the Imdy or in some e.vteiisive vascular area, causes the pressure and the \.'locity of the bl(K>d to be in- creased in the remaining; vessels, provided, of course, the heart beat is unclianjjed. A dilation of the arterioles, on the other hand, results in a fall of j)ressurc and a decrca.se in the velocity of the .bl(M)d. In the same way also an increase or decrease in the action gf the heart will result in an increase or decreas*- in the l»ressure and velocity of the bloml. The dei)cndciice of flie.se two factors, i. c, the ! rt and th» vascular system, on the mainteii'incc of the normal blood pres sure, is .seen in the fact that, with a fa.st heart and dilated blooii vessels, the blood |»res,sure may be exaetlv the same as when th.- heart is beatiufr very slowly l)ut the arterioles are all c(mstricted. It is apparent, therefore, that the velocity of the l)lood in the ves.sels is dependent du the pressure of the blood and the extent of the viiscular area at the time in (|Ucstion. The Velocity of the Blood.— Hy the velocity of the flow of blood we mean the actual time it takes for a particle of blood to jtass between two points. If the rate were uniform throughout the vascular area, we could compute the time which a particle of blood would take to j)ass through the circulatory system. This is not the ca.se, however, for tlu- flow of blood is much swifter in the aorta than in the snudler vessels, and here again our analogy between the circulatory system imd the city water system applies. 178 rHVsl(ll,(H;V Fi)H hlATAI, STIIHATS. I . s Just as tlic coniliiiKMl cmss area of the small pipes Icadirif,' from flic main pipe of the water svstem is greater l»y many times than tlie area of the main jiipe. so it hits been estimated that the total cidss section of the eajiilinries of the IxmI.v is HUO times lar>rer than that of the a.irta. It has been estimated that the rate of l)l(M)d flow in the aorta is about ;{20 nnu. ju-r second. The aveui^ • rate of flow in the capil- laries must then be f<()0 times less than that in the a(»rta, or 0.4 nun. per second. As the lenytli of a capillary has been estimated to Im' about 0.r» trim., the blood takes about a sicond to j»ass through them into the veins. This has been verified by mici'o- .scopic txiiiiiination of the bhxxl flow in the capillaries. The velocity of the Mood must be altered whenever the size of th e.\ le viisi' liar area is ( linnncd. and since during!: a cardiac cycle iicfl.\ till- same .iino'aiit of blood is delivcj-ed into the ri|^ht auricle as the left ventricle forces out into the aorta, it follows that the same amount must pass thron^di the vascular area of the body in the .same time. In other words, the amount of blood which flows in a jfiven series of blood vessels in a lit by the contraction of the heart is used to overcome th;- rr,i.stance offered by the walls of the ves- .sels and the capillaries. In coiLseipieiice of this, the velocity and the ])ressure of the blood on Mie sides of the vessels are much i-e- ilnced. The blood is collected fidin the capillaries by the veins, and since the volume of the veins is l.-ss than the volume of tin cai)il- laries its velocity i,-; mueh iiicrea.sed. The relatively lai'jje calibre of the veins, however, ort'.-rs little resistance to the flow of blood and the eiieixv rcmainintr from that imparted to the blood by the . heart has full power to niake it.self felt. Nevertheless, this is not TiiK ("iRrrr.ATioN tim;;. 179 sufficient alone to foree tlie Itlooil onward an. I liael; to tlie lieart. Hnliiin llu i-( nous n liini. Tlie veins are eiiuiiiped with eup-sha|>eIo(kI only in one direction, i. e,, towards the heart. Kvery movement of a muscle therefore si|neezes some of the lihwid onward. This massajfinjf influence of the m'lscles is very im- portant. Its absence accounts for the fact that it is impossdile to stand .still for a lonn jM'riod of time without th.' Iind>s 1 m- \i\g very painful, especially in the case of varicose veins, where the valvcH of the veins are no longer functional, .so tliat there is nothing to prevent the blood from returning to th" more iid is the aspiratory ctFect of the thorax at each inspiration. This action will be considered in the study of the i-espiratory mech.in- ism. Circulation Time. — The actual time which is taken fUi i>ir uiiinih li, lach hinidrnl firamuus of ornmi have been (b'tcrmined experimentally: lj,.g .") c. c. Liver (venous).... ")!> c. c. Head 20 " Liver (arterial ) . . . 'i'y Stomach 21 " I'.rain \'-M> Intestines ... .;n " Kidney l-'iO Spleen -"iS "' Thyroid MH) " The Effect of the Circulation on the Blood.— If llu- of some obstruction or change in one of the vessels. When wo analyze the pulse wave obtained by a spliymograph taken, for example, from the radial artery, it is seen that the 182 PIIYSI0L(10Y FOB DENTAL STUDENTS. heart to maintain thrcugh all parts of the botlv at all times a .stream of blood which would be large enough for all emergenci.-s There must be sonje way of controlling the blood flow accordin- to the needs of the body. This function is served primarily by the central nervous sy.stem. which is connected bv means of i.erves with the musculature of the heart and the bloo,l ve.s.sels. an.l .secondarily by .secretions from the .so-called ductless gbmds th.- best known of which are the adrenal glands (see p. 12!)). The Nervous Control of the Heart. The Cardiac Nerves.-The heart is supplied with b„th s.-n- sory and motor nerves. Sensory nerves carrv stimuli from th.' per.i)he-a) regions to the brain and are known as afferent nerves Motor nerves, on the other hand, carry stimuli from the brain to the mu.scles or glands, and are known as efferent nerves The efferent nerves of the heart are found in fib-rs coming from the s|)inal cord by way of the .sympathetic .sy.st.-.n, and bv tiu- vagi or the tenth pair of cranial nerves (.see p. 26.'.). It m.i.st be clearly understood that the nerves merely regulate th.- h.-art beat, but have nothing to do with its occurrence. In other words the heart continues to beat aft.-r nil the nerv-s hav.- b.vn .s..vereH( iilorij nerves. The Inhibitory Nerves. — The vagi are a pair of nerves arising on eaeli side of the medulla, and running a eourse downwards through the neck into the thoraeie and abdominal eavities. This pair of nerves sui)ply fibers to the various organs of these regions Time in icconds FiK. 2.1. — Kffect i>f stimuliitiiiK vaKUs and s.viniiuthi'lk- luTvcs lui tln' fn hi'Uit. ineluding the heart, whieb receives branches from both vagi. It is passible l»y simple exporiiiiouts to demon.strate the function of these fibers. For example, if the vagus on one side be cut. the heart rate will increase a little; if both vagi be cut, the beat is still more markedly (luiekened. and the increased discharge of blood from the heart produces a rise in the arterial blood pressure (Fig. 26, No. Ill ). By cutting these nerves we remove the infiu- •;ice which the central nervous system exerts through them on the heart rate. Since flu heart beats faster after this operation, we nui.st conclude that this organ constantly receives stimuli from the brain through the vagi, and that these stimuli cause - }■' ■ f- ♦ 186 Kldn«y Vplmm PIIYSIOMKIY FOR DENTAL STl'DENTS. y />/vA' Kidrny Volumt • Stimulatien aplenchnic Tlnn m Mcond) No.I No.n _Kldr)«y Voiu">c idity v/olume Blood pr*>}ur« ^ ^ . . >«rv« Cut Muod pressure * Iniccfcion of dilute odrcnolin solution. Tin* in Mconds Tinie In seconds no.ni No.EZ' Kidney Volvme Rapid bleedinj 'Alow bleedins Time in seconds No.Y FlK. 26. — Tradiiss of arterial hluud pressuiv (taken with apiiaratu.s in Fis- 21) and of Itidney voluiHf (tal<' incivascd five or hix timcH. as can be judKcd from tlic amount of carbon dioxide jyivcn off by the Inn^rs. Since this increase is due to the activity of the nmscles. it in iii'ce>wary that thew obtain a Rrcater Hupply of oxygen, and that they lie able to rid them- selves of the carbon dioxide which is a waste product of their activity. Kvery other or^^an re(|uires an increased blwxl supjily when it becomes active, so that blood has to be divei-ted from the inactive to the active tissues, and the least imp(U'tant activities of the body have to be subordinated to tiie one which is most needed at the time in <|UeKtioii. This action is l)rou«ht about partly by the central nervous system, actin^r tiiroujih its afferent and efferent nerves on the musculature of the blood vess.ls of the bwly. and partly by means of chemical substances which are produced at an early stajje of the activity itself. The Vasomotor Nerves. — It was disecivered in the middle of the past century by th French physiologist, ("laude lleriiard. that st'ction of the cei'viCvd .sympathetic nerve in the neck of the rabbi' causes a marked dilation of the blood vessels of the ear, and that during stimulation of the nerve with an electric cur- rent, the blood ves.sels become very small, and the ear coum - (|Uently colder. This experiment .shows that the nervous system plays an important role in the control of the flow of blood through the tissues, and from it many important truths about the nervous control of the blood vessels nuiy be deduced. If cutting a nerve will cause the blood vessels to dilate, and stimulating the same nerve with an electric cui-rent will cause the vessels to constrict to much less than their normal size, it follows that the blood vessels must be normally held in a state half way between ex- treme dilation and constriction by stimuli received from the nervou.s system. The nerve fibers which carry the stimidi, be- cause of their power of pro«lucing constriction of the blooil ves- sels, are known as vasoconstrictor nerve fibers Tlx-y are cnii!- 190 riivsinr/Kiv poh dkntm. sTrnrxTs. Ul ''■1 paruMf in action to th.- acfi-U-iHtor n.'ivts to tin- li»-ai-t. Hincr Htim- ulation of ritlicr t.V|H' of n.-rv.- U-iuU to |>nHliic.' an iiiercaw in th«- l)looy <|iiic|«Miin(f tho h.-art rate ami th.- other by ponstrictinK thf blmxl vt'sufls and incn-asiiiK the rt'siMt- nn(v to the fl«»w of bloo*!. The prewncc of the vasooonstrietor AJhth in the Nvnipathetic nerves is easily shown l»y the fact that stininhition of these nerves to any part of the hotly produces a marked diminution in the size of tile part to which the n.-rves are connected. At the sani" time there is an increaw in the (^.|u•ra) bh)od pressure, Depause the freedom of outflow of blood from tlie arterial system is soine- wlmt reduced. The lar^re nerves which supply the limbs also contain vasoconstrictor nerves. These are derived from fibers coming from the jranglia of the sympathetic chain in the thorax and abdom. n and .ioininj? with the roots of the spinal nerves in order that the filx-rs may'be distributed along with the cerebro- spinal nnves to the jtart in (picstion (see p. 277). After section of the spinnl cord, th.- l)lood vessels of the part of the hotly .supplied with v)i.skI><*» behind tiie stoinaeli, wliieli is ealleil the .S7 tnilioitir (jiiugUon of the solitv i>}< ms. If wiiilc the normal vol- ume of th«' kidney is IteiuK reeordid, the splanehnie nerve of the eorrespondiiiK side of the body is eut, the kidney will show in- crease in volume, due to the loss of the vasoeoiistrietor nerve eontrol on its vessels. On the other haii-' stimulation e' the ;i «' minution in the vohune of the vessels of the kidney and of t'' ■ wlmh- splanch- nic area, .since the si)laiu*linic nerv >'ipi>l.v n. i .miy the kid- neys, but the wh' ' ' intestinal tract \s .i. va.socoiistrii'tor fibei*s. Vasodilator Nerves. — There is another class of efferent nerve fibers to the arteries, which are known as the vastwlilator nerves. When stimulated they briuK about an actual dilation of the arte- rioles, and allow a j»reater amount of blood to pass through tin vessels. Vasodilator nerve fibers are found in all the spiiuil nerves, aiul they run to the blood ves.sels alonjj with the nerve trunks supplying the various oi-^ans. Tnlike the vasocon.strictor nerves, they '<' ♦' -\|)cniiicMt. Ill the iiifaiivvliih' tlic vasoponstrictor filx'i's (lie. iiiid di! itors n-iimiii alive, so that their action can be shown l»y takintj a volimie record of the limb before and diiriiijr the stiimilation of the nerve. Vasomotor Reflexes.— In tlie same manner that tli<' heart is iiitlueiiced liy afferent stimuli reachinjj cardiac centers from peri- plieral pi.rts of the body, we find afferent stimuli affecting the size of the blood vessels retlexly by way of the vasoii.otor center —located in the medulla near the vagus center— and the vaso- motor nerves. Some of the afferent imi)ulses cause dilation of the blooti ves.sels. wliile others cause constriction. Perha]>s the most iiii])ortant of the s<'iisory nerves, which, when .stimulated, jirotluce a dilation of the blood vessels, is the cardiac depressor, which we mentioned in connection with the afferent nerves of the heart. Jt will be remembered that this nerve has .sen.sory endings in the left \entricle and in the aorta, and that these are stimulated when the blood i)ressure in the arterial .sy.stem reaches t(M) great a height for the safety of the individual. The stimuli originating in the .sen.sory endings of this nerve are carried to the cardiac center and are then transmitted to the heai't through llie vagus nerves, besides the slowing of the heart which is thus produced, there also occurs a dilation of the i)eripheral vessels brought about by the action of the stimuli on the vasomoter center. This is easily demonstrated by electrically stimulating thi' cardiac depr.'s,sor nerve after both vagus nerves have been cut in the neck and the retle.x vagus action thus removed. The fall of blood pres.sur.' which is obtained under these conditions is due to an inhibition of the con.strictor center and a stimula- tion of the dilator (■(■titer of the vasonmtor nerves. Tile stiiiiulation of many of the afferent or sensory nerves of the body is followed by a change in the blood pressure. Just what this change may be it is often impossible to predict. Strong sensory stimuli of short duration may j)roduce a marked rise in blood j)ressiiri'. the constrictor center iM'ing the most affected. On the other hand, if the stimuli are very strong or continued over a long period of time, the constrictor nerves may become exhaustetl. as it wore, resulting in a dilation of the arteries and TIIK. VASOMOTOU KI'.hM.KXKS. 193 H fall ill the general l)Ioo(l pressure. Like phenomena are often seen following fright, pain, grief, anil exeitenieiit. The patient Iweonies suosed that normally the nerves of th.- vasculai- system function to control the blood flow tiirough the various organs according to their resjjective needs. Whenever the work of an organ is increased, the blood ll.nv like- wise is augmented in the i)art. while in the rest of the botly the blood flow is diminished to a greater or less extent. The blootl supply is continually changing according to the call of the vari- ous tissues for blood; now the muscles, now the digestive organs, now the brain demand more blood, and this is supplied in tin' l>roper amount by the nervous syst^-m conunanding some arte- rioles to dilate and others to constrict. Haemorrhagre.— The action of the vasomotor )nechanism is beautifully shown in the cas«" of ha-morrhage. As blood is with- ilrawn, the vasomotor nerves are .stimulated by the falling i)res- suie in the brain. This brings about a more powerful tonic con- striction of tlie ves,sels through the action of vasoconstrictor nerves, the vascular area becomes smaller and smaller in size. and less blood is re(iuire(l to maintain the blood pre.s.sure. Be- cause of this nu'chanism a relatively large amount of bloofl can be lost without affeeting the general blood pressure (Fiff 26 No. V). ' The Regulation of the Blood Supply by Chemical Stimuli.— The calibre of the blood ves.sels may be influenced by other means than through their nervous mechanism. Acids in very small concentrations cau.se a vascular dilation. For e.xample. lactic acid and carbonic acid, both of which are formed during nuiscu- lar work, may ju-oduce a local dilatation of the blood ves.sels, the j)henomenon thus constituting an automatic nu'chanism for deliv- ering more blood to a part when it is needed. On the other hand, the secretion of the adrenal and of a portion of tlie pituitary gland (see p. LSI) i)roduces a constriction of the vessels and thus tends to maintain the normal blood pressure. Recently it has been shown that during i>eriotls of excitement aiul sensory pain the amount of the adrenal secretions may be increysed and ASPHYXIA. 195 the arterial blood pressure raised as a result of general vasoooii- strietion. Beeause of its vasocoiistrietiiig i)roj)erties, extraet of the adrenal glands {" ndrrnnUn" or "rpincphrin") is us«'d in local anesthetics, as in eooain solution, to prevent bleeding and to minimize the absorption of tiic eoeain into tlie general eireu- lation (Fig. 26, No. IV). Asphyxia. — Whenever the amount of oxygen whieli the blood mu.st supply to the tissue falls below the miiiimuin amount re- ipiired, a condition known as asphyxia develops. If tlie nervous centers are intact, any interference with the respiratory function, as by obstruction of the resj)iiatory pas.sages, lack of ogygen in the atmosphere, or the i)resence of irrespirable gases in the at- mosphere — such as carbon monoxide, wliich reduces the oxygen capacity of the ha'moglobin. interferes with tlie blood sui)ply of the brain — and will i)roduce a train of phenomena in which tiu' respiratory and circulatory changes are i)rominent. in ordinary asphyxia two factors may be involved, a deficiency of oxygen and an excess of carbon dioxide in the blood. The i)h(nomena following each are cs-sentially the same, and may be divided into three typical stages. In the first stagtN that of hyperpna'a. tlie respirations are increased in rate and amplitude. This stage merges into the second, which consists of exaggerated expiratory efforts, loss of consciousness, .stimulation of the vascular centers in the brain causing general vasoconstriction accompanied with vagus slowing of the heai1. Tiie net result is a rise in blood ])ressure. In the third stage, the expiratory eflforts give way to slow deep inspirations followed by expiratory convulsions. The pupils dilate widely, the heart becomes very weak from lack of oxygen and overwork, and death occurs from cardiac failure. The changes jiroduced in the resjiiratory movements, as well as those of the vascular system, are caused by the direct stimula- tion of the respiratory (see n. 220^ and vascular centers, by ex- cess of carbon ilioxide and by tlie lack of oxygiii in tiie bloml. Nitrous Oxide. — The circulatory and respiratory ciianges ac- comi»anying the administration of nitrous oxide gas are very similar to those produced in asjihyxia. Tlie asphyxia produced by the lack of oxygen and the excess of carbon dioxide in lie 196 PllVSIOLiXn- FOR nENTAL STUDENTS. i blood during gas anestlu^sia, stinuilates the vasooonstriotor cen- ter, procliicing a rise in blood iiressure. The nareotie action of the gas depresses the inhibitory effects of tlie vagus cardiac wn- ter on the heart. Tlie lieart is therefore f|uickened and tends still further to increase the blood pressure. For these reasons it is not wise to u.se niiious oxide in the ca.se of elderly patients with weakened sclerosed arteries, or in the case of those suffering from cai-diac disi'ase. When oxygen is given along with the nitrous oxid? the asphyxial phenomena are reduced. Cocain.— The effect of cocain injections on the circulation are both central and peripheral, and vary according to the dose and the individual susceptibility. Very small doses generally cause a slight fall in blood pressure, due to slowing of tlie heart from stimulation of the vagus. The vasomotor center is likewi.se stim- ulated, but the resulting vasoconstriction does not compensate for the fall in pressure caused by the decreased action of the heart. Mo" blood, which is well adapted thus to transport the oxygen and carbon dioxide, first because it contains chemical bodies with whicii the gases can unite, and secondly becaiise it comes in close contact with tlie tissue ceils in the i)eripheral portions of the body, and with the atmospheric air in tlie capillaries of the lungs. The study of the resjiiratory function therefore includes the mechanism of the gas exchange between the ♦issues and the bloo^h the oxygen of the air combines with the 197 198 niYSIOUKlY FOR PENTAIi STUDENTS. JiydroKfii aiul carlwii of llu- foodstuffs to foi-m wjitcr and carbon dioxide gas. Oxidation in the Tissues.— The actual mcclianism whicli unites tlie oxyjren with the carbon and hydrop>n of the food- stuffs within the tis.sue ceils, is not entirely known. In spite of the fact that the processes of condmstion of hydrocarbon matter outside the body yields the .sani.- end products as the oxidations takinj? place within it. the two i)rocesses are not strictly analo- prous. An important point of difference lies in the fact that the intracellular matei-ials— fats, jiroteins. and carbohydrates— arc oxidized with relativ.'ly ^jn-at rai>idity at low temperatui-es (88"), whereas the same reactions outside the body re(iuirc a v»'ry high temperature. Let us take as an exami)le the cell of the yeast plant, in which there is a sub.stanee. under the influence of which, the sutfar molecule Iw'comes .sjjlit uj). at a temperature below that of the btMly, to produce cai'jon dioxide and water. Similar sul)stances are i)resent in the tissue cells of plants and animals; thev ar." the ferments or enzymes (see p. :{4). and they act as catalytic agents. The function of these bodies is to increase the velocity of many chemical reactions which otherwi.se proceed so slowly that they may be said in some cases not to exist. A class of these substances is present within the tissue cells, which at the (h'mand of the tissues control the extent and the velocity of the union of oxygen witli the hydrocarbons of the food. Such en- zymes are known as oxidases. What evidence have we. how.'v.-r. that this oxidation takes idace within the tissues and not within the l)lood itself? It is conceivable that the substances that are to be oxidized are col- lected from the tissues by the blood, and that the oxygen condjines with them in this fluid. It is quite po.ssible that some oxidation takes place in the boo.' witli- iii tlic body can take place in a solution of sodium chhn-idc Kki.ation of ()xn)ATivK pRoct>;s TO Activity.— L'lulcr ordinary conditions the hlond has a suitply of food and oxyscu sutHicicnt for the needs of the body. An excess of either does not intensify the oxidative prcM-ess. An aninud will jrive otT the same amount of carbon dioxide in an atmosjjhere of jiure oxygen as it will under ordinary conditions. This fact indicates that the oxida- tive jirocesses are governed not by the supply of food or oxyjien, but rather by the actiud needs of the tiss\ies. \ muscle freshly removed from th ■ body nuiy Ix' made to contract, and will jrive otr carbon dioxide for some time in the entire absence of oxygen in the surrounding medium. Another feature of this experiment is that for a time after the muscle has ceased to contract, i* will produce heat and take up a large amount of oxygen. Indeed the maximal intake of oxygen and output of heat often occurs after the actual period of work. In this respect the mnsde can be likened to a storage battery which is charged by the actual expenditure of energy and delivers .|uickly the energy stored up when the circuit is closed. If the volume intake of oxygen and output of carbon dioxide is measured, it will be found that the amounts are greatly increased during jM-riods of tissue activ- ity. Kxperiments have demonstrated that a muscle at full work will us<' up its owif volume of oxygen in ten minutes. To supply such an amount of oxygen re(|uires'a very high degree of effi- ciency on the part of the distributing agent, the blood. PirvsiCAi. Laws (Jovkkmnc; Soi.ition op Gases. — A brief re- view of the i)hysical laws governing the solution of gases in water will help us materially to understand the mechanism of the traii.s- portation of oxygen and carbon dioxide by the blood and the respiratory mechanism in general. The sohd)ility of a gas in a fluid is measured by the number of cubic ci'ntimetres of gas which one cubic centimetre of fluid will dis.solve under standard conditions of temperature and pres.sure. Such a figure is known as the cm-fficient of solubility. For ex- ample, pure carbon dioxide gas under standard conditions of temperature and pres-sure (760 mm. pri'ssure and 1.")..') degrees 200 I'lIYSIOUXSV FOB DENTAIi STHDENTS. Cent.) Will dissolve to the amount of one c. c. in one e. e. of wat.-r ILiuler like conditions only 0.04 e. e. of oxygen will be dissolved. 1 he eoeffieient of solubility of carbon .lioxide is therefore 1.0 and 01 oxygen 0.04. The amount of gas whieli will go into .solution in water d.-n.-iuls on three faetoi-s: the temperature of the water, the s<,lubilitv of the gas in water, and the pressure whieh th." gas e.xerts on' the surface of the water. As a rule.the higher tl... tenip..rature of the water the less gas will go into solution, or in other words, the solubility of a gas varies inversely with the temperature The pressure which a gas ex.-rts on the surface of a fluid is expressed in terms of millimetres of mercury. The prc^ure of an atmosphere is e(,ual to 760 mm. of mercury at .sea level and V, 5 degrees temperature. This is known as the standard barometric pressure If in place of having pun- gases ov.-r a fluid, a mixture ot several gases be present, then we find the .solubility of each of the ga«.s varying directly with the pressure it exerts on the sur- face of the fluid. Su,.pose that in place of .-xposing a cubic centi- nietre of water to oxygen at 760 mm. pressure, we exi)ose it to oxygen at a pressure of 152 mm. n.ercury-tl.,. normal pressure of oxygen in the air 1;5 of an atmasphere)-it would aksorb 1/", of .04 c. c. or .008 c. c. of oxygen. The pivsence of other gases does not enter into consideration, for accor.ling to Dalton-IIcn- ry s law, when two or more gases are mixed together, each of them produces the same pres.sure as if it .separately occupied the entire space and the oth.r gases were aksent. Wh;n the fluid has taken up all the gas it can, an e.)uilibriun. becomes estab- lished between the gas in the atmosphere an.l the gas within the fluid. The pr..Nsure which the gas in the fluid exerts on the gas m the atmosphere is known as the tension of the gas, and e.,uals the pressure of the gas in the out.side atmosphere to which it is exposed. This can be easily measured. Since the pressure of the oxygen in the air ,n the lungs is less han that in the (Hit.side atmos,,here, it is apparent that if the blood should carry the same amount of oxygen as water, the amount would be very s^nall indeed. Analysis of the amount of oxygen m arterial blood shows that it contains 40 times the Il.KM()aiA)BIN. •_»()! amount iicr f. c. that wat«'r vnii dissolve uikUt like romlitioiis. For oxamplf, U-t us iiuaghu' human blood to Im- water. It wouM earry then only 1 -^O oi the volume of oxyjren that it does, and the body would need the vaseular system of an eh-phant or tlie tissues of a rabbit in order to obtain as mueh oxygen as normally is supi)lied by the blood. Therefore it is obvious tliat the laws for simple solutions eaii apply oidy in a sliyht i.i ilie baro- metrie pressure bein<; due to nitrogen) is due to the absence of any ehemieal body within tiie blood plasma which will unite wilii nitrojren. Of the 20 volumes per cent of oxyjien found in arterial bloo?en which is within two-thirds of that present in air (iM'twecii !»0 and l.'»2 mm. of mercury) are all almost satu- rated with o.xyjjeii. In other words, at these pres.siires the hu-mo- Klohin i-xists entirely in the form of oxyliji'inoglobiii. In the tube containiiiKT one-half the pressure of oxyjfcn in air (i. e., almost 7<) mm. Hg.;. the ha-moKlobin solution is !»0 \wv cent saturated. M about one-fourth the norinal oxygen j)ressuie in air (i. e.. 40 mm. Hr.), it is a»M)Ut 84 per cent saturated. At lower partial pivs- Hures of .).\ygen, the ability of Irn'moglobiii to unite with oxyjfii very rapidly decreases. From these obsci'vatioi'.s we must conclude that, as the jires- sure of oxygen in contact with the luemoplobin .solution increases above zero, by •rraded stages, the amount of oxygen, per unit of increase of oxygen pressure, that combines with lucmoglobin at low j)rcs.sures is large, but liecoiiies relatively less at higher pres- sures. Or. conversely, if the lucmoglobin saturated with oxygen !)♦■ subjected to decreasing oxygen jiressure. the combined oxygen is set free at fir.st slowly and then more rapidly. If the oxygen-coiiibiiiing jmwer of hlaotj be investigated in ex- actly the same way as described above and the results compared with those of a pure liaMiioglobin solution, a marked difference will be observed. At low pressures the oxygen is more easily re- leased from the lucmoglobin of the bloo .solu- tions of ha-moglobin. An iiKpiiry into the cause of this difference has revealed the following facts. The rate at which oxyhremo- globin breaks down into oxygen and ha-mogloVin, depends on other factors besides oxygen pressure. These are: (1) tempera- ture, (2) the presence of inorganic salts, and (:5) carbon dioxide or other weak acids in the blood. If ha'moglobin be dissolved in a s,!liiie .solution containing the same concentration of inorganic salts as is f(mnd in blood, it will take up oxygen in a manner somewhat similar to blood under like oxygen pressures. The similarity will become perfect if the saline .solutions of ha'mo- globin be subjected to the same pri'ssure of carbon dioxide as that II.KMr«'ssun's; /». tli.' nuMlifi- cation in tlu- tlt'Krcc of tin- association produced by the presence 100 ^^^ rr 90 so 70 60 ^' ^ Z^ J /. ^. ^ IT / / // r 1 f 7> / SO / j / HO / / 7 30 7y f — W / / W n ^ ^ \ BA £ A tn Fin. -l- Ordlnatt-s— I'.ivoiitiiKf Hiituiation of ha'inoKlol'in with oxvK. ii. VbsiisHH.-— Tnisiiin of oxyKcn in mm. of meii'ury. Curve A— IX'Kiv.. of saturation of pure ha-moK in solutionw at varyini; l)rfsaures. Curve B-Mo.ll«»ation of .l.'Kr.e .if saturation lause.l l.y presence of sallK in tlie lilood. Purve r— Kffecl of 20 mm. C"Oj pressure on almve solution. Curve U— The saturation cur.e in normal bioud at H» mm. Ci*rl>..„ dioxi.le pressure. ■''I' 201 I'llYSIOl^HlV FOR DENTAL sTrilENTM. |!;l U of thf Wilts of th." hlmMJ; < and «', th.- .fT.-ct of (■ail>oii p.-i- .•cut of th.- total lucmoKlobin at a carbon dioxide piVHsiirc of ,") mm., whereas at a pressure of 40 mm. of carbon dioxide the amount of o.xyha-mofflobin is only 2!>..") jier cell*. InaMiiucli as the amount of carbon .lioxide is coii- stHiitly chai./ing in arterial and venous lilooti, the iiresciice of thi.vi tins would seem to Ik' an important factor in the eonti-ol of the oxidiition or thr dissociation of the ha-iiioKlobin compounds. At any rat^s it would help to account for the ease with which ox.vffen is bn.keii from the oxyha'inoKlol.in molecule in the ea|.il- laries which are imbe.hled in the tis.siies where the carbon di(.xide is formed, and its pressure is correspondingly lii^h. The Mechanism of the Respiratory Exchange.—Tlu oxygen in the alveoli or air pa.ssajjes of the lungs comprises about 14 to ir» per cent of the total air. an?en much l.-ss than 100 mm. of mercury. There are, tlii-refore, very favorable conditions in the lungs for ha-moglobin to take up oxygen from the air. It must be under- stood, however, that the luemoglobin does not obtain oxvgen di- rectly from the air. The ha'moglobin is held in the bIool)iii is very irreedy for oxyjjiii. There in awonliiiKly a tlitfiTt'iice in the oxyp-ii |>reH8ure in the plasma of the eapillaries of the liiiijrs. siirtieient to aeeoiiiit for th«' abHorption of oxy«eii hy the h«'nio>flol>iii of t'le hhioil. The hlood leaving the Umtts is delivered into the left ventricle, from which it is distrihuti-d over the body. Since oxidation takes place within the tissue cells, oxy>f<-n is bein« continually called for, nnd the lymidi Hurroun- ply is short, the phenomena of asphyxia ilevelop (see p. llt.'n. Kkfkct ok (".'.rhon Dioxiuk <>\ t>xvii.K.M.M!i.(tiu\. — As a result of the oxidative changes which take place within the cells, carbon dioxide is i)n)duced, and the tension of ti ^s >ras rises in the tis- sues. It will be remembered iti the di>M'Hssu)n of the dissociation of oxyha'inojilobin. that the et!Vct of increased tensions of carbon dioxide is to increasr the rate of reducfioii of (ixyluenu)f,'lobin into oxy^'en and hu-moRlobiii. Since there is a hijih tension of car- bon dioxide pi-esent in the tis.sues and at the site of the capil- laries, the effect on the reduction of oxyha-mo-iiobin is very marked, and has a fireat influence on the rate at which oxygen is supplied to the tis.sues. Just as there is a desceiidinji pres,sure of oxygen from the air iu the lunsrs to the cell, so is there a dc- cnase in pressure from the carbon dioxide in the cells to the air of the luuKs. This gas therefore parses through tlu' lymph to the plasma and out of the i)la.sma through the juilmonary epitheliuin bv tlie simple proce.vs of diffusion. The Exchange op Carbon Dioxide.— Analysis of venous blood 206 I'llYSKlLOCV FOK I)i:\T.\r. STIDENTS. m shows tliat 100 c. v. contains alwut 45 to r)0 c. o. of carbon diox- ide, and that th.- jjas ,.x,.rts a prcssun- or tension of al)<)ut 40 nun. mercury, which is c.|ual to about five i)ei nt of iin atinosplierc. Now water will dissolve under tiiese conditions about 2K, c c of earbon dioxide jn-r 100 c. c. This woui.l leave tlie nicm't of the carbon dioxide of tlie blood unaccounted for. in case the blood lias the same solvent i)ower foi- the jras that wat.-r has. The rest of the carbon dif.xidc then-fore must be accounted for as beinfi in chemical cond)ination with the constituents of the jdasma and corpuM-les. Th.- major j)art is probably held i,, the form of sodium carbonate and bicarbonat.-, the remainiif(l). The External Respiration. Anatomical Considerations. — Tin- coiistjnit call of the 1 issues for oxygen and tlu' foniiatioii of the waste jjas. carbon dioxide, demands a nicclianisni l)y whicli the blood can contin\ially renew its sui)ply of oxygen {"iid excrete its excess of cirbon dioxide. This cxchangre. as we have .seen, is eti'ected in the lunf,'s, which are built up in tlie followinjf way: The nasal and oral cavities lead to the i)harynx. from which open two tubes: one ])ostcrior. the d-sophaftus. jroin>r to the ali- mentarv tract, and the other, anterior the trachea. j,'oinj,' to the Kis,'. 2S. — ni.iniaiii "f structun (■hiole.« iiiid alveoli. >f luiiBs .^linwiii;;' liiiynx, Inoiii'hi. Imiii- Innijs (Fifj. 2S). At the befrinninp of the trachea is |)laeed the larynx, or the voice box, the openinjj of which is tjuarded by a flap of tissue, the epifilottis. Within the larynx are the vocal cords. The trachea, or windpipe, is a relatively laryre tube, about four and one-half inches long, which, after its entrance into tlie thorax, divides into two tubes, the bronchi, each of which subdi- vides again and again, the branches gradually growing smaller until they are mere twigs, and are known as bronchioles, or small 207 208 l"IIYSI()r,(KiY FOR HKNTAI, STIDEXTS. broiiclii. The hini.-ii of tli." tni'Moa and bronclii is niaiiitaiiiod patent 1»> cailila-rf l>latfs, which arc imlx-dih'd in tiic walls of the tulh's. The l»foiichiolcs, however, liavc no such plates, their walls heinfj conijmsed of fibrous and elastic tissue, in which is a layer of smooth muscle. The whole syst.'Ui of tubes is lined with a layer of ciliated epithelium. The lironehioles terminate in wide air .sacs or cavities, the in- fundibuli, from the walls of which extend numerous minute cavi- ties, the alveoli. The walls of the alveoli are very thin but stroiiff. and are composed of a layer of elastic tissue lined with a sin«,'le layer of flatt.'ticd epithelium. It is estimated that the epi- thelial surfaces of the alveoli, if they were s])reail out on a flat surface, would cover about 1.000 sipiare feet. Such a lai'fje area exposed to the air of the huifis oflTers the best of facilities for the ra|)id exchanjje of the respii'atory jjases. and in fact the walls of the alveoli are the true respiratory membrane of the lunfj. for throuffh them the exchanfre of ulmonary artery in a rejjrular shwork: so numerous, indeed, aiv they that I'ach individual erythrocyte is able to come in ch.se contact with the air in the alveolus, separ- ated oidy th.'refrom by the liriinjr of the alveolus, the wall of the artery, and the plasma of the blood. This arran>;emcnt Tiiakes possible the I'apid e\ehan!.'e of jrascs which must take place with- in the Iunaiiy the n-spiratory inovi'iiifiits. Mechanism of Breathing.— Nornial hn-atliiiifr lias the olOcct of briiifiiiifr about a constant renewal of air in the luiifrs. and it is etTeeted by niovenieiits of the thorax and dia|)liratrni. When- ever the cavity of the thorax is eidar^'cd. as in the act of inspira- tion, the hinfrs must increase in size to fill the space, and air is I'iK. 2:". —Til.' iicisitiim nl Ow liiiiKs in ihf thmux. ( T, Wimiiilc 'I'liild ) pushed into the respiratory tubules and the air sacs by the pres- sure of the outside atnuisphere. At exi)iration t!i(> reverse takes l)iace. and the air is expelled. A very fjood c()ncei)li()n of the mechanism by which this is brought about nuiy be had by refer- ei.'-e to Fig. :{(). Any increase in size of the bottle, as by i)uHing ■ ■own the bottom ru])lM'r meiubrane, will cause air to expand the rubber sacs coming in by the tube passing through the cork of the bottle. When the size of the cavity is ilecreased by releasing the meinbi'ane, the revei'se takes jdace and air is exi)el!ed from the rubber sacs. With every in.spiration the thorax is increased in size in all ft r 210 IMlVSIOI.CHiV FOR DKNTAI, STIDKNTS. (liaiiit'tcrs, from almvc (lowiiwiinls l»y the contnictioii of the (li«l)iiraKm, and in tlic transverse diameter by tlie movement of tlie rilw. TiiK Part Pi.avkd bv tiik DiAi-iiRAcai.— The diai>liragm is a circular sheet of miisele whieh .livides the body eavitv into two compartments, the u|)i)er l)ein^ th.- thorax, th,' lower the abdom- li' -^ FiK. 30.— H.-rin>rs iiDi.aiatus f„r denionstratiMK the action of the resnirn- .7r„\'r'\ '^^*' '^'TV '■''"'•'■«"'••"' '->• " '"'«"-■ th.. diaphraKm by a sheet f UM... • forn.mK .t.s l,o„o,„, the tra.hea hy a tube „a«.si„^ through the 1 ': h ." IT" !';' '"■" ''"' '"'""'■ '""" ' '*''" "'"- "f •■"•^'-'- tuhint, COS.,.,, the bottle. 'lh>« ,e|,.esent.s the h.-art. The action of the dla,.hraanyins blood vessels and air passages. The ab- (loniinal cavity contains the di-.-stive organs and glands, as the hvcr, kidneys, spleen and ivproductive organs. The perii.heral edges of the diaphragm are iittached to the lumbar vertebnc at the back, to llie lower border of the libs on the sid.-s, and to the tip of the sternum in front. The muscular fibers radiatt' to- TlIK MECHANISM OF BRKATllINO 211 wards the centor iiiid t'nd in a ttMidinotis sheet of tissue ealled tlie central tendon of the diaplirajjin. When these filters are relaxed, tile dia|)hrajrni is pushed u)) into the thoracie eavity, foiinins a dome-shaped areh. This is eaused by the pressure of the ahdoini nal organs, supported by the nmseular walls of the abdomen, on its lower siirfaee, a suction pressure on the up|)er surface of the diaphragm iM-ing maintained by the natural tendency of the lungs to contract. The central tendon is pulled downwards and the arched dome is flattened on contraction of tiie diaphragm, Fi»r. 31 1. .xpii'Ht -ratii to show mfivemi-nt of diaphraKni (iuriiiK icspitiilioii : normal ins|>iratioii ; Ml. fori ni in-spiration. thus increasing t!ie size of the thoracic cavity (Fig. 111). An- other result of the lowering of the diai)hragm is the slight i)ro- trusiou of the abdomen due to the pressure exerted on the vis- cera. This type of .breathing is therefore known as abdominal or diaphragmatic breathing. TiiK Part Pi.aved by tiik Thorax. — The action of certain muscle-s attached to the ribs also produces an enlargement of the thoracic cavity. Kach pair of corresponding ribs, which arc ar- 212 PHySIOI/X5Y FOB DENTAL STl'DENTS. ticulfitcd posteriorly witli the vcrtcbml column and anteriorly with the Ntermun, forms a rinj? directed ol)li(|Uely from behind forwards and downwards. Any muscles whose action would l)ring about a raising of the anterior ends of the ribs, would therefore lessen the obli(|ue position and increase the distance be- tween eadi i)air of ribs, and also add to the anterior posterior diameter of the thorax. Moreover each rib increases in length from above downwards, and as the ril>s are raised, the lower longer rib occupies the j)lace i)reviously held by its shorter neijjli- bor. This movement therefore causes the dome or a})ex of the thorax to become more flat and broad. Moreover the lower ribs are so articulated with the spinal column that they exhibit an up- ward rotary movement, which i-esembles that made by a bucket handle, and which increa.ses the lateral or transverse diameter of the thorax. The iimscles which are responsible foi- the insi)iratory eleva- tion of the ribs are mainly the external intercostals, aide«l by other muscles of the thorax, some of which are called into use only when very powei'ful respiratoi-y movements are necessary. Normal expiration is almost entirely a passive act. The re- coil of the stretched elastic tissue of the lungs, after the in- spiratory muscles have ceased to act, returns the diaphragm and thoracic cage to tlie expiratory position. This is aided somewhat by the actions of the internal intercostal nniscles which lower the ribs. By increasing the size of the thoracic cavity, inspiration causes a corresponding increase in volume of the thoracic organs: viz., the lungs and the vascular structures, because the thorax is a closed cavity, so that when it expands it must either produce a vacuum between tlie organs which fill it and its own walls, or the volume of the organs nuist increase. It is the latter process which mainly occurs, the result being that air is pushed into the lungs by the atmospheric pressure whenever the thoracic cavity is increased in size. TiiK Movements of the Lungs. — The changes produced in the size of the thoracic cavity and the lungs during normal res- l>iratioii or in disease, are easily determined by noting the sounds which are protlueed by tapping or percussing w ith the fingi-rs the TIIK MECHANISM Ot BREATIHNO. 213 tlioracic walls duriiiK inspiration an.l expiration. A lo\v-i>itc-l>".l n-sona»it sound is elicited over the lunRS eontainu.K air. whereas a hijrh-i)itehed non-vosonant or tynipanitie liollow sound is heard over the soli.l viscera an.l ahdoininal orjians. Tn .lis..as..s where ,.|,anjies take place in tlie substance of tlie liinjjs, as in tubercu- losis pneumonia, etc.. alterations occur in the tone .•lieited on percussion. These alterations are ..f jjreat dia-nost.e miport- anee In pleurisv, a condition in whicli the pleural surlaces are roughened, a friction rub or vibration. i)roduced by tlie rubbiiiK of tlie roughened surfaces of the pleura of the lungs on that o tlu- thorax can be detected by placing the hand over tlu- atTt'ctcil a.va The pain following a broken rib is caused by the irritation of the pleural membrane by the broken edge of the rib. It is al- leviated bv making the ribs immovable by tightly strapi-mg the thorax with adhesive plaster over the region of the pain. Ri-si'iRVTOPY SoiNn?.— Accompanying inspiration a rustling sound described as a vesicular sound may be liear.l over most of the lung area. It is produced by the dilatation of the alve..li and H„, i,,„„chi. Over the larger air ;.as.sag.'s a high, sharper tone is heard called the bronchial breath sound. In diseases in which the alveoli are de-stroyed and the lung fills ui) with Huid. etc.. tlu- bronchial breath sounds replace the vesicular sounds^ Effect of Respiration on the Movement of the Blood and on Blood Pressure.— Within the thorax the changes in pressure accompanying each respiration affect the heart and s. influence somewhat the Miovement of the blood. In thin individuals it is ..asv to confirm this by observing the cfTect of breathing on the blood flow through the jugular vein. At each nisi.irat.on the jugular vein is seen to empty, and during expiration to fill, it simultam-ous records air taken of the blood pressure and re- spiratory movements in or.liiiary breathing, it will generally be observed that during inspiration there is a rise of blood pressure and during expiration a rail. This phenomenon is explained as follows: During inspiration the heart is better supplied with b'ood an.l can fill more .|uiekly an.l perf.-ctly than .luring .-x- piration. becaus.- the .lecrease in the {.ressure in the thora.x at this period serves to accelerate the movement of venous blood II 214 PHYSIOUXIV FOB DENTAL STrDENTS. I: I into the tliorax by .'xpanding tlio larjrtT veins. The .'xpaiision of tile luiiffs at inspiration also dilates the eapillaries and arteri- oles inibed.led in tiiese tissues, henee a greater volume of l.Ioo, the increased amount of blood pumped during insj)iration will cause the blood pres- sure to rise. It is well to bear in niiiul that imder abnormal conditions the respiration may alfect the blood i)ressure to a dangerous extent. For instance, in the attempt to force air from the lungs under pressure into a vessel, as in blowing up a football or testing the strength of exj)iration on a machine made for the purpos«\ the air pressure can be increased within the thorax to more than e(|ual the pressure in the vessels of the lungs, and the circulation is temporarily .stopped in the pulmonary ves.sels. The blood be- comes dammed up in the venous system and forceil out of the lungs by the pressure of air. This experiment is dangerous in one who has not a first-class heart and vascular system. The ef- fects on the lungs and blood pre.ssun> of sucking, inspiration and ♦■xpiration can be conveniently reproduced on an artificial schema whicli represents the thoracic cavity, lungs, heart and related vessels, as shown in Fig. .'51. Variations occur in the respiratory movements under various emotional and physical conditions. Any foreign or irritating boily within the air i)assages will cause a coiif/h. This consists in a forced expiration, during the first portion of which the glot- tis is closed. The irritating substance is likely to be expelled bv the sudden oj)ening of the glottis. The presence of irritating sulwtances in the nasal cavity gives rise to sneezing, a sudden and noisy expiration through the nasal passages preceded by a i-ai)id and deep inspiration. In cri/ing, inspirations are short and spasmodic, followed l)y prolonged expirations, whereas laughing IS ijuite the n-verse. Yawning, the expression of drowsiness or ennui, consists in long deep inspirations followed by a .short ex- piration. Jliccoitghiny is due to spasmodic contractions of the diaphragm, the peculiar sound being due to sudden closure of the glollis. AHTII-'IllAI. HKSl'lUATloN. 215 Artificial Respiration.— In ciis.'H of siisp.nil.'il iM'spiraiimi in human li.-iiifrs caiis.'.! hy ref.'ral)ly on the jrrouml. with a thick folded garment underneath the chest and ei)i^'astrium. The operator puts himself athwart or at the side of the subject, facinir ViK. 32. — I'oHition to 1>*' inlniit.Ml for (Schiifer.) i'fr.K\TS. MOO c. c. more air into tlic lungs. This amount is known as tlir il, mrnlal nir. Lik.'wisc aft.T a normal expiration al»out i:>()0 C-. c. more air can he .•xp.'ll..,! from thf lungs. This is known as fh.' supphmnilal air. In spit.- of forcfd expiration tli. iv will still remain within the lungs a'oout 2000 e. e. of air whieh fills the alveoli and air tul).-s. known as the nxutml air. This air remains in the air spaees after the fore.-d expiration heeause tlu' lungs eannot relax to their fullest extent, l.eing held open by the suc- tion prcHNure of the thorax. In other wor.ls. the thoracic cuvity is larger in the expiratory |Mtsition hy 2000 c. e. than the lungs are. That this is the ca.se is shown hy the immediate contraction of the lungs into a small volume when the thorax is opened, for then the atmosjiheric pivssure comes to he equali/ed on the out- side anirfd jrascs. This suh.jtrt is t'lili.v d<'sri-ii»,d iiiidiT tlir li.';id ol' nsiiiniliirii niinlitul in the ciiaptci- on nwtat)olisin * p- '*1'- Tlii'Hc observations do not .'nalilc ns to dtcide wii.tlirr liif laws of diffusion of jrascs apply to tlif jrasi-ous cxclianp' of tin- lnn>,'s. To do tills w.' must know tlif actual pnssun's (d' tlif nspiiatorv >.'HSfs in tlif vfiions MimxI i-oiiiiiur to tlif luiitfs and in tlif air of the alvfoli. Many typ.'s of f xpf .iiiifnts liavf hfi-n df \ isfd to ,ili tain tlifsf vahifs. and altlioimli the actual tii.'iii-fs vary soiiu'wliat ill the hands of ditVfrfiit investigators, the results :is a wliolf in .licate that the khwous fXt-hantre of thf luiijis is dei'cnd /nt solely on thf prfSfiice of a hijjlifi' iiressure of oxyjreii and a lower pr.s- sure of carbon dioxide in the alveolar air tlian are pivs.'iit in the blood coniiiiK to the Iumks. Tln' ability of ha-iii.>nlobiii to take up oyy^reii with Kn-at rfadiiicss at oxytreii pressures which ex .1 ■")() or (iO iiiiii. mercury pressure indicates that Uie blood can Mill obtain oxygen from air which contains only oiielialf of the nor- mal pressure (d" oxy-rcii. In whatever way we estimate it. the oxytren |)ressui-e in the alveoli is always -greater than this. \Ve will not fio into details i-e<;ardin^r the iiietliods whicli have lu'cn eiii|iloyed in solution id' these jirobleiiis; suflice it to say that a very fair sain|)le of alveolar air can be secun-d by collectiii« a sami»le of air from a tube throu<,'li which a forcfd expiration has ))een made. The last portions of such expired air must obviously be . eolar air. Mechanism of Gaseous Exchange in Lungs.— We have seen that ill the blood thi" pressure or ti'iision of the oxygen is 'as that «*" the CO., is less than in the tissues. Tiiese rela- tions will a( , .(Unt for the sjas excliaii ami nifrojrcii, ami is n'lativciy coiiHtant iimli-r onli- nary comlitioiis. The cxpiri'd air varies Hoim-wliat accordiinr to till' nitt' Hiiil ficpth of respiration. The foIiowiii« tahii' jjivcs the awrm^e |>t'rcciitaKi' coinposition of inspired and ex|)iretl air: NitroKPii liiHplred alp 7!t Kxpired air 7y + Oxynen <"() 20.96 1) .(I 16.02 4.38 ("IIAl'TKU XXIII. TIIK HKSIMHATION (((.ntdi. Nervous Control of Respiration.— TtniiT nonnal rondiiions we hrciitlii' t'ntiii 14 to 1H tiin.-s a iiiiimtc. AcconliiiK to the do- inaiKJ of tlif tissins for o.xyKiii. we Itn-atlif fast or slow, but the ri'spiratioiis an- rlivllimic in tiiiH and luiti.-r lik.- conditioiiH arc i>i|iial in volume. Tlic respiratory inovenn'nts, unlike thow of the heart, are entirely dependent upon iiuixilses transmitted from the central nervous system. These come from the so-ealled respiratory centers in the medulla olilonjrata ( p. 2.")«i). Anatomic- ally these centers cannot he sharply l(M-ali/ed. hut destruction of the portion of the medulla in which they exist causes an imme- diate cessation of respiratory movements. The centers are con- necteil with the muscles of res|)iration. by the phrenic nerves— to the diaphragm.— the intercostal nerves— to the nmsclcs of the ,.il,s, — and by the nerves running to the larynx and nares. Liki' all other nerve centers, the respiratory center is influenced by af- ferent impuls«'s. the chief ones of which come from the lun^t^i by way of the vapus. but there are many others. In fact all the sen- sory U'Tves of the body, as well as the hijjher centers of the brain. a»- able to influence the respiratory center. Disease of the phren- ic nerves causes paralysis of the diai)hraKm. and impairs the ven- tilation of the lunjrs. Likewise ])aralysis involving the s|)inal cord below the exit of the phrenic nerves may i)aralyzt" tin; nerves of the thoracic nniscles. and throw the whole work of respiration on the diaphrasjm. If the vajrus nerves of a dog or eat are cut in the neck, the respiration becomes deejier and slower, yet the volume of air re- si)ired per minute is not -rreatly altered. This chan«re is due to tlu' elimination of stinudi normally cominir from the lunps by way of the va^i to the respiratory center, which serve to control the depth of respiration. It can be experimentally demonstrated 219 ■gr w ii ML ~«fef^ fS^ : tc- ^ mJi^JiiJtll^Mm " 220 I'nYSI()I,(MiY FOR DENTAFi .STl'DENTS. tliat the colliipsc of flic Jilvcoli of tlic hiiifis wliicli occurs iit the cud of iiorinal cxpii'atioii. and the strctdiiiip of the ahcolar walls wliicli ocelli's at the end of noriiial inspiration, cause stimuli to he passed aloiifj the vajri to the center, and tliat these stimuli l)rinjij on the next jtliase of respiration. The hreakiiig of the connection hetweeii the lunjis and the alveoli destroys this influence and the respirations liecome deep and slow. In the ahsence of the vagi, the hifjrher centers assume ])artial control of the rejjulation of the respiratory moveiiieiits. If they also ar(; destroyed, however, hi'eatliiii}; becomes inadeijiiate to maintain life, altlioujrh the center itself is still able to keep up a modified, rhythmic respiration. Hhfi.kx Resi'IKATory MdVKMKNTs. — The cutaneous nerves, es- jK'ciall.v those of the face and abdomen, have a marked intlueiice on resjjiration. These can be excited by heat or cold or pain ; for instance, a cold bath will cause a deepenin<; or quiekeniiifr of tiie I'cspiration. An example is found in the forced expiratory etfort made on inhalation of acid or sharp snielliiir\- cliapter the physico chemical projierties of the blooil and tissue tluid:i were discussed. It will be recalled that these are practically neutral fluids, that is. they show an al- most exact balance in the number of hydrofren and hydroxyl ions, a condition wliieii determines the neutrality of a fluid. Any increasi' in the amount of carbon dioxide in the blood would form proportionately more carbonic acid, \\iiicli yields hydrogen ions, and thus tend to destroy the neutral balance of the blood. This Ij CIir.MKAI. (•(•NTHDl, OK |{1>1'IH ATldX. 221 f { s increase in the liydrofren ion eoneeiitration in tlie l.loo.l is sutli- eient to stiniwli.te the respinitor.v eent.T an.l iniy;nient th.' rMv ir,(l (leptii of respiration in order to expel the earlx.n .lioxhie an.l thns r.Mluee the aei.iity of the hioo.l. All aei.ls whieli vi.l.l hv.lro^en ions in solution have tins etV.'et on r.'spiration when tiiev are in.jeete.l into the hioo.l. La.-tie aei.l. whi.-h is forni.'.l whi'n the oxy^."n supply to the tissu.-s is .lin.inishe.l ..r ina.le- • luate. is perhai)S th.' in.«st important laetor eoininj: int.) i.hiy in th.' stimulation of the r.'spiratory eent.M' whi.-h o.-eurs .luriiu; exereise. The earhon ilioxi.U' tension of tin- l.io.ul .lurini: ex.r- cis.' mav h.- actually .leer.-ased .nvin-j: to the inerease.l v.'ntilati.m of th.- lunjrs as a result of the present of laetie aei.l in tli.- hioo.l. Th." increase in breathiuf; .lu.- to lack of oxyjren is not nearly so easilv .-lioitea as that caused by .'x.vss of acids. In fact, th.' l>erc.'nta<,'e of oxy-r.-n may h.' .liminish.'.l t.) ahout on. '-half of that fonn.l in the atnmspii.MV before bn-athin- is marU.-.ily af- f.'cted. In disturbances of the ^'ase.uis ex.-haufre of the luufrs. th.' r.'- spiratorv center attempts to compensate for the chan^'e by in- cr.'asinjr the number an.l th.- .l.'ptli of th.' respirations. If th.' Has .'xchange be markedly insutiHcient. th.' bn'athing b.'c.)m.'S v.'rv nmch exa-fierated. and practically all possible r.-spirat.iry muscles ar.' call.-d into play. This is the .-ase .lurin- an atta.-k of asthma, in which the muscles of the arms an.l ab.lom.'U ar.' used bv the pati.'ut in his .'tforts to .)l)tain .'uoujih air. Ditli.-nlt br.>athinK of this kin.l is known as (hisptxnt. If th." jras ex.-han-r.' is very insuflicient. the phenomenon of osphiijio sets m. The eontn.l of th." r.-spiration. th."r.'l'.)r.". may be sai.l t.) b." a double one. one .h'l.en.lent .m th." n.'rv.' supply of the r.'si>ira- torv center from the atferent seiisoi'y an.l eer.'bral n.'rvs, an.l th.' other on the chemical constitution of th.' I.Io.mI. whi.-h stimnlat.'s the center directly. Hoth play an im|)ortant part in tlu- .-ontrol of the respiratory mov.'ments. The hroinhiol nuischs are su|.pli.'n an.l const ricti.m ..f tii.' broiu'hi. ,Iust what the normal con.litions are whi.-h call for th.' action of these nerves is not known. It is generally thought thai 223 I'HYSl(>I,(MiY FOR DFATAI, sTIUKNTS. Hstliniji is cauHcil by the coiistrictioii of the broiidiiolcs by spasm of till" bronchial imisclcs. Atropiii. a dnif,' which jiaralyzcs cer- tain nerves is of therapeutic use in this disease, since it jiaralyzes the nerve endings in the bronchial muscles. Adrenalin is also sometimes of use. The Effect of Changes in the Respired Air on the Respiration. A very slight increa.se in the percentage of carbon dio.xide in the (ih'(ohtr air is accompanied by a vei'v marked (|uickening of re- spiration. On the other hand, the carbon dioxide pont<'nt of the (it)iiospknr nuiy be increased to ii. DUt one per cent without em- barrassing the respiratory function, except during muscular work, and it is only at concentrations of carl)on dioxide of three or four per cent of an atniosi)here that the resj)iratory function is seriously excited. The rea.son for this is that the inspired air becomes greatly diluted before it reaches the alveoli, so that n slight increase — up to one per cent of carbon dio.xide — in the atmosphere only (luickeiis and ply the \m-iU-i\ oxygen, respiration must heeoine more rapid. This, however, hy washing out the earhon dioxide, serves to reduee the tension of earhon dioxide in the alveoli and blood to syeh an extent that the aetion of this (jas on the n- spiratory center is weakened, and breathing; may be very slow or cease for a time. i)rodneinji a condition known as aitnea. Tiie lack of oxyjien weakens the heart, the sli-;htest muscular move- ments are accomi)lished with ditlHculty. and the individual suf- fers from nausea. v headache and general weakness. After livinjj for some t'l ' leh altitudes a person becomes accus- tomed to the rarit.> ,• The atmos])here and in some maimer is able to compensate for the lessened oxygen in the air. Vkntii.ation. — The ilisafrreeable 0(h)r of a crowch'd room and the symptoms which accompany it are well known and are usual- ly attributed to tlie rebreathing of air. In support of this the historical incident of the lilack Hole of Calcutta, in which many jteo|)le jierished from lack of air. is often citeil. We liave already seen that atmospheres up to one per cent of carbon dioxide, or containing less than half of the normal j)ercentage of oxysreii. can be respired with no ill etfects. lUit tin- i)ercentaKe of carbon dioxide in the worst ventilated room does not. as a rule, rise above five-tenths per cent, or at most over one per cent, of an atmns- ])here. That this amou!it atfects our btnly metabolism is imi)os- sible. since the carbon dioxi"o.lih.-,l upp.-r portion of th.- trach,-a. whi.-h contains tlie vocal ••onls; an.l th.- j.harynx. an.l uj.p,-r air i.a.ssag.-s. Th,- larvnx forms th,- .-ntran..,- iuto tlu- trael,..a. It is compos.-.l of a numb,-r of eartilagu.ous plat,-s which are unit.-.l in a manner to form a box. Str.-tcli.-.i from front to back on .-a.-h side acrixss th,- upper portion of th,. larynx are thin sliarp-,-,lg.-,i m.-mbraiL-s. the vocal cords. The attachments of the muscl.-s to th.- cartilages and th.- Jirticulations of th.. s..v.-ral cartilag,.s with ea.-h ..thei-; an- so ar- ning,-,l as ,-ither to tighten or loo.s.-u the tension, or in,.r..ase or •l.'crea.s.. th," op,.ning betw,.,-!, th,- edges of the cor.ls. The cleft b,.tw,M.n th.. .-or.is is .-alL-.l th.- glottis. The length of the vo.-ai <'or.ls varn.s fr.,m 11 to l.'. mm., being l.H.ge- in m..., than in woni,-n and children. ]Jranches of the vagus and th,- sjiinal ac- Tin; voicK. 225 ct'ssorv ncm-s supply tlic imiscl.'s ..f tlu" larynx with im.tor nerves. The sensory nerves, arisinK in the epithelium of the larynx, are also l.ranehes of the vajrus. Meehanieal stimulation of the mueous memhrane of the larynx or eleetrieal stimulatu.n of the superior larynK<'iil U'-rve will cause a eoiij?h or a toree.l expiratory movement. , n j The Changes Which Occur in the Position of the Vocal Cords .iurinji the j)nuluetion of eertain s(mn.ls may he stu.lie.l l.y the ns.' of the lar,,n!)osn>l>'. the prineii.h' of whieh is shown in Fi«. ;!:j. The view obtained from sueh an instrument is shown in Fi.'s. :i4 and ;!•'). The hase ..f tlu' ton-rue ai)pears at the toj): hc- ' depressor Pij; :?s._ni;,f,iaiii of liiryiiKosooiw. low this is the e.l-.. of the epi-h.ttis. the flap of tissue guanhnfi the eiitranee to the larynx, and below in tlio middl.' hiu' an- seen tlie true voeal cords as white shining' membranes. Just above these, on both sid> s. are two pink flaps of tissu.-. the false rocal cmh These secr-l" a fluid which moistens the true cords. The Production of the Voice.~lf the vocal cords are put in i, Stat.- of tension ami tin- aperture between them be narrowed, eausing them to ortVr a resistance to the- j.assa-e of air issuing from the lungs, thev may l)e made to vibrate ami to pro.luce sounds. It has been exi..'rimeiitally defrmiiied that a pr.'ssure of expired air of from 140 to 240 mm. of water is rcpured to »26 rHYsloLiKiV POK OKNTAI, nTIDKNTS. prodiuv a sound of th.- onliiijiry i)itcli iiiid loii.liii'ss. while in loud shoutiiiK niuch •jri-t-iitci- jji-cssui-cs arc necessary. The sound of the voice, like any other sound, may varv in I»itcli. loudness an toih- which the string imxlucrs hy thr vihiiiti..M ot its ..ntir." h'ugth is th.. h)U.h-st an.l U.w.-st in pitch, it is p.ckc.i out as the fuiulamcntal tone. The fun.la.nciital tones of mstrn- ,„,.nts n.av he exactly the same, hut the tones yet .liirer from one anotluT liecause of the numher an.l the int.^nsity of tlie over- tones. Tlie .|uality of th.- voice .h-pen.is m. the overtones ,)ro- .luce.I an.l intensifi.-.l in th.' piuirynx an.l upp.-r air .•hamh..rs. Speech. Th.- pure, nuisical tones pr<..lnc.Ml hy th.- vocal cor.ls ar.- m...ii- fi,.,l hv chanfr..s in tiu- charact.-r of liu- air passaf?.-s alu.v.- tlu-m. The various comhinations which are i)r.Hh"-.-.l fiiv.- ris.- to smin.is which make up sp.-.-ch. Many of the simple c.mihinations are foun.l iu ail lansuajics. hut .-very languaj,'.- is charact.-riz.-.l hy certain sounds which are p.-culiar t(» it. The soun.ls pro.luc.-d in speech may h.- .livi.h-.l into two firoups. the vowels an.l th.- c.)ns..nants. Th.- vow.-l s.nui.ls ar.- contiimous and arc fonn.-d in th.- low.-r air i.assa-.-s with tin- h.-lp of the }rl.)ttis. Th.- consonants an- pro.lnc.-.l hy moiv or l.-ss compl.'t.- interrui)tions of th.- .nitdowiiifr air in .litren-nt l)ortions of th.- vocal tract. All the vow.-ls can he i)roduce(l in tli.- whisp.-r.-.l voic.-, that is. thev can he pro.luced with.mt th.- actual vihration of th.- vocal cords. The mouth cavity, how.-v.-r. assumes th.- .saim- position in th.- case of th.- whisp.-r.-d vowel as it .lo.-s f.)r th.- spok.-n vowel. Hy clianjiiiiff th.- shape of th.- air passages- the various vow.-l tones arc pr.xliice.l. In Fijj. :{6 an- s.-eii th.- various positions of the toi.gu.- an.l palat.- f..r th.- pro.iuction of th.- .litf.-n-nt vow.-ls. When v.)w,-ls are heiiii; utt.-n-d, th.- s.)ft palate dos.-s th.- .-n- t ranee to the nasal cavity. The consonants an- nam.-d acconling to th.- position at which th.- interruption of the air <-urn-nt tak.-s place. Th.- lahials an- formcd at the lips: p, h; tlu- .l.-ntals. h.-tw.-.n the toiiKiu- an.l th.- tccth: t, d. The {?utterals. k, K, c.i. aris.- hctw.-.-n th.- post.-rmr portion of the arclu-d toufiue an.l tlu- soft palate: an.l th.- (i.-r- maii r is produced with the help of vibrations ol the uvula. w.cm 228 I'llVSIoriCHlY FOR DENTAIi STt'DENTS. Sounds like in. n. i\g. an- tcrnit'd nasal consonants, since they Jirc sounded throusjli the nasal cavity (sec Fi}?. 'M\). ViK. H«. — The iioHiti.in i>( tlir tcinKiii' ;mcl lips (liiiiiiK the ult.niiK.' iif llii' l>>ttiis iiMliciit.'d. !^4 (ilArTKK XXIV. TIIK Ki.rii) EXCHl-noNS. The Excretion of Urine. The Composition of the Urine.-Tl.o wnst.- sul.stan-y nsuli i„.r from th.' pnuTssrs ..f mrtaholism in th.- tissurs a.v v\unmn\M iZm th." l.o(lv in a Kasoous. th.i.l. or solid stat... VV.th llu- .■x.-..,,- tion of tlu' carbon .lioxi.l.' aiul water of the .■xpnv.l air. an. I c'r- lain substances whicl. arc excreted into the intestn.es or api.ear in the secretions of the slvin plands, the metabolic i.ro.hn-ts are eliminated in the ui -le. Tin- composition ..f the urine is theretor.. rather complex an. varies .'rcatlv with th.- nature ..f the foo.l an.l th.. amount o water tak.-n.' i'.v car.dul amdysis of the urin.- from a nund.er ot in.livi.luals on or.linary di.-t, the avrajje amount of the various eonstituents in what may be consi.h-r...l a norn.al urn... can .e estimated. Fresh hun.an urine is a .-lear >'f;;;,^.'';'/' J'''; heuvi.-r than water, having a specific gravity of l.OK. to l.U_ It tested with litnms paper it usually shows an a.-i.l r..act.on. wh.eli is n.ainlv due to th.. pres..nci. of aci.l salts, such as so.hum dd.y- drogon i,h..sphates. but partly also to acid substances .l.-nv...! from proteins. H.-rbivorous animals secrete an alkaline .nine wl.i.h is no do.d.t caus...l by the pn-s.-nc of tl... large amount of alkaline earths and th.> relatively small amount of l.rot.'in mat- ter in their diet. The human urine becomes alkaline in rea.-tmn when vcKctables are the main infrredi..nts of th.' diet. The character of most of the urinary eoiistitu..nts an.l th.. man- „..,• bv which thev arc .lerived from th." foo.lsti.tfs have b....ii dc- serib.'.l ill the chapt.'r on nu'tabolism, an.l in th.- f.)llowiiig a-- ,.ount only a bri..f r.'vi.'W of th.ir i.hysi.-al and eh..mi.-al natur.' is necessary. Tin: t>R.i.\Nic SiBSTANC-KS ov Tin: rKiNF..-rii..se eompris.. a number nf nitrogenous compounds. The toUowing figuivs. ..b- 229 -•'^0 l'IIY.sHir,(H)Y KOB DKNTAIi STIDENTS. t)iiiic to 6% r/7(j.— Krorii thf iihovc fiKUivs it is sfcii tiuit tiit- Ki-cattT part of the nitrofri'ii cliniinHtcd l)y man ai)p(ars as urea. The relative amount of iii-ea eliminated depends very larjfely on the diet, be- ing !»0 ])er eent or more of the total nitrojjen exeretion on a full • HOtein diet, and «() per cent or less during starvation. The total amount exereted is about :{0 fjrams |»er 100 (jrams of protein in the diet. Cliemicaliy urea has the following,' formula : -Ml, OC \ Ml, If prepared pure it forms long colorless needles or four-sided prisms. It is very soluble in water. Hot alkalies, sueh as sodium hydoxide. deeompose it into ammonia and carbon dioxide. The same reaction occurs in case of bacterial decomposition by the niicrococcns urea, and accounts for the ammonical odor of urine after standing in the air. The significance of urea in regard to I)rotein metabolism and the method of its formation are dis- cu.ssed on page lOS. Ammoitid. — This. cond)ined with chlorine or oth.-r acid radi- cles, is normally found in small amounts in the urine. It is one of the important agei:cies in maintaining the neutrality of the tissues, since with acids it forms ammonia salts, which are neu- tral in reaction and which are eliminated in the urine. ('natiniu.—Tht' amount of this substance found in the urine THE (•|lKMI>'rKY HI-' rUINK. :M IS vt TV constant from day to day, am I is iiidcpcndrnt of tlir a .1.- If Si2 i'llY.sllll.iMiV Kull IlKNT.M- >TI DKNTS. ■1 jiosit, of <'iilciiiin or iiiiiu'iKsiinn plmspluifr. This will .|i.s.siilv.- whfii till- urine is r.rnlcr.d faiiitly iici.l. AhNmUMAI, CnXSTITl KNTs ny TMi: rK|.M:._.Ma„ v „( thr Mil,. stjiMn-s found in tli.- hloo,| ,„-,.nr in niiinit.- tnicrs in Wu- urin... Wh.'n imy of tii.-s.- l)<),ii,H jnv incr.-asc.l to an unusual annMUil in tin- urine, they Ix-com.' what we may term pathitlo^ieal mu- stituents. The ho.lies most eoi ,nly atVeete.! are the proteins an.I sup.rs. The fin.linjr of a |.rot..in sue!, as all.umin. in m.wv than the faintest trace, is an indication of luphrilis or l{ri,/hfs (iisrasr. The presence of alhumin may he detectd |,y lieatinjr h. a t.-st tube a slightly aci.Julated sample of urine. Normal urine contains the faintest trace (.f the l.lood suyar (h-xtros.-. hut in ahnormal conditions, as in tlie disease ,ii,il„l,s or after h meal rich in sugars, a larjre amount of dexiros,. ap- Itears in the urine as a result of an increase in the sHn»r of the blood. The condition probably repr.'.sents tli. inalulitv „( th.- tissues to make us.' of their carbohydmte f.,od in the proi.er man- ner, and the kidney thendore excretes \hv sujjar as if it wen- a waste nuiterial. The Organs of Excretion, The Kidneys. Projecting from the jmst.'rior wall ..i the abdumina! cavity at th.' level of the lower ribs and on each side „f the vertebral col- umn ar.. the kidneys, the organs of urine excretion. Kadi kidiirv is of the nature of a tubular gland of a very complex striietuiv. anatomically adapted to bring a large amount of blood at ,i hi-di pn'ssure in close relation with the excn ting epithelial cells which ' ♦'"' ^^"""-^ "f the gland Inhuhs. The tubul,.s emptv into a jmuch-shaped sac on the ini:.-r e.lge ,d' the kidney, the pelvis of the kidney, and this is connecti'd with the iiriiiarv bi.idder bv means of a small tube, the ureter. A brief review of the essential {)arts of the uriniferous tubuh' and the organs of micturition is ...■•v^,,.rv in ord..r to underst.'Md liie mechanism of urine excn^tion. and iU student is advise.l to consult his textbook of anatomy and lii.stoin^^v for a mor.. .-om- prehensive desciiption than is li.ie ^iv,n. The urinif.rous tu- bules may be divide.! int., (h ...r.-tory portion ;m.l th.. coll.-ct- ing portion. The tubules arise in the outer j.art of tn,. ki.|ii..y m if' U Q' ' i Kit?, ST. — KhiKiiim iif tlif \iiiiiiriTinis luliuli'S (I. luck), the aiti-ilcs (icil) ;iriil till' Veins (liiui-) iif tlie kiilinv. THE EXCRETION OP TRINE. 233 in the region called the cortex, as a body calli-d tin- .Miilpit,'liian corpuscle. This corpuscle consists of the dilated nid of a tul)ule whicii is invaKinated to form a e>ip-sliaped vessel, witliin the cup of which lies a tuft of capillaries. The eapiilarifs compose llir structure known as the glomeridu.s, and tiie tubular part, tlir capsule of Hownuin. Prom Bowman's eapside a short neck leads into what is known as the convoluted tubule, which is a very tortuous vessel lined with very large ei)ithelial cells. This structure lies in the cortex of the kidney and is nourished by the blood which has already been through the glomerular capillaries. A loop of the tubule leads down into the center or medullary portion of the kidney and back again to the cortex, where the cortex again becomes very tortuous. This finally empties, in company with many otie i- .siuular vessels, into a common collecting tubuh', which leads to the pelvis of the kidney. TiiK Bi,(W)i) Sii'i'iA- OK THE Km)\i;v is very large compared with that of the other organs of the same size. The renal arteiiis come from the aorta and distribute their blood directly to the glomeruli and the inner medullary jwrtions of the kidney. The ves.sels of the glomerulus are collected into an afferent vein, which again breaks up into capillaries to sup])ly the remaining struc- tures of the cortical portions of the kidney (Fig. .{7). The Xerves of the Kidnev. — The kiite of the many at tempts to explain the nature of urine excretion, there remain many steps in the process which are not fully undeistood. The con.stitueiits of the urine are formed by other organs than the kidney, and are present in the blood plasma. Tlu; function of the kidney is to remove the.se .substances from the blood. .Many bodies are j)resent in the blcod i)lasma which are imt found in the urine, and again some of the urinary constituents are found in far greater concentration in the urine than in the blood plasma. 2U I'llYSIOI/HlV Vim DK.VTAr^ STI'DKXTS. To ('xj)laiii these fncts. Ludwig. a famous physiolofrist of the iiiiieteeiitli eeiitury. foritiiilated what is known as the nieehanieal theory of urine exeretion. Impressed hy the peeuiiar rel:itioii- sliip of Bowman's eapsuh- ami the jrlomerular eaj)inaries, he eon- ehuh-d tliat tlie .Malpi^liian eorpusele is a filterinfi apparatus whieh sejjarates. in dilute solution, a portion of all the ditfusihle suhstaiices of the blood. The absenee of sueli diffusible sub- stances as sujfar in nornu'! urine and its presence in th<' blood in a relatively lar^'e amount. \\<- believed to be due to the ability of the epithelium of the tubules to reabsorb these substances from the dilute urine. Likewise, the hiifh concentration of .salts and nitrogenous bodies, such as urea, he explained by reabsorption of water through the tubules into the bhxxl. In supi)ort of tliis theory Lmlwig demonsti-ated that the urine excretion varied directly with the blood flow and the blocMl pressure of the kid- ney. In other words, the great.-r the su|)ply of blood and the greater its itressnre. the more rapidly will the watery solution of flu urine be filtered from the blood. He was not able, how- ever to bring any satisfactory |)roof of the reabsorption of water or other .substances by tin- epithelium of the urinary tubules. Indeed, most experiments show that this does m)t iccur. It is impossible to exj)lain all the facts of urinary excretion by simple physical laws. For example, urea and dextrose are both found in the blood and both obey the same pliysico-cheniical laws: nevertheless the one is excreted in the urine and the other is retained in the blood. Furthermore, when certain |(igments are injected into the blood, they are excreted by the kidney cells, but do not ajipear in tho.se of other parts of the bod-. That an increase in the i)res.sure of blood in the renal vessels has a very marked accelerating effect on the excretion of urine, is not necessarily evidence that the increased blood supply is the cause of the excretion. That other factors are concerned is demon- .strated by the action of drugs which cause an increase in renal ex- eretion. For example, digitalis, a drug stimulating the circulatory ai)paratus, causes a marked i ihe act. The afferent or sensory stinnili which initiate tin- act ire excited by the distention of the bladder, or by the j)ass- aj;e of a few 00 LM-ams) i.. a .lav. Altl..mj.h it is v.-ry .liHieult to obta.n pu.v sw.-at u..n.ix.-.l with tl..- s.-.-r.-tions of tl..- ..th.-r -lan.ls ot th.- skin we know that it e.msists for tl..- n.ost part of wat.-r, hav-. ff a spi-eifle fjravitv of about 1.004. Th.- salty taste is .1...- to ...or- ^a.iie salts an.l to th.- in.puriti.-s whieh tl..- sw.-at .l.ssolv.-s o.. tl..- surfaee of th.- skin. Tl..-r.- is m.ly a trae.- ..f u.-.-a an.l re at.-.l substanees. an.l probably th.- sw.-at -lan.ls n.-ver ai.l th.- k..l...-ys in the .-xe.-.-tion of th.-se bo.li.-s. The most in.iM.rtant function of th.- sw.-at -lan.ls .s t.. .-ontrol the t.-mperatun- of th.- bo.ly by r.-srulating th.- .-at.- ot its l..-a1 loss Dry air is a po..r .-on.luetor ..f h.-a1. an.l to va|)(.ri/.- wat.-.- n-.,uir..s"a larjt.- amount of h.-at. As th.- water of the sweat .s .-vaporat,..!. the bo.ly los,-s heat rapi.lly. This pr.n.-.l.le is pra.-ti- callv ai.i.li.-(l bv th.- hous..wiv..s of tropi.-al eountn.-s. Th.' wat.-r is lilae.-.l in ponnis pots an.l tl..- rapi.l .-vap..ration on th.- ...it- .si.le of the pot eools the wat.-r within. The secretion of sweat, lik.- the secretion of saliva, is un.i.-r the .-ontrol of th.- c.-ntral n.-rv..us syst.-ni. as can b.- .l.-nu.nstrat.-.l y,y ^.l,.^.t,•icalh• exciting the nerv.-s supplying the paw of a eat or 2:{H I'irYSIOlAHiV FOR OKXTAI; STlOr.XTS. I,i i (loj;. Following such stiinulatioii drops of sweat ai-c found on tlic paw. The secretion is not due to an increased Mood flow, as can be shown by stiinulatin»r the nerves in a iind) severed from its blood sup|)ly, in whieli case a few drops of sweat will still appear. A center in tiie brain and subsidiary centers in tlie sj)inal cord have been found which, when stimulated, j)roduce a .secretion of sweat. Some drugs have the peculiar action of exciting the s<'cretion of sweat, either refle.xly through the nerve center or by stimuia- tion of the nerve endings about the cells of the glands. To the f(»'mer clas.s belong such drugs as strychnine and i)icrotoxin, and to the latter, pilocarpiii. Atropin, on the other hand, iidiibits the .secretion by i)aralyzing the secretory nerve mechanism. An increa.se in the external temperature will cause a .secretion of sweat only when the seii.sory and motor nerves of the j)art are both functional. To stimulate the sweat nei-ves, heat therefore must act refle.xly through the sensory nerves and the centers of the brain or si)inal cord. The Seb.vceois (iL.\.\i).>^. — Uesides the sweat glands there an; numerous other glands in the skin. These aiv as.sociated with the hairs, and are called sebaceous glands. They secrete an oily semili(|uid uuiterial which atl^'ords protection to the hair and the skin. Its oily nature j)revents the hair from becoming to<» brittle, and })rotects the skin from moisture. Tjie Secrktio.v of Mn.K. — The mammary glands are modified sebaceous glands which secrete a nutrient rluid. milk. The glands are much better developed in the fenude than in the male, and are excited to i)liysiological activity at the birth of the child. Human milk is a white or yellowish fluid, without odor and with a peculiar sweet taste. It contains i)rotein substances called caseinogeii, laet-albiuiiin, and lact -globulin ; also a .sugar called lactose or milk .sugar, and fats and inorganic matter, as the chlo- rides of sodium, jiotassium ami calcium. Human milk is by far the l)est food for the infant, and should be replaced by other food onlv when absolutelv necessarv. CUAPTEU XXV. THE NKHVOIS SYSTEM. The General Functions p d Structure of the Nervous System. — Wlu'ii a unicfllular nrtfa...sMi. siicli as tin- anm-1)a. is stimiilal.'.l it ivspoiuls l)v a inov.M.KM.I l.r.-ausc its |.n.t()|.lasn. p(.ss..s..rs anunifi its oth.T piop.-rti.s tl.os.. of .-xcitability. coiuluctivity aiul contractilitv. In tlic cas.- of niulticvlluinr organisms, soin. lis art" s.'t asi(i." for the assimilation of food. oth.Ts for niownicnt. others to ree.-ive stimuli from tiie outsi.le. others to eomi.ose t..ii^'lier i.roteetive tissues on the surfa.-e. and still hthers. in many auinuds. to eompose deHiiite or-aiis of ott'ense. This loea- tioii'of speeitie fuiietions in eertai'i frroup of eells makes it neees- sarv for the welfare of the orjranism as a whole, that some means of eommunieation he provided between th." ditl'erent parts of the animal, for otherwise the cells whieh ar.' oecu|)ie.l. say, in al)- .sorhin^r food, woul.l he unahle to move away when some destruc- tive asreiicv approached them, and in.ie.-d the moving (mns.-h') cells couhi never know when they onjrht to become active. In some of the lower orfranisms thes.. messa«es are carri.-d by chemi- cal substances present in the tiuids tliat bath.' the cells. These lu'long to the uroup of hormones which we hav.- aliva.ly studied in connection with the ductless frlamls (see p. 12-i). The iv- spc.nsi's mediated in this way are. however, too slow for the .,ui.-k adaptMtion which it i.^ necessjiry that tin- (.r-anism should un- dergo ill its battle for lit'.-. If it had to .lep.'i.d on such a mech- anism alom-. the oi-anism would alivady be within llw clutches of its enemv before it could mak.' any attempt to .hdVnd itsell. Some more sensitive mechanism, both for receivinti and for transmitting impulses tliroufihout the organism, becomes nec- essarv. This is furnished by the nervous system, which, in Us simpier torm. consists of a c.-ll on the surface of the aniimd so specialized that it i-siionds to changes in the .'iivironinent. This 240 I'llVSlOl.OCV FOR OrNTAh STfOKNTS. III i' 1 nitphir ••('11. as it is ciillcd, is i)rolonjr(Ml inside tlu' iiuiinal as a fiber, the lu rr( jilu r. wliieli )iasses to (ffiriitr (tils specializ'-d either as inuscle fibers or Kbiiid cells. Wlx-n a stiriiulus acts on tbe leei'ittor Cell it therefore sets u|) a nerve iiiipulse whicii causes effector cells to become active, so that the animal either moves away or jirepares to d.-feiid it.self by seen fiiij? some jioisonous substance or inakinjr sonu defensive movement. There are. h(»\v- ever. very few. even of the lowliest oi'-ranism.s. which have so simple a nervous system as this, for the nerve fibers from ditfer- ent recejitors usuall.v join tojiether to form a mm iili.nis and tliev ilo not run directlv to the effector cell, but to another <'ell. KiK. ;!'.". — .SclniiiM <>t siiiipl"' i>ll>'X Mil-; )' Ilium-; (I. MtTiiiiit liliir : .v. s,\ iiiipsis ; <. iiit\. hi, cITfctiii- iiii;:iii. ii'cipliir ill Mil ciiithi'liiil imiii- cill iif (-.•iitir; r, .■tYfifiit tibir; Hu C( niral uirvt ///((//«/>. The nerv.- impulse can travel from th.- Hber throuj;li its syna|>sis on to th.- n.-rve cell, which this sur- roun.ls. but it cannot trav.-l in tin- oi)posite direction. This valve- like action at the synapsis explains why a nerve impulse trav.-ls along a refl.-x arc in on.- .lir.-.-tion .mly. Each nerv.- c.-ll with its axon and d.-n.lrit.-s is call.-.l a nniron,. U.-f1.-x arcs are th.-n- fore comp.is.-.l of two or mor.- neui-on.-s. a!i.l th.- n.-rvous syst.-m is built ui> of ^'reat nundx-rs of r.-flex arcs. Th.- nerve cells which constitute the centers are usually eol- l,-<-t.-.l in t?roui).s call.-.l ,ian„lio. In th.- s.-gm.-nte,l invertebrat.-s, such as the worms an.l crustac.-ans. then- is on.- such fjanfilion for each segm.-nt. .-a<-h Kan{rli.)n b.-insr conn.rt.-.l with its neijrh- hoi-s l)v nerve fib.-rs. thus forming a chain along th.- ventral asp.-et of the animal, and also having num.-rous nerv.- fibers con- n.'cting it with the various r.-c.-ptors and .-tT.-etors of t!i.- K.-gment (Fif. 40). At the h.-ad .-nd of th.- aidnnd s.-v.-ral of these gang- lia become fuse.l together tr form a larg.-r ganglion, which li.-s just behind the gull.-t an.l from which two fib.-rs pass around the gullet to nidte in front of it in a large ganglion, which usually shows thrcv lob.-s. Th.-s.- larg.-r h.-a.l ganglia r.-ceiv.- the afT.r- ent nerve tibn-s from th.- a.l.jac.-nt pro,jicient sense organs, n-imelv. the eves, the ears, the organ of smell, and the antenna- or feelers: tiies.» being really receptors which have become 242 I'llVSlor.iMiY Kol{ HKNTAI, sTI l>i;\T.'>. hijfhly s|itfiiilizc(| for tin- j)Ui'|>(isi- of i-ccciv- in<; impn-ssioiis from ii ii(iI. tlics.' incliidc a receptor, an afferent fiber, a i.erve eenl- r, . h efferenl filler and an etVeetor orjfan. Thk KkckI'Tok. — The reee|iti)r e.xist.s M one of tin si-nsorv nerve terininators situated in the skin (extero-eejitorsi or in the ili-ep tissues, such as the joints, the .inscles or the vis<'era (pr.)prio-eept. rs). Many receptors are inj.'hl.\ speciali/ed so as to respoml only to ono kind of stiuiuhi-;, and v.n-h special kind of receptor is located where it will he of nio-st use. Thus, there ail' special receptors for s«'nsations i)f heat, others for cold. oth'Ts for touch. othcfH for pain. The / In ncrptor^ are distributed more or less uniforndy over the bmly. Tiiey ar'- jiresent in tlu dee|)er structures, such as the teeth, the .joints and the sero\is coverinjfs of tiie vi.scera. Sonietintes. as on the ci rnea and in the pulp of the teeth, they are the only kind of > -ceptor i)resent The touch ncrptors are collected in small ai'' called "touch spots." which are mudi more numerous on the . of tl tongue, the lips, or the tips of the finjfers than on thi ^-'.n of tlie lejf- the arms or the back of t!)< trunk. The fre(|U«ii< » f toinh .spot- on the tip of tile tongue inaiies a foreign bo': ii 'Ik mouth ap pear to be larger than when we feel it wth touch spots on the fingi r tips may acijuir :.'r. eeption by education, as in 'he ca.se of a bii"i to use his fingers for reading. The remark distribution of touch spots may he very bcis finding out how far apart the points of a pai 1h> from one anoflier in order to be di.stinir This distance is not more than ;' mm. for the tij'S o i lingers Til.- t acuity i- |).T- [)crson. \i ■ ll.lS irn birt: r of ifuli itw- by >f ealii if: ilS ■ 2M I Ki(f. 41. — Thf siinplisf ifrUx iiic in tin- spiiiiil niiil. ( Aflii- KiHIikor. ) Till' iifTiTcTit tlliir in tlif piisli'iior loot (In l)liir the aiilii'iiir limii i in nd). the axnns iif whicli fiirin tlif clTiirnl lilnis of tin- aritt'iior loots. ( Knitii Howi'll's riiysiolos.v. ) REFLEX ACT1«>N. 245 but it is over 60 mm. for the skin of tho back of tl\t' iifck. Tlic tvmpf rat tire naptors arc still more definitely located in areas, some "iH'ing specialized for heat and others for cold. These so- called heat and cold spots are most frequent on the portions of the bmly that are covered by clothing, for example, the skin of the thorax, than on thoye that are exposed, for example, the face. They arc fairly frequent on the skin of the dorsum of the hand, where their existence can be very easily demonstrated by slowly drawing a pencil gently over the sidn. At certain places tlu^ point of the pencil feels hot, at othei-s cold, and in others it causes no temperature sensation whatsoever. All varieties of receptors are present on the skin of the hand, but in certain dis«'ases of the nerves or spinal cord, one kinil of receptor may become inactive, thus causing, when the absent sen- sation is that of pain, the condition called andUfrsiu, which nuist be distinguisiied from that of ancsthtsia, when all sensations are paralyzed. In analgesia a pin prick causes only a sen.sation of touch. When the nerves of the arm are cut and the cut ends then sutured together so that the nerve fibers regenerate the skin sensations do not all return at the same time. Those of pain and of extreme degrees of heat and cold return in from six to twenty- six weeks, whereas those of touch and th. iiner degrees of tem- I)erature do not return until after one or two years. The power of localizing the point of application of the stimulus is also late in returning: thus, if we touch the finger of such a person and ask him to tell us where, he may indicate some spot that is quite a distance away from the one actually touched. Certain drugs, such as cocaine, have the power, when applied locally, of ren- dering all the receptors insensitive. The Afferent Fibre.— Another name for this is the sensory nerve, because it carries the sensations received by the receptors up to the nerve center. All afferent fibers enter the spinal cord i)y the posttrior turve roots, on each of which, it will be remem- iM-red, is situated a ganglion, the posterior root ganglion. The cells of this ganglion are connected with the afferent fibers by a short branch running at right angles to the latter (Fig. 41). The function of the cells is to maintain tho nutrition of the affer- 246 PHYSIOLOGY FOR DENTAL STinENTS. 1 : I' I cut fibers, for if tlieso bo divided before tliey reaeh the ganglion, the periplieral or far away t'lid aniakv NkihoM'-s.— When the ent.-rinK nerve impulse tnivels by a collateral to an anterior horn cell. w.> have the simplest tyi.e of reflex action, namely, one iuvolvint? a receptor, a sen.sory nerve tiher. the post.-rior r(M>t, a collateral, the anterior horn cell, tlu' anterior root, a motor nerve fiber and an effector organ. But such a simple reflex seldom 248 I'll YSK )!,()« V P;)K DKNTAI- STIDKNTS. occurs in the higher animals. The afferciit i:npulse when it en- ters the cord is more liitely to travel up the posterior columns and then, as alreaily outlined to the cerebrum, where it einls on the large i).vramidal nerve cells of the gny matter. From the pyramidal cells spring the fibers of the itfinimidul Inicts, which, as they pass downward through the white matter of the cerebrum, crowd clo.ser and closer together until, by the time the basal ganglia arc reached (optic tha'amus on the inside, and corpus striatum on the outside), they form a narrow bun- dle which occupies the middle portion of the strip of while mat ter which lies between these ganglia. This whiti' matter is called the iiifiniiil caitsiih (Fig. 46), and it is of very great clinical interest because, being in the neighborhood of a large artery (branch of nnddlc cerebral), which sometimes bursts in elderly peo])le, it is apt to become torn up by extiavasated blood, thus destroying t!ie i)yramidal fibers and causing paraly- .sis. This is what occurs in apoitlrxt). Helow the internal capsule the fibers run into the crura cerebri, then into the pons, thence into the ledulla oblongata, in the front of which thi'v form a dis- tinct bulging called thi pijramid ; hence their name pyramidal fibers (see Fig. 45). In the lower portion of the medulla, a most interesting thing occur-s, namely, three-fourths of the fibers cross to the oppo- site vside, thus constituting the di cussution of the pi/nimids (F"'ig. 44). These crossed fibers run down in the lateral columns of the spinal cord as the crossed pyramidal tracts. The j)yra- nddal fiber.s which do not cross in the medulla form the direct pyramidal tracts of the cord, and they gradually cross in tin- cord itself. The pyramidal fibers end by synapsis around the cells of the anterior horn, so that all fibers from the cerebrum ultimately cross to the opposite side before they reach the anterior horn cells, for which reason it hai)pens that a lesion involving the pyramidal trait anywhere above the decussation, such as the luemorrhage in the internal capsule above referred to. always causes paralysis of the opposifr s)d( of the body (hemiplegia). These facts regarding the course of the pyramidal fibers have U'cn ascertained by micros<'opic examination of sections from Ki„ 4:i -_K,.||..x an lluoiml' Hi" xpin^'l '"i'"- "' »"'''' •'" inf'"" >li'"V n.-uiono Hn blu.O .-visls t,..t«...M ll„. MlT.nMt miM .■n-..,v,>t ...unm.s. .It..,,. IliiwiU's l'liysii>lii>,',v.) >w^*.'«*'" KiK t^- — ''"I"'*"' " f till' pyiiiniiiUil lilH'is in till' 111 inl : ixlul /, tillers to nil' fiKin ■lei i(f riiinial iiffvrs 111.' il.iiil mrl.x U Hill .1, niiiis w liiili ilo iiiit -' 111 nil illlll;l ■iissi'il pyirini ili.l ti:iil I I Afli r lliiwill I 7^i'S»>Ci«3h«W6W-*r ",'■• yi--^:-': «"_ 1. if • - i!;l4 lii I : i j- :i if" KKKI.KX ACTUiN. 24! » various li'vcls of tlic spinal cord soiiio tiiiic aftt-r «lfstructiori of tilt' KolHixlic area of the ccrchrmn (sec p. 270). Thr jn riuiii(i;il fil)crs arc (it'KCiifratt'd and they occupy tiic areas iiidiijilcd in Fijf. 42. Since the degeneration occurs helow the ih-structi.m. it is called descending de.'e si/e anil anRular shape, and they liecome jrreatly increased in num- ber in the |)ortions of the cord from which the nerves K'»""'>-' <" tile extremities oi-ifjinate. The fibers spriinrinn from tiiein pass out in the anterior roots. If th lis are destroy<-d or the an- terior r(M)ts cut, defeneration cccurs below the lesion, and |)ara- lysis of the etfector organs (muscles) to which they run results, but this i)aralysis is very sli^lit in decree unless the lesion af- fects s<'veral roots, or the cells of several adjacent levels of the cord. The rea.son for this is that the nerve colls of one level of the cord only partially supply a given muscle or group of mus- cles with nerve fibers, thus showing that even the small nmscles receive their nerve fibers from several ad.jacent levels of the cord. The anterior horn cells sometimes become tlcstroycd by disease, namely, in infantile i)aralysis (poliomyelitis anter- ior). The resulting paralysis is never recovered from. Types of Reflexes.— Having traced the paths through whi
  • liifil (nii)titil, for it is only after we have done .so that it will be itt)ssii)le for us to determine what influence the briin has in modifying the spinal refl. xes. Tiie spinal animal (dog, for example) is prepared l.y cutting across the spinal cord some- where below the origin of the phnnic nerves. After the immc- di.ite eti'ects of the operation have been r.-coverd from, the regions of the animaKs body, lying lu'low the level of the sec- tion of the cord, suffer from a i-omlition called spnni shock. All reflex nu)vements are absent, the sphincters ai paralyzed so that incontinence of urine and fa-ces exists, and various "tro- phic" or nutritive changes occur in the skiii (ab^.rsses form, hair falls out, etc.). After some lime, the length of which de- pends on the po.sition of the aiiiinal in the animal ^eole. the sphincters regain their tone and the reflexes gradually reappear ItKlM-KX ACTION. 251 i„ til.' i.nnilyzcl n^um. thv tirst to .1.. s.. U'Um: \hv i-rofTtiv.- rttl<'X.-s, of whicli th.' fluioii nfhr is tlir tvi.c Thr rt.-xion n-H.-x is .licil.il l.y iiii.v stiiimlns win.li woul.i .-inisr ,,,,i„ i„ an animal .•ai-abl,- -f \W\\l^^^. Surh slin.uii an- rMvd lux-uoiis an.l tlic ivfl.'X ivspons.. is ahvavs o( s.i.-h a nat.iiv- usuallv H.xion— as to caus- llw injuiv.l part to 1h- r.-niov.,! from fi.rtluT .lannmr. Tlu' nturn of tl..- H.-xion r.-flrx is s.Mm r„ll,mv.l l)v that of til. kix, ././•/.. which is .'licitr.l hy taj.i.n.t; th.-. patellar t.Mi.lon aft.r putting it on ti... stnt.-h l.y passivly iM.n.linK tlu' kn.-.- joint. Somr^hat lat.-r in many annm.ls ^...^' . ,1,,^;) //„ svrolrh nfl<.r ai-lu-ars. so-call.-.l l«-.'«us.. it consists ,.t a scratcl.ii.p movmcnt of th.- hin.l l.-« in n-sponsc to mechanical irritation of the flank of the aniu.ii: It is a retlex of very K"eat i.iteivst iH'cause it illustrates to what a remarkable d. «! the .spinal cor,!, unaided hy the brain, is capable of brinnuiK about eomplicated and i.nrposeful eo-onrmated movement. I-ater still, in the lower animals. practicall.N all the reflex movements which a normal animal exhibits may ivippeiir. When the con! becomes severed in man. as by spinal fracture, spinal shock is extremely profound, and in order to keei. the pati.nl alive -tvat car.' must !«■ tak. n, ..n a.-count of the mcon- tinonco of uriii.-. to pr.veut inf.'ction of the bla.l.ler an.l ki.lii.'.ys an.l to prot.'ct th.> skin fr..tn ulcration (be.l soros). Kvcn in such cases, howev.-r, many of the reflex.-s r.'cov. r in the para- lyzed regions, but the recovery is slow and th." limbs invariably atrophv. It is particularly important to note that th.- time of re- app.-aranc- of th.- reflexes b.-ars a relationship to th.- .IcKreo of d.-velopment ..f the c.-r.-bral hemisphen-s. thus r.-iul.-riiifj it .-vi- d.-nt that spinal shock is due to a br.-ak in the n.-rv.- paths which lead to ami from the brain. Th.- hijjher the animal, th.- moiv fr.-.!U.-ntlv do all r.-flex acts involve a .-er.-bral path inst.-a.l of takinji tli.- short cuts available through the collat.-rals (see i-. 24:^. Knim usaire. as it were, the c.-r.-bral paths b.-come so w.-ll dev.-l..p.-.l that wh.-n th.-y an- sudd.-nly s.-v.'r.-d. th.- n-fl.x action b.-.-..m.-s impos,sibl.- until the ent.-ring attVr.-nt impuls.- has learned to use th.- hitherto unus.-d short cuts available through collaterals. When completely .-ecoveivd from spinal shock, an rif» •>.v> UYSIdltKlY KitH DKNTAI. STIOKNTS. aiiiiiiiil. May a dotr. in so far as voluntary inovfin.-iit is i-oii- (-.•nuMl. is .•ntir.lv paraly/.'.! in all |)ortii)ns of tho »»oaiM or any other sensation hclow tin- icsi.Mi. ami y.i wh.'U approj.riatcly stiniii- iat.'.l. the |taraly/.'.l limbs nniy nil. xly undergo various, often very coniplicate.1 inovemenf^ The Essential Characteriitics of Reflex Action.— As sfu.li.^-vuu-u\ ..f th- .-onl. or its .kUuhwu it. tli- Lnui, is t;,k.i, „p hv somr ..th.T stiimili.M. a .vflx aliva.l.v in art...,,. ..r aLui.t to a.-t. is .l..|.iv,vs...|. I'ain. sii.-l. f..r .xaini.lr as t.M.tharl,.., may lik.'wis.- !..• I.-SS.M.MI l.v applyiiilf rount.T irritation sii-h as a l.list.T to somr n.itfliborii.K skin an-a. - :f. I'.y m.-ans of .vrtan, ,ln.«s knou n as anrstla-ti.-s. wl.i.-h .l.-l.'''"'''* '>"' ••x.-ital.il.ty ol tlu. iirrv.' '•.'Us. (4) lU- fatiK'iir. Thr -H.-x inovHa.M.t may hv ' >is,,l: H) L;. a|.pl> imr a s..-o,ul s, Mulus to son,.- oth.-r a ■ ^ ■■' ^i-ii. of tl.. samr liu.-l l-s^ o. hv ai.i»lvi>.u' ..lr.-tri<-Hl stimuL ..... ! >■• ^--r'tml .;n.l <'t '•'"• „f lis sensory nrrvs; (U > Uv n.. n :. v ,■ , s.-ita'.ihty ol th. ,H.,-Nr ....nt.Ts by n-rtain .Irnjrs. sr. . .^ >t rv.,;M.nr ; Ct i hy t.rst „r „11 ..Musinjr th. inov.-inrnt to .lis,.,,,..-. . , M:..UKh th.. stnnuh.tmn .•ausinn it is maintain.Ml. In .x.-itinw son..- ..tn.T |.ait ..I th.- ho,ly (s..,. ahov.-i. Wh.^n th.. r..f1..x n-ai.iH.ars it is much mon- prononni'f.l tlian forna-rly. Muscular Tone and Reciprocal Action of Muscles. Ilavm^r .l,,,rn.Ml son,., of th.. ^..n.fal .■ha,.a.-..risti,-s ..f th- n-H-.x n.ov..- „„.„ts w m.tv i,ow p.-oc...Ml to in.iui.... into th.. m.th...l I.n whu-h th.. spinal ...nl is ..nahl.-.l. hy its..lf. so t.. .lir...-t th.- alT..r.M.t „n- .,„ls..s \vhi..ii ..nt.-r it, that ti,.. n.-rv.. ....lis of th.- ant..i-,or h..rn ,'ns..har>r.. siiitahh. iinpuls. s f. brin^' ahont su.-h .•.m,pli..at...l m„v..,„..nts as I.mn jnst h....n .l.-s.-rilH-.i. Wh.-n a motor n.-rv or an ant.-rior spi„„i n..)t is stimulat.-.i. iIh- mus.-h-s Nviu.-h ..mi- ti-a.-t ar.- imt j;i-owp.-.l in su.-li a way as to .-aus,- any pi,rpos.-l„l ,„. ,.o.oi-.li„at.-.l in..x -u.-nt. C.nti.a.-tors. ..xt..ns..i-s. a.i.lu.-t..i-s a„a ahdm-tors ar.- Mint- lik..|: all t.. .-ontra.-t at on.-.- an.l hy thus (.|.posin« oiu- aimth.r to ..tf'.-.-t n.. .l.tinit.- m..v..m..nt. \N h..., sm-h stimulation is .-xf-nsiv.- (.-.jr., involv.-s a .-onsi.l.-rahl.- num- l„.r of motor tib..rs), it is .-oinmm, to Hn.l that th.. .•xt..ns.,r „mse-U-s pi-..dominat.- ov.r th. oth.-rs. so that th.- limb b...-o.n.-« .•xtind.-.l. Such is th. cas,. wh.-n some p.»isonous siibstanc- c-aus.-s irritation of th.- n.-rv.- .-.-nt.-i-s in th.- spinal cor.l. To i-aus.^ a i-o-onlinat..! niov.-m.-nt it is n.-.-.-ssary that oii.- sjrmip of mu8<-!.-« shonl.l b.-.-om;- ...lax.-.l whilst th.-ir antap,nistic group is uiulerKoiuK contraction. Now, it might at first sight 1... E:m . 2.'.4 l>nYSI<>I><»nY FOR HKNTAI. STinEXTS. r: It imagined that this n'laxatioii is iiuTcly a passive act. that is to say. that the uiu-ontractiiiji Kroiip of iiiusch-s (h) iiotiiiiin iiioiv tl-.aii rcinair .iiii«'»<'<'"t 'i'"! l>*'rinit tht'insflvcs to Ik- stretohcd. Hut such is not the case ; on the contrary, they become aetively extended. This they are enaWed to do because of the fact that, even when api)arently rebixed, a niuseh' is really not so. but exists in a eondition called touf, that is. in a sliglitly eontraet.Ml state. This tone becomes greatly diminished during sleep, and it can be caused almo.st to disappear by deep anesthesia. It is for this purpose, as well as to abolisii pain, that anesthetics are administered before attempting to reduce a dislocation. Tone is maintained by the nerve cells of the anterior horn ot the spinal cord. When therefore an aflfereiit impulse brings about flexion at the knee joint, it does so by exercising two diametrically opposite influences on the anterior horn cells: it stimulates thos«- which preside over the flexor nmsdes and (h- pnssrs the tonic influence of those supplying the extensors. This tone-depres,sing action recalls the inhibitory influence which, the vagus nerve exercises over the heart beat (see p. 185). and since it always occurs along witli a contraction of antagonistic nniscles it is callcf/ ncijirocil inhibilion. Certain jmisons. par- ticularly strychiiine and tetanus toxin, cause this reciprocal action to break down so that all the nniscles around a joint con- tract at the .same time and phmIucc an extension. Tetai'.us toxin is the poison |»roduced in the blood by the tetanus bacillus, and its interference with the reciprocal inhibition of the muscles of the lower jaw causes lockjaw. Symptoms Due to Lesions Affecting the Reflexes.— From what we have learned regarding the functions of the spinal cord, it is easy for us to explain the following symptoms anas- sively on thi- stretch, either by sitting with th.- fe.'t swinging on the edge of a table, or by crossing one knee over ilie other. I'aiiis, called crises, are also usiud in various |)arts of the bo«ly. Later svmptoins are inability to staii.l without falling when tiie ey.-s are shut, inco-oi-dinated walking, in which the foot is lifted too higli and is brought down to the ground again too violently, loss of .sensation of the .skin of the foot and leg. and changes in th.- pupillarv reflexes of tiie eye (s.>e p. 2H4). The .ioints also be- come swollen and the articular surfaces roughened so that a grating sensation is experienced when the joint is bent (Char- cofs joint). The condition gradually gets worse, so that the patient becomes bedridden. Death is usually due to comi)rica- tions. 2. Destruction of the anterior horn cells not only causes absence of ivHcx action, but is followed by marked atrophy of the atVected muscles. It has been supposed that this i)oints to a so-called trophic influence of these nerve cells, that is to .say. a i)ower of influencing nutrition. Such changes occur in infan tile paralysis (poliomyelitis anterior) :{. Stimulation of the above HImm-s may cause exaggeration of the reflexes, as in the earlier irritative stages of neuritis, in tumors pressing on the nerve roots, or when the membranes of the cord become inflamed, as in meningitis. 4. Kemoval of impulses coming from the cerebrum by way ol the pyramidal tracts causes exaggi-rated reflexes. Such occur in paralysis of both sides of the bo.ly in j.arapleiria. and on one side, the ))araly/ed. in hemiplegia. In a paraplegic patient the weak.'st stimulus applleil to the skill of the paralyzed portion of the bodv will cidl forth a wide- spread aud much exaggerated lu-flex contraction. CIIAI'TKH XXVir. TIIH NKUVOls SYSTKM (Coiifd). The Brain Stem and the Cranial Nerves. The Brain Stem. — The mtMlullii. the |)()ns varolii, iiiui IIh- inid- liniiii ( Kisr.s. 4.") and 4()), (•oiiii)osc tlic brain stem, wliicli is n-aliy an ui)\vanl extension of the nwy matter, ami of certain of the columns of the spinal cord, into the base of the brain with special nerve eenler.s and especially larjrc bundles of intei-eonnectinfr nerve fibers superadded. It is becau.sc of the crossing; in various directioUK of these bundles of tibers that the structure of the medulla, pons and nii'sencephalou is .so ditTicult to und-M'stand. The prey matter, as in the spinal cord, lies deeply and the tibers superficially. < ►f the latter, the |)yramids and fillet, already de- scribed, are the most im|)ortaiit. and their direction is loniji- tudinal. The most i)iominent of the eomiectinp or coinmisural nerve bundles ai'e the upper, iiiichile and lower i>((lnntlis of flit CI n hilhiDi. or snuill brain, which, it will lie remembi-red. lii's over anil at the side of the pons .irolii and niidbram. The hr.vT peduneh's spring' from tlie mh dnila and etmnect the spinal cord with the c< iebelhim. They form the lowet edges of the fourth ventricle Th» middle peduncles I'uter the sids of the pons iri which they cross at ri^rht anjjles with the pyramidal tibirs I p. 24Si. Tln^y connect the ..•rebellum of one side with the ci I'ebrum of the oj)|)osite side. The superior peduncles .jo:n the ene.phalon just under the jtosterior corpora quadrijrennna. and 'he fibers eomiiosintr them di cussate to the oth.'i' side to be- come eoiniicted with certain of tb-- so-called basal u'anfrlia. The hiisal niiiiiilid are the o| he Ihalanuis and the corpora stri- ata, tni; larye collections of nerve cells |)riitrudintr into the third and lateial ventricles of the brain and havinjr the internal capsule between them see |i. 24is J . Tile nerve cells eomposiu'T these f.rangli;i receive impulses from tiei've fibers arriving at lliem both 2Sm TlIK BKAIN STKM. ::.)( from l.rlow (cDiirmjr fntiii the spmal cord) or from abov.- (coni- iim from til." (•(•rcbrmn). Tli.-y tli.-ii transmit tlu'sc impnls.s aloti" tht'ir own ii.rvf fibers, wbidi may run to various otlicr Via (.'. - rmhi .ispiil of hiiMKin luiiiii. Iti tln' .'fiit.-v Inu' „|,u;.nls HI- s.-,-n a s...-lion .-f th.- uppiT .'M.! ,.( th.- spin;,! coni. :.t..l .u.-ihillM .ilil.iiiy-iitii n»l, with .■.■iiHin <>{ itu- tiMiii^i 1„ f,,,nt of Uiis is \h, p..nw <;.). witii th.> law lifHi ...iv.- ..risit.K ffn.H ;,,..! ill.' iiiiil.ll.- pedun.l..« ..r ill.' v.-i,u.-\lum iM. r<.l} imumuk mt.. it.- '■•■> l„.|liirn 1.1' Til. r.mtwl.T Im.iM.'s ;,i,i.i,''^ to the \ixux i.iv ih \'«v:< i'l' memina ir,,i i., •!, si-l,..| iUM. i .1 ( .•otislHM tl„ .•.■i,i;,in.l..| ..I- tlu ,li:ivvinK , r,,.m a p: . p.iiMti... !■> r M Spiirn.-v. . 2."^ fIIYM(»lAX;V F>il{ DiATAI. ^TIHENTS. \tiirU o\' ^^■^ l)raiii. Th. optic flialanHK, as its iiaiiic signifit's, ts '•itiiiiati'l\ iisKooiatiil vvitli the opti«' iktvps. Allotllcr iiaportailt CKilci-tloii of nerve eells oeeiU'S ill the ii>riK>rii ifiKtfiriffi "H»(i. Thesi- ixnit as t'onr uuiKled swellirms. two oil litller side, just where tim- s«|*eri(ir jietiiiiielcs df the cere- liellum come tofft'ther Their nerve eellv wrve a-> distrt^watiiitf centers for visual and auditors intfut^se-".^ cjirried T(» them throu;;!' ti-aets of nerve fibers oinieetMi with ihc optic and auditory KlS. 4ti — Vertical trimsverKt stM-tmn iif liumaii hniin Below is n soctioii (if tin- imiis I /'I .shiiwiiiB the lilitM!< which luiiiu-it Ihi- liniin stt-m ami letf- hiuiii railiutiiiK up ihrouKh thf Intel iial caimuh' (l('). which Ih liouiul.il in.-siallv hy thf optic thalmus (T^. ;iiii laterally by the corpus stiiatuni (/-). Till- thiril (Ill-V) and lateral ventricles i LV ) i)t the brain are seen in the ciiiiii (hlaik) The thickness of the Krev matter ami the infoliiiiiK of lie' surfaees, as eonvoUitions. should )»■ noted. i I'"rom a preparation hy I' M Spuriiej , ) Mifvs. Tile corpora i|Uadri^eniina are usually iiioi-e developed in the hraiii of the lower animals than in that of man. The Cranial Nerves.— On aeeount of the iMtrodiietioii of the new struetures described above theiv is no regularity in the TIIK CRAMAI. NKRVES. 259 iinangi'iiicnt of tlic {in-y niattcr in tlic bmiii stem .is tli.'iv is in tilt' conl. Instead of forming liorns. tlic ^'n-y iiiiitlcr is .sc.it- ti'U'd ill colonics or nnclci, many of wliicli arc centers for tlic. Hhcrs of tlic cranial nerves. Sonic of these filters arc. of course, afferent and sonic ctfercnt. Since many of the cranial nerves are connected with the no.se. mouth and teeth, it is im- jiortant for us to learn soniethinji conccrniiiit the location of their centers and the jjeneral function of the nerves. There are twelve pairs of cranial nerves, and the last ten of these orisrinate from the sfrey matter of the medulla, pons or midhrain. The followin(r list indicates the fifK'i'al functions of the nervc> : 1. Olfactory. ]>. Opuc. ■;. < >nulo m«H»r. 4. TTcwchl .»r. »;. AfbdHe»*n8. .'i. Trigeminal. 7 Kacial. 5. Auilitor\'. !t, (i1o980-pharyn- gpal. Iti. Vagus. 11. Spitial iiceessory. nerve of smell, nerve of sight. nerves to the mii.s- cles of the eyeball sensory nerve of face, main motor nerve of face muscles, nerve of hearing and of semicircular canals, motor nerve of phar- yn.\. sensory nerv^* of taste, efferent and aS'-rcni nerve to -•rimis viscera mainly blends with vagus motor nerve for tongue muscles arises from fore- brain arises from fore brain. arise from midbrain. arises mainly in pons. arises in pons a'ul medulla. arises in pons arises mainly in mMliiIla. arise* in rowJulla. arises with vagua except spinal por tton, whicti extends down into spinal cord arises in medulla 12. Hypoglossal. It is imi)ort:iiit to note that, like the spinal nerves many of the cranial nervi-s arc compiscd of two roots, motor and !k-nsory. 260 PIIYfsntl-nCY POK OENTAl, STTPKNTS. .■ach liaviiip its own center. This fact justitics tlic statement whieii we luive aliva.ly mad.- that the brain stem is really an up- ward prolongation of the spinal eord. and just as we saw that eaeh posterior root of the spinal eord is eharaeteri/.ed by pos- sessinK a ganglion, so also is there a gitnglutn in Ihr sensory divisions of thi cranial nrrns. This ganglion, however, is often diffieult to tiud. The nerve cells which compose it unite with tlu' fibers of tlu' sensory root by a T-shaped junetion. and the fibers terminate by .synapsis around th.' cells of th.' sensory nuclei. The ganglion of the fifth nerve is the (lasserian. Those for the eighth are the ganglia found in the cochlea and internal auditorv meatus (Scarpa's ganglion). The ganglia of the ninth and tenth nerves are situated along the course of the nerves. The approximate position of the various ganglia will be best learned by consultation of the accompanying diagram (Fig. 47). In the brain stem there are three sensoru or affrrent nuclei, a l(.ng. combined one for the ninth, tenth and eleventh nerves, ex- ten.ling practically from the upper to the lower limits of the m.-dulla, one for the eighth in the center of the pons, and a very long one for the fifth, extending from near the upi)er limit of "the pons down into the siiiiial cord. The motar or iff»- Hfiinory iiu<-!«*i .trv <-o'ort( roUfHi- pi-fHt'iil on hold snit- THE IKANlAli NKRVES. 2(il objcus arc at a .listance (louK HJght) ; (3) sMuiut of tho .-.w s. that it is aircctetl outwanl and downward. Sud. a paralysis of tlu- eye is soinrtin-rs a.-.-om,.an..d -y . partial h. ,ni,»l..gia (sv- p. 271) of tlu- opi.os.t. s.do ot 1,.. l.o. v. ,u,s iduat.n. that son,. d.-struHiv. U.ion ( haMuorrhag. d. structivo tunu.ur) exists on one si.!, of the nudbra.n. so lu .t iMVolvos tin. nnd.us of origin of tin- third n.-rvo and a s<, the nvranndal fibers lyi..g near. Sin.v the fibers ot the th.rd ne, .■ lu, not erass to the opposite side, but those ot the pyranuds do (see p 2A:\), we get a crossnl or altn;,othu, parahisis. Son.e- times onlv one part of the third nerve nn.y be paraly/ed tor ..xan.pb-Zthat portion going to the nn.seles of aeeonuno,lat.on. T..K FciKTii AM. Sixth Nkkvks.-TIu- fourth ami sixth nerves supplv the two extra-m-ular ninsdes not sui.plie.l by the third. viL the superior oblique (fourth) and the external iretus (sixtli). respt-etiveiy. . , , . .• .i. , TlIK FlhT.l NKKVK.-The i\n\ nerve IS the hll-esl ot h- ,,,,nial nerves, ami is a rei.n.s,.iitative inixe.l nerve. It sn,.plies the te.-th The .nnlor hr,tmh runs to tlie niiiseles ..t nuiNtiea- tion the tensor nnisele of the pnlale. the inyiohyoi.i n.usele (m the floor of the nioutiH and the anterior belly of the .iigastne. Thes.. last two ineiitioiie.1 inuseles pull the liyoi.l bone an.! then- r.„-,. the root ..f the tongue upwanl and forwar.l ^lurnig the .n-t <,f vv.allowi.ig. lioth niastieation and swallowing are seru.usly i,„,,,in.d wh n this nerve is paraly/ed. The s, „son, phns are ,o,n,eeted witli the reeeptors for u\\ tin- eoininoi. se'-sat.ons o t,,„ i,„a,l and fae,-. As already explained, they aiv e.n.neet ■- Nvitli the iierv,. eells (d the Ca.serian ganglion, whieh is t nlge.l i„ a .lepres,sion near the ap.-x ..f the petrous porlu.n ol the ,,.,„poral bone. Shorttv ifter leaving this ganglion, the nerve .livi.les into thive bra.: ,: (1) the upper or ophthai.nie. ean-y- i„<' the s..nsorv nerxr iibers for the ron.junetiva. the nu.eons ,„.Mnb,an, of the nasal fossa-, and the skin of the eyebrow, t.nv- li.-.d and nose (2> Mi.hlle or superior maxillary, sui.plymg the meninges the low.-r eyelid, the skin of the side of the nose an.l up|..-r l,p nml all tlie t.-eth ami gums of the ui.pev jaw. ( •! i iMf.ri.n- inaxiilarv. supi-lying the teeth and gums ot the lower -^ . 262 PHYSIOLOGY FOR PFVTAL STUDENTS. tt- . ■■ I %\ jaw, the skin of the temple and external ear, tlie lower part of the faee and the lower li|i. riKI.ATKlNSIHI* Ob TIIK FlKTIl NkRVK T(» TIIK TkKTII. — III ah.V 111- Haniniatory eoiidition (if tlie teeth, the terminations of the sen- sory fibers iHH'onie .•stinuilated, eansing extreme pain. Tliis is toothaehe. The relationship of the fifth nerve to the teeth ex- plains \v'i disturbanee in the latter should often eanse the \m'\\\ to be referred not to the tooth tliat is involved, but to some skin area on the faee. This is called rcfnrcd pain. The skin areas eorresponding to th<' different teetli have lM>en worketl out by Uiiid. nnd iu inditated in tlie .iceoinpanyinfr diagrams ' Fiijs. 48 and 49 i. Not only may the pain be referred to the skin area, hut tlii^i ilvli may Ixm mie hyp( rsensitivr Theie is. moreover, in each areii asually a maximal spot at wLii h the pain .n.d ten- derness are most marke«l. The sensory nerve < ndinfrs in the teeth arc all of the nature f)f l)ain receptors; then nre no temperature or tactile receptors, these latter s<'n.>,itions heinjj particularly developed in the ton^fue and lips (see p. _'i4 . The pain receptors of the teeth, like those ol the cornea, react practically in full intensity to every strength of stimulus. This explains wiiy a small decree of irritation, as that due to caries, mny cause as painful a toothache as an in- tense irritation. As we have already explained, the purpose of liiunlul or nocuous sensation is protective, causing, for example, witiidrawcil of the irritated portion of the body or some move- ment of offense (see p. 2r»l). In the case of the teeth it Kcrves a; a warning that something must be done to arrest wli.itcv'r condition is causing it. The enamel and cement are devoi-n:is:il iii-iM ( miixil I liiiy iiicisiiis). M;isill:ii>- Miia ( iii:ixilhii.\ si'iiiiiil pii'iniilMi' iiiKl lii'st iniilar ) . Miiitiil iinii ( iimnililiii';!!- rst |ill MllllMI). Till' iJiiints of in;ixiiiiiiiii ititriisily ;ii'>' lill^;l■ll. I INasn-lal.iMl :.r.-,i . m:.xilh.iy | 1 M.mImI mi.m , mi.M.lilm^;,. 1 J ruiiiH. i.rnl tirst pivMinlMi). I I l-»i.s..,s, ...nin.- mimI ImsI KiK. 4S. — IHimraiii tii slmw aniis of r.fiii.cl pain in ilisti Mml ii^ii >•( lilili IiiTVi' (lui- til afTfrtii.iiH iif tlir variiius liilh iKniTil \ ii w I i I'l'uMi iliawiiiu liy T. Wiiinati' 'riiilii.) 1.0 I.I 1^ |7B m itt 1^ lU 1^ lit lu b& 1.4 1^ 2.0 1.8 1.6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI and ISO TEST CHART No. 2) THE CRANlAr. NERVES. 263 Tlie fiftli luTvi' is vorv commonly th.' s.'at of ncuri.ltrin. winch mav affect one or all of its brandies. This is .allc.l •'/„ ,l,H,loiirr„.r'- or tri-facial ncunilKia. Th.- atta.-ks come in spasHLS, an.'. l).-si.l.'s th.' ,.xcrucialH>fr i.ain, th.-n- is often twitch- i„fj of the muscles or flushing of th.- skin of the- fac.-. Pr.>ssi re at tlic points when- the branch.-s of tlie nerve com.- out of the skull as at the supra or infra-orbital n..tch.-s. is usually espe- Hallv painful in tic An unh.-altliy .-on.liticm of the teeth is often responsible for the sympt.mis. but if d.-ntal tr.-atnu-nt and general m.-.lical care .lo not ivmov.- the neuralgia, it is usually advisabl.- to cut out a portion of the n.-rv.- or ev.-ii t.. remove the entire (Jasseriuii ganglion. Som.-times the fifth nerv.- b.-comes p.mihizrd. causing an.-s- th.-sia involving the area ..f its .listribution. Tingling, numb- ness or lu-uralgic pains often pr.-.-.-d.- the anesth.-sia. Sine.- tlu- eonjunctiva los.-s its seiisitiv.-n.-ss, i.articl.-s .)f .lust. etc.. are not n-nioved from the .-ye by th.- t.-ars so that th.-y set up inflam- mation, which may d.-v.-lop an.l cause ulceration of the corn.-a. For the same reasmi, or perhaps because the n.-rv.- mdeix-n.l.-ntly controls th.- nutrition of tissu.-s. the gums an.l .-hecks may be- come ulcerated an.l tlu- t.-eth loos.-n,-.l. Partial loss of tast.- and inability to sn..-ll pungent vapors, whi.-h act ..n s.-nsory n.-rv-s. are also common symptoms. The Seventh NEKVjtLr-Th.- s.^x.mtli m-rv.- is piir.-ly motor m function /-.dTth^-' facial muscles, except those conoorn.Ml in mastication, the platysma of th.- n.-.-k. th.- p,.st.-rior b.-lly of tlie di-'astric and on.- of the muscles of th.- mi.1.11.- .-ar (th.- sta- pedius^ are supi.li.-.l by it. On a.-count of its tortumis .-mirs.- the seventh nerve is p.-eiiliarly liabh- to inflammation an.l com- lUTSsion. Thus tumors ..r inflammati.m locat.-.l at th.- bas.- of the brain mav inv..lv.- that i.orti.Mi running b.-tw.-.-n the upp.-r end of the m.-dulla .oblongata an.l th.- int.-rnal aii.litory m.-atus. where tlr nerve .-nters the a.|U.-.lu.-t of Kallopiiis. In tins r.'gion it is lik.-ly to b.-com.- involv.-d wli.-n th.-n- is .liseas.- <)t the internal .-ar or mast.iid sinus (mastoiditis). After its exii from tile skull (by tlu- styhmiastoi.l f.iramen") its .-l.is.^ asso.-iatDii with the parotid gland renders it liable to be involved in eel- 264 Ov- PHYSIOLfKJY FOR DENTAL STVDENTS.- lulitis of this gland, and on aecount of its superfifial position, it may 1h' injured by blows on thf side of the licad. Quite eoni- inoidy the seventh nerve beeonies the seat of inflanimatiou after j'xposure to a draught, as by sitting at an oj)en window. Tiie paralysii is almost always one-sided. The eyelii.l on.' functional. The anatomical diff.-ren.-.- is that .-v.-ry nerv.- hb.-r bccom.'s conn.'cte.! through synaps.-s with n.rve c.-Us locat.'.l peripherallv (i. e.. n.-ar the end of the nerve), an.l tl..- ax.ms oi th.. ..-lis .-ontinue th.- impuls,- on to the structure; th.' lunct.onal ditfercnc.. is that tlu- auton.m.ic fib.M-s, as th.-ir nam.' ui.licat.'s cntrol antomati.-ally-actinn ..r inv..luntary functn.ns inst.'a.l ot voluntary movm.'nts. as is th.- cas.- with th.- ..r.hnary ..r somat... cei-ebrospinal n.'rv.' fibers. Th.' most important of th.' vajrus aul.>nomic fib.'rs run to th.' heart (s.-e p. is:.). the o-sophaKUS (p. 'nK the stomach U'- •'"' an.l the int.-stin.'s (p. 7!»). Th.' vai.M.s also ....ntams atl.'r.'ut fibers which hav.' th.-ir .-.'11 stations in gan^'lia situat.'.l m tin trunk of the n.'rve. Th.-s,- fib.-rs carry s.'usory nMpuls.-s par ticutarlv fron. th.' laryn.x an.l lun-s ( ,.. 21!)'. Kurth.'r .l.'ta.ls n.>;ar.lini>s.sihl.' without tin- (•.•rt'hniiii. thus supportiiit,' the conclusidn. which w- have alr.aily .Irawii (stv p. 24:{). that th.' (■.ivl.niiii coiu.-s to 1„. ;i III ssary part of every retlex action in th.' Iiijjher animals. Cerebral Localiiation.— The varinus runelimis of the cere liruin are located in ditfereiit portions of it. This liM-aii/ation (if cerebral functions lias lieeii very extensively studied duriiitf recent years, partly by exiieriinental work on the higher niam nialia and iiartly by clinical studies on man. Careful observa- tions are made of the behavior of the various functions of the animal either after removal or destruction of a portion of the cer.'iiiinn. or during its stimulation by the electric current. Im portant ailditions to o\ir knowledUe of cerebral localization are also beinn maile by eorrclatinjf the symi>toms observed in insane persons with the lesions which are revealed by post-ninrteiii examination. It has been found that there are roughly t!ree areas on the cerebrum with distinct and separate functions ( Kiy. .'lO). I. In the jiortions of the cerebrum which lie in front of the ascending,' frontal convolutions — [tn frontal nuioii— art' located the cente of the intellect (thouKht. ideation, memory, etc.). Tills part of the cerebrum is aecordin«ly by far the best de- velofied in man ; it is much less so in the apes and monkeys becomes insignificant in the dog, and still more so in the rabbit. It has been destroyed by accident in man with the result that all the higrher mental |)ower.H vanished. II. The i!','xt i>ortion includes routrhiy the reF.\TS. HI i (p. 248). nml tlius* (Mimu-H with lli.' iiiitfrior lioni cflls of the spinal pord. l!i the liuhindU ana, as it is CHllcd, is tli.n'forc sitiiatftl Ww iH'ivbral link in tin- rliaiii of iiciiroins (s«m' i». 24!t) through wliieh tlif oniiiiary luovcnu-nts of tlu' IxMly taite place. Such iiiovt'iiU'iitH iiia.v Ih- set ajfoiiift. <'itlifr by stimulation of tlic Holandii' n. rvc cflls through atTcn-nt filM-rs— a pmv ivH.'X— or by impulses coniinK to tlx-ni from tlu- i-nt«"rs of volition situated KiK. r.0.— ("Drtloal centfiB in iiiiin. Of the thitv Hhiul.d airas boiil.-iiiiK on the Holamlie tlMMure (ffof.). the most anteiior is the preceiUral iissmriatUinal area, the middle one is the motor area (the poHitioii of the l.ody areas ar. iiKlle'ateil on it), and the most posterior is the sensory area, to the lells oi which the fillet Hb.rs proceed. The centers for seeinR and hearing an- also shown. The unshaded portion in front of the l{olantrn(I<'' .liuiiib uiidiTiiois a slow, purposcriil. i'o-i,.ili iiat'ii iiiovciiiciit : and so on fur tvtry otln ' i-t-ntcr. Or, if in Ntrad of MtiniiilatinLT. w«' cut away one • rt-ntt'is and allow the animal to rta-oV' r from the iminrdiatc ctTrcts of the opera- tion, it will hv found that all the more finely eo-ordinated move- ments of the eorresj) )Mding part of the IiikIv hase disappeared. alt hough K'"'*'* reHex niovenieiits may he possible, 1 ause tlie ^piiud retlexes are still intact. Jf the entire Kolandic area on nuv siartic, -ly in tlie .-ase of younu aninuds, the paralysis becoi is iict.vcred from, thus in- dieatinur that Home other i)ortu)i;, )f the brain have assumed the function of the destr ved cent > If the stimulus is a very stntnj? one, the movenii ^ do not i nuiin confined to the cor- res,,. idiny musdi f^roup, but the.v spread on to neijfhboriiif; jrroups until ultimately the whole extremity or |>erhaps i ten all the muscles of that .side of the body arc involved. These experimental results find their exact counterj'Mrt in )li)ii<(il ( j-pi rifiKi . Thus when some center becomes irritated by i)re.ssure on it of some tumor >»rowinj? in the membranes of the brain (meningeal tumor), or by a piece of bone, as in de- pressed fracture of the skull, or by blood clot, convulsive at- tacks (known as Jacksonian epilepsy) become common. The fir.st sign of such an attack is v lally some i»eculiar sensation (aura) affecting th.e part of the body which corresponds to the irritateil area, then the nuiscles of this part begin to twitch and more muscles get involved until ultimately all those of the coi-- responding half of the bod.v become contracted. There is. how- ever, no loss of consciousness, which there is in true epilej)sy. The evident cause of those symptoms has clearly indicated the proper treatment for such cases, namely, surgical removal of the cau.se of irritation. Fi.r this purpose a very careful .study is first of all made of the exact i-ouj) of muscles in which the convulsions originate, the location of the area on the cerebrum is thus ascertained and a trephine hole is made in the correspond- 272 I'llYSI(»I,(>i;\TS. iiij,' j>ai't of the craiiium and tlirough this liolc the tumor or ])lootl c'l t is rciiiovt'd. 111. Tlicsf so-called motor areas are of course also snisorif areas in the sense that the atrerent stimuli which come up from the spinal cord run to thi'in. They are really sens<>ri-nu)tor centers. For some of the more hifjhly specialized proficient sensaticnis such as vision and hearino; (see p. 2T'.M, tlir - are, however, special centers. These alonpr with an extensive field of as.socialiona1 or junctional yrrey matter constitute the third nuiin division of the cerehral cortex and occupy the t?reater liart of the i)arietal, the temporosphenoidal .and the occipital lobes. The risi(((l is the most definite of these centers. Thus if the occipital lobe he removed or destroyed by disease on one si(h'. tile correspondinj,' half of each retina becomes blind. It is by studyintr the exact nature of the involvement of vision in sucli cases that the physician is able to locate the position of a tumor, etc. The center for lunrinn is in the temi)orosphenoidal lobe, hut its location is not very definite. It will be seen, however, that the visual and auditory centers take ui> but a small part of this third division of the cerebnun, the most of it Ix'in},' occupied by (issK.NTS. |i '! volv.'s son... of tlw (M.iit.TS i.onc.'r.i.Ml in the lii^'hor control of th." nnis.-l(s wliicli an- iis.'.l in si.r..cl.. and very .•onin.only it is situat.Ml in tiic l.-ft si.!.- of ti..- (•.-n-hrnni. In all thr.-e forms of aphasia tli.T.' is more or l.-ss dc-n-asc in th.- ni.Mital powers. Cerebellum. Ti.c atr.Mvnt inii)iilscs s.'t up by stinnilaiion of the nerves of tile hkin in a spinal animal, and due therefore to ehauKes in the (iivironment. after .■ntering the spinal eord travel to the various eeiit.-rs in the eor.l. Althoufih eomi)lieated movements niav result (e.ft.. the srrateh reflex), there is an entire absence of the power of maintaining bodily e.|uilibrium, and the animal cannot stand because the muscles are not kept in the degree of ton.- which is necessary to k.-ep the joints properly stiffened A similar inability to maintain tlw center of gravity of the body results from removal of the cerebellum, or .small brain, which it will be r."memb»-red is situat.-d dorsal to the medulla iind pons, with whicii it is connected by thnv peduncles. The crebelliim consists of two hit< ml Jomisphfrrs and a median lobe called th, nrmis. The remarkable infol.ling of the grey matter which composes its surface, and the large number of nuclei which lie eiidu'd.led in its central white matter are struc- tural peculiarities of the cerebellum. Th.- imm.-.liate results of removal of the cen-b.-llum consist in .-xtr.-me restl.-s.sn.-ss and inco-or.lination of movements. The animal is con.stantly throwing its.-lf about in so violent a man- ner that unless controlled it may dash itself to death, (h-adually the .■.Kcitement gets l.-ss until aftt-r several weeks all that is noticed is that there is a condition of muscular wi-aknc-ss and tremor, and difli.-ulty in maintaining the body e.|uilibrium. Quite similar symptoms occur wh.-n the cen-belliim is .liseased in man (as by the growth of a tumor), the ..'oiLlition being call.-d c.-r.-b<-liar ataxia, and being characteriz.'d by the uncer- tain gait which is like that of a drunken man. These ob.st-rvations in.licate that the function of the c.-rebellum is to harmonize the actions of the various muscular group.s. so Tin; FINCTUINS OF Till. CKliKRI'.I.I.l'M. :(.) tliat any (iisturlmiict' in tin- I'l'iilcr of jjnivity ol' Ihc ImhIv in.iy he subconsciously rcctifi<'(l Ity iipproid-iatc action of the various muscular groups. It evidently represents the nerve center liav- iiiff supreme control over other nerve centers, so that these may not brinj; about such movements as would disturb the i.) apparatus above described is lo..ate,l. It is evident that when the head is moved in any dinrtim. tl... tluid m some of these eanals will be set in motion. It is this nu)vm.-nt ot the fiuid which stimulates the hair cells. That this is really the function of the sen.icircular canals is proven by the fact that if they are irritated or destroyed, grave disturbances occur in the bojl.ly movements. This is what occurs in Meniere's disease, m which attacks of giddiness, often severe enougii to cause the patient to fall and accompanied by extreme nausea, are the chief symp- toms the lesion being a chronic iuHammation involving the THE SYMPATHETIC NERVOl'S SYSTEM. 277 Homiciri'ular canaN It is bolioved by some tliat tlif cmistaitt movonioiits of the Hnid in tho st'iiiicircular canals is tli.> cause of sea sickness. The unusual nature of these movements causes confusion in the impressions transmitted to the cerebellum from the canals, but after a while the cerebellum becomes acc\istometi to them antl the sea sickness pas.ses away. The Sympathetic Nervous System. Along with the vagus and one or two less prominent cere- l)rospinal nerves, the sympathetic constitutes the iiiiliniinnif nervous system, .so called because it has to do with the innerva- tion of automatically acting struct\ire.s, such ns the viscera, the glands and the blood vessels. Tlie characteristic structural f,-a- tnre of the nerves of this system is that they are couuected witli nerve ganglia located oufsi' ^'""K'' ""'^ >** calltMl til." stillair ijatiiiUon. Its pnstKaii«lionic fiUi'rs coiistitutf the vasomotor iii'i-v.-s of tlif l)loo(l v.'sscls of the antt-riitr fx- tivmitv, aiul th.- s.viupatlictic fib.Ts to tbt- lu'art. Sonu" pn-gan- ttlioni.' filxM-s run tlirou^'h the st.-llatc ^riU'Klion to pass u|) tlic neck as th." a rvUal s>n„i><'ll'< ti<'. th.-ir 80-i!allo(l ooular muscles. Tlicrc arc therefore three functions involved in the act of scciuK: (1) That of the retina, in reaetiiiK to li^lit. (2) That of the cornea, etc.. in focusin« the li^'ht. (:5) That of tlie ocular muscles, in moving tiie eyeball. The Optical Apparatus of the Eye. It will readily be s.'cn that the eye is constructed on niucii the same principle as a i)hoto>irai>hic camera, the r.'tiiia beiiiir like the .sensitive plate. There is, ho\vev«-r. an important dif- ference in the manner by whidi objects at varying distances are brought to a focus on the sensitive surface in tiiese two cases: in the camera, it is done by a.ljusting the distance between the lens and the focusing screen; in the eye, it is done by varying the convexity of the lens. In order to unch-rstand how the optical apparatus works, it is necessary to know something about the refraction of light. When a ray of light i)as.ses from one medium to another, it be .•omes bent or refracted. When it passes from air to water or glass, for examide. it becomes refracted so that the angle wliieh the refracted I'ay makes witii the perpendicular to the surface is less than that of the entering ray. In other words, the ray Ix'comes bent towards the perpendicular. The greater the dif- ference in density between the two media, the greater is the diflfcrence iH-tween the two angles. A figuiv expressing the ratio between these two angles is called the iii(h.i- of r< fraction. If the ray of light leaves the d.-nser medium by a surface which is parallel with that by which it entered (as in passing tiirougii a pane of glas.s), it will be refracted back to its old direefu.n, b\it if, as in a prism, it leaves the denser medium by a surface which forms an angle with that by which it entered, the original refraction will be exaggerated. If two prisms be i)laced with their broad ends t<.gether, parallel rays of light coming from a certain direction will be Ix-nt so that, on leaving the prisms, thev meet somewhere behind them. Two prisms so arranged are virtually the .same as a bkonvc.r }n,s. It is plain that the VISION. 281 fociisiiijf power of such Ji Ifiis will (Ii'ImmiiI mi two things: first its index of refraction, mid. secondly the curvature of its sur- faces. A considerahle part of the actual retraction of the lays which enter the eye is accoiiij)lislied at thi' curved surface of the cornea, a .smaller def,'ree of refraction takinj,' place at the leiLS itwlf. The rea.son for this is that the refractive ind'X from air to corn. ;i is mucii )jreater than that between the lens and the humors of the eye in which the lens is suspended, tli se humors and the cornea lia'iiiu very much the same refract ive indices. The eiitoriiifr '"ays are therefore iifracted at two phii-es in the eye. namely, at the anterior surface of the cornea and on i)a.ssiiig through the lens. \'\H. rrj. — Kiiiiiiiitidii III' iiniiH:!' on r<'tiiia. O..I. i.s the nptir axis. Accommodation of the Eye for Near Vision. — When the eye is at rest, its optical system is of sui n i strength that parallel rays. i. e.. rays that are reflected from objects at a distance, are brought to a focus exactly on the retina. The picture thus formed is, liowever, upside down jr.st for the same reason that it is so on the .screen of a camera (Fig. .V2). When the object looked at is so near that the rays reflected from it are diverge'it when they enter the eye, it becomes neces-sjiry. if the image is still to be focused on the retina, that some adjustment take jUace in the ojitical system of the eye. This could happen in one or two ways, cither by the :».. If th. 1—.. is MOW toi.l to r.,ar.l so.... ' KiK. ^3.-S...•. through ,h.- »" ;;"J" ::;!',, ;a the nmrsin. : /-. tho l..ns. fi. th- .mary >'-;"7;;^,';:^^ '" n;:^ ,"■„,.,:..,..„. hy .-. M. spur- <,tU' or oUl.T prot.clive coal ..f th.' iM . I I iify. ) ob,..t h.Ul .los. to hi,... it will h. s.... that th. iris is p..siu.l forwanl ...a.vr to th. .o.-...a. That th.s .s .-.ally .h.c to a b,.l« r t^. a..t.,-io.. su.-fa.. of th. i...s ca.. b. show., by , aeu'f 'a,..ll. to o... si.l. a,.d a l.ttl. i.. frc.t of th. h.a.l an.l the.., •n, t .. oth..- si.l.. vi.wi,., th. i...a,.s of th. .a..cU. «a,.,. 1^ ; ... ..ast oo tl y.. It will b. s..... that o... ....a^. oc.,... " ' ;„t..,.io,. su.fa.. of th. .o,-...a. a..a a..oth..- l.ss d.st....t. a he utorior su.-face of th. l...s. This i.,.age f.-o.u the l.us VISION. 283 will !)»' sfcii to mi>vi' forwanl— that is to say. clowr ti» tin- iiiiatfi- at tilt' coriii'a — wIumi tin- pci'siiii sliifts lii.s Kii/c from a diMtaiit to a near ohjci-t. Wy usiiiK optical apparatUH for iiH'a.Huriiif; the si/i' of the iiiia^fcs. the dctrrcc to which the cimvi-xity of the Iciis has iiicn-ascii, as a result of the Itiiijriiitf, can Im' accuratt'ly Mit'asuriMl. This fliaiinr ill the convexity of the lens (lepcmls on the fact that it is composed of a hall of transparent elastic material, which is kept more or less tiatteiied antero-posteriorly iM-cause of its beiii); slun^ in a capsule which compresses it. The edjjes of the capsule arc attached to a fine lijranient (the suspensory lijfa- meiit), which runs backwards and outwards to l>ecome inserted into the ciliary prm-esses (V'm. '>•"{). These processes exist as thickenings of the anterior portion of the choroid, or pi^riiieiit coat of the eye. and they can he moved forwanis by tiie action of a small faii-shai)ed muscle, called the ciliary muscle, which at its narrow end originates in the coriieo-schleral .junction, and runs back to Im' attached, by its wide end, to the ciliary pro- cesses. When this muscle is at le.st. the ciliary processes lie at such a distance from the edues of the lens that the suspensory lifjament is i)Ut on the stretch. When the ciliary ninscle coii- traets, it pulls the ciliary i)roce.s.ses forward, thus slackenins? the sus|)ensory ligament and removinj; the tension on the capsule of the lens, with the result tliat the latter bulges because of its elasticity. The ability of tlu' lens to become accommodated for neai" vision depends, therefore, tirst. on the elasticity of the len.s. and secondly, on the ac^" ♦" the ciliary muscle. Inter- ference with either of these i ' iccommodation faulty. For example, the lens along witi. .lU) other elastic tissues of the body |e. n., the arteries (p. 17.">)|, becomes less elastic in old aj?e, thus accountinj; for the ■■loiifr-sightedne.ss" (ov presbvopia) which ordinarily develops at this time. Paralysis *>; the ciliary muscle produces the same effect in even more marked dejfree. which explains the utter inability to bring about any accommo- dation after treating the eye with atropin, which is given for this i)urpo.se before testing the vision in onh'r to find out the streiigth of ienst's reiiuirod to correct for errors in refraction. 284 riIYKK»l-iH}V FOR nr.NTAli sTinENTfl. ipl it • J- Th. runction of the Pupil.-Evory optical in-tnunont con- tains n so-calloa .U.M.hr„„n. which is a black curtan. havn.K u "ntral apcrtu,-c, who.- .iia.nctcr can he altcrd to "»>;-' size. The object of thin is to prcv-nt all »nncceH..tv n>s t «ht fn.n. entering the optical instr.nucnt thus -;•;••;«- ..n-asinK the .listinctncs of the ima,e. In the eye t .s ^ ut is perfornu-d by the iris with the ,>up.l n. Us center Th /^ .,,• he pupil is alterea by the action of two s^-ts ot nu.scle 1 be, s , t!u. iris. One of these runs in a circular n.anner aroun.l th •„„„., ...l«e of the iris: by contracting it causes const net ...n of „„. pupil. „„ ..vent which ..ccurs. alon« with the buku.« of the 1 iLriuK acc«nun.Hlation for near visio.. The other layer of tibers runs in a ra.lial n.anner. an.l by contract.n« <-au.-s .hla- „,„,„ „, ,„, p„pi, This ocurs in partial '^''-ij--;;;; ;;;;',; ..v.. .s at rest (aaln.uKh not .luru.K sleep,. T'c e.rcubu hb rs an- supplied bv the third nerve, and the ra.lnd hbers by the sv„,pathetic. rn.ler ordinary conditions both nu,s..les are n- a :;ate of tonic contraction (see p. 2.>:n. so that the actual s./.e „,• „,, pupil at any n.on.cnt is the balance between two opposn.fx ,„nsc,dar forces. This ren.lers its ad.justn.ent in s./.e very s..ns,. li^vo Kor exan.ple. it can becon.e dilated either by stnnulatn.n of the svn.pathetic (which occurs when any irritative tumor ..ffects the cervical synipathetic nerve), or by paralysis of the third nerve (as by piviufr atropin). Convers.dy. constriction o the pupil mav be the result of stimulation of the third nerve (as by a tumor at the base of the brain) or paralysis of the sympa- ^''tIicsc local conditions actinjr on the offm „t nerves to either pupil are not nearly so often calle.l into play as conditions actuiR nfli xhj on both eyes at the same time. ^ • . Certain of the affe.vnt impulses whieh call these reflexes into plav travel by the optic nerve to the nerve centers for the pupil, such for example as the stimulus s.-t up by liRht talhns on the n-tii.a The atr.nnt pathway concerne.l in the contraction ot the pupil, which occurs in accommodation, mu.t. on the other hand, be a ditT.rent one l>ecause in the .lisease loco.notor ataxia (see p 254) the pupil contracts ou accommodation, but does not VISION. 28:» i1<> Sit wlifii li«ht Ih tlirowii iii(i> tin- vyvs. Tlif iifi-vr cfiitfi-H for the pupil air vfi-y Mfiisitiv.' to jffinTiil ihivouh cuiHlitinnH. tints iHM'ouiitinj^ for tlif ililatation of tli«' pupil wliicli occui-h duiiim fright or otii.-r r. notions, or |>«iii. The pupils iin- contracted in tlic early sta>?cH of asphyxia or ancsthtsia. as in tlic early stajrcs of nitrous oxide atiiniiiistration. ImM they become dilated when the aiiesthcNia or asphyxia becomes profound. Their condition hel[)s to serve as a ^auKc of the depth of anesthesia. Imperfections of Vilion.— The ojitical system of the eye is not perfect. Sotnt of thc.v impi rfiitloiis i< . whilst otiiers are only oecasioiml. The errors in every eye are those known as speiical and chronuitic a' i-rratioii. Sphi riirl i.-|p, r.4— .4. spherical ali.Tiiillon. Tlif ni.vs wlii.h strikf Hit- M.ainiiis nf the lens aif IroUBlit to a focus li.li>i.- tliosi' .^trikiiiK near tlir nritt-T. /■'. Cliroiiiatic .ilxiration. The ray of whit.- liwht ( H') is .lisscrial.il l.v th.- l.ii.s Into lh«- siKMtral c.lors, of n-liich thus.- at thf r.il .'iiil (/.') ar.' lint hriniKht to a fixiw fio sunn as th... at tin- vioUt itul ( I). iilxrnilioii (FiK.-r)4), occurs because the cdijeH of the lens have a higher refractive i)ower than the center, so that the imatjc on the retiiui is surrounded by a halo of overfociised rays. Chm- wtilic ahirndion is due to the fact that white lifsitioii into its constituent colored rays (the rainbow colors), of which certain (vi/., those towards the violet end of the si)ectrum) come to a focus sooner than others (viz., tho«e towards the red end'), thus creating a colored tfdge on the focused imrge. The.se errors are greatly minimized, although not entirely removed, by the pupil, which cuts out the peripheral rays. The ocamonal errors are long-sightedness or hypennetropiji. 286 IMIYSloI.niiV FOR PFATAI. STIOKNTS. i sl..>rt.si.rlit.-.iiirss or niy..l.ia. iin.l asti-niatisin ( Fip. ....>. //.'//'"•- »M/ro,,/a is -In. t«» 11... ...svimll 1..m>,« to.. sl....-1 s., tl.at th.- focus of tl... i.na«.- is l...iM..,l ti>,. ivlina. Tl..- .-rmr is .-om-.-t...! by pn-scribiM- .-onvx ^'lass..s. M iiopia is .In.' to tl..- opi.os.t.' von- k Vi^r "r.^.-ICn-rs in r..fn.o.u.n : K shows th. rormalion of tho ImaRe on £?'rv;;r;;;:;:;::;;rr:s:r.':r=,''v;;:rr;;":s: Uon in short-siKht, or mvo,.m, wh.-re the ..y-hall is too Ion.'. .lition, that is. th.- .-y..ball is too lonfj. so that tl..- focus occurs i„ front of it. roucav. fjlass.-s corr.-ct it. Asti;,m„tuwi is duo to tlu. lens ...• crnca bcin^r of unequal curvature ui its aiff.-n-nt VISION. 287 iiicridiiins. This causfs tlif rays of liylit in (»iic plaiir to U- hroii^lit to a t'liciis Ix-forc tliosc in otlitT planes, so thai tlii' two hands of a clock, when tlicy arc at rifilit antjlcs to cai-ii other, cannot ]>c seen distinctly at the same time, althoiifrb they can he success! v.'ly focused. A certain amount of astisrmatism exists in every eye. Itut when it becomes extreme, it is necessary to correct it by i)resci-ibin^' glasses which are astijimatic in the o|)|)osite meridian to that of the eye. Surb •.'lasses are called cylindrical. Astijjnujtism may t)ccur along with either myopia or hyper- metropia. and when any of these errors is only slight in degree, the |)atieMt may be able, by efVorts of accommodation, to over- come the defect. The strain thus thrown on the ciliary muscle is. however. i|uite connnonly the cause of severe headache. Tiie correction of the errors should never be left to untrained j)er- .sons, but a proper oculist sliouiI,i..;Y for DKNTAIi STmKNTS. The filuTs nil conv.Tj,'.' to tlic optic disc, wliicli is a little to the insi.l,' of tl... post, i-ior jmlc of tlic cvcball. At this point the fibers of the nerve fiber layer bend backwards at rifjlit angles and run into the oj.tic nerve, thus crowding out the other layers and causing the .'xisten.-e of a blind spot, which can be readily . 2.')!»). The images in the two eyes cannot of course fall on auatoniiealiy identical parts of the retina-, but they fall on parts that are physiolofrically identical. Thus, an object, say on the ri^dil of thi' Held of vision, will cause an inias.'e t() fall on the nasal siile of the rijriit retina and on the teniiioral side of the left return. We do not, however, see two objects because by ••x|>erience we have come to learn that these are rornsixnidiittf pnliils on the retina'. When an object is brou^'ht near to the eye, tiie two eyeballs nmsl converge so as to brin^'; '' ■■ visual axes on to the corresi)ondin}; points. This converjrence of the eyeballs con- stitutes the third cliaUfTe occiirriuf; in the eyes during' acconi- niodation for near vision, the other iwo beinfr, as we have seen. buljfinj,' of the lens ami contraction of the i)U|)i! It is interest- ing; that these three chanjies are controlled by the third nerve. If anything,' hapi)ens to throw one of the iniay:es on to some other i)ortion of one retina, double vision is the result. This ^ it is called stnihisinus. This condition is usually congenital, and cm often be rectified by surgical operation. Judgments of Vision.— Hesides these purely physiidogieal f ■' ■ 290 |MlYSIOl,(KiY K(.K nENTAL STIDKNTS. ,,,obhMns of vision. th.Mv an- n.any oth.-rs of a ^^yf-'r^^'^ osi.al natu.v. Sud, for .-xan.pL' are the v.sual judg.ne, ts of sL distanee, solin,o.lation necessary to obta.n sharp d.-ti .- Hon. and V•^) the an.ount of ha/.e .hich appears to surround he object. Judgment of solulU, depends on the tact that u iniges pro.luced on the two retin.e are not exactly fron. 1. sam^ point of view; they are like the two photographs of a oscopic picture. The brain on receiving these two sh^ht^v different ni-tures fuses theni into one. but judges the sol.d.t.v of tlie obiec! rom the difTerences in the two pictures. Judgments of coJor, ..r eolor vision, forn.s a subject of great complexitv. It apparently depends on tlH'.'Xistence in the re- tina of three varieties of cones, one variety for each of the thr e pnn.ary colors. The prinuu-y colors are red, green and v.ole ; ,„d bv mixing then, on the retina in equal proportions (as In rotating a dis<. or to,, on which they are pau.ted as sectors a sensation of white results; by using other proportions any ot th. other colors of the spectrum n.ay be produced When one ot these primary color receptors is absent from the retina, color MindLs exists. Thus if the red or the green receptors an absent the patient cannot distinguish b«4ween red ami green lights. Such persons cannot be employed in railway or nautic-U work. CIIAPTKH XXX. THK SI'KCIAL SKNSKS K'niitdi. Hearing. Like lipht. sound travels in waves. Imt iint r.s tniiisverse waves of the ether tliat fills space, but as l()Mf;ituI-OOY FOK DKNTAI, STinKNTF!. sl.ortor -hair- .-.•Us h-.unu^ up against tl.nn. ,.artu-ularly on th. si.l. away fnun tl,.. .-.ntral ....lun.n. The sound vvav.-s w'.jeh a.-t on tho basilar nn-n.bran.. are transnutt.-.l to the fluul whu-l h\hi\n „p,,,nnost of tl... tlnvc divisions of the .-o.-hloar lulu, (sot ^ i^ .-ii; through a n..n.l.rano coverinR an oval-slmped opc.nng ( 1 . oval window) in tl.. bony pa.titio,. s..parat.n« »'." n.t.iM.al tr m tl... n.iddl.. ,.ar. Aft.-r .-..a.-LinK tii.' ap.-x ..t th.> .•o.;l.lea tb.- p-ss thnni-h a s...all ap...-t,.r.. in tl... basilar n...n.bran.. u.t.. tl... lowst ixteinal au.lituiv m. auis . '• ><,,.et.hli.jr across it ami t...- l-:ustai'.iiai, canals; .v, cochl.a ; Vt. upper canal o. .ocl.l.a , / (. lo«i' (Kroni Howtlls I'liysiolopy.) canal, d.mn wl.i.-l. tliry tn.v..l to los.. tl..M,.s..lv.-s against tl.o num.- brane cov..ri..g a,.otl...r o,,..ni.., (tl... '-'"''! -•""'7\^'7; I'! near th.- oval win.low i.. tl.f san... partition ot bono. As tlie.v pass alont? tli..s.. .-aiials tlif waves .-aus.. tl... basilar ........bran., to inoy.- or vibrat... The vibrati,.n atT...-ts the .-..Us ..f the Organ ot (.orti. and so sets up n. .v.. impulses whieh ar.. transinitb-d to the coch- ,,,, „,,,, b, ,„eans of nerv,- fibers which connect with ea^ of the main c^'lls of the Organ. A fine membrane (called Ttc- lar n\- uss )Vt' I'ti. cb- KiK. r.T mt'Mihi'iiMt' ■iiipliiiMiiis; -KiiiKiMintiiMlic view i>f the otKMii if Cuiti ( 'I't'Stut I : /». li;isiliii .1. fi. illTK •I- ami (lUttT roils i>f I'oiti hitir iKT.in\ Huwrlls rhysidlduy. I ec- ill HEARING. 293 torial) rests on Xho tops ..f tb.- l.air .-.'Us. an.l by rul.hin« o,. th.^ ;,.,,.„ tlH.y num.. this nuMubran.. au.n.u.nts tb. a.-fon ot tb- biisibir int'inbraiic. , , , W^ nu.st now .-onsbb..- bow tb. soun.l wavos a.v b,-ou«bt f,,,„, tbe outsule to tb. oval win.low. Tb.. pn.na oftb. .a, . 1- .,s th. sound wav.s tVo„. tb. ontsbl. and .hn-.ts tb.n. u.to t . rtcrnol au.Ur '^^;-;-: 3 stretcbed b>os.l.v in an obli.,ne d.re.t.on. a.ross b. . al n. .opposed partly of Hb.rs wbi.b rad.at. to tb. .... o < „„,„ bran, froni tb. ba.ull. of tb. n.allens. a proe.ss ot on, ..f . u. itorv ossi.l.s. t.. wbieb it is atta.b.d. l'..eanse of b.s. !;;;rti.s;tb. tyn,pani. „>.n.bran.. unliU. ^y-^^'^^-y'^^, H eapabl. of vibratin^^ to a pr.at var,.ty ot not.s. and 1 ,i,„, tions .ans. tb. bandl. of tb. n.all.us to n.ov. n. an.l m l-..tw.en tb. tynM.ani. nuMobnuu. and tb. eoeld.a .s !u. n dd^^^^^ ,;„. or 1>,mi»nnn» .onsistin- of a .av.ty a.ross wlu.b stu l..s „Jon, ossirirs .onu>os.d of tbr.. sn.all bon.s. tb. nn. ..s t,,.. incus and tb. stap.s. U.sid.s tbe Ion, pro..ss or ban.ll. aln.adv des.rib.d. tb. n.all.us consists of a rounded bead s t- uat^Mfabove and forn.ins a saddl.-sbap..l arti.ulat.on w,tb tb. ,,,,, „f tbe in.us and a sbort pro..ss wbi.b runs t-n. ,us 1>^ l,nv tb. head to the ant.rb.r wall of tb. tyn.panun,. The in. u is somewhat like a bieuspbl tooth, the nudleus «'-t-^-^" "'« the crown, and bavin,' two fan,'s. a sbort one passu.. bacU. rd „„, H Ion, one vertically .lownwanls. Tb.s proe.ss, at its lo. , . ,.,Hl, suddenly bends inwar.ls to fo.-n. a ball and so.ket .on, with a stirrup-shaped bone (tbe stapes), tb. foot p..ce of wb.<-h is oval in shape and fits into tb. oval window alr.ai;nt\i. STI dknts. i hiilf tiiius Mn.ii«.-r. Til.- incivasr in fore. witl. whi.-li tli.- iiiov.-m.'iits ol' til.' tyiiii.aiii.- m.-inhraii.' aiv conv.-y.-.l to the oval win.low is still flirt Inr inamiiti.-.l l.y tl.r fact that tin- latt.-r is onlv oiu.-iw.-nti.th th.' si/.r ..f tl,.' fornnT. It is l.v tlus.- n.nvr- m.-nts at th.- ..val wiii.low that waws an- srt up m tli.- fluid ,KM-.i|.viii« th.' iipiMTiiiost in.'iiil.iaii.'ous till).- of llu- nK-lilm aii.l thus actihjr on the hasilar iii.iiil.raMr. Th.- tvii.|.aiii." cavitv or ,,sV in.us . ik- l.Uuspi.l ..-tin with ...... ,.n..v«s (<) at.a .unniiiK ,l.,wn«Mnls t.. ;iili.ul;.f at :> m.,.1 n. tli.' "■";" >;''^. 'r ,;::;;.'un:ua.:;..... .., ,„., .„..,.,...■ .k,..,.. ,..,«- i-ll's I'hysi.il.iK.v ) . tvn.panun, a.-n.ss whi.-h tl... .-hain of ossi.l.s strffhcs is k.pt at atn,osi.hfri«- l-r.-ssuiv l.y th. l-.shnlnnn /./.<. wluH, roiMH..-ts it with thf posterior iiarcs. Ihafmss m,i!i hi K oK T.wri:. 2!».') of III' w- pt rts IfS ati.l th.- li>r..i...-nts wl.i<-h hol.l th.-m ii. plan- in tli.- tvnipain.' ravitv Fl.'xihilitv of tlu- joints U\vi,vu Wu- ossw1,.h pn-vontii su.l.i;n jars at th.' oval win.low. for tl..- joint iM-tw^.n tin- mal- leus an.i incus. Wmg sa.l.ll.-.Hliap.-.l. unl.H.ks whcncv..,- ahnorn.al „r ..xn-sHivo niov.MM.-nts aiv trans.nitt.-.l to tin- u.all.'us. :{ IMockinK of tlu- Kusta.-I.ian tuU'. Tl.is is .,uit.- .-om- n.onlv a ivHult of a.l.-noi.ls or it may !«■ .in.- sin.plv f. a .atarrh of th".' tul).-. Tl..' n-sult of tl... l.i.M-l< is that tlir p.vssu.v <.n tin- tvn.pani.- cavitv tails h.-low that of th.- atmosph.-n-, iH-caus.- of absorption of oxygen into th.- hloo.l. an.l tin- ty.npan..- n..-.M- bram> bulges inwanls an.l b.-.-on..-s str.-t.-h.-.< s.. that it .-annot vibrat. iToptTlv to th.- sonn.i wav.-s. '•„.. .l.-afn.-ss ... th.s .-as.- is .-asilv .vinov.-.l by r.-op.-ninj.' tl..- Knsta.-hia.. tnlM- by l...y...tf air into it This .-a., b,- .Ion.- by atta.-l.i..^ a la.-^'.- sy....n.- In.lb to o... ..ost.-il. .-losi-.K th.. oth.-r ..ost.-il. a,..l whil.- th.- pat..-..t .s swallowinn a .....utl.ful of wat.-r. s...l.l.-..ly .•on.l.r.-ss.njt th.- b..lb. Th.. a.i.lit..rv .listivss whirl, is ..xp..ri..n<....l hy a i-.-i-s.... on «oinK i..to con.p.-.-s.s.-.l ai.- (as i.,to a .-aisson) is also .1...- t,. .lis- t„rb.n.... in th.- ty...pani.. p.vss..n-. for it tak.-s a f.w ............ s b..fo.-.- this r.'a..h..s that .... th,- ontsi.l.-. lil..wi..g tl..- ..os- UM.ally r..i..ov..s tl... K\T.M. !«TII>KNTS. on tl.rsr l.airH tlut .•.rtain .iiss.,lv,.l sul.st. s n.-t ii|> a sUmu\m of t..Ht... This stimulus is llMt. n.nvv...| l.y tine n.Tvv til.rrs whi.-l, arboriz.- arou.nl tl.. tast- .•.Us. t.. tl- .-in.r.la ty.npan. ami linjrual n.TVs in it... ai.t.imr p.M-ti..n ..f th.- t.m>ru.. an.l tin- jfl.Hso|.harvn>r..al i.. th.. ,M.st...i..r part, Tl.n.UKl. th.-s. u.-rvs tl,.. s..ns«ti«..H an- .-arri.-.l I., t Mnnl.i 1 alV..r..nt nu.-l.us ol th.. fifth an.l ninth n.-rv.'s in tli. m..iulla ol.l..nj:ata . s.-.- 1- itf. 5!)). %^tn\ttiiAV^ <\ '[^rrowni. '\\ \.',K .v.. -S,h,..na to show 111.- .•ours,- of Ih.. tMSt.- tib.TS (> .,n U.w^u,- to i„«-s o.,s,.,va.ioi,s. TlM- ftiU bla.'k H...-S nnlirat.. M.,...l..r path l.> « .1.. i„„,uls,.s n.ay .va.-l, tl..- i..aii,. . K....n H..w.ns l-hys.olosy.) Suhslancfs .-annot hv tastcl unh'ss tii.'.v arc in soluti...!. Iluis. ,|„i„i,„. pow.l.r is tastcl.'ss. On.' nf tli.' functions ..f saliva is to britif: suhstanc-s into s..lntion in nnl.'r Unit tti..y may i... tasted. Th.MV an- f.uir fumlamcntal tast.. sensations: sweet, saline, bitter ami sour ..r aei.l. The ability to .listin-uish .'aeh of th.'s.- tast.-s is not ewnly .listribut.-.i owr tlie ton^'ii.-, but oeeurs in .letiuite areas whieli can be inai-iM..! ..ut by api.lying solnlion.^, TT .^ifU TIIK SKNSK OK TAVrK. 21)7 poMMcssiiiK oiu' or otlirr of tln'Nc tiistt'S, liy mfiiiis of ii fiin- ••miifl- Imir hniHli to diffcri'iit portions of tin- tonjruc, iiftir ut f' >■ 2<»8 |'HYSl(lI. those of sn.ell as in the ease of wnies ami flavored fi; ; The n Portane,. of the sense of smell in "ta-st.n. ex- it th loss of this ability during nasal eatarrh or cold n It; Wad l" der sueh conditions an apple and an on.on may ''t:!^\ir,„s when applied to the tongue ^^^^ ^^^J^^^^ • vtr .,,...♦ ,l..ffrees Thus cocaine tirst ot all pdrai\/.■ «.„««tio„ (a,trhw...<-.v. .<•:) Wins. l.o.vv..r, unaff....,-.!. The Senae of Smell. I„ ,„„„ tl,,- s,„s,. of smoll » v,.,-.v f..l.l.- W1.-1I c-oi,.l.an.l will. .,iff,,«,t ■n.livi.ln.l.. It is. n.on.ov..,-. .v».i,l fat.g . . t^ i: r.": ;:;';,:; if a t^-ifta, i.,..*. ^v, ,nvi,.. ^. bulb. After making conmH-tions witli nerve cells here, the path THE SENSE (IP SMEIiL. 299 wav is coutiinu'd along tli." olfactory tract to tlu" hii)pof'aini>al • ri-f^'ion of the brain. As wc would oxpcct. this portion of tli.- brain is much developed in these animals having a very acute sense of smell. . The olfactory ei)ithelium is kept constantly moist with fluid and substances cam.ot be smelle.l unless the odorous particl.'s wiiich they give off become dissolved in this fluid. These odor- ous particles diffuse into the upper nares from the air curi-ents wliich, with each respiration, are passing backwards and for- wards along the lower nasal i)assages. There is no actual move- ment of air over the olfactory epithelium. Xatikk (»k Stimilcs.— It is impossible to state just exactly wliat it is that emanates from an odorous body to excite the ol- factory si'nse. All we can say is that it does not reciuirc to be present in more th«n the merest traces in the air in order to un- fold its action. Thus even in the case of man, with liis undevel- oped sense of smell, 0.000.000,000.04 of a gramme of mercaptaii. suspended in a litr." of air. can be smelled. ami in the case of the dog. the dilution may no doubt.be many thousand times greater. The sense of smell is th.' most important of the projicient sensa- tions in certain aciuatic animals, and is very closely associate•» <^^ r ':; ;;,r: ;i;;. vnis sv'st.-ni acting on another property ot nmsele. -anu-lN its •■•-r'''f/v:;:;;r;::t ■•"■r::ti :H,,!";:u.n;:;'io.. ot ,».,,. ot » t,,« ,„»,■ .,o „,„.,. ,,; .". s g .,,,,1 .,.».-lnnR o„o ,.,,,1 .0 a sui.aH.: ■ a,„„ no, . ■ f l,d a . n»olc b» olitrically .K.-it,.!, it will mor,l ,1, e.,.,- JLclTo,' L : ™,-v,. on tho smokod surface ot ,i,o papor. »...! *ow 300 TlIK, MlsriliAK SYSTF.M. 301 1. nuinbcr of iiit.'resting details as to the properties of eontraetinp imiseles. The muscle iloes not begin to contrmt at tl>e exact moment that tlie stimulus is applied. A very short latent period (.01 sec.) elapses between the stinndus and the beginning of the contrac- tion. During this time llie iiuiscle is undergoing some internal change which must precede the contraction. The period of active contraction is relatively short (.04 sec.) and the period of relax- ation somewhat longer (.05 sec). The ordinary movements ot the body cannot obviously be of the nature of a single muscular contrj' for they much exceed one-tenth of a second in dura- tion. . re in "fact produced by a prolonged contraction of inuscl. - d by the fusions of several single contractions. This is known as idank contmcilon, and it can easily be produce,! in the muscle preparation described above by giving it a seri.-s of electrical stimuli from an induction coil. If the .stimuli be properly timed, a contraction curve somewhat higher and showing no relaxation phase will be prmluced. When the ex- citation is di.scontimied. the mu.scle returns to its normal length. Tlu- amount of load which the muscle lifts has a peculiar effect. I'p to a certain point an increase in the load increas*>s the effi- ciency of the nnisde and the nmscle will actually perform more work with a moderate load than with no load at all. After a certain load is reached, the efficiency of the muscle begins to diminish and further increase of the load decreases the work accomplished by the nuisde. The principle involved here is made use of by fork and shovel manufacturers, who are careful to make their implements carry the load best suited to develop the maximal efficiency of the muscles of a normal average man. Al- lowing the laborer to chooSi> his own shovel is not always the best for the .aborer or for his employer. Another interesting fact is that a contracted muscle is more ihtitk than a relaxed nuisde. E-.-,r.,„^ with energy, so to speak, (lunn. eause tl.ey have beei.n.e deprive.! of oxygen. CHAPiKR XXXII. KKPUODICTION. TlH- most iniportin.t function of an AumnxVA lifo is the produc- tion of a new imlivi.lual which in all peculiarities of function and structure is essentially like the parent. The fundamental prob- lems of the proc'ss of repro The miflfar clfniciits of and the tVnialc c'll or ovum, to moNT an.l 1o p.-n.^trat." th.' ovum, botl. MU unit., t.. forn. a u..w nu.-l..us, wlu.-l. .s then .-apa .U ot un.l..r,.>in,r a \ou; s-.ri.-s of sub.livisi..ns. In <• han^.-s wlu.-l. p.v- ,,,1.. f..rtili/ation. tl... uu.-l..ar mat.-rial ori.Mnaliy pn-s.-nt m l.otl. „„,.. ,„., f..,nal.. -..lis is r...lu.....l. an.l wh..n ti,.; .-.lis tus... t ..■ r.- sultin- nucl..us .-.mtains a n.>rmal quantity ot uu.-l.-ar matnial. The Accessory Phenomena of Reproduction in Man. Tl... lH.-iMninu of tlu' a.-tiv.. s...xual litV in n.a.. is b.-tw-.-n th. ,...s of f..urt....n an.l sixt....n. an.l is .-all...! tlu- a,'.- .>t pub-rty i:, b..tl. bovs an.l V'irls th.. whol.. b.xly -bows a nuu.k...l .l."v..l..p- ,„.,„t at tbis tin.... Tl.e Knmtb of bai.' on tbe pub.e r.-g.ons a,..l ,,,,. pits, a...l .m tl... fa.... of b..ys. tb.- .b...p..n.n^' of tb.. n.al.. v.,b.... an.l tl... .l..v..loi.n...nt ..f tl... br..asts i,. tl..- t..n.al.. an- al ,.,,.,„pa„yin,^ plu.non...na of tl... ,b.v..l..p,......t ot P'''-'^.- ,.,.,.,ab.s tl... a... is n.ark...l by tb.. -'-V;\'''7'f '"""^'r-,: .", ...nsists of a p.-rbuli.- tlow ..f n.m-us a>..l bl.,.,.l tr.m. tb. ut... ..s Tb.. ti.>w lasts fr..... four to five .lays, a.i.l r..cu..s w.tb -r.-at r.-s,'..- la,.itv about ..v..ry f..ur w....ks. In ...al..s fu^X t'orn-.^l s..nuna tlui.l. ontainin^ liv.. sp..rm e.-lls, is s..,.r..t...l. an.l en.etu.ns ot tb. ocnis (X'.'ur. The Female Organs of Rcproduction.-Tbese ar.^ tb.^ ovari.s. ovi.lucts. ,.t..rus an.l tb.- vagina. Tl..- ovaries ar.- pair.-.l bo.l..-s Ivin,. in tl..^ low..r part of tl.e ab.lon.inal cavity am held ui p..s,- tion by the broa.l ligament. The eells from wlneb tb.. ova d.- v.-b.p are imbe.l.le.1 in the fibrous tissue of the ovary A numb., of tl .^s.. eells, better .level.>ped than their f..llows, and surn.uii.l...l bv a lav..r ..f cells, whieh f.,rm a sort of follicle, he near h.. su.- fa,., ot- tl... ova,.y. Th.... are tb.. araafion foIM.., ni wbu-h 1... ova .1..V..10P till th..y are rip... when tb..y are extru.l.-.l into th.- abdominal cavity by rupture .,f the follicle. In v..ry ^-^o- ''PI- sition to the ovari..s is a tul>e. the oviduct, whu-h lead t^> - uterus. The outer end of this tube is fimbriated, and it is t i- nished with cilia, the movements of which cause currents m the i;KI'm'l"<"'"'"^'- :'.'.)' Hauls of th..MlHlon,inar.-avity. and wl.i.-h .InvH tW ova -b - :Un..nnlu.iolli.-l.- into tin. ovi.l,u.t. T'-'l^'— -J - " s M.l or..... with ...us..ular walls, it is about ..•.., ... 1.-..'11. ' l;:;sonu.up,K.rdilat..po.1ion...alU..lt..^ ,, ,,,,, ,.o„stn.-t...l portio... .-all-.l th. <-..-v.x. M.. ••.-v.x op ..s,.u.llap..,-tu.vi..totl...va.i,.a.wl.i..l..s a ....... ~^ ,;,„„„ u) .M... lo..,' .■xt....li...' to th.. va,..,al outlet at th. . NtM,.al "■^ILe Organs of Generation a.v tl.. t..sti..l..s -s .||-1V';-- s....i..al v..si..l..s. tl..- ..'■..is, tW p.-ostat.. ,^la...l. a...l .. ,,u,..l... sL.all t;laii.ls aloi.n tl.c ...vtl.ra. , , ■ , : Unl.n- Tlu t.-sti.-l.-s ,.,>..sist of two pa.-ts. a port.o.. ot wh.-l. .s "l . ■. ,„a is .on.-... ...a in tl... .i..v..lop.......t of tl... sp-n.-ato/... a...l . : ;:: ..all.... tl... ..pi.n.lyn.is. ..ontaini... ti... 1..W... po.^^ lu- v.rv 1....^' a,..l .■o..v..l..t...l .lu-t. tl... vas .l.-t.-.v .s Fh.s 1 . on. ..^"s tl... t..sti.-l..s with tl... s,„.i..al v.-si.-l-.s. wln.-h h.- a tl. ■ r , t l>l-ia...- .....1 i.. -los.. .vlatio.. to tl... pn^stat.. .la...l. •::.. alv..si,.l..sa,-,.....it...ll.yasl..u-t.h.-tw.tlnl....u...lu.., ri;i.ristl....>utMto..tl.....x.-...t..>..s..fl...tl.tl...k..l,...ya...ltl... '■Th!''sp......,ato.oa a,... .l..v..lop...l i.. th. t..sti.-U;s a,..l Hud th..ir .a V to 1... s..n.i..al v.-sh-Ls through tl..> vas d.-t.-.-..-.^. •• tl . .,;- th..v b.ro..... iuix...l with a nu,..l...r ..f fliu.l s...-,-.;t u.ns. th. tf o whi.h an. a..riv..l f.-o... tl... s....inal v.s..l..s ot tl..- pn-s- ;.;;:, ;:n.l a,..l or tl..- .lan.is .,f Cnvp..,-. Tl... n-s,.lt,n« ....xt.u-. is th.' seminal fl.ii.l. ... , .„.., Impregnation.-Tl.. s...„inal «u,.l ...nta.n.n^ th. sp.-n. ato/oa is a^l in th.^ va.i..a .luvin, .-.>itus. Att.-a.t.-.l hy tlu- a. .1 ,.-,..tL .>f th. s......tions of th.. ut..-us or u.ul.-.. a.. ....known ...- tt n th.. sp.-r,nMozoa soo.. .-..t..- th.- ut.-rin.- -av.ty thn.... h ftl rPui,., i.lto tl... vagina. a,..l ti,..l th.-i,- way to tl... ov..l...t. wh...... th.v .-.Mnai.. waiting' f..r th.' ..vu.n to app..ar. ;^latK,n.-At a .out th.' ti,n.' of a ......st.-.w.l p..-.o. an ovu.n is .lis..ha..,.'.l fm.. . rip.n...l (J.-aatia,. UAWU- a... t-'l^ ^^ - into th.. ovi.hu't hy way of tl..' fi...b,..at...l ..xt.......ty .jt h tu . o\vM whi.h it is .0 ..lu.t...l t.. th.' ut.rus. It .s a .l.hat...l MU.s- ?^ ^ o what th. . xa.t r..latiou b.tw..... n....st..uatu,n an.l ovu- ;{06 I'I1YSI()1<«X1Y F<1R DKNTAI. STT'DENTS. lation niav l»'. Whether ovulation preeinles or follows inonstrua- tion is not known, but the w.'iRht of evidence favors the belief that menstruation serves to prepare the uterine walls for tbe reception of the fertilized ovum should one be diseharged. In animals there are periods, ealle.l the rutting period, during which imprcKuation of the ovum with the spermatozoon is pos- sible Precei>i''Ti«»N. :!()■; lit".', since tlirouali its plncfiitiil v. protliicts for tlu' (ixy^'fii iiiid iioiii-is cxcliiiiim's its fiTi'ti' liiiifiil coiitaiiu'tl in the niotlii-r's blood. Birth.— Wliil'' II"' "'^■""' is liciii}: (U'Vi'lopcd into ii iiuiimn iM'iii" bv division o1' tlu' onjrin uterus beeomes very inui ll cetl of ttie t'ertiii/e.l ovuni. tile i/e ll eiilaryiiMl. and its walls ineivase in s f niuseular tissue. .\t the end of api'i-ox"" l)y the fjrowtli o •_'S() ilavs from the date of iiiipn^'iia mient is eom l)lete and birth takes phn ately tioll of the ovum, the devel Tiiis consists in the 'xpulsion Direct f the fu'tus by musciilai- ( ontractions of the uterus. ly the child is born, the placenta begins to separate from 11 and is soon exp.-lled. The child depriv.'d of its list now be>.'in an independent life, it the uterine \va placental nourishment in mus' t take in its own oxy deduced. Tlu-re can bf no doul.t tliat attual laboratory work for ."arh siuilmt i« the Ideal to strive for in the teaching of physi- ology, but limited time allotted to the subject and the expense which Hudi a laboratory incurs prohibit the nenerai adoption of the method in most dental schools. The authors have found the followliiK experi ments to be of value in their dental classes, since tliey increas.' the in- terest of the student in the more important facts of the circulatiim. respiration, and secretion. They are given as demonstrations Ijefore small sections of the class. Tlie following outlines are not intended to give complete directions for the experiments, but to explain the various steps of the experiments to the individual students. Full laboratory directions for all the experi- ments are found in Professor G. N. Stewart's Maiiunl of l'lvisi;ln power lens of a microscope. The general charac- ters of the flow of blood through the vessels can be seen (p. 17!)). B. The Nature of the Cardiac Contraction. The brail! of a turtle is destroyed by a sharp blow on the head. The ventral portion of the carapace is removed by a saw cut along each side and bv dissecting it fron. the tissues, care being taken to avoid hemor- rhage" The heart, beating inside the pericardial sac. is seen posterior and dorsal to the pectoral arch. By tying the fore-limbs firmly above the head the pectoral girdle is pulled apart and more space is obtained for the observation of the heart. The pericardial sac is incised and the auricles and ventricle exposed. The auricles appear as two thin-walled sacs above and to each side of the ventricle If the tip of the ventricle be raised the sinus venosus is brought into vie-. It receiver t.ie supe- rior and interior vena cava, and joins the right -ricle. 309 :no |MlV>IOl,.MlY yon DKNIAI. >'n KK.NTS. At each canllac cuntraCion, .!..■ sinus is s.-.n to boa. "-•;;.?;;';*;,• „„mrdla.ely followed by th. contraction of both ^"■•'-'-, ;'';',. in followed by the ventricular contraction. It hn>n.orrhaKe has Inn. vo eXlhc heart ..ur.n« diastole is tilled with bloo.l and its chan.ber« are pink and soft, DurinK systole the chambers become pale. firm, and H uaUer In si^e. The nun.ber of hear, beats per n.lnu,. .s est,n,at.Mr • 1 R nier-s solution^ a saline solution suitable for ,he heart poured Ln the heart, is seen to slow the beat, and warmer solutions increase the r-,te Heated above 40 centlRrade the solution will stop the heart A-reco d o the auricular and ventricular beat is unuie by attachi,.. with a Pin and string, the tip of the auricle »';'', ' '"';;■ ^^Ir'^'^^' which write on the smoked paper of a revolviuK dn-e I F K, - )• A Tra ng sin,ilar to Ki«. LT. is obtained. The auricle is seen to beat before the ventricle. A .tring tied tightly about the groove separating the auricles and ventricle will stop the ventricular contraction for a time, ZcTZ it removes the control which the auricle nornu.lly e.xerts on the vehicle. After a short time the ventricle will begin to beat aga.n. but ar a slower rate and with no relation to the auricular beats (see p. 164). C. The Action of Inorganic Salts on the Heart. A turtle's heart Is prepared exactly as in B. The auricular I racing however may be ousted A sn,al. cannula, tilled -^u Unger s s U solution and attached to . perfusion bottl- by n.eans "^ "';^* ^^^^^^".^^ ,s inserted through a V-shaped incisi.m e th-r ^'^'Vith a stlk thread auricle of the heart, and is securely tied In position w th a silk thread The arge arteries leading fron. the heart are cut with a scissors to InoJ the Ulngers solution to flow out freely If. in place of K.ngers :luon one made of pure sodium chloride and disti'.ed water 0. per cent is used, the heart beat will slow down and f.naly cease It a few drops of solutions o. potassium an.l calcium chloride be added the TlT the heart will again beat normally. If after restoration ot the LaJ-asoltTo containing only sodium and potassium salts be perfused ?he heart will cease to beat in extreme .li.s.ole: if one eontain.ng oni.N di m and calcium is used, it will cease to beat in extreme systole. A. ORMONSTRATION No. 2. The Factors which Maintain the Blood Pressu.e. A small animal i. iai... ith morphine, and ^ft-^-'/'-^^^J-; comes very d.owsv. a soiut. :. of -eth^ ;- - -^ ;; ^ "^^ -'^^ finn ner kilo in 2n C C. water, ui).l.> Aelg..,I tb ill- '.lui . the stomalh tube. After the animal is co.tpletely unconscious, .t is tied ^'m AITENI'lX. 311 „„ a Hultabl. op«.rat'.nr board, and a cannula placed In th. traclu-a. Hn » adUta n. ,ho Hdn,i„lHtrati.,n ..f .-.Iut. which n.av .... nec.««ary n ,rde to "'oUHh all renexe«. A cannula 1h inm-r...! In .he caro.ld «r ..r> Tdl a.u. d to the recording apparatus an deHcrihed on p no nee vlt -.1, When all 1h ready, the drum Ih H.arted at a «low npe^d. and he r.; on^he artery renu.ved. A traclnK of the '''-'J.,^--:;;;::; « the individual hear. hea.K U made on the drum ^ '' ; ,' ^^'^^^ tlon, a small chanRe in the preH«ure Is recorded, .he ' ■• ^ ''^' ' ^, hiihe«t during the latter par, of inspiration, and fall.n, duriu. expiration. B. To Show the Effect of Varying the Pumpinfl Action of the Heart on the Blood Preeeure. The vaKUS n. rves on either side of ,he neck are found in ,he sheath Wiethe euro Id artery. A threa. ,s ,.ns -d loosely about t.oth. A shor :it'.;lrma. tracin/is made o.. . .... dru.n, -;;V;: j:;:;,;;" and a minute later the opposite one is sever^-d. This U follow ea..> a markerincrease in the blood pressure and a ..ulckenlng in the hear beat The peripheral end of the vagus on one side Is then st.mu ated M means or electrodes attached to an induction coll kIvw.k a teta. .z^ 'uK^rent The heart Is slowed or ceases to beat for a short perl.u and the blood pressure falls to zero. The heart soon beats again or the vagus is not able to Inhibit Its action for a long period of time p 000) This experiment shows that the pumping action of the hear L necessary to maintain the Mood pressure, and .l>at an in.reased rate'rthe'h^art is accompanied with an increase in blood pressure, other things remaining equal. C. TO Show the Effect of Varying the Peripheral Re.i.tance on the Blood PreMure. The stimulation of the splanchnic nerve. Tl e e t splanchnic nerve Is exposed Just above the -P-----' -^^ sule and is laid on a pair of electrodes. While taking a -"-'■•-'« simulate the nerve with a weak electrical current and the, w.t^h 8 ronger currents. A great increase in the blood pressure ,s obtaln,.d, due to h' constriction of the vessels of the viscera and the Increase 1 the resistance which they offer to ,he How of blood through ,hen, (see p. 000). D. To Show the Actual Change, m the Kidney Ves.ei. Accompanying the Stimulation of the Splanchnic Nerve. The left kld,H.v i« incased in a plethysmograph. which is co.inected with ' ibber tubing to a tambour equipped .>iti. a wrUiuB st; .f . i> 312 IMIYSlOl.udY Kn|{ 1>KNT.\1. STIDKNT!^. 1 h •'. i >^ 1, i 81 i,.crea«e or decrease in the volume of the kidney w.U «how an up and down movement of the style. The pulse tracing obtained shows tha the irstrument records even small changes in the kidney volume It the splanchnic nerve is stimulated, with the plethysmograph in place, there is a great decrease in the .ize of the kidney as shown by h fall in the writing style of the tan.bour. This is brought about b> the great vasoconstriction which accompanies the stimulation ot the nerve (see Fig. -6). DEMONSTRATION No. 3. Factors which Influence Blood Pressure. A. The Effect of Afferent Stimuli on the Respiration and the Blood Pressure. The lingual branch of the fifth nerve i. exposed on the under sur- face of the jaw. and electrodes are placed on the central end (the end towards the brain) of the divided nerve. While a normal blood pres- sure tracing is being tak.'n the nerve is excited by stimulation from an induction coil with tetanizing shocks. .\ rise in blood pressure and iueivased respiratory movements are observed with strong currents i„ most cases. This is due to the afferent stimuli alTectmg the vaso- n-otor and respiratory centers and refle.xly influencing control ot the elTerent respiratory and vascular nerves B. The Effect of Stimulation of the Central End of the Cut Vagus Nerve. The vagus on one side is cut and the central end is stimulated with stimuli of varying strength. With very weak stimuli a fall in blood pressure is usually produced. Stronger stimuli may produce a marked rise in pressure. The effect is due to a reflex stimulation or inhibition of the vagus and vasomotor centers. C. Effect of Haemorrhage on the Blood Pressure. A cannula is inserted into the femoral artery, and while a normal blood pressure tracing is being made, the artery is opened. It will he found that when the artery is fully opened, there is an immediate lall in blood pressure, due to lessening of the peripheral resistance. It the artery is onlv partially opened, considerable bleeding may occur before the blood pressure is affected. The explanation for this lies in the vasomotor center being stimulated by lack of blood and causing a generally increasing vasoconstriction over the body. D. The Effect of Gravity on the Circulation. Through two staples on the under surface of the dog board and op- AITKNDIX. ■m:\ posite tlir insertion of tlie carotid cannii la is passed an iron rod. and by ■d to two stout retort stands, means ui v inmi/a n.> >..-■■ " A short piece of normal blood pressure tracing is taken on the drum and then at a Riven moment the dog is placed in a vertical feel-down position, by rotating the board (the dog must be carefully tied on the board) The blood pressure falls, but shows some tendency to return to normal while the dog is still upright. If the animal be very d.^eply under an an.>sthetic there will be a very marked fall in blood pressure with no tendency of the blood pressure to return, since the va.somotor nerves and center ure no longer able to compensate for the hydrostatic effect of the blood in the vertical position (see p. VX>,). E. The Effect of Asphyxia on the Blood Pressure (see p. l:t,^,). \ respiratorv tambour is applied over the thorax or abdomen and connected bv tubing with a recording tambour, the writing point of which is accuratelv adjusted so as to write in the same vertical line as the writing point of the mercury manometer The tubing conunL' iron, the cannula is clamped and the effect of liie resulting asphyxia on the respiratory movements and on the arterial pressure is noted. The three stages, as described on p. (HKI. should be obtain.'d. but wli. n the third stage is reached the clamp must be removed from the tiaclieu so IS to allovs- the animal to recover. Note— 1, the slowing of th<' heart; 2. the gradual, often insigiiilica.ii, ris.> in blood pressure: :!. the elTect of the respiratory movements on the blood pressure. Moth vagus nerv.^s are cut and the above experi ment repeated, noting the difference in results. The rise in blood pressure is very gieat. since now the heart is no longer slowed by the vi-nis stimulation brought by the excess of the carbon dioxide in the blood. DEMONSTRATION No. 4. The Mechanism of Glandular Secretion. A. Salivary Secretion. The animal is anesthetized and prepared as in demonstralion No 1 \n incision is ma.le along the internal border of the .jaw Ixme. The internal border of the digastric muscle is thus exposed. This is pulled aside bv a hook so as to expose the transverse tibers of the mylohyoid muscles. The mvlohyoid is carefully severed following the li .1 the digastric muscle. The edges are pulled to one side and the lingual nerve is s.'en emerging from under the ramus of the jaw. In its trans- versa, course to the middle of the jaw. i( crosses the ducts of th.' sub- maxillarv and sublingual glands. Where it crosses the ducts it giv.-s off a small branch, the chorda tympani. A ligature is placed beneath pnYSKJLOOy FOR DENTAL STrDENTS. ' ! ■ ■I .\ i ! i ;ii4 the .lnB«.l nerve 1. divided cen.r.l lo "= "j""". JJrt/,™„„, „ cannula is Inserted into exposed a little behind the ::r r j»rrier„rf ^e . .e d,.uo„ . ^^^^^^^^^^^^ vesBels. showing the presence of vasodilator nerves in 'TfTe' cannula in the duct be attached to a mercury -an°"eter con- It saliv^is not filtered from the blood into the salivary tubules. B Action of Secretin on Pancreatic Secretion (see p. 72). rn7rer;rrinir":n:,:/:o*rnea.e, .^d .... .. ... ^r~ittnr:r''nirrjr.^i':n-:"^^^ ^kr%SLr,.!rrd:;=;"rc.r9^^^ no^nt where the head of the pancrea. ieaves the duodenum. A iga- tue is plced under it and the duodenum is opened by an incision along ts free border. The cannula is then inserted through the open- Cof he duct in the duodenum, this opening being marked oy a papilla. It is then tied in place by means of the previously applied "Thrdrops of the secretion, if any, are counted. 20 c. c. of the secretin isTnjecteT nto .he femoral vein. The effect is to produce an increase n the secretion. Also the effect of the injection on the respirations and the Jl pressure and pulse should be noted. The Injections, using larger amounts if necessary, are repeated. n INDEX. Abducens or sixth nerve. 261 Aberration, cliromatlc, 285 spherical. 285 Abborption, 80 Accelerator nerves of heart, 181 Accommodation. 281 mechanism, 283 pupil in, 284 Acidity, :!0 of gastric juice, 64 of saliva, 48 Acromegaly, 131 Addison's disease and adrenals. 129 Aorenalin. 130 Adrenals (suprarenal capsules). 12!t .Xdsorption. 33 .M'terent nerve paths, 245 Albumin, 22 Albuminuria. 232 Amino bodies. 22 .\nioeba. 18 Animonla, 108 in urine. 230 Amlopsln, 74 Apesthesla. 245 Analgesia. 245 .Anaphylaxis. 151 Animal heat. 134 .Antibodies In blood. 148 Antlenzymes, 36. 77 .Antipyretics, 138 Antithrombin, 148 Antitoxin. 130 Apex beat of heart. 162 Aphasia. 273 Appetite. 43, 60 .Arterial blood pressure, 173 .Asphyxia 195 Assimilation (s.f Metabolism) As-,sociation areas of cerebrum, 272 fibers of cerebrum, 272 .Associative memory, 273 Asthma. 222 Astigmatism, 286 .Atmosphere and metabolism, 88 Auditory areas of cerebrum, 272 .Auditory ossicles, 293 Angmentor nerves of heart, 184 Auricle. 167 Aurlculo-ventrlcular valves. 1!J9 Auscultation of lungs. 213 Autonomic nervous system. 277 Bacterial digestion, 66. 76 Beat of heart. 161 Beef 'ea, 107 Beriberi, 121 Bile, 71 Binocular vision. 28',< Bladder, urinary, 23,''< Bind spot. 288 Blood. 140 coagulation of. 147 functions of. 140 gases of. 201 microscopic characters of. 140 physical properties of, 140 plates. 145 plasma. 145 Blood corpuscles. 140 enumeration of, 141 s.Airce of. 143 Blood flow, rate of, 179 Blood pressure, 173 Uicod vessels, nervous control ot 189 Bodv fat. source of. 115 Bvain. 256 Bread. 105 Breathing, mechanism of. 209 Bright's disease. 232 Bundle of His, 165 Butter, 106 Calcium, 120 Calcium salts and coagulation ot blood, 148 Calorimeter. 85 Calory. 84 Capacity of lungs. 216 Carbohydrates, 24 food values of. 84 metabolism of, in6 relative metabolic importaii'e. 113 Carbon dioxide; effect of oxyhcemoglobin. 2ii2- 206 mechanism of exchange. 205 production of. 197 Cardiac cycle, events of, 167 Cardiac muscle. 163 Cardiac depressor nerve. 187 Centers, vascular-nervous, 187 315 \i\i\ INDKX. in modifying re- •>Vi 71 nitrous . iratory ('(•lebelluni. 274 rt'reals, 105 t'erebruni. 268 function of. flexes. 270 localization in. 26;t relation to recept_or system, siensory areas. 272 Cheese. 106 Chemical composition ot body.i.i Chemistry, of bile, 7:J of foods, 104 of gastric juice, 64 of pancreatic juice, of saliva, 46 of urine, 22fl Childbirth, 307 Cholesterol, 24 Chor'lae tendinese. 163 Chyme, 68 Ciliary muscle, 283 Circulation. 180 diagram of. 159 influence of arteries, i'-: ''' cocain. 196; of gravity. I'.tl; of haemorrhage. I!t4; of ner- vous svstem. 184; of oxide, 1!»5; ot rei. movements. 183 pulmonary, 182 renal. 233 time of. 17i> venous, 178 circulatorv system, anatomy Circumvallate papilla?. 2'.t5 Clothing, 136 ,_ Climate, effect of temperature. l..( Coagulation of blood. 147. 148 Cocain. 196 Colloids. 32 Coinplemental air. 216 Condiments. 107 Cones of retina. 287 Consciousness. 268 Consonants. 227 Contraction of muscle. 300 tetanic contraction. 301 Coordination, function of cerc- belhnn. 274 Cord, spinal. 245 Cords, vocal. ';25 Cornea. 282 Corpora quadrigemina. 2;i( Corpuscles of blood. 141 Corti. organ of. 291 ( oughing. 214 Cranial nerves. 2.59 Creatinin. 230 15it 174 Cretinism. 126 Cream, lob Crying. 214 Crystalloids, 27 Cystine, 112 Deglutition. 55 Dentrite. 241 Determination of blood pressure, 174 Diabetes, 117 Dialysis. 27 ,ui„ , Diaphragm, relation to breathuu. 210 Diastole of heart, 167 Diastolic blood pressure. Dietetics, 99 Diet, suitability of. Wl fundamentals of, lo3 Digestion: hacterialiutestine, of cellulose, 76 necessity of, 37^ in intestine. 71-75 in mouth. 39^ in stomach. 60 object of, 37 resume of digestive terments, 82 Direct pyramidal tract, 248 Disaccharides, 24 Ductless glands. 124 Dyspnea. 221 76 Kfferent nerve paths. 250 b-'ggs. 106 Klectrolyles. 28 _ Knamel. action of saliva on. .;>l Energy balance (,s.< Metabolism) Enterokinase, 74 Enzymes. 34 Erepsin, 75 Erythrocytes. 141 Eustachian tube, .'M , E.xcreta, endogenous and exogen- ous. 112 Excretion, from lui.gs. 2iiti renal 229 Exercist. muscular, and metabol- ism. 114 Exogenous excreta. 112 Expiration, 209 Expired air. composition ot, -IS Eye (.S(i' Vision) Fat. chemical con.position of. 2'! food value of, 84 of body, source of. 115 structure of. 24 ll 11 INDKX. 317 rflative nii'labolic import ance of. 11 H metabolism of. 11" Ferments. 34 Fertilization. 303 Fetus, nutrition of. 306 Fever. 137 Fibrin, source of. 1-17 Fibrinogen. 147 Flavor. 307 Foods, common composition ol. 104 Fovea centralis. 288 Gall bladder, 71 stones. 74 Ganglia. 241 spinal. 242. 277 sympathetic. 242. 277 Ganglion, definition o.. 241 Gasserian. 261 semilunar, 191, 278 Gas. absorption of. by liquid. VM\ partial pressure of. IW Gases of blood. 201 Gas exchanges, in lungs. 217 in tissues, It'S Gasserian ganglion. 261 Gastric digestion, Gi Gastric juice, constituents of. "^ Gastric secretion, control of. tU Giantism. 131 Glands, ductless. 124 gastric. 60 mammary, 238 pancreatic, 71 salivary. 39 sebaceous. 238 of skin. 336 sweat. 236 thyroid. 125 Globulin. 23 Glomerulus. 232 Glottis, 225 Gluten, 104 Glycogen. 116 Glycoprotein. 23 Glycosuria. 116 Goiter. 128 Graafian follicle, 304 Growth, curve of. 07 Hair-cells of cochlea. 242 Hoptophore group. 150 Hearing, 292 Heart, anatomy of. 160 BUgmentor nerves of. 184 heart block, 165 cavities of. 16tl change in form of, 161 contractions, nviximal. 163 influence of salts on. 166 Inhibitory center of. 187 inhibitory nerves of. 18". nerves of. 184 passage of beat o\er. 164 pace-maker of. 164 physiological peculiarities ot, 163 position of, 160 refractory period of. 160 rhythmic action of. 163 sounds of. 169 valves of. 162 vascular mechanism of. 166 work of. 172 Heart valves. 16J Heat, animal, souices of. 134 value of foodstuffs, 85 Hematin. 141 Hemorrhage. 194 Hemoglobin. 141 absorption of oxygen by. 201 chemical nature of, 141 estimation of. 141 influence of acid. 2ii2 of carbon dioxide, 202 Hiccough, 214 Hippuric acid, 112 Hormones, 38. 124 Hunger, 81 Hydrogen i( . 30 measurement of. 31 Hydrogen electrode, 31 Hydrochloric acid in gastric juice, 64 Hyperglyciemia, 116 Hypothyroidism. 128 Hyperthyroidism. 128 Immunity, Ehrlich's theory of. l.'>o specific nature of, 151 Immunization, 151 Impregnation. 3it5 Infection-resisting mechanism. 15o Infiammation. 149 Inhibitory nerves of heart. 185 Inorganic salts, metabolism. 119 Inspiration. 209 Internal capsule, 248 Internal secretion, 125 Intestinal digestion, 75 Intestinal juice, 75 Intestine, large, movements of. 79 Intestine, small, movements of. 78 Ions, 28 318 INDEX. |5!^ ■ \} i - Ionization, 28 Iron, 120 KataboUc processes, 84 Kephalln. 148 Kidney, blood flow through, 2S.^ blood supply of. 233 minute structure of, z.ii nerve of, 333 Knee jerk, 251 Lactation. 238 lACteals, 155 Lecithin, 24 Lena, crystalline. 283 Leucocytes, movements of. 144 funetlcri of, 145 Lipase, in gastric juice. 67 in pancreatic juice, 74 Lipoids. 23 Liver, excretory function ot. 7m glycogenetic function of, 117 Localizing power of retina. 289 Locomotor ataxia, 254 Lungs, changes of blood in. 21 1 movements of, 213 Lymph, movements of, 157 formation of, 156 glands, 158 relation of, to blood, 15a resorption of. 157 vessels, 157 Lymphagogues, 156 Lymphocytes, 144 Lymph nodes, 158 Maintenance food. 99 Malpighian capsule. 232 Malpighlan pyramids of kidney, 232 Mammary gland, 238 Mastication, 53 saliva and, 54 Material balance of body^ 91 Measurement of arterial pressure, 175 Meat, 106 extract, 107 Menstruation, 304 Mental process, 273 Metabolism, general, 83 Influence of atmosphere, 87 muscular work. 87 surface area, 87 basal neat production, 87 specific dynamic action, 87 Metabolism, special, 108 carbohydrates, 116 fats, iir> Inorganic salts, 119 proteins. 108 Middle ear, 292 Milk, composition of, in.) Micturition. 236. Monosaccharides. 24 Motor area of cortex, 269 Mountain sickness, 222^ Mouth, .ligestion in. 4. Muscles. 300 Muscle sense, 275 Muscular elasticity, 301 Muscular energy, source of. l.t.t Muscular tone. 253 Muscular work, expenditure or energy, 99 Myopia. 286 Myxoedema, 127 Nausea, 58 Nerve: abducens, 261 auditory, 264 cranial. 259 depressor. 187 facial. 263 glossopharyngeal, 264 hypoglossal, 266 inferior maxillary, 2»>1 oculomotor, 260 olfactory, 298 phrenic, 219 sciatic, 219 spinal accessory, 265 trlgenlnal, 261 vagus, 265 Nerve Impulse, 239 Nerve paths, afferent. 246 efferent, 250 method of tracing, 245 Nerve plexus, 240 Nerve system, 239 sympathetic, 277 Neurones, intermediary, 247 Nitrogen equilibrium, 94 balance sheet, 94 Nucleoprotein, 22 Nutrition (sri- Metabolism) Nutrition of embryo, 306 Nutritive value of foods, v^i Obesity, treatment of, 95 Oculomotor nerve, 260 Opsonins, 163 Optical defects. 285 Optic thalami. 247 Organ of Corti, 291 Osmosis, 28 INDF.X. :n9 Osmotic pressure. 28 Oviduct, 304 Ovulation. 305 Ovum. 304 Oxidase. 1»S Oxidation. In tissues. 198 as source of animal heat. IM Oxygen, absorption of, by blood. 201 Oxy haemoglobin, effect of CO on, 205 Pain, 245 Pancreatic juL . 71 composition of. 74 Pancreatic secretin. 72 Pancreatic secretion, control of. 71 Paralysis. 255 Parathyroids, 125 Pepsin. 64 Pepsinogen. 64 Peptone, 21 Peristalsis, 79 Perspiration. 237 Phagocytosis. 152 Physico-chemical laws. 26 Physiological division of labor. 18 Physiological properties. 18 Physiological systems. 19 Pituitary body. 131 Platelets, or plaques, of blood, H.'i Plasma, blood. 145 Pneumogastric nerves. 26.') Polypeptide. 22 Pons Varolii. 246 Postsphygmlc period, 167 Potassium sulphocyanide in sa- liva, 47 Precipitins. 151 Pregnancy. 306 Presbyopia. 286 Pressure, arterial. 175 Intrathoracic, 211 osmotic. 28 Fresphygmic period, 167 Properties of body, physical and physiological, 20 Proteins, chemical composition of, 21 compound, 22 Insoluble, 23 irreducible minimum, 96 nutritive value of, 94 relative metabolic importance of, 113 requirement of body for, 100 simple, 22 sparers of, 95 subdivisions of Proteose, 21 Protoplasm, composition of. 19 primary constituents of. 19 secondary constituents of. 20 Ptyalin. 47 Puberty. 304 Pulmonary circulation, 182 Pulse, use of. in diagnosis. 18" tracings, 180 wave. 121 Purin bodies. 110 Pyloric sphincter, control of. 68 Pylorus. 67 Pyramidal tracts. 248 Range of voice. 226 Rate of olood flow. 179 Reaction of blood. 32 of body fluids. 30 Reason, faculty of, 273 Reciprocal Inhibition, 254 Receptors, 151, 244 Red blood corpuscles, 141 Reflex animal, characteristics of. compared with normal. 251 Reflex arcs. 240 Reflex action. 252 Reflex paths, 244 Reflex time, 250 Reflexes, function of spinal cord in, 2i'.0 types of, 25(t Renal secretion. 232 Reproduction, sexual. 303 Reproduetory organs, accessory : female. 304 male. 305 Residual air, 216 Respiration. 197 artificial. 214 control of. 221 external. 207 Influence of. on circulation. 213 internal. 197 nerves of. 219 volume of air in. 225 Respiratory center. 219 exchange, 204 movements, 211 organs, 207 quotient. 91. 216 reflex. 219 sounds. 213 Rickets, 120 Rolando, fissure of. 269 Roots of spinal nerves, 246 :V2() INDKX. 71 Saltva, character or. 46 dental caries and. r>l function of. 44 neutralizing power of. 4.t reaction of. 48 tartar formation and, ;>! Salivary calculi. VI Salivary fslands, ;?!• nerve supply of. 40 nervous control of. \'i- secretion of :!!• Scratch reflex. 2.">1 Salt hunger. 120 _ Sea sickness, 2?" Sebaceous glands. 2.'>8 Secretin, gastric. 6;! pancreatic. 71 Secretion: control of, 38 gastric, control ol. ''1 milk. 2;i8 pancreatic, control ot, salivary, control of. 41 sebaceous. 2.38 Secretory process: hormone control of. 38 nervous control of. 38 __ Semicircular canals, bony. -••• Semilunar ganglion, li'l Semilunar \alves. l»>t>. lt>. _ Semipermeable membrane... i Sensory areas of cortex. -M Shivering. 138 Shock. I!t3 Sight. 279 Skin, function of. 236 Smell. 2!>7 Sneezing. 214 Solutions, isotonic. 30 hvpertonic, 30 hypotonic. 30 Sound, loudness of. li.^ Sounds of heart. 169 Special senses. 279 Specific dynamic action of foods. 87 Tartar. .52 Taste. 296 Taste-buds, 296 Tectorial membrane, 29- Teeth and fifth nerve. 261 Temperature of body. 134 lemperature. effect of, on mus cular contraction. 13!> Temperature sensation zero, 1.4.-> Temperature sense, 245 of. Temperature of. 135 Tetany. 128 Thorax, contents movements of. i 211 Thrombin, 148 Thrombogen, 148 Thymus, 133 Thyroid gland, 12i. Tidal air. 215 Touch, sensations Toxins, bacterial. Toxophores 150 Trigeminal nerve. Trypsin. 74 Trypsinogen, 74 bodily, regulation 207 respiration. of, 244 149 261 190 Urea. 108. 230 Uric acid. 110. 230 Urinary organs. 23- Urinary salts, nitrogen. 108 I'rine, ammonia, 108 excretion of. 229 nature of excretory process, 2.... Vasus nerve, action of. on heart. Valves' of heart. 162, 170 Varicose veins. 179 Vasoconstrictor nerves. Vasodilator center, 18 1 Vasodilator nerves. 191 Vasomotor tone, 194 Veins, blood in. 178 _ Velocity of blood. 1 1 i \entilation. 223 Vision. 279 color. 290 stereoscopic. 290 Visual defects. 284_ treatment of. 285 Vital capacity. 216 Vitamines. 121 Vocal cords, false. 224 relation of. to pitch. 2... Voice. 224 Vomiting. 58 Vowels. 227 Water, proportion of. in body, phvsiolngical properties ol. Wheat fl<.'ir, 104 White blood-corpuscles, 144 20 20 Xanthin bodies, lio Yawning, 214 2tt 20 em