IKEtEY 
 
 tfBRARY 
 
 UNIVERSITY OF 
 
 CALIFORNIA 
 
 BIOLOGY 
 LIBRARY 
 
THE LIBRARY OF MEDICINE, 
 
 COMPRISING A SERIES OF 
 
 ORIGINAL DISSERTATIONS, 
 
 ARRANGED AND EDITED BY 
 
 ALEXANDER TWEEDIE, M.D. F.R.S., &c. 
 
 DISSERTATIONS ON PRACTICAL MEDICINE, 
 
 BY DOCTORS ALISON BENNETT G. BUDD W. BUDD BURROWS CHRTSTISON CARPENTER 
 
 FERGUSON GREGORY HOPE JOY LOCOCK PRICHARD ROWLAND SCHEDEL 
 
 SHAPTER SYMONDS TAYLOR THEO. THOMPSON W. THOMSON WATSON WILLIAMS. 
 
 In Five Volumes, post 8vo, price 10s. 6rf. each, cloth. 
 
 CONTENfS OF VOLUME I. 
 
 Introduction Inflammation Fevers Continued Fever Plague Intermittent Fever 
 Remittent Fever Hectic Fever Yellow Fever Infantile Gastric Remittent Fever Small 
 Pox Measles Scarlatina Puerperal Fevers Diseases of the Skin. 
 
 CONTENTS OF VOLUME II. 
 
 Diseases of the Nervous System Inflammation of the Brain Hydrocephalus Apoplexy 
 Insanity Delirium Tremens Cephalalgia Epilepsy Catalepsy and Allied Affections 
 Spinal Irritation Spinal Meningitis Myelitis Hvdrorachis -Spinal Apoplexy Chorea 
 Hysteria Tetanus Hydrophobia Neuralgia Paralysis Barbiers Inflammation of the Eye 
 Amaurosis Inflammation of the Ear. 
 
 CONTENTS OF VOLUME III. 
 
 Diseases of the Organs of Respiration Laryngitis Tracheitis Laryngismus Stridulus 
 Nervous Affections of the Larynx in the Adult Acute Catarrh Bronchitis Bronchorrhoea 
 Bronchial Congestion Spasmodic Asthma Hooping Cough Structural Lesions of the Air- 
 Tubes Pleurisy Pneumothorax Pleurodynia Pneumonia Pulmonary OEdema Emphy- 
 sema Consumption Malignant Growths in the Lungs Diseases of the Bronchial Glands 
 Influenza Asphyxia Diseases of the Heart Nervous Palpitation Syncope Angina Pectoris 
 -Neuralgia of the Heart Pericarditis Endocarditis Carditis Hypertrophy of the Heart 
 
 f ditto Atrophy of ditto Changes in the Consistence of 
 
 ditto Rupture of ditto Polypous Concretions of ditto Hydropericardium Secondary Effu- 
 sions into the Pericardium Pneumo Pericardium Displacement of the Heart Hernia of 
 
 Dilatation of ditto Real Aneurism o 
 ditto Rupture of ditto Poly 
 
 sions into the Pericardium 
 
 ditto Malformations of ditto. 
 
 CONTENTS OF VOLUME IV. 
 
 Diseases of the Arteries Stomatitis Gangrsena Oris Diseases incident to the Process of 
 Dentition Glossitis Parotitis Angina Diseases of the OZsophagus Gastritis Organic 
 Diseases of the Stomach Dyspepsia Gastralgia Gastrorrhcea Inflammation of the Duodenum 
 Ileo-Colitis Dysentery Inflammation of the Caecum Diarrhoea Cholera Haemorrhois 
 spasmodic Stricture of the Rectum Colic Lead Colic Torpor of the Colon Tympanites 
 D eritonitis Diseases of the Mesenteric Glands Diseases of the Biliary Organs Inflammation 
 f the Liver Diseases of the Pancreas Diseases of the Spleen Calculous Diseases Diabetes 
 -Suppression of Urine Hypertrophy of the Kidneys Inflammation of ditto Glandular 
 Disease of ditto Diseases of the Bladder and Urethra Diseases of the Uterus and Ovaria. 
 
 CONTENTS OF VOLUME V. 
 
 Haemorrhage Epistaxis Haemoptysis Hsematemesis Haemorrhage from the Intestines 
 
 Isematuria Haemorrhage from the Uterus Scurvy Dropsy Cerebral Dropsy Thoracic 
 
 Oropsy Abdominal Dropsy Scrofula Bronchocele Rheumatism Gout Worms 
 
 formulary Index. 
 
 A SYSTEM OF MIDWIFERY. 
 
 By EDWARD RIGBY, M.D., Physician to the General Lying-in Hospital, Lecturer on Mid- 
 rifery at St. Bartholomew's Hospital, &c. In one vol. post 8vo, 10s. 6rf., cloth, forming 
 Volume VI. of the LIBRARY. 
 
 DESCRIPTIVE ANATOMY. 
 
 By J. CRUVKILHIER, Professor of Anatomy to the Faculty of Medicine of Paris, &c. 
 Translated by Dr. W. H. MADDEN, and Revised by Dr. SHARPEY, Professor of Anatomy 
 and Physiology in University College. In two vols., containing 123'2 closely printed pages, and 
 upwards of 3*00 Illustrations, with a copious Index, &c. Post 8vo, price 18s. each, cloth, 
 forming Volumes VII. and VIII. of the LIBRARY. 
 
 WHITTAKER AND CO., AVE MARIA LANE, 
 
 AND TO BE HAD, BY ORDER, OF ANY BOOKSELLER. 
 
BESEARCHES 
 
 MOTION OF THE JUICES 
 
 IX 
 
 THE ANIMAL BODY. 
 
RESEARCHES 
 
 MOTION OF THE JUICES 
 
 THE ANIMAL BODY. 
 
 BY 
 
 JUSTUS LIEBIG, M.D., 
 
 PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF GIESSEN. 
 
 EDITED FROM THE MANUSCRIPT OF THE AUTHOR, 
 BY 
 
 WILLIAM GREGORY, M.D., 
 
 PROFFSSOR OF CHEMISTRY IN THE UNIVERSITY OF EDINBURGH. 
 
 LONDON: 
 PRINTED FOR TAYLOR AND WALTON, 
 
 UPPER GOWER STREET. 
 
 1848. 
 
Printed by J. & H. COX (Brothers), 74 & 75, Great Queen Street, 
 Lincoln's- Inn Fields. 
 
EDITOR'S PREFACE. 
 
 IN the Editor's Preface to Baron Liebig's " Re- 
 searches on the Chemistry of Food," in which the 
 Author gave the results of his investigation into the 
 constituents of the juice of the flesh, I mentioned 
 that Baron Liebig had been led to study the subject 
 of Endosmosis experimentally. The results of this 
 investigation are contained in the following pages ; 
 and the reader will, I trust, be satisfied that the 
 motions of the animal juices depend on something 
 more than mere Endosmosis or Exosmosis, and that 
 the pressure of the atmosphere, as well as its hygro- 
 metric state, by influencing the transpiration from 
 the skin and lungs, are essentially concerned in pro- 
 ducing these motions. At the same time, the pre- 
 sent work is to be regarded, not as exhausting the 
 subject, but, on the contrary, as only pointing out 
 the direction in which inquiry is likely to lead to 
 the most valuable results. 
 
 While it is proved that the mechanical causes of 
 pressure and evaporation, and the chemical com- 
 
 253 
 
vi EDITOR'S PREFACE. 
 
 position of the fluids and membranes, have a more 
 direct, constant, and essential influence on the mo- 
 tion of the animal fluids, and, consequently, on the 
 state of the health, than has been usually supposed, 
 it is evident that very much remains to be done in 
 tracing that influence under the ever varying cir- 
 cumstances of the animal body, and in applying the 
 knowledge thus acquired to the purposes of hygiene 
 and therapeutics. But it is equally obvious, that 
 the above-mentioned mechanical and chemical 
 causes are not alone sufficient to explain the phe- 
 nomena of animal life, since they are present equally 
 in a dead and in a living body ; so that while every 
 advance in physiology enables us to explain more 
 facts on chemical and mechanical principles, some- 
 thing always remains, which, for the present, is 
 beyond our reach, and which may for ever remain 
 so. However this may be, the facts established in 
 this and in the preceding work of the Author have 
 very materially extended the application of the well- 
 known laws of physics and of chemistry to phy- 
 siology, and have also furnished a number of the 
 most beautiful instances of that infinitely wise, but 
 exquisitely simple adaptation of means to ends, 
 which characterizes all the works of the omnipotent 
 Creator ; but which is nowhere more admirably dis- 
 
EDITORS PREFACE. VI 1 
 
 played, than in the arrangements, imperfectly known 
 as they hitherto are, by which life is maintained. 
 
 In connection with the Author's remarks on the 
 effects of evaporation in plants, and the conse- 
 quences of its suppression, and with his opinions as 
 to the origin of the potato disease, I beg to refer the 
 reader to the Appendix for a very ingenious and ap- 
 parently well-founded plan for the protection of the 
 potato-plant against the terrible scourge under which 
 it has lately suffered. The views of Dr. Klotzsch, 
 the author of this plan, as to the nature of the 
 disease, coincide remarkably with those of Baron 
 Liebig, as explained in the present work. 
 
 WILLIAM GREGORY. 
 
 EDINBURGH, 3rd March, 1848. 
 
PREFACE. 
 
 THE present little work contains a series of ex- 
 periments, the object of which is to ascertain the 
 law according to which the mixture of two liquids, 
 separated by a membrane, takes place. The reader 
 will, I trust, perceive in these researches an effort 
 to attain, experimentally, to a more exact expression 
 of the conditions under which the apparatus of the 
 circulation acquires all the properties of an apparatus 
 of absorption. 
 
 In the course of this investigation, the more inti- 
 mate study of the phenomena of Endosmosis im- 
 pressed on me the conviction that, in the organism 
 of many classes of animals, causes of the motion of 
 the juices were in operation, far more powerful than 
 that to which the name of Endosmosis has been 
 given. 
 
 The passage of the digested food through the 
 membranes of the intestinal canal, and its entrance 
 into the blood ; the passage of the nutrient fluid 
 outwards from the blood-vessels, and its motion 
 
X PREFACE. 
 
 towards the parts where its constituents acquire 
 vital properties, these two fundamental pheno- 
 mena of organic life cannot be explained by a 
 simple law of mixture. 
 
 The Experiments described in the following pages 
 will, perhaps, be found to justify the conviction that 
 these organic movements depend on the transpira- 
 tion and on the atmospheric pressure. 
 
 The importance of the transpiration for the 
 normal vital process has indeed been acknowledged 
 by physicians ever since Medicine had an existence ; 
 but the law of the dependance of the state of health 
 on the quality of the atmosphere, on its barometric 
 pressure, and its hygrometric condition, has been 
 hitherto but little investigated. 
 
 By the researches contained in my examination 
 of the constituents of the juice of flesh, as well as 
 by those described in the present work, the com- 
 pletion of the second part of my Animal Chemistry 
 has been delayed ; but I did not consider myself 
 justified in continuing that work until I had ex- 
 amined the questions suggested by, and connected 
 with, those researches. 
 
 DR. JUSTUS LIEBIG. 
 
 GIESSEN, February , 1848. 
 
CONTENTS. 
 
 ON the phenomena accompanying the mixture of two 
 
 liquid^ separated by a membrane Page 1 
 
 Relation of porous bodies to water and other liquids ... 2 
 The moistening of porous bodies depends on capillary at- 
 traction ... ... ... ... ... ... ... 4 
 
 Pressure required to cause liquids to pass through mem- 
 branes ... ... ... ... ... ... ... 6 
 
 The pressure varies with different liquids ... ... ... 7 
 
 The absorbent power of the membrane has a share in the 
 
 effect 8 
 
 Action of brine, oil, alcohol, &c., on moist membranes ... 10 
 Cause of the shrivelling of membranes when strewed with 
 
 salt 12 
 
 Animal tissues are permeable to all liquids ... ... 15 
 
 Saline solutions, alcohol, &c., mix with water through 
 
 membranes ... ... ... ... ... ... 16 
 
 Change of volume when two dissimilar liquids mix through 
 
 a membrane ; Endosmosis ... ... ... ... 17 
 
 This change of volume does not depend alone on the dif- 
 ferent densities ... ... ... ... ... ... 18 
 
 Phenomena of the mixture of two liquids through a mem- 
 brane 20 
 
 The mixture is the result of chemical attraction . . . ' ... 25 
 
 Chemical attraction is everywhere active ... ... ... 27 
 
 Examples. Crystallization ... ... ... ... 28 
 
 Action of solids on dissolved matters ... ... ... 30 
 
 Laws of the mixture of two dissimilar liquids ... ... 33 
 
 Effect of the interposition of a membrane ... ... 38 
 
Xll CONTENTS. 
 
 The change of volume in two liquids which mix through a 
 membrane is the result of chemical affinity modifying 
 
 capillary attraction ... ... ... ... ... 40 
 
 Effect of evaporation on liquids confined by membranes ... 42 
 
 Views of MAGNUS on Endosmosis... ... ... ... 43 
 
 Remarks on his theory ... ... ... ... ... 44 
 
 The nature of the membrane has an important influence... 47 
 
 Unequal attraction of membranes for different liquids ... 48 
 The action of two liquids, separated by a membrane, is 
 
 equivalent to pressure, unequal on opposite sides '. . . 51 
 Causes which influence the mixture of two liquids se- 
 parated by a membrane ... ... ... ... ... 57 
 
 These causes produce, in the animal body, absorption of 
 
 the fluids of the intestines into the blood 59 
 
 Effects of drinking water and saline solutions of different 
 
 strengths 60 
 
 Influence of the cutaneous evaporation on the motion of 
 
 the animal j uices ... ... ... ... ... ... 64 
 
 Experiments ... ... ... ... ... ... 65 
 
 Influence of the atmospheric pressure ... ... ... 68 
 
 Water passes through membranes more easily than air does 70 
 
 Experiments on evaporation through membranes ... ... 71 
 
 Importance of the cutaneous transpiration... ... ... 73 
 
 By it the fluids acquire a motion towards the skin and 
 
 lungs 74 
 
 Effects of dry and moist air and of elevation on the health 75 
 
 Causes of the efflux of sweat ... ... ... ... 76 
 
 Fishes die in air, because the due distribution of the fluids 
 
 is prevented ... ... ... ... ... ... 77 
 
 Experiments of HALES on the motion of the sap in plants ib. 
 
 This motion is caused by evaporation ... ... ... 79 
 
 Force with which the sap rises ... ... ... ... 80 
 
 The atmospheric pressure is the active force ... ... 81 
 
 The sap absorbs gases ... ... ... ... ... ib. 
 
 The evaporation supplies food to the plant ... ... 83 
 
 Influence of suppressed evaporation on hop-vines 84 
 
CONTENTS. Xlll 
 
 Observations of HALES on the blight in hops, &c 84 
 
 Fire-blasts in hops .. ... ... ... ... ... 85 
 
 HALES recognized the influence of evaporation on the life of 
 
 plants ... ... ... ... ... ... ... 86 
 
 The origin of the potato disease is probably similar to 
 
 that of the blight in hops ... ... ... ... 87 
 
 The disease long known ... ... ... ... ... ib. 
 
 It is due, not to a degeneration of the plant, but to a com- 
 bination of external circumstances ... ... ... 88 
 
 It is connected with the weather, and particularly with the 
 
 temperature and hygrometric state of the atmosphere ... 89 
 The life of plants is dependent chiefly on four external 
 
 causes ... ... ... ... ... ... ... 90 
 
 Only one of which, namely, the quality of the soil, is in 
 
 the power of the agriculturist ... ... ... ... 91 
 
 Effects of suppressed evaporation ... ... ... ... ib. 
 
 The fungi and putrefaction follow the death of the plant 92 
 Observations of HALES on the rise of the spring sap in 
 
 perennial plants ... ... ... ... ... ... ib. 
 
 Views of DUTROCHET ... ... ... ... ... ib. 
 
 Objections to these views ... ... ... ... ... 93 
 
 The cause of the rise of the sap is transient, and depends 
 
 on external influences ... ... ... ... ... 94 
 
 It exists, not merely in the spongioles, but in all parts of 
 
 the plant ... ... ... ... ... ... ... ib. 
 
 Experiments of HALES ... ... ... ... ... 95 
 
 His conclusions ... ... ... ... ... ... 97 
 
 Gas is given off by the sap 98 
 
 The rise may therefore be due to disengagement of gas ... 99 
 
 The gas is probably carbonic acid... 100 
 
 [APPENDIX 
 
XIV CONTENTS. 
 
 APPENDIX. 
 
 Account of a plan proposed by Dr. KLOTZSCH, of Berlin, 
 protecting potato-plants from disease ... ... 102 
 
 This plan published by authority of the Minister of the In- 
 terior of Prussia, on the favourable report of the Presi- 
 dent of the College of Rural Economy at Berlin ... 108 
 
 Conditions on which the reward, claimed for his plan, if 
 found effectual, by Dr. KLOTZSCH, has been granted ... ib. 
 
ON THE PHENOMENA 
 
 ACCOMPANYING 
 
 THE MIXTURE OF TWO LIQUIDS 
 
 SEPARATED BY 
 
 A MEMBRANE. 
 
 THE constituents of the food, which have assumed The food 
 a soluble form in the alimentary canal, are thereby 
 endowed with the property of yielding to the in- 
 fluence of every cause which, in acting on them, 
 tends to change their place or the position which parts ' 
 they occupy. They are conveyed into the blood- 
 vessels, and from thence are distributed to all parts 
 of the body. 
 
 The movement and distribution of these fluids, 
 and of all the substances dissolved in them, ex- 
 clusive of the mechanical cause of the contraction 
 of the heart, by which the circulation of the blood 
 is effected, depend, 1, on the permeability of the General 
 walls of all vessels to these fluids ; 2, on the pres- 
 
 sure of the atmosphere ; and 3, on the chemical 
 attraction which the various fluids of the body 
 exert on each other. The motion of all fluids in 
 the body is effected by means of water ; and all 
 
2 RELATION OF THE ANIMAL 
 
 parts of the animal system contain, in the normal 
 state, a certain amount of water. 
 
 Relation of Animal membranes, tendons, muscular fibres, 
 sues to cartilaginous ligaments, the yellow ligaments of 
 the vertebral column, the cornea, transparent and 
 opaque, &c., all contain, in the fresh state, more 
 than half their weight of water, which they lose, 
 more or less completely, in dry air. 
 
 On the presence of this water depend several of 
 their physical properties. The fresh, opaque, milk- 
 white cartilages of the ear become, when dried, 
 translucent, and acquire a reddish yellow colour. 
 Tendons, when fresh, are in a high degree flexible 
 and elastic, and possess a silky lustre, which they 
 lose when dried. By the same loss of water they 
 become, further, hard, horny, and translucent, and 
 when bent, split into whitish bundles of fibres. The 
 sclerotic coat is milk-white when fresh, and becomes 
 transparent by desiccation. 
 
 When these substances, after having lost, by 
 drying, a part of the properties which they possess 
 in the fresh state, are again placed in contact with 
 pure water, they take up, in 24 hours, the whole 
 original amount of water, and recover perfectly 
 those properties which they had lost. The opaque 
 cornea, or sclerotic coat, which had become trans- 
 parent by desiccation, again becomes milk-white, 
 while the transparent cornea, which had been ren- 
 dered opaque by drying, now becomes again trans- 
 parent. The tendons, which, when dried, had become 
 
TISSUES TO WATER. 6 
 
 horny, hard, and translucent, now again become 
 flexible and elastic, and recover their silky lustre. 
 The fibrine and the cartilages of the ear, which 
 desiccation had rendered horny and transparent, 
 again become milk-white and elastic. 
 
 The power which the solids of the animal body The tissues 
 
 absorb 
 
 possess of taking up water into their substance, and other flu- 
 of being penetrable to water, extends to all fluids 
 allied to water, that is, miscible with it. In the 
 dried state, the animal solids take up fluids of the 
 most diverse natures, such as fatty and volatile oils, 
 ether, bisulphuret of carbon, &c. This permeability 
 to fluids is possessed by animal tissues in common 
 with all porous bodies ; and no doubt can be enter- 
 tained, that this property is determined by the same 
 cause which produces the ascent of fluids in nar- 
 row tubes, or in the pores of a sponge ; phenomena, 
 which we are accustomed to include under the name 
 of capillary action. 
 
 One condition, essential to the permeability of The moist- 
 porous bodies for fluids (or their power of ab- 
 
 sorption), is their capability of being moistened ; or 
 the attraction which the particles of the fluid and 
 the walls of the pores or tubes have towards each 
 other. A second condition is the attraction which 
 one particle of the fluid has to another. We have 
 no means of estimating the absolute size of the par- 
 ticles or molecules of a fluid, such as water, but 
 they are certainly infinitely smaller than the 
 measurable diameter of a tube, or of the pores of 
 
 B 2 
 
4 POROUS TEXTURES ABSORB WATER 
 
 a porous body. It is obvious, therefore, that in the 
 interior of a capillary tube or pore, filled with a 
 fluid, only a certain number of the fluid molecules 
 are in contact with the walls of the tube, and at- 
 tracted by them ; while in the middle of the tube, 
 and from thence towards its parietes, fluid molecules 
 must exist which only retain their place in virtue of 
 the attraction which the molecules attracted by the 
 parietes exert on those not so attracted ; that is, 
 by the cohesive attraction of the fluid. 
 
 Liquids flow out of capillary tubes, which are 
 filled with them, only when some other force or 
 cause acts, because capillary attraction cannot pro- 
 duce motion beyond the limits of the solid body 
 which determines the capillary action. 
 
 depends on The penetration of a fluid into the pores of a 
 attraction, porous body, is the result of capillary attraction ; 
 its expulsion can be effected by a mechanical pres- 
 sure; and may be accelerated by increasing this 
 pressure, and by all such causes as diminish the 
 mutual attraction of the fluid molecules, or the 
 attraction of the walls of the pores for those mole- 
 cules. The condition most favourable to the passage 
 of a fluid through the pores of a porous substance 
 under pressure, is when one fluid molecule can be 
 displaced so as to glide away over another. 
 
 The slightest pressure suffices to expel the dis- 
 placeable particles of water from a sponge ; a higher 
 pressure is required to express the same fluid from 
 bibulous paper ; and a pressure much higher still is 
 
BY CAPILLARY ATTRACTION. 5 
 
 necessary in order to cause water to flow out of 
 
 moist wood. We may form some idea of the force Prodigious 
 
 with which porous organic substances, such as dry 
 
 wood, absorb and retain water, if we remember, that 
 
 by inserting of wedges of dry wood in proper cuts, water * 
 
 and subsequently moistening them, rocks may be 
 
 split and fractured. 
 
 When we compare with the properties just enu- 
 merated, which belong to all porous bodies, those 
 properties which are observed in animal substances 
 under the same circumstances, it appears plainly, 
 that these animal substances have pores in certain Animal tis- 
 directions, although these openings are so minute porous! 
 that they are not, in the case of most tissues, per- 
 ceptible even with the aid of the best microscopes. 
 
 It has been mentioned that tendons, ligaments, Amount of 
 cartilages, &c., contain, in the fresh state, a certain peiied by 
 amount of water, which, according to all experi- fom tis- 
 ments made on the subject, is invariable ; and that 
 several of their properties depend on the presence 
 of this water. (CHEVREUL.) When these sub- 
 stances, wrapped in bibulous paper, are subjected 
 to a powerful pressure, a certain proportion of this 
 water is expelled. Fresh and flexible vessels lose in 
 this way 37*6 per cent., and the yellow ligaments of 
 the vertebrae lose 35 per cent, of water. This pro- 
 perty, namely, that of losing water under pressure, 
 is only found in porous substances. It is obvious 
 that by pressure, that is, by diminution of the size 
 of the pores, only that portion of water can be 
 pressed out which is not retained by chemical 
 
6 PASSAGE OF LIQUIDS THROUGH 
 
 The portion attraction. It is in the highest degree worthy of 
 
 of water not 
 
 chemically notice, that this water, not chemically combined, 
 
 combined, 
 
 has the seems to have the greatest share in the properties 
 share in the which these animal substances possess in the fresh 
 of the tis- state, for the pressed tendons and yellow ligaments 
 become transparent; the former lose their flexi- 
 bility, the latter their elasticity ; and if laid in 
 water, they recover these properties perfectly. In 
 the pores of a porous substance, the fluid molecules 
 are retained by two kinds of attraction, namely, by 
 the affinity which is exerted between the walls of 
 the pores and the molecules of the fluid, and by the 
 cohesion which acts between the molecules of the 
 fluid itself. It would appear as if the molecules of 
 water were thus brought into different states, and 
 this seems to be the cause of the differences ob- 
 served in the properties of these animal substances 
 when they contain different proportions of water. 
 Pressure If the wide opening of the tube, Fig. 1, 
 
 required to 
 
 cause water be tied over with a portion of bladder, 
 
 and other -,- f 
 
 liquids to and water poured into the wide part of 
 
 pass 
 
 through the tube as far as the mark a, we shall 
 
 membranes. , , , . 
 
 find that, when mercury is poured into 
 the upright narrow part of the tube, to 
 a certain height, the whole external 
 surface of the bladder becomes covered 
 with minute drops, which, if the column 
 of mercury be made a few lines higher, 
 unite so as to form large drops. These 
 continue to flow out uninterruptedly, 
 if mercury be added so as to keep the a. 
 
ANIMAL MEMBRANES. 7 
 
 column at the same height, till at last the wide part 
 of the tube is emptied of water and filled with 
 mercury. 
 
 Solution of salt, fat oil, alcohol, &c., behave ex- 
 actly as water does ; under a certain pressure these 
 fluids pass through an animal membrane, just as 
 water does through a paper filter. 
 
 The pressure required to cause these liquids to 
 flow through the pores of animal textures depends 
 on the thickness of the membrane, as well as on 
 the chemical nature of the different liquids. 
 
 Through ox-bladder, j^th of a line (rai^h of an The pres- 
 inch) thick, water flows under a pressure of 12 with dif- 
 inches of mercury ; a saturated solution of sea salt 
 requires from 18 to 20 inches; and oil (marrow 
 oil) only flows out under a pressure of 34 inches of 
 mercury. 
 
 When the membrane used is the peritoneum 
 of the ox, -^th of a line (i^oth of an inch) in 
 thickness, water is forced through it by 8 to 10 
 inches, brine by 12 to 16 inches, oil by 22 to 24 
 inches, and alcohol by 36 to 40 inches of mer- 
 cury. 
 
 The same membrane from the calf, jOT^n f a 
 ^ ne (i9 1 92 n( ^ f an inch) in thickness, allows water 
 to pass through under the pressure of a column of 
 water 4 inches high ; brine passes under a pressure 
 of 8 to 10 inches of brine, and oil under a pressure 
 of 3 inches of mercury. 
 
 In making experiments of this nature, we observe 
 
8 ABSORBENT POWER OF MEMBRANES 
 
 that, after they have continued for some time, the 
 
 pressure required to force the liquid through the 
 
 membrane does not continue equal. If during the 
 
 first 6 hours a pressure of 12 inches of mercury were 
 
 necessary, we often find that after 24 or 36 hours, 
 
 8, or even 6 inches will suffice to produce the same 
 
 effect, obviously because by long-continued contact 
 
 with water the membrane undergoes an alteration, 
 
 in consequence of which the pores are widened. 
 
 The pas- From these experiments it appears, that the 
 
 ujuids power of a liquid to filter through an animal mem- 
 
 membranes hrane bears no relation to the mobility of its par- 
 
 portion P to" tides; for under a pressure which causes water, 
 
 their fluid- b rmej or O ji to p ass through, the far more mobile 
 
 alcohol does not pass. 
 The ab- The capacity of the animal membrane for being- 
 
 sorbent 
 
 power of moistened by, and its power of absorbing, the liquid, 
 
 the mem- . 
 
 brane for nave a certain share in producing the result of its 
 has a share filtration through the membrane. 
 
 The following table will shew this fact : 
 
 100 parts, by weight, of dry ox-bladder, take up 
 in 24 hours, 
 
 Absorption of pure water 268 volumes 
 
 saturated solution of sea salt (brine) ... 133 
 
 ,, alcohol of 84 per cent 38 
 
 oil of marrow 17 
 
 100 parts, by weight, of ox-bladder, take up in 
 48 hours, 
 
 of pure water 310 parts by weight 
 
 a mixture of water and f brine ... 219 
 
FOR DIFFERENT LIQUIDS. 9 
 
 of a mixture of J water and \ brine ... 235 parts by weight 
 ,, ,, -J- > 288 
 
 -J alcohol J- water 60 
 
 > "3" " 15" '* *'* '^l > 
 
 1 f ... 290 
 
 100 parts of dry pig's bladder take up in 24 
 hours, 
 
 of pure water 356 volumes 
 
 brine 159 
 
 oil of marrow 14 
 
 From these experiments it appears that the ab- 
 sorptive power of animal membranes for different 
 liquids is very different. Of all liquids, pure water 
 is taken up in the largest quantity ; and the absorp- 
 tive power for solution of salt diminishes in a certain 
 ratio as the proportion of salt increases. A similar 
 relation holds between the membranes and alcohol ; 
 for a mixture of alcohol and water is taken up more 
 abundantly the less alcohol it contains.* 
 
 * In regard to this property, membranes differ in no respect 
 from other animal textures, as was long ago proved by Chevreul. 
 This distinguished philosopher found that the following sub- 
 stances absorbed, in 24 hours, of water, brine, and oil, 
 
 100 grammes 
 
 100 
 
 100 
 100 
 100 
 100 
 
 100 
 
 ( 
 
 of cartilage of the ear 
 
 Cubic 
 Centimetres C. C. C. C. 
 Water. Brine. Oil. 
 231 125 
 
 178 114 8-6 
 148 30 7-2 
 461 370 9-1 
 319 3-2 
 
 301 of water and 148 of 
 alcohol of 69 per cent. 
 
 (Liebig.) 
 
 184 parts by weight or 
 1 54 by volume of brine. 
 
 tendons , 
 
 yellow ligaments of spine. . . 
 cornea 
 
 cartilaginous ligaments ... 
 dry fib line absorbed 
 
10 ACTION OF SALT, OIL, AND ALCOHOL 
 
 Effects of Animal membranes do not acquire, by absorbing 
 &c. on ' alcohol or oil, those properties which they exhibit 
 
 membranes _ . 
 
 when dry, when saturated with water. A dried bladder con- 
 tinues hard and brittle in alcohol and oil ; its flexi- 
 bility is in no degree increased by absorbing these 
 liquids. When tendons, ligaments (CHEVREUL), the 
 yellow ligaments of the spine, or bladder, saturated 
 with oil, are placed in water, the oil is completely 
 expelled, and they take up as much water as if they 
 had not previously been in contact with oil. 
 and when in It has been mentioned, that 100 parts of animal 
 state? " membrane (dry ox-bladder) absorb in 24 hours 268, 
 in 48 hours 310 volumes of water, and only 133 of 
 saturated solution of salt. It follows, of course, that 
 when the bladder, saturated with water by 48 hours' 
 contact, and well dried in bibulous paper, without 
 pressure, to remove superfluous water, is strewed 
 with salt, there is formed, at all points where salt 
 comes in contact with the water filling the open 
 pores, a saturated solution of salt, the salt contained 
 in which diffuses itself equally in the water of the 
 bladder. Of the 310 volumes of water which be- 
 come thus saturated with salt, only 133 volumes are 
 retained in the bladder ; and in consequence of this 
 diminution of the absorbent power of the bladder 
 for the brine, 177 volumes of liquid are expelled, and 
 run off in drops from the surface of the bladder. 
 
 Membranes, fibrine, or a mass of flesh, behave 
 exactly in a similar manner when in contact with 
 alcohol. If placed in alcohol in the fresh state, 
 
ON MEMBRANES SATURATED WITH WATER. 11 
 
 that is, when they are thoroughly charged with 
 water, there are formed, at all points where water 
 and alcohol meet, mixtures of the two, and as the 
 animal texture absorbs much less of an alcoholic 
 mixture than of pure water, more water is, of 
 course, expelled, than alcohol taken up. 
 
 9-17 grammes of bladder, fresh, that is, saturated Amount of 
 with water (in which are contained 6*95 grammes of peiied from 
 water, and 2*22 of dry substance), when placed in alcohol. y 
 40 cubic centimetres of alcohol, weigh, at the end of 
 24 hours, 4*73 grammes, and have, consequently, lost 
 4'44 grammes. In the 4*73 grammes which remain, 
 are 2'22 grammes of dry bladder, and, of course, 
 2-51 grammes of liquid. If we assume that this 
 liquid has the same composition as the surrounding 
 mixture (which is found to contain 84 parts of 
 alcohol to 16 of water), it will consist of 2*11 
 grammes of alcohol and O40 of water ; and conse- 
 quently, of the 6'95 grammes of water originally 
 present, 6*45 grammes have been expelled, and 
 replaced by 2*11 grammes of alcohol. For 1 volume 
 of alcohol, therefore, retained by the bladder, rather 
 more than 3 volumes of water have been expelled 
 from it. 
 
 Since, in this case, so much more water is ex- Moist 
 pelled than is taken up of alcohol, the first result is shrink 
 a shrinking of the animal substance.* 
 
 * Fibrine and other animal matters exhibit results quite similar 
 to those obtained with bladder. 26*02 grammes of fibrine satu- 
 rated with water (containing 6'48 grammes of dry fibrine and 
 
12 CAUSE OF THE SHRIVELLING OF 
 
 when If the bladder could take up or absorb equal 
 
 strewed 
 
 with salt, volumes of brine and water, or of alcohol and water, 
 alcohol! m then when the fresh bladder was strewed with salt, 
 or laid in alcohol, the volume of the absorbed liquid 
 would be unaltered, and an equal volume of saline 
 solution, or of diluted alcohol, would be retained by 
 the animal tissue. But since the absorbent power 
 of the tissue for water is diminished by the addition 
 of salt, or of alcohol, it follows plainly, that a cer- 
 tain quantity of water must be expelled as soon as 
 its character is changed by the addition of one of 
 these substances. 
 The cause The relation of bladder, fibrine, and other animal 
 
 of this is . , 
 
 the less substances, when saturated with water, to alcohol and 
 the'tissue brine, proves, that the shrinking (diminution of 
 &c * than ' volume) of these tissues does not depend on a sim- 
 ple abstraction of water in virtue of the affinity of 
 alcohol and of salt for that liquid ; for it is quite 
 certain that the attraction of alcohol to water, and 
 that of water to alcohol, are respectively equal. The 
 attraction of the water within the tissue for the 
 alcohol without, is just as strong as the power of the 
 alcohol without to combine with the water within. 
 Less alcohol is taken up, and more water given out, 
 
 19' 54 of water) were reduced, in 45 grammes of absolute alcohol, 
 to 16-12 grammes, losing, therefore, 9'90 grammes. Admitting 
 the absorbed liquid to have the composition of the unabsorbed 
 residue (70 per cent, of alcohol), it appears, that for 1 volume of 
 alcohol absorbed by fibrine, rather more than 2 J volumes of water 
 are separated. 
 
MEMBRANES WHEN STREWED WITH SALT. 13 
 
 because the animal tissue has less attraction for the 
 mixture of alcohol and water than for pure water 
 alone. The alcohol without becomes diluted, the 
 water within becomes mixed with a certain propor- 
 tion of alcohol, and this exchange is only arrested 
 when the attraction of the water for the animal 
 tissue, and its attraction for alcohol, come to counter- 
 poise each other. 
 
 If we regard a piece of skin or bladder or fibrine, 
 as formed of a system of capillary tubes, the pores 
 or minute tubes are, in the fresh state, filled with a 
 watery liquid, which is prevented from flowing out 
 by capillary attraction. 
 
 But the liquid contained in these capillary tubes 
 flows out of them as soon as its composition is 
 altered by the addition of salt, alcohol, or other 
 bodies. 
 
 If we lay together, one over the other, two por- 
 tions of bladder, saturated with solution of salt of 
 sp. g. 1*204, and over the upper one another piece 
 of bladder of equal size, saturated with water, and 
 if we allow them to remain thus, without pressure, 
 we find, after some minutes, when the two pieces 
 saturated with solution of salt are separated, that 
 drops of saline solution appear between them, of 
 which no trace could previously be perceived. If 
 the piece of bladder saturated with water contained 
 5 volumes of water, and the next piece 3 volumes 
 of saline solution, there must be produced, by the 
 mixture of both, 8 volumes of diluted saline solu- 
 
14 ANIMAL TISSUES ARE 
 
 tion, of which each piece of bladder must contain 
 one half, or 4 volumes, if the absorbent power of 
 the portion saturated with the original saline solu- 
 tion were increased by the addition of water in the 
 same ratio as the absorbent power of the portion 
 saturated with water was diminished by the addi- 
 tion of salt. The saline liquid would have given 
 up 1^ volume of saline solution to the other, and 
 would have received from it 2^ volumes of water. 
 In this case, the mixture in the two upper pieces 
 of bladder would occupy the same space which its 
 constituents, water and saline solution, occupied in 
 each singly. But the efflux of the liquid towards 
 the third or lowest piece of bladder, saturated with 
 saline solution, proves, that the two upper pieces 
 retain a smaller volume of the mixture newly 
 formed in their pores, than the one piece absorbed 
 of w r ater alone, and the other of saline solution 
 alone. The power of retaining water is diminished 
 by the addition of salt to the bladder saturated with 
 water ; liquid is expelled ; but by the addition of 
 this water to the bladder moistened with saline 
 solution, the absorbent power of this piece of 
 bladder is increased, not in the same ratio, accord- 
 ing to which the proportion of salt is diminished, 
 but in a less ratio. 
 
 The experiments above described shew that the 
 attraction of the porous substances for the water 
 which they have absorbed does not prevent the mix- 
 ture of this water with other liquids. 
 
PERMEABLE TO ALL LIQUIDS. 15 
 
 The permeability of animal tissues to liquids of Animal tis- 
 every kind, and the miscibility of the absorbed permeable 
 liquids with others which are brought in contact ^r^kfndt 
 with the tissues, may be demonstrated by the sim- 
 plest experiments. 
 
 If we moisten one side of a thin membrane with 
 ferrocyanide of potassium, and the opposite side 
 with chloride of iron in solution, we perceive in the 
 substance of the membrane a spot of Prussian blue 
 immediately deposited. (Jon. MULLER.) 
 
 All fluids which, when brought together, suffer a which act 
 
 . .1 .on each 
 
 change in their nature or in their properties, ex- other in the 
 hibit, when only separated by an animal membrane, O f the tis- 
 exactly analogous results ; they mix in the pores of s 
 the membrane, and the decomposition commences 
 in its substance. 
 
 If we tie up one end of a cylindrical glass tube 
 with bladder, and fill it to the height of 3 or 4 
 inches with water or strong brine, neither the water 
 nor the brine flows out through the pores of the 
 bladder under this slight pressure. 
 
 But if we leave the tube containing brine ex- Deposition 
 posed to evaporation in the air, the side of the 
 bladder exposed to the air is soon covered with 
 crystals of salt, which gradually increase, so as to form 
 a thick crust. It is obvious that the pores of the 
 bladder become filled with brine ; that, on the side 
 exposed to the air, the water evaporates ; its place 
 is supplied by fresh brine, and the dissolved salt is 
 deposited, at the external minute openings of the 
 
16 SALINE SOLUTIONS, ALCOHOL, ETC., MIX 
 
 pores, in the form of crystals. If the tube be filled 
 originally with dilute saline solution, the crust of 
 salt is not formed on the outer surface of the 
 bladder until the solution in the tube has reached, 
 by evaporation, the maximum of saturation. Be- 
 fore this takes place, we can perceive in the tube, 
 if we set the liquid in motion, two strata, a heavier 
 and a lighter, the latter swimming on the former. 
 When these strata can no longer be observed, the 
 liquid is in every part saturated with salt, and now, 
 by further evaporation, crystals are deposited on the 
 outer surface of the bladder. This last circumstance 
 proves that the amount of salt in the liquid is uni- 
 formly distributed from below upwards, from the 
 specifically heavier to the specifically lighter part. 
 Saline so- If we immerse the tube closed with bladder, and 
 very rapidly filled with saline solution, in pure water, the latter 
 bladder. acquires the property of precipitating nitrate of 
 silver, even when the contact has lasted only the 
 fraction of a second. The brine filling the open 
 pores of the membrane mixes with the pure water, 
 and the latter acquires a certain quantity of salt. 
 
 In like manner, the pure water acquires a saline 
 impregnation, when it is placed in the tube instead 
 of brine, and the outer surface of the bladder is 
 placed in contact with solution of salt. 
 
 When the tube, closed with bladder, and filled 
 with brine, is left for a long time with the closed 
 end immersed in pure water, the amount of salt in 
 the latter increases, while that of the brine dimi- 
 
WITH WATER THROUGH MEMBRANES. 17 
 
 nishes, till at last the two liquids, separated by the 
 bladder, contain the same relative proportions of 
 salt and water. 
 
 If the liquid in the tube contain, dissolved, other The same is 
 substances which give to it properties different from mSk^ne', 
 those of pure water, and if these solutions be mis- s im ' &c ' 
 cible with water, the mixture of them with the 
 water takes place exactly as in the case of brine. 
 This is true of saline solutions of every kind ; of 
 bile, milk, urine, serum of blood, syrup, solution of 
 gum, &c., on the one side, and pure water on the 
 other. The concentrated liquid loses, the water 
 or diluted liquid gains, in regard to saline impreg- 
 nation. 
 
 If we fill the tube with water, and place it in a 
 vessel with alcohol, the water becomes charged 
 with alcohol, while the alcohol becomes diluted 
 with water. 
 
 There is observed, in these circumstances, that is, Change of 
 when two dissimilar liquids, separated by a mem- wheTtwo 
 brane, mix together, a phenomenon of a peculiar liquids mix 
 kind ; namely, in most cases, a change of volume in Lldder. a 
 both liquids, while the mixture goes on. The one 
 liquid increases in bulk, and rises ; the other dimi- 
 nishes in the same degree, and consequently sinks 
 below its original level. 
 
 This phenomenon of mixture through a mem- Endosmosis 
 brane, accompanied with change of volume, has Exosmosis. 
 been distinguished by DUTROCHET, under the name 
 of ENDOSMOSIS and EXOSMOSIS ; endosmose is the 
 
 c 
 
18 CONDITION OF THE MIXTURE, 
 
 name given when the volume increases exosmose, 
 when it diminishes. Very generally, however, we 
 attach to these terms the idea of the unknown 
 cause or group of causes which, in the given case, 
 produce the change of volume ; in the same sense 
 as that in which the term capillary action includes 
 the causes which determine the ascent of liquids in 
 narrow tubes. 
 
 In all cases the increase in volume of the one 
 liquid is exactly equal to the decrease in volume of 
 the other, after making allowance for the contrac- 
 tion which the liquids undergo by simple mixture 
 (as in the case of alcohol and water, oil of vitriol 
 and water, &c.), as well as by evaporation. The 
 unequal concentration, or the unequal density of 
 the two liquids, has a decided influence on the 
 rapidity with which the change of volume takes 
 place ; but this cannot be viewed as the cause of 
 that phenomenon. In most cases the denser liquid 
 increases in volume, in others the reverse occurs. 
 The change When, for example, the tube contains brine, and 
 
 of volume 
 
 does not the outer vessel pure water, the brine, that is, the 
 
 depend 
 
 alone on denser liquid, increases in volume ; but when the 
 density of tube contains water, and the outer vessel alcohol, 
 the water, that is, the denser liquid, diminishes in 
 volume. 
 
 With regard to the mixture of the liquids, the 
 bladder takes a distinct share in the process, inas- 
 much as it has pores, through which the two liquids 
 are brought in contact. 
 
THROUGH MEMBRANES, OF TWO LIQUIDS. 19 
 
 With reference to the porosity of the bladder, 
 the rapidity of the mixture of the two liquids is 
 directly proportional to the number of particles, 
 which, in a given time, come into contact ; it depends 
 also on the surface (the size of the membrane), and 
 on the specific gravity of the liquids. 
 
 The influence of extent of surface on the time influence 
 required for mixture requires no particular elucida- equaf U 
 tion ; that of the unequal specific gravity is rendered the tSo 
 evident by the following experiments. qm ' 
 
 R . 2 If the bent tube a b (Fig. 2), one end when the 
 
 of which is tied over with bladder, liquid is 
 and the other open, be filled with brine membrane. 
 coloured blue,* and if pure water be 
 placed in the tube c, there is soon per- 
 ceived under the bladder a colourless 
 or nearly colourless stratum of liquid, 
 which continues for hours to float in 
 the same place. If the bent tube a b 
 be filled with colourless brine, while c 
 is filled with pure water coloured blue, there is found, 
 after a time, above the bladder, a colourless or 
 nearly colourless stratum of liquid. 
 
 It appears from this, that an exchange of both 
 
 * For this purpose it is best to take a solution of indigo in 
 sulphuric acid, diluted, and after adding subacetate of lead as 
 long as sulphoindigotate and sulphate of lead are precipitated, to 
 separate the precipitate by nitration and dry up the filtered liquid 
 in the water-bath. A mere trace of the blue residue suffices to 
 colour blue large masses of liquid. 
 
 c2 
 
20 PHENOMENA OF THE MIXTURE OF TWO 
 
 liquids goes on through the substance of the blad- 
 der ; in the first experiment colourless water passes 
 from the tube c to the coloured brine in the tube 
 a b ; in the second, colourless brine passes from the 
 tube a b to the coloured water in the tube c. 
 
 It is obvious, that the brine in the tube a b, 
 which is in contact with the bladder, becomes 
 diluted by the addition of water from the tube c ; 
 but this diluted brine is specifically lighter than 
 the original brine which is below it, and remains 
 therefore floating at its surface. 
 
 On the other hand, the water in the tube c, when 
 mixed with brine from the tube a b, becomes 
 heavier than the pure water, and rests therefore on 
 the upper surface of the bladder, or that which is 
 turned towards the water. 
 
 Hence it follows, that from the moment when 
 these two strata have been formed above and below 
 the bladder, neither concentrated brine nor pure 
 water comes any longer in contact with the bladder. 
 
 From the bladder downwards in the tube a b are 
 strata of liquid, containing successively more salt ; 
 from the bladder upwards in the tube c are strata 
 containing successively more water. 
 
 In the beginning of this experiment we observe, 
 that the volume of the water and of the brine 
 changes in both tubes ; the liquid in the limb b 
 rises from 1 to 2 lines ; but as soon as the strata 
 above mentioned have been distinctly formed above 
 and below the bladder, hardly any further rise is 
 
LIQUIDS THROUGH A MEMBRANE. 
 
 21 
 
 perceptible, although the mixture of the liquid pro- 
 ceeds, and the water in c becomes constantly more 
 charged with salt, while the brine in a b loses salt. 
 
 If we reverse the positions of the two liquids in when the 
 the apparatus Fig. 2, or what is simpler, if we close 
 with bladder a tube 1 centimetre (-r^ths of an inch) 
 wide, fill it with brine, and immerse the end closed 
 with the bladder in a wider vessel filled with pure 
 water, giving to the tube an inclination of about 45, 
 we may observe (most distinctly when both liquids 
 contain some fine particles of indigo suspended) in 
 both liquids a continual motion. 
 We see in the tube (Fig. 3) a cur- 
 rent of liquid rising from the blad- 
 der in the direction of the arrow, 
 and flowing down again on the op- 
 posite side. A similar circulation 
 
 is observable in the 
 
 vessel of water. 
 
 If the tube #, with brine, is about 
 2 centimetres (fths of an inch) wide, 
 and if we support it vertically in the 
 vessel b of water, the motion proceeds 
 from the middle, and in both the tube 
 and the vessel we perceive currents 
 in opposite directions. (Fig. 4.) 
 
 These currents hardly require explanation. To 
 the brine in the tube a, pure water passes through 
 the bladder ; there is formed above the bladder a 
 mixture containing less salt, and therefore specifi- 
 
 
22 PHENOMENA OF THE MIXTURE OF TWO 
 
 cally lighter than the brine ; this mixture rises, and 
 the denser brine descends to occupy its place. 
 
 On the other hand, the pure water receives 
 through the bladder salt, and becomes thereby spe- 
 cifically heavier ; while it sinks to the bottom of the 
 vessel, its place is supplied by water containing less 
 or no salt, and therefore specifically lighter, which 
 again comes in contact with the bladder. As long 
 as the motions just described are perceptible, we 
 observe a constant increase in the volume of the 
 brine in the tube a (Fig. 4), or a diminution in 
 the volume of the pure water in the vessel b. When 
 the motions cease, the rise of liquid in the tube is 
 arrested, and when this takes place, the two liquids 
 are found to possess almost exactly the same specific 
 gravity. 
 
 When the two strata of liquid on either side of 
 the bladder are little different in composition (as 
 soon comes to pass in the experiment (Fig. 2) 
 where the saline contents of the liquid which fills 
 the pores of the bladder can hardly vary from that 
 of the next stratum), the mixture of the liquids 
 takes place, but without further change of volume. 
 But when an exchange of the mixtures on the 
 opposite sides of the bladder can occur in conse- 
 quence of their different specific gravity, and when 
 a continued difference between the strata on oppo- 
 site sides of the bladder is thus determined, then, so 
 long as (in the case of brine and water, for example) 
 one side of the bladder is in contact with a con- 
 
LIQUIDS THROUGH A MEMBRANE. 23 
 
 centrated, the other with a more diluted solution, 
 the change of volume in the two liquids continues. 
 
 As appears from these experiments, the change 
 of volume depends on a difference in the cha- 
 racter of the two liquids which are connected 
 through the bladder; and the time during which 
 change of volume occurs is in direct proportion to 
 the time during which this difference in character 
 subsists. The greater the difference in character 
 and composition between the liquids, and the more 
 rapidly this difference is renewed by the exchange 
 between the strata in contact with the opposite sides 
 of the bladder, the more rapidly does the one liquid 
 increase, and the other diminish in volume. 
 
 The following apparatus is very convenient for The change 
 measuring the change in volume, caused by the maybe 
 mixture of two liquids separated by a membrane. 
 
 The tubes a and b (Fig. 5) are of 
 equal width, and are best taken from 
 the same tube ; a is closed with bladder, 
 and filled up to a certain point with the 
 liquid whose increase in volume is to be 
 determined. It is then fitted by means 
 of a good cork into the wider tube c, 
 which contains distilled water, care 
 being taken to exclude all air-bubbles. 
 At d lies a small lead drop, which acts 
 as a valve in shutting the opening of 
 the capillary tube connecting c with b. 
 Pure water is now poured into b, and 
 
24 THE CHANGE OF VOLUME IN THE TWO 
 
 in order to keep in equilibrium the lead drop at d, 
 rather more water is added than exactly suffices 
 to bring the liquids to the same level in both 
 tubes. 
 
 The liquid in a increases in volume, and the 
 height to which it rises may be read off by means 
 of any division into equal parts by measure ; the 
 level of the liquid in b sinks in an equal ratio. If 
 we keep the liquid in b, by the addition of fresh 
 water, at the original level, and if we ascertain the 
 weight of the added water, by pouring it out of a 
 dropping bottle, and determining the loss of weight 
 in the dropping bottle, we learn at the same time 
 the weight and the volume of the water which 
 has risen from c into a. This apparatus admits, of 
 course, of a number of variations and improve- 
 ments. I have employed it to determine the rela- 
 tion between brine and water, under the circum- 
 stances just described. It appeared, among other 
 things, that when the tube a is filled with saturated 
 solution of sea salt, the volume of the liquid in- 
 creased by nearly one half; that is, 200 volumes 
 of such a solution increased to 300. These deter- 
 minations are, however, not the object of the pre- 
 sent investigation, and therefore I pass them over 
 entirely. 
 
LIQUIDS MAY BE MEASURED. 25 
 
 The following arrangement (Fig. 6) 
 will probably be found preferable to the 
 one just described, in many cases. Its 
 construction depends on the observation, 
 that for the phenomenon itself, and for 
 the result of the experiment, it is entirely 
 a matter of indifference whether the tube 
 be closed with a single, double, or treble 
 layer of bladder.* For experiments on 
 very thin membranes which are permeable 
 to liquids under a very low pressure, the 
 apparatus (Fig. 5) is obviously better 
 adapted. For the explanation of the phe- 
 nomenon we have to distinguish 
 
 1. The mixture of different liquids. 
 
 2. The change in their volume. 
 
 As to the mixture of two liquids of dissimilar Causes of 
 
 the mixture 
 
 nature and characters, this always depends on a ofdissimi- 
 
 . lar liquids. 
 
 chemical attraction. In a mixture of alcohol and 
 water, or of brine and water, there is in every part 
 the same proportion of particles of alcohol and 
 water, or of salt and water. If in the former, the 
 lighter particles of alcohol lying at the bottom of 
 the vessel were not retained, in the place and 
 
 * In these experiments membranes of all kinds may be used. 
 With the thinner membranes, such as the bladder of the calf and 
 the pig, the experiments are more rapidly completed than with 
 the thicker, such as the gall-bladder and urinary bladder of the 
 ox. The peritoneum of the ox and calf is preferable to all 
 others. The tube c is tied with bladder under water. 
 
26 
 
 THE MIXTURE OF LIQUIDS IS 
 
 Chemical 
 affinity is 
 the chief 
 cause of 
 mixture. 
 
 arrangement which they occupy, by the surrounding 
 particles of water, they would undoubtedly rise to- 
 wards the surface. In like manner, the particles of 
 salt in the brine are sustained and prevented from 
 sinking by the lighter particles of water which sur- 
 round them. 
 
 Without an attraction, which all the particles of 
 alcohol or of salt must have towards all the parti- 
 cles of water, or all the particles of water must 
 have for all those of salt and alcohol, a uniform 
 mixture cannot even be conceived. If but one 
 particle of alcohol were less powerfully attracted 
 than the surrounding particles, it would rise to the 
 surface ; and in like manner, the particles of salt 
 would, in consequence of their greater specific gra- 
 vity, gradually occupy the bottom of the vessel, 
 were it not that a cause prevents them from rising 
 or falling ; and this cause can be nothing but an 
 attractive force, which retains them in the place 
 where they happen to be. 
 
 The cause which effects a change in the place or 
 in the properties of the ultimate particles or atoms 
 of dissimilar substances, when these particles are in 
 absolute contact, or at infinitely small distances 
 from each other, as well as the cause which mani- 
 fests itself as a resistance to such changes of place 
 or properties, we call CHEMICAL ATTRACTION; and 
 in this sense the mixture of two dissimilar liquids, 
 the simple moistening of a solid body, the penetra- 
 
A RESULT OF CHEMICAL AFFINITY. 27 
 
 tion and swelling of it by a liquid, are effects in 
 which chemical affinity or attraction has a decided 
 share; and although we are accustomed to limit 
 the notion of affinity to such cases as exhibit a 
 change perceptible to our senses, in the properties 
 of the substances employed, as, for example, when 
 sulphuric acid and lime, or sulphuric acid and 
 mercury combine together, this limitation arises 
 from the imperfect apprehension of the essence of 
 a natural force. 
 
 Everywhere, when two dissimilar bodies come in 
 contact, chemical affinity is manifested. It is a 
 universal property of matter, and by no means be- 
 longs to a peculiar class of atoms, or to a peculiar 
 arrangement of these. But chemical combination 
 is not, in all cases, the result of contact. 
 
 Combination is only one of the effects of affinity, Affinity is 
 
 everywhere 
 
 and occurs when the attraction is stronger than all active 
 the obstacles which are opposed to its manifestation. bodLTin 
 When the forces or causes, which oppose chemical 
 combination, heat, cohesive attraction, electric at- 
 traction, or whatever they may be called, prepon- 
 derate, then chemical combination does not take 
 place ; and effects of another kind are manifested. 
 
 Melted silver in a crucible, surrounded with red- 
 hot coals, in a place, therefore, where we should 
 hardly anticipate the presence of free oxygen, 
 absorbs as much as ten or twelve times its volume 
 of that gas. Metallic platinum exhibits the same 
 property in a far higher degree ; for from the 
 
28 CHEMICAL AFFINITY IS 
 
 atmospheric air, a gaseous mixture in which oxygen 
 forms only the fifth part, that metal (in the form 
 of a black powder) condenses on its surface, at 
 the ordinary temperature, an enormous quantity of 
 oxygen gas (without any nitrogen), and acquires 
 thereby properties, which it does not otherwise 
 possess.* And when oxide of chromium, fragments 
 of porcelain, or asbestus, at high temperatures, 
 effect the combination of two gases, oxygen and 
 hydrogen, or oxygen and sulphurous acid, which 
 gases do not combine at the same temperature, 
 unless when in contact with thee solid bodies, it is 
 to the chemical attraction or affinity of these solid 
 bodies that we must ascribe this effect. 
 
 The solution of a salt in water is an effect of 
 affinity, and yet no one property, either of the salt 
 or of the solvent, is thereby altered, except only the 
 cohesion of the saline particles. 
 
 Sea salt, the crystals of which are usually anhy- 
 
 tion of sea 
 
 salt. drous, takes up, at very low temperatures, 38 per 
 
 cent, of water of crystallization ; not because any 
 new cause acts which increases its affinity for the 
 particles of water (for cold is no cause, but the 
 absence of a cause), but because the higher tem- 
 perature acted as an obstacle, opposing their 
 chemical combination. The force of affinity is 
 all the time present and undiminished. 
 
 * According to Dcebereiner, platinum black condenses 252 times 
 its volume of oxygen. Its effect in oxidizing alcohol, pyroxilic 
 spirit, &c., is familiar to every chemist. W. G. 
 
UNIVERSALLY DIFFUSED. 29 
 
 When we add alcohol to the solution of a salt in 
 water, we observe, that now the salt separates from fromits S 
 the liquid in the form of crystals, doubtless only alcohol* , 7 
 because, by the addition of another chemical force, 
 the amount of attraction between the particles of 
 the salt and those of the water has been altered. 
 
 The aqueous particles, which were combined with 
 the saline particles, manifest an attraction for the 
 particles of alcohol ; and as the latter have no affi- 
 nity, or only a very feeble affinity, for those of the 
 salt, the attraction of the saline particles for each 
 other is strengthened. This attraction was present 
 in equal force before the addition of the alcohol, 
 but the resistance which opposed their union (the 
 chemical attraction for them of the aqueous parti- 
 cles) was more powerful. The alcohol was not the 
 cause of the separation. The cause of the separa- 
 tion of the salt from the liquid, its crystallization, 
 is at all times the force of cohesion ; and by the 
 alcohol the cause which opposed its manifestation 
 was removed. 
 
 The affinity of potash for sulphuric acid is known, O f sulphate 
 and sulphate of potash readily dissolves in water, byc^ic 
 If we add, to a saturated solution of that salt, an po 
 equal volume of aqua potassse of sp. g. 1*4, there 
 is immediately formed a crystalline precipitate of 
 sulphate of potash, and the sulphuric acid is sepa- 
 rated in this form from the water. 
 
 In these cases the chemical effect (the separa- 
 tion) depends on the presence of a certain quantity 
 
30 PRECIPITATIONS BY ETHER, ETC. 
 
 of the liquid which is added (such as aqua potassse, 
 alcohol, &c.), but in many other cases there is re- 
 quired only a slight alteration in the quality of the 
 solvent to effect separations of this kind, 
 of ferrocy- When hydrochloric acid is added to a solution of 
 
 anic acid by i P 
 
 ether; ferrocyamde of potassium, ferrocyamc acid is set 
 free, and remains dissolved in the liquid. If now 
 the vapour of boiling ether be passed through the 
 mixture, there occurs, after a few moments, a com- 
 plete separation. The whole of the ferrocyamc 
 acid is deposited from the liquid in the form of 
 white or bluish-white crystalline scales, which 
 generally appear in such quantity as to render the 
 whole mass semisolid. In proportion as the vapour 
 of ether is dissolved by the water, the latter fluid 
 loses entirely its solvent power (its affinity) for the 
 ferrocyanic acid. The coagulation of albumen by 
 ether depends on a similar cause. 
 
 The capacity of solids to become moistened by 
 liquids, and, in short, all phenomena connected with 
 chemical affinity, are affected, altered, increased, or 
 destroyed, by causes quite analogous. 
 
 of sus- After heavy rains, the water of many rivers be- 
 
 mudby comes turbid and opaque from the presence of a fine 
 clay. These suspended particles of clay are so fine 
 as to pass through the finest filters ; and their adhe- 
 sion to the water is so great, that such water does 
 not clear after standing for weeks. The water of 
 the Yellow River, in China, possesses, during the 
 greater part of the year, this character ; and from 
 
ACTION OF SOLIDS ON DISSOLVED MATTERS. 31 
 
 the French missionaries we know that alum is uni- 
 versally employed in Pekin to clear it. In fact, if a 
 crystal of alum be held in such a water only for a 
 few seconds, we observe the sediment separating 
 in large thick flocculent masses, the water becomes 
 transparent, and hardly a trace of dissolved alum is 
 to be detected by the most delicate re-agents. 
 Chemistry is acquainted with a number of similar 
 means for causing the separation from liquids of 
 suspended precipitates. 
 
 In these cases we see, that by an alteration of 
 the quality of the water, produced by what we call 
 mere mixture with a foreign body, its -power of 
 combining with others is destroyed or weakened. 
 
 It is well known that the force with which, in a Action of 
 solution, the particles of the liquid and those of the dissolved 
 dissolved body attract each other, is very unequal in 
 different cases ; and in this point of view the action 
 of many solid bodies on saline solutions is very 
 remarkable ; inasmuch as it is thereby demon- 
 strated, that the molecular force, which deter- 
 mines the phenomena of cohesion, and the moist- 
 ening of solid bodies by liquids appears to be 
 identical with chemical affinity, since chemical com- 
 pounds can be decomposed by means of it. Pro- 
 fessor GRAHAM has shewn that common charcoal, 
 deprived by acids of all soluble ingredients, com- 
 pletely removes the metallic salts or oxides from 
 solutions of salts of lead, tartar emetic, ammoniated 
 oxide of copper, chloride of silver in ammonia, and 
 
32 ACTION OF SOLIDS ON DISSOLVED MATTERS. 
 
 oxide of zinc in ammonia; while other solutions, 
 such as that of sea salt, suffer no such change. A 
 bleaching solution of hypochlorite of soda loses 
 entirely its bleaching properties by agitation with 
 charcoal ; and iodine can be removed by the same 
 means from its solution in iodide of potassium. 
 Every one is familiar with the action of finely-di- 
 vided platinum, with that of silver on the deutoxide 
 of hydrogen ; as well as with that of charcoal on 
 dissolved organic matters, colouring matters, &c. ; 
 and freshly-precipitated sulphuret of lead, sulphuret 
 of copper, and hydrate of alumina, resemble the 
 latter in their action. Many organic substances, 
 such as woody fibre and others, act on dissolved 
 matters, such as salts of alumina or of oxide of tin, 
 just as charcoal does ; and we know that the appli- 
 cation of mordants in dyeing, and dyeing itself 
 depend on this very property. The adhesion of the 
 solid colouring matter to the cloth which is dyed 
 with it is the result of a chemical affinity so feeble, 
 that we hardly venture to give the molecular force 
 that name in this case. From a piece of woollen 
 cloth dyed with indigo, the indigo is completely 
 separated, by mere beating, continued for some 
 time, with a wooden hammer, so that the wool is 
 at last left white. 
 
 The surface of the solid body exerts, as these 
 facts prove, a very unequal attraction on the mole- 
 cules, which come in contact with it. 
 
 Researches on capillary attraction have shewn 
 
OF TWO DIFFERENT LIQUIDS. 33 
 
 that, with one and the same liquid, water, for ex- 
 ample, the substance of the solid body has no in- 
 fluence on the height to which the liquid rises on 
 it. On slices of box- wood, clay-slate, or glass, the 
 rise of the liquid above the surface of the water is 
 the same exactly as in the case of a plate of brass. 
 (HAGEN.) In the case of other liquids, the par- 
 ticles of which are entirely homogeneous, the same 
 law may be assumed in theory ; but with such 
 liquids as contain foreign bodies in solution, a 
 change in the capillary attraction must be produced 
 by the presence of these bodies, because by them 
 the cohesion of the liquid is altered ; and, perhaps, 
 still more because the liquid ceases to be homoge- 
 neous, when the attracting wall has a stronger affi- 
 nity for the particles of the dissolved body than for 
 those of the solvent. 
 
 From what has been stated, it appears, that the 
 mixture of two liquids is the result of a chemical 
 attraction ; for how otherwise could chemical com- 
 pounds, such as the solution of a salt in water, 
 be decomposed, or a chemical attraction be over- 
 come, by its means ? 
 
 Two liquids of different chemical properties, Laws of 
 which are rniscible together, and which, therefore, S^o liquids, 
 have a chemical attraction for each other, mix 
 readily at all points where they come in contact. 
 By motion, shaking, &c., the number of points of 
 contact within a given time is increased, and the 
 formation of a uniform mixture is thus accelerated. 
 
 D 
 
34 LAWS OF THE MIXTURE 
 
 If these liquids be of equal, or still better, of 
 unequal, specific gravity, they may be, with the aid 
 of some precaution, stratified one above the other. 
 This is, in point of time, the most unfavourable 
 case for the mixture, since proportionally small sur- 
 faces come in contact. But wherever they do come 
 in contact, it is, after a very short time, impossible 
 to detect any limit between them, 
 
 In a cylindrical vessel, containing solution of 
 salt, the saline particles at the surface are attracted 
 and sustained by aqueous particles, which exist at 
 the sides of the saline particles, and from the sur- 
 face downwards. From the surface upwards, the 
 attracting aqueous particles are absent. 
 
 Now it is evident, that when the surface is brought 
 in contact with pure water, a new attraction is added 
 to those previously existing, which acts in an oppo- 
 site direction, namely, the attraction of the aqueous 
 particles floating on the surface for the saline par- 
 ticles, and vice vers& (the attraction of the saline 
 particles to the aqueous particles in contact with 
 them). 
 
 At the place where pure water and brine are in 
 contact, there is thus formed a uniform mixture of 
 the two, which upwards is in contact with pure 
 water, downwards with brine. 
 
 Among these three strata, of which the upper 
 contains no salt, the lower less water, a new division 
 takes place ; the more strongly saline stratum loses 
 salt, the pure water becomes saline, and in this way 
 
OF TWO DIFFERENT LIQUIDS. 
 
 35 
 
 salt and water are at last uniformly distributed 
 throughout the liquid. 
 
 If we fill one limb of the tube (Fig. 7), 
 as far as 0, with brine coloured blue, 
 and the other limb with water, we find, 
 in the course of a few days, the water 
 coloured blue, and the proportion of 
 salt in both limbs equal. It has been 
 mentioned at p. 16, that, in a tube 
 closed with bladder, filled with diluted 
 solution of salt, and exposed to evapo- 
 ration, the salt is not deposited in crys- 
 tals on the outer surface of the bladder till the 
 whole liquid in the tube has reached, in consequence 
 of evaporation, the maximum of saturation. The 
 water evaporates from the exterior of the bladder, 
 but no salt is deposited, as long as a liquid exists 
 within which can still dissolve salt ; and in this way 
 the heavier saline particles are distributed towards 
 the interior, and upwards through the whole liquid, 
 or, what amounts to the same, the lighter aqueous 
 particles, which can still dissolve salt, are distri- 
 buted downwards towards the external surface of 
 the bladder. 
 
 This distribution of salt through water takes 
 place in the same manner as the conversion of bar 
 iron into steel. Rods of malleable iron, as is well 
 known, are kept ignited between strata of charcoal, 
 whereby the surface of the iron in contact with the 
 charcoal takes up carbon, and becomes a carburet of 
 
 D2 
 
 Experi- 
 ment shew- 
 ing the uni- 
 form mix- 
 ture of two 
 liquids. 
 
 The distri- 
 bution of 
 salt through 
 water re- 
 sembles the 
 conversion 
 of iron into 
 steel by ce- 
 mentation. 
 
36 LAWS OF THE MIXTURE 
 
 iron. The stratum of iron lying next under this 
 surface, which has the same attraction for carbon, 
 acquires carbon from the superficial stratum imme- 
 diately in contact with it, and in its turn gives carbon 
 to the stratum below itself. This process, if con- 
 tinued long enough, has no limit till all the strata of 
 particles have acquired an equal proportion of car- 
 bon, that is, till they are all saturated with it. A 
 piece of red-hot malleable iron, if kept a few mo- 
 ments in contact with pig iron (a carburet of iron) 
 is found to be already converted into steel at the 
 points of contact. The mixture of liquids depends 
 on the same principle ; and we may suppose that 
 their distribution is mutual, because their particles 
 may move in all directions, and that consequently 
 saline particles move towards aqueous particles, as 
 well as aqueous towards saline particles, in virtue 
 of their mutual attraction. 
 
 From a solution of sulphate of copper in ammo- 
 nia, placed in a tall glass cylinder, there is gradually 
 separated, if we pour a stratum of alcohol on the 
 surface, and if we prevent the formation of a cohe- 
 rent crust which impedes the contact of the liquids, 
 the whole of the ammoniated sulphate of copper, 
 while the deep blue solution becomes colourless, 
 because by the distribution of the alcohol through 
 the solution a mixture is formed, in which the salt 
 is insoluble. 
 
 ^ e rapidity of mixture of two liquids depends 
 by chemical on the degree of their chemical affinity; and the 
 
 affinity, 
 
OF TWO LIQUIDS. 37 
 
 unequal mobility of the particles of one or the 
 other liquid has a favourable or unfavourable in- 
 fluence on the result. 
 
 When the one liquid is heavier than the other, by un- 
 
 equal mo- 
 and of tough, viscid consistence, a much longer biuty, and 
 
 time elapses before the ingredients of the tougher 
 or heavier liquid reach the surface from the bottom 
 of the vessel ; and in this case the greater density 
 and the less mobility of the particles are obstacles 
 to the mixture. 
 
 On the other hand, if the heavier or more viscid 
 liquid be placed above the lighter, the mixture 
 takes place rapidly ; at the points where both liquids 
 are in contact is produced a mixture, which, being 
 heavier, descends, whereby the heavier liquid above 
 is continually brought in contact with new surfaces 
 of liquid. 
 
 The very same phenomenon is observed in solu- Effect of 
 tion. A fragment of sugar, when covered with 
 
 water at the bottom of a narrow cylinder, dissolves 
 very slowly, while, if suspended just below the sur- 
 face, it rapidly disappears. In the former case there 
 is produced round the sugar a thick syrupy viscid 
 solution, which protects the undissolved part of the 
 sugar for a long time from contact with the water ; 
 in the latter there is formed at the surface a solution, 
 which descends in striae, and gradually disappears, 
 while by the change of place thus induced, new 
 portions of water are constantly brought in contact 
 
38 LAWS OF THE MIXTURE OF TWO 
 
 with the undissolved sugar, and are thus enabled to 
 exert their solvent powers. 
 
 If skin and membranes consist of a cohering 
 system of very narrow tubes, it is obvious, that when 
 two dissimilar, but miscible liquids are separated by 
 such a tissue, the pores of the tissue will fill with 
 each of the two liquids. In all situations, where 
 the liquids came in contact in the substance of the 
 membrane, a mixture takes place, and this mixture 
 is extended equally towards both sides. 
 
 If there be brine on one side of the bladder, and 
 water on the other, there must be formed, in the 
 middle, or at some point of the bladder, a diluted 
 brine, which on the side in contact with the water 
 yields salt to that water, while on the opposite side 
 the strong brine mixes with the diluted brine in the 
 bladder. 
 
 The substance of the bladder has no influence on 
 this mixture, because it can produce no change of 
 place on the part of the saline or aqueous particles, 
 for this is the result of the chemical affinity acting 
 between the particles of salt and those of water. 
 Rapidity of Now since the rapidity of the mixture of two 
 liquids stands in a direct proportion to the amount 
 of their surfaces coming into contact within a 
 given time, and since the liquids, separated by a 
 bladder, can only come in contact through its pores, 
 while the number of points of contact is diminished 
 by the presence of the non-porous parts of the 
 
LIQUIDS THROUGH A MEMBRANE. 39 
 
 bladder, it follows, that, exclusive of all other 
 effects, the time required for mixture must be 
 lengthened by the interposition of a bladder. In 
 the absence of the bladder, the mixture would take 
 place exactly as when it is present, except in regard 
 to time. 
 
 When the heavier brine is under, the water above 
 the bladder, the two liquids mix more slowly than 
 without the bladder. 
 
 But since a bladder, inasmuch as a feeble hydro- in certain 
 
 circum- 
 
 statical pressure is not propagated through its pores, stances, the 
 allows us to place a heavier liquid above a lighter, turn of a 
 and to retain it in that position ; this circumstance ^de^tes 
 has the effect of promoting mixture, the ultimate 
 cause of which is, not the bladder, but the specific 
 gravity of the liquid. The bladder is a means of 
 enabling the specific gravity to influence mixture. 
 The foregoing remarks appear to me sufficiently to 
 elucidate the share taken by the bladder in the 
 mixture of two dissimilar liquids placed on opposite 
 sides of it. 
 
 With respect to the change of volume in the two change of 
 liquids which become mixed through the bladders, liquids 
 
 which mix 
 
 we must consider, that the moistening or the ab- through a 
 sorbent power of a solid body, as well as the power 
 of a liquid to moisten other bodies, is the result of 
 a chemical action. 
 
 Liquids of different properties, or of different is the result 
 
 of chemical 
 
 chemical characters, are attracted with unequal 
 
40 CAUSE OF THE CHANGE OF VOLUME IN 
 
 affinity mo- degrees of force by solid bodies, and exert towards 
 them unequal degrees of attraction, and if we alter 
 
 even in a system of capillary tubes, filled to a 
 certain height with a liquid, the chemical nature of 
 that liquid, we change thereby the height at which 
 the liquid stands. In an animal tissue saturated 
 with water, the water is prevented from flowing out 
 by the mutual attraction, and by the capillary force, 
 but if the attraction of the organic parietes for 
 water be diminished by the addition of alcohol or 
 of salt to the water, a part of it flows out. To this 
 must be added, that the water absorbed by an 
 animal texture when it enters the capillary tubes, 
 exerts, in virtue of its attraction for the tubes, a 
 certain pressure, by which the vessels are swoln 
 and enlarged. The particles of liquid in these 
 tubes undergo a counter-pressure from the elastic 
 parietes, by which pressure, when the attraction of 
 the liquid particles for the solids is diminished by 
 any new cause, the amount of expelled fluid is 
 increased. 
 
 The organic parietes of the tubes, saturated with 
 water, are affected by alcohol just as a salt is when 
 dissolved in water. On the addition of alcohol, or 
 of another liquid, the water separates from the salt, 
 or from the parietes, or the parietes separate from 
 the water. 
 
 If the animal tissue possessed as great an attrac- 
 tion for the newly-formed mixture as for the water 
 
LIQUIDS MIXING THROUGH A MEMBRANE. 41 
 
 alone, the volume of the liquid would not change. 
 The mixture would take place, but no water would 
 flow out. 
 
 A bladder, saturated with water, when brought 
 in contact with alcohol, shrinks together, a part of 
 the water separates from the animal matter, but 
 there always remains in the bladder a certain 
 amount of water, corresponding to its attraction for 
 the bladder and for the alcohol ; just as the solutions 
 of many salts which have a strong attraction for 
 water (such as metaphosphate and acid phosphate of 
 soda), and are insoluble in alcohol, are separated by 
 the addition of alcohol into two strata of liquid, 
 the heavier of which is a more concentrated solu- 
 tion of the salt in water, containing a little alcohol, 
 while the other, the lighter, is an aqueous liquid 
 containing much alcohol. The alcohol and the salt 
 divide between them the water of the solution. 
 
 When we add, to a mixture of equal parts of Action of 
 acetone and water, a certain quantity of dry frag- 
 
 ments of chloride of calcium, the first fragments 
 which are added deliquesce and dissolve entirely in and water ' 
 the mixture. But if we go on adding the salt, a 
 separation soon occurs, two strata of liquid are 
 formed, of which the upper contains acetone and 
 water, the other is an aqueous solution of the 
 chloride with a little acetone. If we add still more 
 of the chloride, water is abstracted from the acetone 
 of the upper stratum, and when a proper quantity 
 
42 EFFECT OF EVAPORATION ON 
 
 has been added, the acetone retains no trace of 
 water. 
 
 If we suppose, that of the two originally formed 
 strata of liquid, one of them, namely that which 
 sinks and contains chloride of calcium dissolved, is 
 in contact with a current of dry air, the water of 
 this solution will evaporate, the solution will thus 
 become stronger, and in consequence of its increased 
 concentration will be able to remove a new portion 
 of water from the mixture of acetone and water 
 above it ; and this will continue till the acetone is 
 entirely deprived of water. 
 
 Effect of If in the place of the chloride of calcium we put 
 through i n a bladder, and, in place of the acetone and water, 
 diluted alcohol, we have the finest example of the 
 
 lol< unequal attraction which the animal tissue exerts on 
 the two ingredients of the mixed liquid. 
 
 It is known from the experiments of SOEMMERING, 
 that spirits of a certain strength inclosed in a blad- 
 der, which is exposed to the air, lose by evaporation 
 only water, and that at last anhydrous, or nearly 
 anhydrous (absolute) alcohol is left in the bladder. 
 When strong spirits of wine are used, the bladder 
 remains dry externally; when weaker spirits are 
 employed, it becomes moist, and alcohol evaporates 
 with the water. In virtue of the unequal affinity 
 of the bladder for alcohol and for water, a com- 
 plete separation is here effected. The water of the 
 mixture is absorbed and evaporates from the outside 
 
LIQUIDS CONFINED BY MEMBRANES. 43 
 
 of the bladder ; the alcohol remains in the bladder. 
 As yet, we are acquainted with no substance which 
 can replace the bladder in this operation ; and 
 indeed the affinity of the gelatinous tissues. (mem- 
 branes, &c.) for water must exceed that of all other 
 animal tissues, since a rise of temperature, of a few 
 degrees only, suffices to enable water to dissolve that 
 tissue perfectly into a jelly. 
 
 MAGNUS assumes, " that the particles of every views of 
 solution, for example, of a salt in water, adhere 
 more strongly to each other than do those of the 
 solvent, for example, of water; consequently, the 
 solution would be less fluid, and pass with greater 
 difficulty through very narrow openings, than water, 
 if we take for granted that the parietes of the 
 openings act alike towards both. It would follow 
 from this, that, the more concentrated a solution, 
 the less easily would it pass through the same 
 openings." 
 
 " Let us now try," pursues MAGNUS, " with the 
 aid of these assumptions, (which, as appears from 
 the experiment Fig. 1, are perfectly accurate and 
 demonstrable for many saline solutions, although 
 there are, according to the researches of POISEUILLE, 
 a number of exceptions*) to explain the phenomena 
 of Endosmosis." 
 
 " Both the brine and the water will penetrate 
 into the pores of the bladder, and brine will pass 
 
 * Ann. de Ch. et de Phys. 3rd series, xxi. pp. 84 et seq. 
 
44 VIEWS OF MAGNUS 
 
 from the pores to the water, as well as water to the 
 brine, in virtue of their mutual attraction, till a 
 complete equilibrium is established. Further, since 
 the force which attracts the water to the brine is 
 exactly the same as that which attracts the brine to 
 the water, as much water as brine would pass 
 through the bladder, if both liquids could pass with 
 equal facility through the pores. Since, however, 
 this is not the case, unequal forces are required to 
 urge the two liquids through the pores ; or with 
 equal forces, unequal quantities of the two pass 
 through in equal times. There is consequently 
 added more of that which passes most easily, the 
 water to the brine, than of the latter to the water, 
 and the level of both liquids must change, if no 
 other force oppose this change."* 
 
 Remarks According to this theory, brine and water exist 
 theory of in the pores of the bladder in a state of motion, 
 and the chemical affinity, which the particles of the 
 brine have for the particles of the pure water, and 
 conversely, which the particles of water have for 
 those of salt, is considered as the cause of this 
 motion. The unequal velocity, which makes more 
 water flow in a given time to the brine than brine 
 or salt to the pure water, is, according to MAGNUS, 
 determined by the unequal resistance which the 
 substance of the bladder opposes to the passage of 
 the two liquids. 
 
 Now, however narrow the tubes may be, in which 
 * Poggendorff's Annales, x. p. 164. 
 
ON ENDOSMOSIS EXAMINED. 45 
 
 molecules are set in motion by an external force, 
 it may always be assumed, that that part of the 
 molecules, which is immediately in contact with the 
 wall of the tube, either is not in motion, or possesses 
 only a small velocity, and the velocity of efflux 
 must be a function of the cohesion, and at all events 
 not dependent on the wall of the tube. 
 
 If now the efflux of the water on one side of the 
 bladder is produced by the attraction of the saline 
 particles for the water, and the efflux of the brine 
 on the other side is produced by the attraction of 
 the aqueous particles for the saline particles, it is 
 impossible to explain how water and brine can 
 move in the same tube with unequal velocity in 
 opposite directions ; the two liquids being supposed 
 to have a mutual attraction, that is, to be miscible. 
 This attraction must act within the tube just as 
 well as without; and we might therefore suppose, 
 that when the two liquids have become mixed, the 
 mixture could only move in one direction with a 
 medium velocity. 
 
 Assuming that a mixture is formed in the open 
 orifices of the pores or tubes, or in any part of 
 them, it is difficult to see, why saline particles 
 should not pass from one side to the water, or 
 aqueous particles to the saline ones in the bladder, 
 since the mutual attraction must be regarded as 
 equal on both sides. The chemical affinity of the 
 two liquids does not explain the efflux. 
 
 If we suppose, that in certain pores only brine, 
 
46 THE MIXTURE IS INFLUENCED BY THE 
 
 in others only pure water moves, the phenomenon 
 ought not to occur when all the pores are filled with 
 water or with brine, or when the tube is tied with a 
 double, treble, or fourfold bladder. But the pro- 
 perties of bladder are seen in the finest as well as 
 thickest membranes, and one, two, or three layers 
 make no difference in the ultimate result.* 
 
 * With respect to the theory, that, when a saline solution 
 is mixed with pure water, if the two liquids are separated by 
 a membrane, particles of salt alone pass through the pores of the 
 bladder to the water, and particles of water alone to the brine, 
 the following experiments may throw some light on the question. 
 For the sake of greater accuracy, the results were determined by 
 weighing. The apparatus Fig. 3 was used. The tube contained 
 8*67 grammes of saturated brine, in which were 2*284 grammes 
 of salt and 6'38 of water. After 24 hours it had gained 1*79 
 grammes in weight, and it now contained only 0*941 grammes of 
 salt. It had therefore lost 1*343 grammes of salt, and gained 
 3' 13 of water. According to the above theory, 1 atom of salt 
 and 15 atoms of water must have moved past each other; but 
 this is impossible, since 1 atom of salt requires 18 atoms of water 
 for solution, (10 parts of salt to 27 of water). The weight of 
 the pure water in the outer vessel was 19*26 grammes ; con- 
 sequently, the weight of the brine was to that of the pure water as 
 1 : 2-22. In another experiment, in which the weight of the brine 
 in the tube was to that of the water outside, as 1 : 7*98 ; the tube 
 gained 0-822 grammes in weight ; the liquid in the tube contained 
 at first 0*947 grammes of salt ; and 24 hours after, 0*148 grammes : 
 hence, 1*621 grammes of water had entered, while 0*799 grammes 
 of salt had passed out. For 1 atom of salt, which passed from 
 the tube with brine to the vessel with water, there passed from 
 the latter to the former rather more than 13 atoms of water; 
 (for 58*6 parts, or 1 atom of salt, 118 parts of water). 
 
ATTRACTION OF THE MEMBRANE FOR THE LIQUIDS. 47 
 
 The kind of influence which the nature of the The nature 
 
 ,1 i. . i , ofthemem- 
 
 partition, or its attraction for the liquids in contact bnme has 
 
 11 . i an iinpor- 
 
 with it, exerts on the phenomenon, is seen by com- ta nt in- 
 paring the action of an animal membrane with that 
 of a thin sheet of caoutchouc. 
 
 In a tube, closed with bladder, which is filled Experi- 
 ment with 
 with alcohol, and immersed in pure water, the bladder, 
 
 volume of the alcohol is increased; more water 
 passes to the alcohol than alcohol to the water. 
 
 If, without making any other change in the ex- and with 
 
 caoutchouc. 
 
 penment, the tube be closed with a thin sheet or 
 caoutchouc, the volume of the alcohol now dimi- 
 nishes, while that of the water increases. 
 
 Here, all the circumstances of the mixture of 
 the two liquids have remained the same, except the 
 nature of the partition, which makes the difference 
 in the result. 
 
 When we fill with brine a tube Experi- 
 
 ment to 
 
 closed with bladder (Fig. 8), and prove the 
 
 attraction 
 
 place it in a vessel of water, so that of the biad- 
 
 i der for t* 16 
 
 the bladder and water only commu- liquid, 
 nicate by a single drop, the liquid in 
 the tube increases in bulk, and rises 
 in the tube, as if the bladder had been 
 immersed in the water ; but the drop 
 becomes gradually smaller, till after 
 an hour or two, a complete separation takes place, 
 and the drop tears itself away from the water.* 
 
 * If we pour into a tube, ^ of an inch wide, and closed with 
 bladder, as much mercury as covers the surface of the bladder, 
 
48 ATTRACTION OF MEMBRANES 
 
 If the cause of the change of volume in this 
 experiment were the unequal resistance which the 
 bladder opposes to the passage of the two liquids 
 with equal attraction (equal force) on both sides, 
 the phenomenon just described would be inexplica- 
 ble ; for a resistance can no doubt impede, but is 
 not capable of producing, motion. But we see, 
 that the water in this experiment is raised to a 
 higher level, and moreover, the tearing asunder of 
 the drop can only be the effect of a powerful attrac- 
 tion, residing in the substance of the bladder. 
 One liquid If the moistening of solid bodies by liquids be 
 another the effect of a chemical attraction, the force of 
 membrane, which is different in dissimilar liquids, it follows, 
 that when a porous body is saturated with a liquid, 
 and brought in contact with a second liquid, which 
 has a stronger attraction for its substance than the 
 first has, then the first liquid must be displaced 
 from the pores by the second, even in the absence 
 of hydrostatic pressure, and this, whether the two 
 liquids be miscible or not. 
 
 We may suppose that the attraction of the 
 second liquid, of more powerful affinity, which dis- 
 places the other, is equal to the pressure of the 
 column of mercury required to force the latter 
 through the porous substance. 
 menTto ^ we *i e over one en( l ^ a cylindrical tube with 
 
 prove this. 
 
 then fill it with brine, and place it in pure water, the volume of 
 the liquid in the tube increases exactly as if the mercury were not 
 there. 
 
FOR DIFFERENT LIQUIDS. 49 
 
 a very thin membrane, saturated with concentrated 
 brine by steeping for 24 hours, and if we dry the 
 outer surface of the membrane carefully with 
 bibulous paper, and now pour a few drops of. pure 
 water into the tube so as just to cover the inner 
 surface of the membrane, the outer surface is seen 
 in a few moments to be covered with minute drops 
 of brine ; that is, brine flows out of the pores of 
 the bladder. 
 
 A thick ox-bladder, saturated with oil, exhibits 
 the same phenomenon in contact with water. The 
 oil is expelled from the pores of the bladder by the 
 water, which occupies its place. 
 
 When the bladder is brought in contact with Explana- 
 tion. 
 pure water, it takes up a certain quantity of that 
 
 liquid. If its pores are previously filled with brine, 
 and if we cover one side of it with pure water, the 
 water mixes with the brine in the pores of the 
 bladder ; and on the side next the water there is 
 formed a diluted brine, which, being in contact 
 with a stratum of pure water, mixes with it, and 
 in this way the successive strata of water receive, 
 from the bladder outwards, a certain quantity of 
 salt. 
 
 In the interior of the bladder, there are formed 
 in like manner, towards the outer surface, mixtures 
 of unequal saline strength. If we suppose the 
 bladder to consist of several strata, all these strata 
 receive, from the surface in contact with the water, 
 a certain quantity of water ; the outer stratum, in 
 
 E 
 
50 UNEQUAL ATTRACTION OF MEMBRANES 
 
 contact with the air, receives least, and is the most 
 highly charged with salt. 
 
 The cause of mixture is the chemical affinity of 
 the salt for the newly-added particles of water ; this 
 affinity is equal on both sides, but the attraction of 
 the substance of the bladder is stronger for the 
 more aqueous or less saline liquid, than for the 
 more concentrated. In consequence of this differ- 
 ence in the attraction of the liquids for the sub- 
 stance of the bladder, a part of the mixture is dis- 
 placed from the bladder ; the less saline liquid 
 takes the place of the more saline ; a part of the 
 latter is expelled, and, with it, a part of that water 
 which has been added to the outer stratum by mix- 
 ture. Brine and water flow out in the direction of 
 least resistance. The efflux towards the side on 
 which the pure water was poured is prevented by 
 the stronger attraction of the more watery liquid 
 for the substance of the bladder. 
 
 If we remove from the outer surface of the 
 bladder the displaced saline liquid (which has been 
 mixed with some water), and put stronger brine in 
 its place, and if on the opposite side we remove the 
 very diluted solution, replacing it by a still more 
 diluted one, the same process is repeated. There 
 arises a permanent difference, and a state of mix- 
 ture and efflux continues till the liquids on the 
 opposite surfaces of the bladder have the same, or 
 very nearly the same, composition. 
 
 If we suppose, that the two liquids moisten the 
 
FOR DIFFERENT LIQUIDS. 51 
 
 bladder unequally, it follows, that in addition to the 
 chemical attraction which the dissimilar particles of 
 the liquids have for each other, a new cause, namely, 
 the stronger attraction of one of them for the sub- 
 stance of the partition, is introduced, which acce- 
 lerates their motion or passage, and must have this 
 effect, that one of them flows out in larger quantity, 
 in the same time, than the other. 
 
 The experiments (Fig. 3) elucidate this process, Mixture is 
 and shew besides, that the exchange of the two determined 
 liquids on both sides of the bladder is essentially equal 61 
 determined by their unequal specific gravities. As theHquids. 
 long as the difference in their composition (which 
 may here be measured by the specific gravity) is 
 very great, the change of volume (increase of one 
 and decrease of the other) takes place rapidly ; but 
 at last, when this difference becomes very small, the 
 liquids mix without further visible change of volume, 
 obviously, because the attraction of the bladder to 
 the mixtures on the opposite sides does not per- 
 ceptibly differ, although the specific gravities are 
 still somewhat unequal. 
 
 In the ultimate result, the action of dissimilar The action 
 
 . of two 
 
 liquids on the substance of animal tissues, in conse- liquids on 
 quence of which their mixture is attended with a tissues 
 
 change of volume, appears to be equivalent to 
 a mechanical pressure, which is stronger from one 
 side than from the other. apposite" 1 
 
 E2 
 
52 THE ATTRACTION OF LIQUIDS FOR MEMBRANES 
 
 Experi- 
 ment to 
 shew that 
 an external 
 pressure 
 prevents 
 change of 
 volume. 
 
 rig.9. 
 
 If the tube (Fig. 9), which is 
 closed with bladder at its wide 
 opening, be filled with brine to 
 the mark a, if so much mercury 
 be then poured into the narrow 
 vertical part as by its pressure 
 to cause brine to begin to flow 
 out in fine drops from the pores 
 of the bladder, and if now, after 
 removing so much of the mer- 
 cury that the efflux is no longer 
 visible, we place the apparatus 
 in a vessel with pure water, co- 
 loured blue, as in the figure, the mercury does not 
 change its level ; and when, after one or two hours, 
 we carefully remove the tube from the water, we 
 find that in the upper part of the wide end of the 
 tube, which contained colourless brine, a dark blue 
 stratum has been formed, which floats on a colour- 
 less liquid. After a longer time, the blue colour 
 spreads gradually downwards, till at last the brine 
 acquires a uniform blue tint. 
 
 It will readily be perceived, that the two liquids 
 here mix, as if no pressure had been applied to the 
 brine, for a mechanical pressure exerts no influence 
 on the mixture ; but, in consequence of the pres- 
 sure, the mixture takes place without change of 
 volume. The mechanical pressure which the water, 
 in virtue of its stronger affinity for the bladder, 
 exerts on the brine in the pores of the bladder, is 
 
IS EQUIVALENT TO A MECHANICAL PRESSURE. 53 
 
 held in equilibrium by the column of mercury, and 
 the result is that exactly as much brine flows 
 out as water flows in. 
 
 Let us suppose the column of mercury to be re- Additional 
 
 . . experiment. 
 
 moved, and the rise of the brine in the narrow tube 
 is explained at once. If we close a short tube, 
 filled with alcohol or brine, with bladder at both 
 ends (an arrangement which may represent a cell), 
 and suspend it in a vessel of pure water, both sur- 
 faces of the bladder become convex outwards ; they 
 sw r ell, but without bursting. As soon as the pres- 
 sure, gradually increasing by the influx of water 
 into the interior of the tube, is sufficient to keep in 
 equilibrium the affinity of the water for the blad- 
 der, and consequently its further influx, the ex- 
 change goes on, for the future, without change of 
 volume. 
 
 Most porous bodies exhibit the phenomena de- Porous 
 
 t bodies in 
 
 scribed in the preceding pages, if their pores are so general 
 
 exhibit 
 
 minute that a feeble hydrostatic pressure is not pro- similar 
 
 phenomena. 
 
 pagated through them. Ihese phenomena may be 
 produced with clay cells* (such as are used for gal- 
 
 * I consider it of sufficient importance to state here that s n ab f 
 porous clay also takes up unequal volumes of brine and water, sorbed by 
 In special experiments made on this subject, cells of clay (mode- baked 8 clay, 
 rately ignited porcelain biscuit) were laid for 24 hours in pure 
 water, then carefully dried externally with bibulous paper, and 
 the increase in weight, that is, the weight of the absorbed water, 
 carefully determined. The clay was then carefully dried, laid 
 for 24 hours in brine, and the weight of the absorbed brine 
 determined in like manner. In a second series of experiments, 
 
54 
 
 ACTION OF LIQUIDS ON THE 
 
 Bladder 
 shrinks in 
 contact 
 with brine 
 or alcohol. 
 
 vanic apparatus) ; with the lining membrane of the 
 pods of peas and beans ; with the fine inner bark of 
 trees ; with the skin of grapes, of potatoes, of apples ; 
 with the inner membrane of the capsules of bladder 
 senna, &c. ; but animal tissues surpass all others in 
 efficacy. Besides their unequal affinity, they have 
 an unequal absorbent power for dissimilar liquids, 
 by which their action in causing change of volume 
 during mixture is strengthened. 
 
 When a tube, closed with bladder, and filled with 
 water, is immersed in alcohol or brine, there is pro- 
 duced at all points, where the brine or the alcohol 
 comes in contact with bladder saturated with water, 
 a change in the properties of the bladder. When, 
 in the open pores, the alcohol or brine mixes with 
 the water already there, the absorbent power of the 
 bladder for the water is diminished ; a smaller vo- 
 lume of the mixture is retained than of pure water ; 
 that is to say, water flows out in the direction of 
 
 the clay cells were steeped in water and brine, and placed in the 
 receiver of the air-pump, under a pressure of 8 lines of mercury 
 ( of an inch) for 24 hours. 
 
 Under the ordinary pressure, and in air the cells absorbed 
 
 Weight. Volume. 
 
 Water. Brine. Water. Brine. 
 100 parts of clay cell I. 15'4 14'6 15'4 12'2 
 
 II. 11-8 11-6 
 
 In vacuo the cells of clay absorbed 
 
 Weight. 
 Water. Brine. 
 100 parts of clay cell absorbed I. 16-5 16'8 
 
 II. 13-8 13-8 
 
 11-8 9-7 
 
 Volume. 
 
 Water. Brine. 
 
 16'5 14'0 
 
 13-8 11-5 
 
MEMBRANE SEPARATING THEM. 55 
 
 the alcohol or brine. This efflux is accompanied 
 bj a change in the volume of the substance of the 
 bladder, for that side of it which is towards the 
 alcohol or the brine contracts or shrinks. 
 
 The opposite surfaces of an animal membrane, in 
 contact with dissimilar liquids, for which they have 
 unequal absorbent power, are in an unequal state of 
 contraction. This condition is permanent, as long 
 as the liquids do not change in their properties ; but 
 it ceases, in consequence of mixture, and is again 
 restored when, by means of the change of place in 
 both the liquids which are in contact with the oppo- 
 site surfaces of the bladder, the original or any 
 other permanent inequality or difference of proper- 
 ties is produced. 
 
 In all cases where a permanent change in the Change of 
 volume of two liquids, separated by a membrane, is 
 
 observed during their mixture, it is always accom- by P mem- 
 panied by a permanent difference in the nature or 
 properties of the two liquids ; and from this it 
 follows, that the molecules of the animal membrane 
 must be, during the mixture, in an alternate state of 
 contraction and swelling, or dilatation ; that is, in a 
 continual motion. 
 
 From what has been stated, it appears that the and de- 
 change of volume of two miscible liquids, separated the un- 
 by a membrane, is determined by the unequal capa- tSon of 
 city of being moistened, or the unequal attraction brane for" 
 of the membrane for these liquids. The unequal 
 absorbent power of the membrane for these liquids 
 
56 EXAMPLES OF CHANGE OF 
 
 depends on the dissimilar nature of the liquids or 
 of the substances dissolved in them. An unequal 
 proportion of the same dissolved matters (unequal 
 concentration), acts in many cases, just as if the 
 liquids contained dissimilar substances. 
 
 Although the experiments hitherto instituted, and 
 the results obtained by FISCHER (who first observed 
 these phenomena), MAGNUS, DUTROCHET, and others, 
 admit of no comparison, since the apparatus used 
 by them shewed only relative change of volume, 
 yet a knowledge of some of these results is never- 
 theless of importance. 
 
 Examples When the two liquids are, diluted sulphuric acid 
 
 ofvohTme; (of sp. g. T093) and water, the acid, at 50 F., 
 increases in volume ; but if the acid have the 
 specific gravity 1-054, the volume of the water 
 increases. 
 
 in acids, Diluted tartaric acid (11 parts of the crystallized 
 
 acid and 89 of water) and water mix through a 
 bladder without change of volume ; with more than 
 11 per cent, of acid, the volume of the acid in- 
 creases ; with less, that of the water. 
 
 and neutral Solutions of animal gelatine, gum, sugar, and 
 albumen increase in volume when separated by a 
 bladder from water ; and the increase of volume in 
 these different solutions, although of the same spe- 
 cific gravity, is very different indeed. When the 
 specific gravity is 1*07, the increase in volume of 
 the solution of gelatine amounts to 3, that of solu- 
 tion of gum to 5, of sugar 11, of albumen 12. 
 
VOLUME IN LIQUIDS. 57 
 
 When a solution of sugar (1 part of sugar to 16 of 
 water) is separated by a bladder from water, it in- 
 creases in volume ; but if we add 1 part of oxalic 
 acid to the sugar, the water, on the contrary, in- 
 creases in volume. If the amount of sugar in the 
 solution be doubled, the liquids mix without change 
 of volume. A solution of sugar, separated by 
 bladder from one of oxalic acid, rises, in the same 
 time, 3 times higher than when separated from 
 water. (DUTROCHET.) 
 
 From these experiments we obtain, as a universal Membranes 
 result (which, however, requires confirmation), that bk power" 
 an animal membrane possesses a less power of ab- fng^ouTtion 
 sorption for solution of albumen than for all other 
 organic substances; and that a small amount of Effect of 
 mineral or organic acids increases the power of adds, 
 transudation of water as well as of the solutions of 
 many organic substances.* 
 
 The rapidity of mixture of two liquids, separated Causes 
 
 ( t which in- 
 
 by a membrane, depends on the thickness of the fluence 
 membrane, and stands in direct proportion to the 
 
 velocity with which the mixture formed in the 
 
 * In order not to be misled in such experiments, we must avoid 
 the employment of all those liquids which alter the membrane in 
 its chemical properties. Such are, for example, acids of a cer- 
 tain concentration, nitrate of silver, salts of lead, chloride of 
 gold, chloride of tin, chromic acid, bichromate of potash, taunic 
 acid, &c. Even in water, the properties of membranes generally 
 undergo a change after some days, they then propagate a far 
 weaker hydrostatic pressure through their pores, and are no 
 longer fit for such experiments. 
 
58 CAUSES OF ABSORPTION OF OTHER 
 
 pores and on both surfaces of the bladder changes 
 its place, and the original difference in the quality 
 of the two liquids is renewed. 
 
 Motion of If we suppose a tube, formed of a membrane (an 
 liquids. intestine, for example), and filled with water, and if 
 we assume that a current of saline solution flows 
 round this tube, in consequence of a mechanical 
 force, the increase of volume of the brine (the pas- 
 sage into it of a certain amount of water) will be 
 effected in a far shorter time than if the brine were 
 not in motion. 
 
 Difference The velocity of transference will diminish with 
 
 tilf of P the" the amount of difference in properties between the 
 
 liquids. twQ ]jq u j^ g ^ t h e Different amount or per-centage of 
 
 salt) ; it will be greatest at first, and diminish as 
 
 the dilution of the brine increases, in proportion, 
 
 that is to say, as water is transferred from the con- 
 
 tents of the tube to the liquid without. 
 
 Effect of The greatest effect, therefore, must occur and be 
 
 tinued re- permanent, when the water transferred to the brine 
 
 is continually again removed from it, that is, when 
 the concentration of the brine is kept uniform. 
 To this end, if we suppose the membrane to be 
 difficultly permeable for one liquid, while the other 
 is easily taken up into its pores, and if we reflect, 
 that this second liquid, on entering into the pores 
 of the bladder, in virtue of the attraction of their 
 walls for it, acquires a certain velocity which per- 
 mits it to pass beyond the extremities of the canal 
 or of the pores, so as entirely to fill the pores, and 
 
ANIMAL FLUIDS INTO THE BLOOD. 59 
 
 to come in direct contact with the liquid on the 
 outside of the pores, it follows, that, when this 
 second liquid moves past the pores with a certain 
 velocity, the absorbed liquid must follow it during 
 the mixture, and there must take place a rapid analogous 
 
 to suction. 
 
 transference of the second liquid to the first, a true 
 suction as if by a pump. 
 
 The animal body is an example of an apparatus * occ v rs 
 
 J in the am- 
 
 of this kind in the most perfect form. The blood- mai body. 
 
 vessels contain a liquid, for which their walls are, in 
 
 the normal state, far less permeable than for all 
 
 the other fluids of the body. The blood moves 
 
 in them with a certain velocity, and is kept at all 
 
 times in a nearly uniform state of concentration by 
 
 a special apparatus, namely, the urinary organs. 
 
 The whole intestinal canal is surrounded with this Absorption 
 system of blood-vessels, and all the animal fluids, liquids of 
 
 in so far as they are capable of being taken up by 
 the parietes of the intestinal canal, and of the 
 blood-vessels situated around it, are rapidly mixed 
 with the blood. The volume of the blood increases, 
 if no compensation is effected by means of the 
 kidneys : and the intestine is emptied of the liquids 
 contained in it. The intestinal glands, through 
 which this transference is effected, and each of 
 which represents a similar apparatus of suction, 
 contain, within them, two systems of canals, blood- 
 vessels and lacteals; the blood-vessels are placed 
 next to the external absorbent surface, the lacteals 
 chiefly occupy the central part of the gland. The 
 
60 
 
 EFFECTS PRODUCED BY DRINKING 
 
 Effects pro- 
 duced by 
 drinking 
 water and 
 saline solu- 
 tions. 
 
 Spring 
 water. 
 
 Solution 
 containing 
 f to 1 per 
 cent, of 
 salt. 
 
 liquids circulating in these two systems have very 
 unequal velocities, and as the blood moves much 
 faster in the blood-vessels, we perceive how it 
 happens, that the fluids of the intestine are chiefly 
 (in quantity and in velocity) taken up into the 
 circulation. 
 
 The difference in the absorbent power of the 
 parietes of the intestinal canal for liquids which 
 contain unequal amounts of dissolved matters, is 
 easily observed in the effects produced on the 
 organism by water arid saline solutions. 
 
 If we take, while fasting, every ten minutes, a 
 glass of ordinary spring water, the saline contents 
 of which are much less than those of the blood, 
 there occurs, after the second glass (each glass con- 
 taining 4 ounces), an evacuation of coloured urine, 
 the weight of which is very nearly equal to that of 
 the first glass ; and after taking, in this way, 20 such 
 glasses of water, we have had 19 evacuations of 
 urine, the last of which is colourless, and contains 
 hardly more saline matter than the spring water. 
 
 If we make the same experiment with a water, 
 containing as much saline matter as the blood (f to 
 1 per cent, of sea salt), there is no unusual discharge 
 of urine, and it is difficult to drink more than three 
 glasses of such water. A sense of repletion, pres- 
 sure, and weight of the stomach point out, that 
 water as strongly charged with saline matter as the 
 blood requires a longer time for its absorption into 
 the blood-vessels. 
 
WATER AND SALINE SOLUTIONS. 61 
 
 Finally, if we drink a solution containing rather Solution 
 
 * f containing 
 
 more salt than the blood, a more or less decided more salt 
 
 than the 
 
 catharsis ensues. blood. 
 
 The action of solution of salt is of three kinds, 
 according to the proportion of salt. Spring water is 
 taken up into the blood-vessels with great rapid- 
 ity ; while these vessels exhibit a very small power 
 of absorption for water containing the same pro- 
 portion of salt as the blood does ; and a still more 
 strongly saline solution passes out of the body not 
 through the kidneys, but through the intestinal 
 canal. 
 
 Saline solutions and water, given in the form of Enemata of 
 enemata, exhibit similar phenomena in the rectum. Sine ^iu- 
 Pure water is very rapidly absorbed, and excreted 
 through the urinary passages. If we add to the 
 water coloured or odorous matters, these appear, 
 more or less changed in the urine. When a small 
 quantity of ferrocyanide of potassium is added, its 
 presence in the urine is very soon detected by chlo- 
 ride of iron, which forms with it Prussian blue. Of 
 concentrated solutions far less is absorbed in the 
 same time, than of diluted ; in most cases they mix 
 with solid matters collected in the rectum, and are 
 expelled in the form of a watery dejection. 
 
 All salts do not act alike in this respect. In Salts differ 
 equal doses, the purgative action of Glauber salt respect. 
 and Epsom salt is far stronger than that of sea salt ; 
 and their power of being absorbed by animal mem- 
 branes appears to be in the inverse ratio of this 
 
62 MEMBRANES PROBABLY EXERT 
 
 effect. It is hardly necessary, particularly to point 
 out that an explanation of the action of purgatives in 
 general cannot be included in the above-described 
 action of saline solutions on the organism. The 
 example which has been given is intended to illus- 
 trate a physical property common to a large number 
 of salts, and apparently independent of the nature 
 of the acid or base of the salt ; for chloride of 
 calcium, chloride of magnesium, bitartrate of potash, 
 tartrate of potash and soda, phosphate of soda, and 
 certain doses of tartar emetic, shew the same action 
 as sea salt, Glauber salt, and Epsom salt, although 
 the bases and acids in these different salts are not 
 the same. 
 
 Organic Solutions of cane sugar, grape sugar, sugar of 
 
 milk, and gum, exhibit, when separated from water 
 by an animal membrane, phenomena similar to 
 those exhibited by the above-named solutions of 
 mineral salts, without causing in the living body a 
 purgative action, when of equal concentration. The 
 cause of this difference may be that the mineral 
 salts, in their passage through the intestinal canal, 
 and through the blood, are not essentially altered in 
 their composition, while these organic substances, in 
 contact with the parietes of the stomach, and under 
 the influence of the gastric juice, suffer a very rapid 
 change, by which the action which they have out of 
 the body is arrested. 
 
 influence Since the chemical nature and the mechanical 
 
 of mem- 
 branes on character of membranes and skins exert the greatest 
 
 secretions. 
 
AN IMPORTANT INFLUENCE ON SECRETIONS. 63 
 
 influence on the distribution of the fluids in the ani- 
 mal body, the relations of each membrane present- 
 ing any peculiarity of structure, or of the different 
 glands and systems of vessels, deserve to be investi- 
 gated by careful experiment; and it might very likely 
 be found that in the secretion of the milk, the bile, 
 the urine, the sweat, &c., the membranes and cell- 
 Avails play a far more important part than we are 
 inclined to ascribe to them ; that besides their 
 physical properties, they possess certain chemical 
 properties, by which they are enabled to produce 
 decompositions and combinations, true analyses ; 
 and if this were ascertained, the influence of che- 
 mical agents, of remedies, and of poisons on those 
 properties, would be at once explained. 
 
 The phenomena described in the preceding pages These phe- 
 nomena not 
 are observed, not in the gelatinous tissues alone, confined to 
 
 thegela- 
 
 but also, apparently, in many other structures of tinous 
 the animal body, which cannot be reckoned as 
 belonging to that class. 
 
 If we tie moist paper over the open end of a Coagulated 
 
 albumen 
 
 cylindrical tube, and, after pouring in above the acts like a 
 paper white of egg to the height of a few lines, brane. 
 place that end of the tube in boiling water, the 
 albumen is coagulated, and when the paper is re- 
 moved, we have a tube closed with an accurately 
 fitting plug of coagulated albumen, which allows 
 neither water nor brine to run through. If the 
 tube be now filled to one-half with brine, and im- 
 mersed in pure water as in Fig. 4, the brine is seen 
 
64 INFLUENCE OF THE CUTANEOUS 
 
 gradually to rise; and in three or four days it 
 increases by from ^ to ^ of its volume, exactly as 
 the tube had been closed with a very thick 
 membrane. 
 
 Influence of the cutaneous evaporation on the motion 
 of the fluids of the animal body. 
 
 influence of When a tube, about 30 inches long, bent in the 
 
 ous evapor- form of a knee, and widened at one end, is tied over 
 
 motion of e at that end with a piece of moist ox-bladder, the 
 
 fluid's 11 bladder now thoroughly dried, and the tube filled 
 
 with mercury and inverted, so that the open narrow 
 
 end stands in a cup of mercury, the mercury in the 
 
 tube falls to about 27 inches (Hessian), and remains, 
 
 if the bladder have no flow, at that height, rising 
 
 and falling as the mercury does in a barometer. 
 
 No air passes through the dry bladder into the 
 Torricellian vacuum thus produced. When, by 
 proper manipulation, we have allowed to pass out as 
 much as can be removed of the air still contained in 
 the tube, we have, in this arrangement, a barometer, 
 containing no more air than would be found in one 
 made with a similar tube hermetically sealed at the 
 wide end, provided the mercury in the latter had not 
 been boiled in the tube to expel the last traces of 
 air. By the desiccation of the bladder, its pores, 
 which allowed a passage to water, brine, oil, or even 
 mercury, have obviously been closed by the adhesion 
 of the successive layers of membrane, which per- 
 haps cross each other, so that the bladder is not more 
 
EVAPORATION ON THE MOTION OF THE FLUIDS 65 
 
 Fr'g-.lO 
 
 permeable for the particles of air than a slice of 
 horn of the same thickness. 
 
 If we introduce water 
 into the tube in the po- 
 sition Fig. 10, to the line 
 marked b, and, after fill- 
 ing the narrow part of 
 the tube with mercury, 
 invert it in a vessel of 
 mercury, Fig. 11, we ob- 
 serve a number of minute 
 
 
 
 bubbles of air passing 
 through the moist blad- 
 der into the tube. The 
 mercury falls to a certain 
 point, which is higher or lower according to the 
 thickness of the bladder ; it stands at a lower level 
 with a thin membrane than with a thick one. When 
 a single layer of ox-bladder is used, it falls to 12 
 inches (above the level of the mercury in the ves- 
 sel) ; with a double layer it stands at from 22 to 24 
 inches. 
 
 If we take care to allow the water standing above 
 the mercury to enter the wide part of the tube, so 
 that the bladder is kept at all times covered with 
 water, the mercury remains stationary at the same 
 level. If, for example, it stood at 12 inches, it 
 remains there, although the quantity of water is 
 constantly diminishing by evaporation from the 
 
 F 
 
 Experi- 
 ents. 
 
66 EFFECTS OF EVAPORATION. 
 
 bladder ; and it maintains its level, even after all 
 the water has disappeared. 
 
 The height of the mercury in the narrow tube is 
 an exact measure of the pressure acting on the sur- 
 face of the bladder. The pressure in the inside of 
 the tube is less than the existing pressure of the 
 atmosphere outside by the height of that column 
 of mercury. 
 
 This difference of level between the mercury in 
 the vessel and that in the tube is the limit of the 
 pressure, under which air passes into the water 
 through the pores of the bladder ; or under which 
 the molecules of water in the pores are displaced 
 by the molecules of air. 
 
 If we fill the tube entirely with water, and 
 place the narrow end in mercury, while the wide 
 end, closed with bladder, is exposed to the air, the 
 mercury rises in the narrow limb, and at last 
 reaches a point, identical with that to which it fell 
 in the preceding experiment. For each specimen 
 of bladder, according to its thickness, the level to 
 which the mercury reaches is of course different. 
 
 When the diameter of the wide part of the tube, 
 which is closed with bladder, is 12 millimetres, and 
 that of the narrow tube 1 millimetre, the mercury 
 rises, with ox-bladder, according to the temperature 
 and the hygrometric condition of the air, to from 22 
 to 65 millimetres in one hour. 
 
 The cause of the rise of the mercury in this 
 experiment hardly requires a special explanation. 
 
EVAPORATION THROUGH MEMBRANES. 
 
 The bladder is penetrated with water, covered 
 
 tion 
 
 on one side with water, and on the other in con- 
 tact with a space (the air) not saturated with 
 aqueous vapour. The water contained in the- pores 
 of the side of the bladder turned towards the air 
 evaporates ; the space which it had occupied in the 
 pores is filled with successive portions of water from 
 within, in virtue of the attraction of the substance 
 of the pores for water. The volume of the water 
 in the tube diminishes, and thus a vacuum arises, in 
 which the mercury is forced to rise by the atmo- 
 spheric pressure. The space formerly occupied by 
 the water which has evaporated is now filled with 
 mercury. 
 
 When the mercury has reached a permanent 
 level, the external pressure, which acts on the 
 water in the pores of the bladder (and which tends 
 to displace the particles of water) is obviously equal, 
 before air enters, to the attraction which the sub- 
 stance of the bladder has for the particles of water, 
 and these last to each other. Were the attraction 
 less, air w r ould enter, and the particles of water 
 could not maintain their position. 
 
 The rise of the mercury, or its motion towards 
 the surface of the bladder, that is, towards the 
 point where evaporation is going on, is the result of 
 a difference of atmospheric pressure, determined by 
 the evaporation of the water, or of the liquid which 
 penetrates through the bladder, and by the ab- 
 sorbent power of the bladder for that liquid. 
 
 F2 
 
68 INFLUENCE OF THE ATMOSPHERIC PRESSURE 
 
 One chief condition of the efficiency of a bladder, 
 in regard to the rise of a column of liquid, is, that 
 it is kept constantly in contact with the liquid, for 
 without this contact the absorbent power cannot 
 manifest itself. 
 
 By the evaporation a continual efflux of water, in 
 the form of vapour, towards the side on which the 
 air lies, is produced ; and by the capillary action of 
 the bladder on the other side water is absorbed and 
 retained with a force which counterpoises 12 or 
 more inches of mercury, according to the thickness 
 of the bladder, 
 influence of Now, since the rise of the mercury is an effect of 
 
 the state 
 
 of the the atmospheric pressure, it is plain, that the height 
 
 barometer. 
 
 to which the mercury rises, must depend to a certain 
 degree on the state of the barometer. 
 
 In a tube, filled with water, and closed with 
 bladder, the absorbent force of which is equal to 
 the pressure of a column of 12 inches of mercury, 
 the mercury rises by evaporation to the height of 
 12 inches, as long as a column of 12 inches of mer- 
 cury can be sustained by the external atmospheric 
 pressure. If this external pressure fall below that 
 limit, the mercury in the evaporation tube falls to 
 the same extent, and if there be water above the 
 mercury, this water separates from the bladder. 
 
 This property of bladder, therefore, would appear 
 unaltered at an elevation at which the barometer 
 should stand at 12 inches ; at a still greater eleva- 
 tion, on the contrary, the liquid would separate 
 from the bladder. 
 
ON THE LEVEL OF THE MERCURY. 
 
 69 
 
 The external pressure has no influence on the Thepres- 
 
 sure of the 
 
 amount or the water evaporating in the pores or the air does not 
 
 affect the 
 
 bladder ; that amount depends on the hygrometric amount of 
 
 evapora- 
 
 state of the surrounding air, and on the temperature, tion. 
 In a rarefied air (provided it can take up moisture), 
 evaporation goes on more rapidly than in a denser 
 air ; and hence it is clear, that at certain elevations, 
 the effect of the bladder on the level of the liquid 
 is more quickly produced than at the level of the 
 sea. The amount of water which evaporates is 
 directly proportional to the surrounding space, and 
 to the temperature and corresponding tension of the 
 liquid. 
 
 When the tube, Fig. 10, is filled with water to 
 b, then entirely filled with mercury, and inverted 
 in mercury, the mercury, as we have seen, assumes 
 a fixed level. If now we keep the upper or wide 
 end of the tube, which is closed with bladder, 
 immersed in a vessel of water, 
 Fig. 12, we shall find, after a 
 short time, that the mercury 
 sinks in the narrow tube. If 
 its level has been 12 inches 
 above that of the mercury in 
 the vessel, it sinks when the 
 bladder is put into water, 3 or 
 4 inches for example, and re- 
 mains stationary at 8 or 9 inches, 
 without sinking further for the 
 
 next 12 hours. 
 
 The sinking of 
 
70 WATER PASSES MORE EASILY THAN 
 
 the mercury is caused by water being forced through 
 the bladder into the tube, in virtue of the existence 
 of an external pressure greater than the pressure on 
 the inside of the tube. 
 
 Water To displace the aqueous particles in the pores of 
 
 through the bladder by other aqueous particles, requires 
 
 moist blad- 
 der more obviously a much smaller pressure than is necessary 
 
 easily than 
 
 air does. to displace them by particles of air. In the one 
 case, where both surfaces of the bladder are in con- 
 tact with the liquid, the attractive force (that of the 
 bladder for the water and of the water for the blad- 
 der) is equal on both sides ; but not so in the other 
 case, where one side of the bladder is in contact 
 with air. If the bladder had the same absorbent 
 power for the particles of air as for those of water, 
 the particles of air and water would pass through 
 the bladder under the same pressure ; the experi- 
 ment shews, that the absorbent power and perme- 
 ability of the bladder for air is far less than for 
 water. Hence it comes to pass, that when, with a 
 given portion of bladder, in the apparatus, Fig. 11, 
 mercury is raised by evaporation to a height of 12 
 inches, less than 12 inches of mercury are required, 
 in the apparatus, Fig. 1, to cause water to pass 
 through the bladder. 
 
AIR THROUGH MOIST MEMBRANES. 
 
 71 
 
 When the tube (Fig. 13) is filled 
 with water, closed with bladder at 
 both ends, and exposed to evapo- 
 ration, the bladders in a short time 
 become concave, that is, they are 
 pressed inwards. As the evaporation 
 of the water through the moist sur- 
 faces of the bladder proceeds, there 
 is formed in the upper part of the tube a vacuum, 
 which is filled with aqueous vapour, and which con- 
 tinues to increase. The place of the water which 
 evaporates is, as in the experiments previously de- 
 scribed, gradually occupied by air, which enters the 
 tube through the bladder. 
 
 It is evident, that when air enters the tube (Fig. 
 13), the pressure on the surface of the bladder is 
 equal to the absorbent force of that bladder for the 
 water. In the apparatus, Fig. 11, with the same 
 bladder, the mercury might have been raised, in 
 consequence of the evaporation, to a height of 4, 6, 
 12, or more inches, according to the thickness of 
 the membrane. 
 
 When the longer limb of the bent 
 tube, after it has been filled with 
 water, and closed at both ends with 
 bladder, is placed in a vessel contain- 
 ing brine, and exposed to evaporate in 
 the air, as in Fig. 14, it is plain, that 
 when the atmospheric pressure, in- 
 creasing in consequence of the evapo- 
 ration of the water on both "the sur- 
 
 Experi- 
 ments with 
 a tube 
 closed at 
 both ends 
 with blad- 
 der: 
 
 with one 
 end in 
 brine, the 
 tube being 
 filled with 
 water : 
 
72 EVAPORATION THROUGH MEMBRANES. 
 
 faces of the bladder, reaches the point at which the 
 brine flows through the pores of the bladder, then 
 the place of the water which evaporates is occupied 
 by brine. 
 
 In fact, when the brine is coloured blue, we ob- 
 serve, after a few hours, that a blue stratum forms 
 within the tube, which constantly increases, till at 
 last the vessel of brine is emptied, and the tube is 
 entirely filled with brine. 
 
 with one If the longer limb be immersed in bile instead of 
 brine, the tube fills with bile, and if we employ, for 
 closing one end, a membrane rather thinner than we 
 use for the other, from which the evaporation takes 
 place, and then place the end with the thinner 
 
 and in oil. membrane in oil (oil of marrow), the tube gradually 
 fills w r ith oil. 
 
 In all these cases, no air enters the tube, which 
 continues full of liquid, as it was at first. 
 
 Effect of a If we connect the evaporation tube 
 
 series of 
 
 short tubes, by collars of caoutchouc with short 
 
 both ends bits of tube (Fig. 15), full of water, and 
 
 der. tied with bladder at both ends ; and 
 
 if we immerse the last bit of tube in 
 
 brine, urine, oil, &c., all these cells, 
 
 and at last the evaporation tube itself, 
 
 become gradually filled with brine, 
 
 urine, oil, &c. 
 
 Liquids T;h e most general expression for these experi- 
 
 wards the ments and results is this ; that all liquids which 
 
 membrane 
 
 from which are in connection with a membrane from the surface 
 
IMPORTANCE OF THE CUTANEOUS TRANSPIRATION. 73 
 
 of which evaporation can take place, must acquire evapora- 
 tion takes 
 motion towards that membrane. place. 
 
 The amount of this motion is directly propor- 
 tional to the rapidity of evaporation, and conse- 
 quently to the temperature and hygrometric state 
 of the atmosphere. 
 
 That the skin of animals, and the cutaneous influence 
 
 of the skin 
 
 transpiration, as well as the evaporation from the and cuta- 
 neous 
 
 internal surface of the lungs, exert an important transpira- 
 tion on 
 
 influence on the vital processes, and thereby on the health. 
 
 state of health, has been admitted by physicians ever 
 since medicine has existed ; but no one has hitherto 
 ascertained precisely in what way this happens. 
 
 From what has gone before, it can hardly be Thecuta- 
 
 . neous eva- 
 
 doubted, that one of the most important functions poration 
 
 has an im- 
 
 of the skin consists in the share which it takes portant 
 in the motion and distribution of the fluids of the causing the 
 
 T .. motion of 
 
 body. the animal 
 
 The surface of the body of a number of animals 
 consists of a covering or skin permeable for liquids, 
 from which, when, as in the case of the lung, it is 
 in contact with the atmosphere, an evaporation of j kin and 
 water, according to the hygrometric state and 
 temperature of the air, constantly goes on. 
 
 If we now keep in mind, that every part of the This evapo- 
 ration must 
 body has to sustain the pressure of the atmosphere, produce 
 
 and that the gaseous fluids and liquids contained in pressure ; 
 the body oppose to this pressure a perfectly equal 
 resistance, it is clear, that, by the evaporation of 
 the skin and lungs, and in consequence of the 
 
74 THE FLUIDS ACQUIRE A MOTION 
 
 absorbent power of the skin for the liquid in contact 
 with it, a difference in the pressure below the sur- 
 face of the evaporating skin occurs. The external 
 pressure increases, and in an equal degree the pres- 
 sure from within towards the skin. If now the 
 structure of the cutaneous surface does not permit 
 a diminution of its volume, a compression (in con- 
 sequence of the loss of liquid by evaporation), it is 
 obvious that an equalization of this difference in 
 pressure can only take place from within outwards ; 
 first from within, and especially from those parts 
 which are in closest contact with the atmosphere, 
 and which offer the least resistance to the action of 
 the external pressure, 
 by which Hence it follows, that the fluids of the body, in 
 
 the fluids 
 
 acquire consequence of the cutaneous and pulmonary tran- 
 
 a motion 
 
 towards the spiration, acquire a motion towards the skin and 
 lungs. lungs, which must be accelerated by the circulation 
 
 of the blood. 
 The change By this evaporation, the laws of the mixture of 
 
 of pressure 
 
 influences dissimilar liquids, separated by a membrane, must 
 
 the mix- 
 ture of the be essentially modified. The passage of the food 
 
 dissolved in the digestive canal, and of the lymph 
 into the blood-vessels, the expulsion of the nutritive 
 fluid out of the minuter blood-vessels, the uniform 
 distribution of these fluids in the body, the ab- 
 sorbent power of the membranes and skins, which, 
 under the actual pressure are permeable for the 
 liquids in contact with them, are under the in- 
 fluence of the difference in the atmospherical pres- 
 
TOWARDS THE SKIN AND LUNGS. 75 
 
 sure, which is caused by the evaporation of the 
 fluids of the skin and lungs. 
 
 The juices and fluids of the body distribute them- Effects of 
 selves, according to the thickness of the walls of the moist air, 
 vessels, and their permeability for these fluids, Ration on 6 
 uniformly through the whole body; and the influence 
 which a residence in dry or in moist air, at great 
 elevations or at the level of the sea, may exert on 
 the health, in so far as the evaporation may thus be 
 accelerated or retarded, requires no special explana- 
 tion ; while on the other hand, the suppression of 
 the cutaneous transpiration must be followed by a 
 disturbance of this motion, in consequence of which 
 the normal process is changed where this occurs. 
 
 The pressure, which, in consequence of the eva- The force 
 poration, urges the fluids within the body to move fluids to- 
 
 towards the skin, is, as may readily be understood, 
 equal to the difference of pressure acting on the 
 surface of the skin. 
 
 From the experiment, Fig. 13, it is plain, that the skm * 
 when one of the two surfaces of bladder at the ends 
 of the tube Fig. 12, is exposed to atmospheric evapo- 
 ration, while the other end is moistened with water, 
 brine or oil, these liquids are rapidly absorbed by 
 the membrane, that is, are forced in by the external 
 atmospheric pressure, and it is not less obvious, that 
 the same thing takes place with the liquid with which 
 one of the two evaporating surfaces has been 
 moistened in the middle only ; while the evaporation 
 continues around the moistened spot. 
 
76 EFFECTS OF CUTANEOUS EVAPORATION. 
 
 Liquids If therefore, we moisten with a liquid the sur- 
 
 placed on 
 
 the skin are face of the evaporating skin at any point, the liquid 
 
 by the eva- is forced inwards by the external pressure. 
 
 poration 
 
 of other Let us suppose any part of the skin to be rubbed 
 
 Effect of w ^h ^ at tne transpiration ceases at that part. If 
 
 f now ^ ie S ^ n around the part is in its normal 
 the skin activity, if, therefore, in the surrounding parts 
 liquid is constantly passing off by evaporation, the 
 fat must be urged, by the unequal pressure thus 
 arising, towards these parts, or it is absorbed, just 
 as water, in the apparatus, Fig. 12, is absorbed, 
 when in consequence of evaporation a difference 
 between the internal and external pressure has 
 or on the arisen. If the whole skin were covered with fat, 
 the absorption would be effected by the pulmonary 
 evaporation. 
 
 The blistering of the skin, and the sun-burning, 
 to which men are exposed at great elevations, arise 
 from the extraordinary dryness of the air, the in- 
 creased evaporation, and the pressure by which the 
 fluids filling the vessels are forced towards the 
 surface. 
 Causes of Several causes contribute iointly to the appear- 
 
 the efflux 
 
 of sweat, ance of the sweat, to the efflux of fluid from the 
 pores of the skin. One of these obviously depends 
 on the velocity, which the fluid set in motion by 
 evaporation or by a mechanical cause, acquires from 
 the accelerated motion of the blood. In conse- 
 quence of this velocity, the fluid moves out beyond 
 the limits of the absorbing membrane or skin. 
 
EXPERIMENTS OF HALES. 77 
 
 The changes of the vital process, caused by the Fishes die 
 unequal distribution of fluid in the body in conse- cause 'the 
 
 distribution 
 
 quence of evaporation, are best seen in animals of the fluids 
 
 which live in water, in whom, therefore, the above vented. 
 
 explained cause of motion in the normal state does 
 
 not act. When a fish is held immersed in water, 
 
 so that the head is out of the water, while the rest 
 
 of the body is covered, it dies in a few minutes. It 
 
 dies exactly in the same way when head and gills 
 
 are held in the water, and the body in air ( MILNE 
 
 EDWARDS) ; in both cases, without loss of weight. 
 
 This fact shews that even if the weight of the 
 
 animal be kept unaltered by the absorption of 
 
 water through the body kept in that medium, yet 
 
 the distribution of the fluids in the body does not 
 
 take place in the proportion necessary for the 
 
 preservation of their vital functions. The fish 
 
 dies. 
 
 It is hardly necessary to remind the reader, that 
 
 the experiments described in the foregoing pages, HALES* on 
 
 in so far as they permit us to draw conclusions as O f 
 to the cause of the motion of the juices of the mplai 
 animal body, agree in all respects with the observa- 
 tions made on plants by STEPHEN HALES more than 
 120 years since. 
 
 The experiments of HALES on the mechanism of 
 the motion of the sap, may stand as a pattern to all 
 times of an excellent method. That they remain, 
 to this moment, unsurpassed in the domain of 
 vegetable physiology, may be perhaps explained by 
 
78 EXPERIMENTS OF HALES ON THE 
 
 the fact that they date from the age of NEWTON. 
 They ought to be familiar to every vegetable 
 physiologist. 
 
 In the beginning of his work, HALES describes 
 the experiments which he made on the motion of 
 the sap in plants in consequence of their evapora- 
 tion in branches covered with foliage, in cut plants 
 as well as in those still provided with roots, 
 influenceof He shews by the following experiment the in- 
 
 a column of 
 
 water, with- fluence of the mechanical pressure of a column of 
 
 out evapo- 
 ration ; water, with and without the help of evaporation. 
 
 To a branch of an apple-tree bearing its twigs 
 and leaves, HALES fastened, air-tight, a tube 7 feet 
 long. He kept the branch with its twigs and leaves 
 immersed in a large vessel of water, and filled the 
 tube with water. By the pressure of the column 
 of water, water was forced into the branch, and in 
 2 days the water in the tube had sunk 14^ inches. 
 
 On the third day, he took the branch out of the 
 water, and exposed it to free evaporation in the air. 
 The water in the tube fell, in 12 hours, 27 
 inches. 
 
 and with To compare the force with which water is 
 evapora driven through the vessels of the wood, by pres- 
 sure alone, with that produced by pressure and 
 evaporation, he joined an apple branch, 6 feet long, 
 with leaves, and exposed to the air, with a tube 9 
 feet long, which was filled with water. 
 
 From the pressure caused by the column of 
 water, and by the evaporation going on at the sur- 
 
MOTION OF THE SAP OF PLANTS. 79 
 
 face of the twigs and leaves, the water fell (Xlth 
 experiment), in one hour, 36 inches. He now cut 
 off the branch 13 inches below the tube, and placed 
 the portion cut off (with the twigs and leaves) ver- 
 tically in a vessel of water. This last absorbed, in 
 30 hours, 18 ounces of water, while the portion of 
 wood remaining in connection with the tube, which 
 was 13 inches long, only allowed 6 ounces of water 
 to pass, and that under the pressure of a column of 
 7 feet of water. 
 
 HALES shews, in three other experiments, that the The motion 
 
 of the sap is 
 
 capillary vessels of a plant, alone, and in connection caused by 
 with the uninjured roots, are easily filled with water rating sur- 
 by capillary attraction, without, however, possessing 
 the power of causing the sap to flow out and to rise 
 in a tube attached. The motion of the sap, con- 
 cludes HALES, belongs to the evaporating surface 
 alone ; he proves that it goes on in an unequal 
 degree from the stem, the twigs, the flowers and 
 fruit, and that the effect of the evaporation stands 
 in a fixed ratio to the temperature and hygrome- 
 tric state of the air. If the air were moist, but 
 little was absorbed ; the absorption was hardly per- 
 ceptible on rainy days. 
 
 He opens the second chapter of his Statistics 
 with the following introduction : 
 
 " Having in the first chapter seen many proofs of 
 the great quantities of liquor imbibed and perspired 
 by vegetables, I 'propose in this, to inquire with 
 what force they do imbibe moisture. Though vege- 
 
80 EXPERIMENTS OF HALES ON THE 
 
 tables (which are inanimate) have not an engine, 
 which by its alternate dilations and contractions, 
 does in animals, forcibly drive the blood through the 
 arteries and veins ; yet has nature wonderfully con- 
 trived other means, most powerfully to raise and 
 keep in motion the sap." 
 
 Great force In his experiment XXI., he exposed one of the 
 the sap chief roots of a pear-tree in full growth at a depth 
 of 2^ feet, cut off the point of it, and connected 
 the part of the root left in connection with the 
 stem with a tube, which he filled with water, and 
 closed with mercury. 
 
 In consequence of the evaporation from the sur- 
 face of the tree, the root absorbed the water in the 
 tube with such a force, that in six minutes the 
 mercury rose to 8 inches in the tube. This corre- 
 sponds to a column of water 9 feet high, 
 it is nearly This force is nearly equal to that with which the 
 
 equal tOfc 
 
 that of the blood moves in the great femoral artery of the 
 
 circulation . . 
 
 in animals, horse. HALES, in his experiment XXXVI., found 
 the force of the blood in various animals : " By 
 tying those several animals down alive upon their 
 backs, and then laying open the great left crural 
 artery, where it first enters the thigh, I fixed to it 
 (by means of two brass pipes which run one into 
 the other) a glass tube of above 10 feet long, and 
 ^th of an inch in diameter in bore. In which tube 
 the blood of one horse rose 8 feet 3 inches, and the 
 blood of another horse 8 feet 9 inches. The blood 
 of a little dog 6^ feet high." 
 
MOTION OF THE SAP IN PLANTS. 81 
 
 HALES shewed by special experiments, that the 
 absorbent force which he pointed out in the root is 
 found also in the stem, in each separate twig, each 
 leaf, and every part of the surface; and that -the 
 motion of the sap continues from the root towards 
 the twigs and leaves, even when the stem has been 
 entirely stripped of bark, inner and outer. This 
 force acts not only from the roots in the direction of 
 the summit, but also from the summit in the direc- 
 tion of the root. 
 
 From his experiments he deduces the presence 
 of a powerful attractive force, residing in every part 
 of the plant. 
 
 We now know, that this attractive force, as such, The P res - 
 
 ' sure of the 
 
 did not cause the rise of the mercury or water in atmosphere 
 
 is the active 
 
 his tubes, and it appears clearly from his experi- force. 
 ments, that the absorbent power of plants, of each 
 leaf, of each fibre of the root, is sustained by a f 
 powerful external force, which is nothing else than 
 the pressure of the atmosphere. 
 
 By the evaporation of water at the surface of A partial 
 
 vacuum is 
 
 plants, a vacuum arises within them, in consequence caused 
 
 i within 
 
 of which water and matters soluble in water are plants by 
 driven inwards and raised from without with facility, S. " 
 and this external pressure, along with capillary 
 attraction, is the chief cause of the motion and 
 distribution of the juices. 
 
 With respect to the absorbent power of the sur- The surface 
 face of the plant for gases, under a certain external absorbs 
 pressure, his experiments offer the most beautiful 8 
 
82 EXPERIMENTS OF HALES ON THE 
 
 evidence. HALES says, in his experiment XXII., 
 " This height of the mercury did in some measure 
 shew the force with which the sap was imbibed, 
 though not near the whole force ; for while the 
 water was imbibing, the transverse cut of the 
 branch was covered with innumerable little hemi- 
 spheres of air, and many air-bubbles issued out of 
 the sap-vessels, which air did in part fill the tube 
 e r, as the water was drawn out of it ; so that the 
 height of the mercury could only be proportionable 
 to the excess of the quantity of water drawn off, 
 above the quantity of air which issued out of the 
 wood. And if the quantity of air which issued from 
 the wood into the tube, had been equal to the quan- 
 tity of water imbibed, then the mercury would not 
 rise at all ; because there would be no room for it in 
 the tube. But if 9 parts in 12 of the water be 
 imbibed by the branch, and in the mean time, but 
 three such parts of air issue into the tube, then the 
 mercury must needs rise near 6 inches, and so pro- 
 portionably in different cases." 
 The ab- When, in his experiments, the root, the stem, or 
 
 sorbent 
 
 power di- a twig had been injured at any part, by the cutting 
 by injury to off of buds, root-fibres, or small twigs, the absorbent 
 power of the remainder was diminished in a very 
 obvious degree (because, from these places, by the 
 entrance of air the difference of pressure was more 
 easily equalized) ; the absorbent power was greatest 
 on freshly-cut surfaces, on which, however, it gra- 
 dually decreased, till, after several days, it was not 
 
ABSORBENT POWER OF PLANTS. 83 
 
 greater in these places than in the uninjured surface 
 of the plant. 
 
 The evaporation, further argues HALES, is the Evapora- 
 powerful cause which provides food for the plant 
 and its vicinity. Disease and death of the plant 
 follow, when the proportion between evaporation 
 and supply is interrupted or destroyed in any way. 
 
 When, in hot summers, the earth cannot supply, Effect of 
 
 A ' hot wea- 
 
 through the roots, the moisture which during the ther. 
 day has evaporated through the leaves and surface 
 of the tree, when the tree, or a twig of it, dries up, 
 the motion of the sap is arrested at these points. 
 When once dried, capillary action alone cannot 
 restore the original activity ; the evaporation is the 
 chief condition of the life of plants ; by its means a 
 permanent motion, a continually repeated change in 
 the quality of the juice (sap) is effected. 
 
 " By comparing, "says HALES, " the surface of the Necessity 
 
 for cutting 
 
 roots of plants, with the surface of the same plant the roots 
 above ground, we see the necessity of cutting off planted 
 many branches from a transplanted tree : for if 256 
 square inches of root in surface was necessary to 
 maintain this cabbage in a healthy natural state : 
 suppose upon digging it up, in order to transplant, 
 half the roots be cut off (which is the case of most 
 young transplanted trees), then it's plain that but 
 half the usual nourishment can be carried up, 
 through the roots, on that account ; and a very much 
 less proportion, on account of the small hemisphere 
 of earth the new-planted shortened roots occupy ; 
 
 G 2 
 
84 
 
 OBSERVATIONS OF HALES ON 
 
 Influence 
 of sup- 
 pressed 
 evapora- 
 tion. 
 
 on hop- 
 vines. 
 
 Observa- 
 tions of 
 Hales on 
 the blight 
 in hops 
 
 and on account of the loose position of the new- 
 turned earth, which touches the roots at first but in 
 few points/' 
 
 HALES proves the influence of suppressed eva- 
 poration by the following observations on hop- 
 vines. 
 
 " Now there being 1,000 hills in an acre of hop- 
 ground, and each hill having three poles, and each 
 pole three vines, the number of vines will be 9,000 ; 
 each of which imbibing four ounces, the sum of all 
 the ounces, imbibed in an acre in a twelve hours' 
 day, will be 36,000 ounces = 15,750,000 grains = 
 62,007 cubic inches, or 220 gallons ; which divided 
 by 6,272,640, the number of square inches in an acre, 
 it will be found, that the quantity of liquor perspired 
 by all the hop-vines, will be equal to an area of 
 liquor, as broad as an acre, and yjjy part of an inch 
 deep, besides what evaporated from the earth. And 
 this quantity of moisture in a kindly state of the air 
 is daily carried off in a sufficient quantity to keep 
 the hops in a healthy state ; but in a rainy moist 
 state of air, without a due mixture of dry weather, 
 too much moisture hovers about the hops, so as to 
 hinder in a good measure the kindly perspiration of 
 the leaves, whereby the stagnating sap corrupts, and 
 breeds mouldy fen, which often spoils vast quantities 
 of flourishing hop-grounds." 
 
 " This was the case in the year 1723, when ten or 
 fourteen days' almost continual rains fell, about the 
 latter half of July, after four months' dry weather ; 
 
THE BLIGHT IN HOPS. 85 
 
 upon which the most flourishing and promising hops and other 
 were all infected with mould or fen, in their leaves 
 and fruit, whilst the then poor and unpromising hops 
 escaped, and produced plenty ; because they, being 
 small, did not perspire so great a quantity as the 
 others ; nor did they confine the perspired vapour, 
 so much as the large thriving vines did, in their 
 shady thickets. This rain on the then warm earth 
 made the grass shoot out as fast as if it were in a 
 hot-bed ; and the apples grew so precipitately, that 
 they were of a very fleshy constitution, so as to rot 
 more remarkably than had ever been remembered." 
 
 " The planters observe, that when a mould or fen 
 has once seized any part of the ground, it soon runs 
 over the whole ; and that the grass, and other 
 herbs under the hops, are infected with it." 
 
 " Probably because the small seeds of this quick- 
 growing mould, which soon come to maturity, are 
 blown over the whole ground. Which spreading of 
 the seed may be the reason why some grounds are 
 infected with fen for several years successively." 
 
 " I have in July (the season for fire-blasts, as the Fire-blasts 
 planters call them) seen," says HALES, " the vines in in hops - 
 the middle of a hop-ground all scorched up, almost 
 from one end of a large ground to the other, when a 
 hot gleam of sunshine has come immediately after a 
 shower of rain ; at which time the vapours are often 
 seen with the naked eye, but especially with reflect- 
 ing telescopes, to ascend so plentifully, as to make 
 
86 EFFECTS OF SUPPRESSED EVAPORATION. 
 
 a clear and distinct object become immediately 
 very dim and tremulous. Nor was there any dry 
 gravelly vein in the ground, along the course of this 
 scorch. It was therefore probably owing to the 
 much greater quantity of scorching vapours in the 
 middle than outsides of the ground, and that being 
 a denser medium, it was much hotter than a more 
 rare medium." 
 
 " This is an effect which the gardeners about 
 London have too often found to their cost, when 
 they have incautiously put bell-glasses over their 
 cauliflowers early in a frosty morning, before the 
 dew was evaporated off them ; which dew being 
 raised by the sun's warmth, and confined within 
 the glass, did there form a dense transparent scald- 
 ing vapour which burnt and killed the plants." 
 The mflu- When these observations are translated into our 
 
 ence of 
 
 evapora- present language, we perceive with what acuteness 
 
 tion on the 
 
 life of and accuracy HALES recognized the influence of 
 
 plants re- 
 
 cognized evaporation on the life of plants. 
 
 Hb views. According to him, the development and growth 
 of the plant depends on the supply of nourishment 
 and moisture from the soil, which is determined by 
 a certain temperature and dryness of the atmo- 
 sphere. The absorbent power of plants the motion 
 of their sap, depends on evaporation ; the amount of 
 food necessary for their nutrition, which is absorbed, 
 is proportional to the amount of moisture given out 
 (evaporated) in a given time. When the plant has 
 
ORIGIN OF THE POTATO BLIGHT. 87 
 
 taken up a maximum of moisture, and the evapora- 
 tion is suppressed by a low temperature or by con- 
 tinued wet weather, the supply of food, the nutri- 
 tion of the plant, ceases ; the juices stagnate, and 
 are altered ; they now pass into a state in which 
 they become a fertile soil for microscopic plants. 
 When rain falls after hot weather, and is followed 
 by great heat without wind, so that every part of 
 the plant is surrounded by an atmosphere saturated 
 with moisture, the cooling due to further evapora- 
 tion ceases, and the plants are destroyed by fire- 
 blast or scorching (Sonnenbrand, German, literally 
 sun-burn or sun-blight). 
 
 After the experience and observations of so long The potato 
 a period in reference to the influence of evaporation p robabiy S a 
 
 on the condition of plants, I hardly think that any 
 unprejudiced observer can entertain the smallest 
 doubt concerning the cause of the great mischief 
 which has befallen agriculture during the last few 
 years. If HALES, that unequalled observer and 
 inquirer, had known the potato disease, I hardly 
 believe that he would have ascribed it to an internal 
 cause belonging to the plant, any more than he 
 thought of ascribing the blight of the hop-plants, 
 formerly mentioned, to a special hop disease, or the 
 rotting of the apples to an apple disease. Even The potato 
 PARMENTIER, to whom France is indebted for the 
 
 introduction of the potato, knew this disease, and 
 has very accurately described it. The term " po- 
 tato-rot" has been known to the oldest peasants 
 
88 ORIGIN OF THE 
 
 and agriculturists since their youth ; it has, doubtless, 
 only acquired of late years the frightful significance, 
 which seems to threaten the well-being of nations, 
 since the causes, which formerly brought it locally 
 into existence, have spread over whole districts and 
 countries. The writings of HALES bring to our cen- 
 tury from a preceding one the consoling certainty 
 (and this is especially important), that the cause of 
 it is not this decay is not to be looked for in a degeneration 
 generato" f the plant, but depends on the combination of cer- 
 ut * am conditions accidentally coincident; and that 
 
 tnese > when they are well ascertained and kept in 
 causes* 1 y i ew > enable the agriculturist, if not to annihilate* 
 
 at least to diminish, their hurtful influence. 
 
 The potato- The potato-plant obviously belongs to the same 
 
 of a those ne class of plants as the hop-plant, namely, to that class 
 
 ferg C mosf" wm 'ch is most seriously injured by the stagnation 
 
 fr r ese S d P f their juices in consequence of suppressed trans- 
 
 tk>n P ra ~ piration. According to KNIGHT, the tubers are not 
 
 formed by swelling of the proper roots, but by the 
 
 development of a kind of underground stalks or 
 
 runners. He found that when the tubers under 
 
 ground were suppressed, tubers were formed on the 
 
 stalks above ground ; and it is conceivable that every 
 
 external cause which exerts a hurtful influence on 
 
 the healthy condition of the leaves and stalks, must 
 
 Character act in like manner on the tubers. In the districts 
 
 weather in which were most severely visited by the so-called 
 
 i847, a when potato disease in 1846, damp, cold, rainy weather 
 
 followed a series of very hot days ; and in 1847, cold 
 
 vailed. 
 
POTATO BLIGHT. 89 
 
 and rain came on, after continued drought, in the 
 beginning of September, exactly at the period of the 
 most luxuriant growth of the potatoes. 
 
 In most places no trace of disease was observed la m <>st 
 
 places the 
 
 in the early potatoes before the middle of August ; early P o- 
 and even after that period low-lying, cold and wet caped tin 
 
 J after the 
 
 fields, were chiefly attacked by it. In many plants, middle of 
 in the same field, in which the seed potatoes had 
 been destroyed by putrefraction and decay, the 
 tubers appeared quite healthy, while in others it was 
 easy to see that those tubers alone, which lay next 
 to the old potatoes, were infected and attacked by 
 the disease, and that on the side next to the old 
 tubers. 
 
 In 1846 all the potato-plants in my garden died Theau- 
 completely off towards the end of August, before a Mrieaee i"n 
 
 -I Q J /? 
 
 single tuber had been formed ; and in 1847, in the 
 
 same field, the tubers of all those plants which stood Effect of 
 
 shade. 
 
 under trees and in protected spots, were quite rot- 
 ten, while no trace of disease appeared in spots 
 which were more elevated and more fully exposed to 
 the current of air. The cause of the disease is the The cause 
 
 , ... of potato 
 
 same which, m spring and autumn, excites influenza; blight is the 
 that is, the disease is the effect of the temperature that of in- 
 and hygrometric state of the atmosphere, by which, 
 in consequence of the disturbance of the normal 
 transpiration, a check is suddenly, or for a consider- 
 able time, given to the motion of the fluids, which is 
 one chief condition of life, and which thus becomes 
 
90 
 
 EFFECT OF COLD ON PLANTS . 
 
 Effect of a 
 
 slight fall 
 
 of tempera, 
 
 ture on 
 
 plants. 
 
 The life of 
 dependent 
 
 nai causes 
 
 only one of 
 namely the 
 
 insufficient for the purposes of health, or even hurtful 
 to the individual. 
 
 The whole existence of a plant, the resistance 
 which it opposes to the action of the atmospheric 
 
 i i 
 
 oxygen, is most closely connected with the con- 
 tinued support of its vital functions. The mere 
 alternation of day and night makes, in this respect, 
 a great difference. The sinking of the external 
 temperature by a few degrees, causes the leaves to 
 fall in autumn ; and a cold night is followed by the 
 death of many annual plants. 
 
 If we reflect that a plant, in order to protect 
 itself from external causes of disturbance, or to 
 see ^ tne fd which it requires, cannot change its 
 pj ace . that jfcg nO rmal vital functions depend on 
 the simultaneous and combined action of water, of 
 the soil, of the external temperature, and of the 
 hygrometric state of the atmosphere; that is, on 
 four external circumstances ; it is easy to comprehend 
 the disturbance of functions which must occur in 
 the organism in consequence of any change in the 
 mutual relations of so many combined agencies. 
 The state of a plant is a sure indication of equili- 
 brium or of misproportion in the external conditions 
 of its life ; and the dexterity of the accomplished 
 gardener consists exactly in this, that he knows and 
 can establish the just proportion of these conditions 
 for each species of vegetable. Only one of these 
 numerous conditions is in the power of the agricul- 
 
CONDITIONS OF THE LIFE OF PLANTS 91 
 
 turist, and that is, the production of the quality of quality of 
 
 the soil, 
 
 the soil appropriate for the crop, including the in the 
 
 necessary modification of its composition, by the the agricui- 
 
 mechanical working of the soil ; by the irrigation or 
 
 draining of his fields ; and lastly by the employment 
 
 of manure. When one of the constituents of the 
 
 soil, which, under the given circumstances, is neces- 
 
 sary for the support of the vital functions, is absent, 
 
 the external injurious influence is strengthened by 
 
 this deficiency. Had this constituent been present, Effects of 
 
 the plant would have been enabled to oppose to the senceorab- 
 
 external hurtful influences a continued resistance, single con- 
 
 One day may be decisive as to the life or death of 
 a plant. An accurate knowledge of the influence 
 exerted by the various constituents of the soil on 
 the diseased condition, must enable the agriculturist 
 to protect and preserve many of his fields for a long 
 time from this destruction ; but it is obvious that 
 a universal remedy against this evil does not exist. 
 
 When the vessels of the plant are filled to over- Effects of 
 flowing with water, and the motion of the sap is 
 suppressed, the nutrition, in most plants, is arrested, 
 and death takes place. Every one knows the effect 
 of a sudden or of a gradual overfilling of certain 
 parts or organs, when the corresponding evaporation 
 is suppressed. By the endosmotic pressure of the 
 water flowing towards those cells, which contain 
 sugar, mucilage, gum, albumen, and soluble matters 
 in general, the juicy fruits and seeds approaching 
 maturity burst, and the juice of grapes, cherries, 
 
92 RISE OF THE SPRING SAP. 
 
 plums, &c., passes, on contact with the air, into a 
 The plant state of progressive change. The fungi which have 
 fungi and been observed on the potato-plants, and the putre- 
 
 putrefaction 
 
 follow. faction of the tubers, are not the signs of a disease, 
 
 but the consequences of the death of the plant. 
 observa- Among the most important of the experiments 
 HALES on made by HALES we must reckon undoubtedly those 
 
 the rise of J . J 
 
 the spring on the rise of the spring sap in perennial plants. 
 enniai His observations have been entirely confirmed by all 
 
 those who since his time have studied the subject ; 
 
 but, in my opinion, without our having approached 
 
 one step nearer to the cause of the phenomena. 
 The most recent experiments on this subject by 
 
 E. BRUCKE, leave no doubt in regard to the actual 
 
 state of our knowledge. 
 views of According to DUTROCHET, it is the extremities 
 
 of the radical fibres, called by DE CANDOLLE 
 
 spongioles, which effect the rise of the spring sap ; 
 and he believes (L'agent immediat du mouvement 
 vital, Paris, 1826) that the force, with which the 
 sap is driven upwards, acts from the root. DU- 
 TROCHET cut off a piece of a vine stem, two metres 
 long ; and he saw that the sap flowed steadily from 
 the shortened stem in connection with the root. 
 When he had again cut it off close to the ground, he 
 observed that the portion in the ground continued 
 to pour forth sap from the whole cut surface. He 
 pursued the experiment, going deeper every time, 
 He places anc ^ ne a l wa ys found, that the sap flowed from the 
 fhespo C n- in P art left in the ground, till at last he came to the 
 
THEORY OF DUTROCHET. 93 
 
 extreme points of the fibres, in which he then 
 
 the roots. 
 
 located the origin of the moving force. 
 
 The peculiar activity of the spongioles must, 
 according to DUTROCHET, be ascribed to all -the 
 causes, taken together, which determine the phe- 
 nomena of Endosmosis. 
 
 Now that we are better acquainted with the phe- objections 
 
 to this 
 
 nomena of what is called Endosmosis, we may theory. 
 oppose to this view some well-founded doubts. All 
 observers agree, that the increase in volume of a 
 liquid, separated from another liquid by a porous 
 diaphragm, is determined by a difference in the 
 qualities of the two liquids. If their composition 
 and properties be the same, there is no cause suffi- 
 cient to produce mixture and change of volume, 
 since in this case, the attraction of both for the 
 diaphragm, and for each other, is perfectly equal. 
 
 In the course of his admirable researches, BRUCKE observa- 
 determined the specific gravity of the spring sap 
 which had flowed from the vine. He found it, in 
 one plant, == 1*0008, and in another, = 1*0009. 
 
 These numbers prove irresistibly, that the spe- 
 cific gravity of the sap of the vine is in no way 
 different from that of ordinary spring water, or of 
 the water which has filtered through garden mould. water> 
 In most cases, spring water contains even more 
 dissolved matter. 
 
 The spring sap of the vine, which had the sp. g. Force with 
 1-0008, raised a column of mercury to the height of sap rises. 
 * Poggendorf s Annalen der Physik, Ixiii. 177. 
 
 * f 
 
94 RISE OF THE SPRING SAP. 
 
 174 lines (14-5 inches), and therefore exerted a 
 pressure equal to that of a column of water 195 
 inches high. It is quite impossible to account for 
 this pressure by the difference in the amount of 
 dissolved matter in the water absorbed by the roots, 
 and the sap flowing from the cut surface. In the 
 experiment No. IX., of BRUCKE, made with a vine, 
 the sap of which had the sp. g. 1*0009, the mercury 
 was raised at 7 A.M., to the height of 209 lines 
 (nearly 17'5 inches). 
 
 Endosmosis No one can doubt that what is called Endos- 
 
 Utti^share Eiosis has some share in the rise of the sap of the 
 
 L n omeno P n he " maple and birch trees, which is proportionally rich 
 
 in sugar, and differs materially in composition from 
 
 spring water, as well as on the flow or exudation 
 
 of gummy or saccharine juices ; but the pressure 
 
 exerted in these cases cannot be compared to that 
 
 exerted by the sap of the vine, where the causes 
 
 included under the word Endosmosis cannot act. 
 
 The cause It is evident, that the cause of the pressure of 
 
 of the sap the spring sap must be transient, called into action 
 
 by external causes, and limited to a short period. 
 
 Tne experiment of DUTROCHET, from which he con- 
 mfluences. c i u( j es that ftie cause O f the rise of the sap resides 
 
 in the extreme points of the roots, may be thus 
 it exists in interpreted : " The cause of the efflux and pres- 
 the plant, sure of the sap exists in all parts of the uninjured 
 
 plant, down to the extreme spongioles of the root." 
 The present season does not admit of experi- 
 
 ments on this point; but as spring approaches, it 
 
EXPERIMENTS OF HALES. 95 
 
 may be proper here to develop more clearly the 
 grounds of the opinion, that the cause of the efflux 
 of the sap of the vine is a transient one. Perhaps 
 some one may thus be induced to decide experi- 
 mentally all the questions connected with this 
 remarkable phenomenon. 
 
 HALES, in his experiment XXXIV., cut off a 
 vine-stem 7 feet above the ground, and attached to HALES! 
 the trunk tubes of 7 feet long, joined together. 
 Below the cut there were no branches. This was 
 done on the 30th of March, at 3 P.M. 
 
 As the stem poured out no sap on that day, he 
 poured water into the attached tube to the height 
 of two feet. 
 
 This water was absorbed by the stem, so that 
 about 8 P.M., the water had fallen to 3 inches in 
 the tube. 
 
 The next day, 1 past 6 A.M., the sap stood 3 Ri *e of the 
 
 sap in a 
 
 inches higher than at 8 the evening before. From vine, 
 this time the sap continued to rise, till it reached a 
 height of 21 feet. It would perhaps, says HALES, 
 have risen higher, had the joinings of the tubes been 
 more water-tight. 
 
 Whatever opinion we may entertain as to the This rise 
 cause of the efflux and pressure of the sap, it is 
 impossible to suppose that the mechanical or any 
 other structure or quality of the radical fibres, the 
 spongioles, or the inner parts of the vine-stem 
 generally, can have changed so much between the 
 evening of the 30th and the morning of the 31st, 
 
96 EXPERIMENTS OF HALES. 
 
 as to give rise to two completely opposite in- 
 fluences. 
 
 On the evening of the 30th the water poured 
 into the tube was absorbed; on the 31st it was 
 expelled with a continually increasing force. 
 
 In his experiment XXXVII., HALES fixed, on 
 three branches of a horizontally trained espalier 
 vine, siphon tubes, filled to a certain point with 
 mercury. 
 
 The three branches received their sap from the 
 common stem, that stem from the root. The first 
 branch was 7 feet from the second, the second 22 
 feet 9 inches from the third. The first and third 
 branches were two years old, the middle one was 
 older. 
 
 From the 4th to the 20th of April, the mercury 
 stood, in consequence of the pressure of the sap, 
 higher in the open limb of the tubes than in the 
 other which was attached to the branch. 
 
 The greatest height attained by the mercury was 
 from 21 to 26 inches. 
 
 On the 21st of April, when the flowering was 
 nearly over, the sap in the middle branch went 
 backwards ; it was absorbed, and so considerably, 
 that the mercury stood 4 inches lower in the open 
 limb than in the other. After a rainy night on the 
 24th of April, the sap again rose in the open tube 
 4 inches. 
 
 In the first (lowest) branch, the sap went back 
 on the 29th of April, 9 days after the middle one ; 
 
HIS CONCLUSIONS. 97 
 
 the third (highest) branch only began to absorb 
 the sap on the 3rd of May, thirteen days after the 
 middle one. 
 
 We see from this experiment, as HALES observes, Conciu- 
 " That the cause which produces the flow of the HALES. 
 sap does not proceed from the root alone, but that 
 it belongs to a force inherent in the stem and 
 branches. For the middle branch followed more 
 rapidly the changes of temperature, of dryness and 
 of moisture, than the two others, and absorbed the 
 sap nine days before one, and thirteen days before 
 the other, both of which, during this time, poured out 
 sap instead of absorbing it. (The cause of the efflux 
 and pressure had, in the older branch, disappeared, 
 and given place to an opposite influence, while it 
 still continued active in the two younger branches.) 
 
 " The middle branch was 3 feet 8 inches higher 
 than that next the stem. The height of the mer- 
 cury in the three tubes was, respectively, 14|, 12^, 
 and 13 inches. The maximum was 21, 26, and 26 
 inches. These numbers prove that the greater length 
 of the middle branch had no perceptible influence 
 on the height of the mercury, as compared with that 
 in the other tube." 
 
 In his experiment XXXVIII., HALES observes, Effect of 
 " Moisture and warmth made the sap most vigorous, of shade on 
 If the beginning or middle of the bleeding season, thesap. 
 being very kindly, had made the motion of the sap 
 vigorous, that vigour would immediately be greatly 
 abated by cold easterly winds. 
 
 H 
 
98 THE RISE OF THE SAP 
 
 " If in the morning while the sap is in a rising 
 state, there was a cold wind with a mixture of sun- 
 shine and cloud ; when the sun was clouded the sap 
 would immediately visibly subside, at the rate of an 
 inch in a minute for several inches, if the sun con- 
 tinued so long clouded ; but as soon as the sun- 
 beams broke out again, the sap would immediately 
 return to its then rising state, just as any liquor in a 
 thermometer rises and falls with the alternacies of 
 heat and cold ; whence it is probable, that the plen- 
 tiful rise of the sap in the vine in the bleeding 
 season, is effected in the same manner." 
 HOW is this If we consider, that the sap in spring, even with 
 
 effect to be 
 
 accounted a clouded sky, does not cease to rise and flow, for 
 
 for ? 
 
 this even goes on during the night, we cannot ex- 
 plain the fall of the sap from the moment that the 
 sun was covered by a cloud by a mere change of 
 temperature in the juice, because the time was too 
 short for the cooling and contraction by cooling (one 
 inch in a minute). Heat determined the more rapid 
 rise, and cold the fall, but they acted on a cause 
 which lay higher than the root, and which was more 
 sensitive to heat than the liquid itself. 
 
 Gas is HALES says, in his experiment XXXVIII. " In 
 
 with the very hot weather many air-bubbles would rise, so as 
 to make a froth an inch deep, on the top of the sap 
 in the tube. 
 
 " I fixed a small air-pump to the top of a long 
 tube, which had twelve feet height of sap in it ; when 
 I pumped, great plenty of bubbles arose, though the 
 
MAY BE CAUSED BY A GAS. 99 
 
 sap did not rise, but fell a little, after I had done 
 pumping." 
 
 In his experiments on the amount of air ab- 
 sorbed by plants, chapter V., he observes, " in the 
 experiments on vines, the very great quantity of 
 air which was continually ascending from the vines, 
 through the sap in the tubes ; which manifestly 
 shews what plenty of it is taken in by vegetables, 
 and is perspired off with the sap through the leaves." 
 
 When we take these facts into consideration, the The rise of 
 
 the sap 
 
 opinion appears not untenable, that the mcompre- maythere- 
 
 i . i f re be 
 
 hensible force, which causes the sap of the vine to caused by 
 
 flow in spring, may be simply referred to a disen- 
 gagement of gas which takes place in the capillary 
 vessels (filled with liquid, and keeping themselves 
 constantly full), in consequence of a kind of germi- 
 nation; and it is possible that the height of the 
 column of mercury, or of water, is only a measure 
 of the elasticity of the disengaged gas. 
 
 Let us suppose a strong glass bottle, in the mouth iiiustra- 
 of which a long tube, open at both ends, and reaching 
 to the bottom, is cemented, to be filled with a 
 liquid in which, from any cause, a gas is disengaged 
 (solution of sugar mixed with yeast, for example), 
 it is evident that the liquid must rise in the tube 
 from the separation of the gas. When it has risen 
 to 32 feet, the gas will occupy only the half, and at 
 64 feet, one-third of its volume under the usual 
 atmospheric pressure. In this case, the height of 
 the liquid in the tube is no measure of a special 
 
 H2 
 
100 IS THE GAS CARBONIC ACID? 
 
 power residing in the walls of the vessel ; it only 
 shews the tension of the gas. 
 
 If the walls of the vessel were permeable to the 
 gas under a certain pressure, no further rise, beyond 
 that point, could occur. 
 
 If, in the apparatus, Fig. 4, we push the tube a 
 through the cork down to the little lead drop ; if 
 we then fill the tube c with water to which some 
 yeast has been added, and a with solution of sugar, 
 and expose the whole to a temperature of from 
 68 to 75, the liquid rises in b, from the gas disen- 
 gaged in c, very rapidly, so as to overflow. If c be 
 filled with solution of sugar, and a with yeast, the 
 same rise occurs, and lasts till the disengaged gas 
 puts an end to the contact between the membrane 
 and the liquid. 
 
 It is hardly necessary to point out, that the idea 
 
 above expressed as to the cause of the flow and 
 
 pressure of the spring sap, is nothing more than an 
 
 indication of the direction in which experiments 
 
 must be made. When we know with accuracy the 
 
 volume of the liquid which flows out of a vine at 
 
 the time of flowering, and the quantity of gas 
 
 which is developed at the same time, we shall, I 
 
 trust, find ourselves a step nearer to the explanation 
 
 of this phenomenon. According to the experiments 
 
 The disen- of GEIGER and PROUST, the sap of the vine is rich 
 
 probab?y S1S in carbonic acid ; and it is possible that the gas 
 
 acid. which is disengaged, may be no other than carbonic 
 
 acid gas. 
 
APPENDIX. 
 
 ON THE NATURE AND PREVENTION OF THE POTATO 
 DISEASE. 
 
 AFTER the preceding pages were in print, I re- 
 ceived from Baron Liebig a copy of the Journal of 
 the Agricultural Association of the Grand Duchy 
 of Hesse (Darmstadt), No. 7, dated 15th February, 
 1848, containing the account of a method proposed 
 by Dr. Klotzsch (Keeper of the Royal Herbarium, 
 Berlin, and a distinguished Botanist and Vegetable 
 Physiologist), for preventing the ravages of the po- 
 tato disease. The proposal of Dr. Klotzsch, and 
 his views as to the nature of the disease, are such 
 as materially to strengthen the opinions expressed on 
 this subject by Baron Liebig (see pp. 87, seq.). As 
 a knowledge of the method suggested by Dr. 
 Klotzsch is likely to be interesting to many of the 
 readers of this work, I have thought it right to give 
 it in an Appendix. 
 
 WILLIAM GREGORY. 
 
102 APPENDIX. 
 
 METHOD PROPOSED BY DR. KLOTZSCH, FOR THE 
 PROTECTION OF THE POTATO-PLANT AGAINST 
 DISEASES. 
 
 " THE potato, which is an annual plant, represents, 
 in the tubers developed from the stem, the peren- 
 nial part of a plant. For while the duration of its 
 development is analogous to that of annuals, its 
 functions coincide exactly with those of dicotyledo- 
 nous shrubs and trees. 
 
 " The potato plant differs from all those plants 
 which are cultivated for economical purposes in 
 Europe, and can only be compared to those orchi- 
 deous plants which yield salep, and which are not 
 yet cultivated among us. 
 
 " The tubers, both of the potato and of the 
 salep plants, are nutritious, and agree in this, that 
 in the cells of the tubers, grains of starch, with 
 more or less azotized mucilage, are collected, while 
 the cell walls possess the remarkable property of 
 swelling up into a jelly, and thus becoming easily 
 digestible, when boiled with water. 
 
 " But while the tuber of salep contains only one 
 bud, or germ, the potato usually develops several, 
 often many, germs. 
 
 " The potato plant, like all annuals, exerts its 
 chief efforts in developing flowers and fruit. Like 
 all annuals, too, it has the power of shortening 
 
APPENDIX. 103 
 
 this period of development, when the power of 
 the roots is limited ; as also of lengthening it when 
 the extent and power of the roots are increased. 
 
 " We observe in nature, that plants with feebly- 
 developed roots often have a weak, sickly 'aspect, 
 but yet come to maturity in flower and fruit sooner 
 than stronger individuals, well furnished with roots. 
 
 " In perennial plants we observe a second effort, 
 which is directed towards preparing and storing up 
 nutritious matter, for the consumption of the plant. 
 The preparation of this nutriment is effected by the 
 physiological action of the leaves, under the influ- 
 ence of the roots. The stronger and larger the 
 former are, the more is this preparation of food 
 delayed. 
 
 " The nutritious matters are stored in the coloured 
 stratum of the bark in shrubs and trees, and in the 
 tubers in the potato and salep plants. Not only, 
 however, the nutrient matters, but also the cells, 
 owe their origin to the physiological action of the 
 leaves. 
 
 " On considering these things, it follows, that the 
 potato plant requires more care than is usually de- 
 voted to it. Hitherto the whole cultivation con- 
 sisted in clearing off weeds, and hoeing up the 
 earth round the stems. Both of these measures 
 are indeed necessary, but they are not alone suffi- 
 cient ; for the plant is cultivated, not on account of 
 its fruit, but for the sake of its tubers, and our 
 treatment should be modified accordingly. 
 
104 APPENDIX. 
 
 " The chief points to be attended to, with a view 
 to the attainment of the object, namely, the increase 
 of tubers, are 
 
 1. To increase the power in the roots, and 
 
 2. To check the transformation which occurs 
 in the leaf. 
 
 " We obtain both ends simultaneously, if, in the 
 5th, 6th, and 7th week after setting the tubers, 
 and in the 4th and 5th week after planting out 
 germs furnished with roots, or at a time when the 
 plants reach the height of six to nine inches above 
 the soil, we pinch off the extreme points of the 
 branches or twigs to the extent of half an inch 
 downwards,* and repeat this on every branch or 
 twig, in the 10th and llth week, no matter at what 
 time of day. 
 
 " The consequences of this check to the develop- 
 ment of the stem and branches, is a stimulus to the 
 nutrient matters in the plant in the direction of the 
 increase, both of roots and of the multiplication of the 
 branches of the stem above ground, which not only 
 favours the power of the root, but also strengthens 
 the leaves and stalks to such a degree, that the 
 matters prepared by the physiological action of 
 these parts are increased and applied to the forma- 
 tion of tubers, while at the same time the direct 
 
 * Any one would be bitterly disappointed, who on the prin- 
 ciple that " there cannot be too much of a good thing," should 
 take off more than is here recommended, in order to use it as 
 fodder. 
 
APPENDIX. 105 
 
 action of the sun's rays on the soil is prevented by 
 the thick foliage, and thus the drying up of the soil 
 and its injurious consequences are avoided. 
 
 " The checking of the transformation in the leaf 
 is equivalent to the interruption of the natural 
 change of the leaves into calyces, corollae, stamens, 
 and pistils, which is effected at the expense of the 
 nutrient matters collected in the plant ; and these, 
 when this modification of the leaves is arrested, are 
 turned to account in the formation of tubers. 
 
 " Led by these views, I made, in 1846, experi- 
 ments on single potato plants, carefully marked, by 
 pinching off the ends of the branches. They were 
 so readily distinguished in their subsequent growth 
 from the plants beside them, by more numerous 
 branches, larger and darker foliage, that in truth no 
 marking was necessary. 
 
 " The produce from these plants of tubers was 
 abundant, and the tubers were perfectly healthy; 
 while the plants next them which had not been so 
 treated, gave uniformly a less produce, at the same 
 time the tubers were rough on the surface, and in 
 many instances attacked with the prevailing disease. 
 This experiment was incomplete, and did not give 
 a positive result, but it was yet encouraging for me. 
 
 " In the middle of April, 1847, an experiment 
 was made on a low-lying field with the round white 
 potatoes, generally cultivated here, a variety which 
 had not suffered much from the disease which first 
 
106 APPENDIX. 
 
 appeared here in 1845. The potatoes were planted 
 in the usual way by an experienced farm servant. 
 
 " After weeding them in the end of May, I re- 
 newed my experiment by pinching off the points of 
 the branches of every second row, and repeated this 
 in the end of June. The result surpassed all ex- 
 pectations. The stalks of the plants not treated on 
 my plan were long, straggling, and sparingly fur- 
 nished with leaves, the leaves themselves small and 
 pale green. 
 
 " In the next field, potatoes of the same variety 
 were planted on the same day, and left to nature. 
 They appeared in the first six weeks healthy, even 
 strong, but gradually acquired a poor aspect as the 
 time of flowering and fruit approached, and finally 
 exhibited precisely the same appearances as the 
 rows not treated by pinching off the extremities in 
 the field in which my experiments were made. 
 
 " The harvest began in the surrounding fields in 
 the middle of August, and was very middling. The 
 tubers were throughout smaller than usual, very 
 scabby, and within these fields, to a small extent, 
 attacked by the wet rot. 
 
 " In the end of August, the difference between 
 the rows treated by me and those not treated 
 became so striking that it astonished all the work- 
 people in the neighbourhood, who were never tired 
 of inquiring the cause. The stalks of the rows left 
 to themselves were all now partly dried, partly 
 
APPENDIX. 107 
 
 dead. On the contrary, the rows treated as above 
 were luxuriant and in full vigour, the plants bushy, 
 the foliage thick, the leaves large and dark green, 
 so that most people supposed they had been later 
 planted. 
 
 " But the difference in the tubers was also very 
 decided. The tubers of the plants in the rows 
 treated on my plan were not indeed larger, but 
 vastly more numerous, and they were neither scabby 
 nor affected with any disease whatever. A few had 
 pushed (which was to be ascribed to a late rain), 
 and were apparently incompletely developed, while 
 scab and wet rot attacked more and more the tubers 
 of the other plants, which also fell off on the 
 slightest handling. 
 
 " Although I am far from believing that I am 
 able to explain the nature of the potato disease, 
 which has visited us of late years, yet I feel certain 
 that I have discovered a means of strengthening the 
 potato plant to such a degree as to enable it to 
 resist the influences which determine such diseases. 
 
 " Should any one be deterred from continuing the 
 cultivation of potatoes, on account of the manipula- 
 tion here recommended, which may be performed 
 by women and even by children, I would remind him 
 that the same field planted with potatoes is capable 
 of supplying food to twice as many persons as when 
 employed to grow wheat." 
 
 (From the Annals of Agriculture in Prussia, edited by the 
 College of Rural Economy.') 
 
108 APPENDIX. 
 
 DR. KLOTZSCH presented to the King of Prussia 
 a memorial offering to give to the world his method 
 of preventing disease in potatoes, provided he were 
 assured of a remuneration of 2,000 dollars (about 
 300), if, after three years' experience, it should be 
 found efficacious. 
 
 The king handed the memorial to the Minister 
 of the Interior, who requested the College of Rural 
 Economy to discuss the matter with Dr. Klotzsch. 
 
 The president of the college undertook the 
 arrangement, and, after Dr. Klotzsch had explained 
 to him privately his method, reported most favour- 
 ably of it to the College, which unanimously recom- 
 mended that the very moderate remuneration asked 
 for by Dr. Klotzsch should be secured to him on 
 the following conditions, which were accepted by 
 him. 
 
 1. That the College of Rural Economy should 
 be the judges of the efficacy of the proposed 
 method. 
 
 2. That their decision should be given, at 
 latest, within three years, provided the 
 potato disease, against which the plants are 
 to be protected, should appear during that 
 period. 
 
 The Minister of the Interior approved of the re- 
 commendation, and authorized the College to con- 
 clude an agreement with Dr. Klotzsch. 
 
 The agreement has been concluded, and now the 
 
APPENDIX. 109 
 
 method is published, that it may be tried and tested 
 as widely as possible by comparative experiments, 
 similar to those made by Dr. Klotzsch himself. 
 The cost of it is stated not to exceed Is. 6d. per 
 acre in Germany. 
 
 It is very desirable that this method should be 
 tried in the British Islands, and as the season for 
 trying it now approaches, I have here given Dr. 
 Klotzsch J s account entire. 
 
 WILLIAM GREGORY. 
 
Printed by J. & H. Cox (BROTHERS), 74 & 75, Great Queen-street, 
 Lincoln's-Inn Fields. 
 
PROFESSOR LIEBIG'S WORKS. 
 
 RESEARCHES ON THE CHEMISTRY OF FOOD. By 
 
 JUSTUS LIEBIG, M.D., Professor of Chemistry in the University of 
 Giessen. Edited from the Author's MS. by WILLIAM GREGORY, M.D., 
 Professor of Chemistry in the University of Edinburgh. 8vo. 5s. 6d., 
 cloth. 
 
 " The medical man will find in these ' Researches ' a prospect of many and great improvements 
 in practice, whether as regards dietetics or the action of acids, alkalies, and salts on the digestive 
 and respiratory processes ; and with respect to both, it is to Chemistry he must look for assistance 
 in his efforts to advance. Lastly, the present work contains some most valuable practical applica- 
 tions of the chemical discoveries therein detailed, to an art which immediately concerns the whole 
 of mankind, namely, the culinary art." Editor's Preface. 
 
 " The practical applications of these ' Researches ' are of great value, and, in many points, claim 
 the attention of all domestic economists. There are so many curious subjects and practical 
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 II. 
 
 CHEMISTRY, IN ITS APPLICATIONS TO AGRI- 
 CULTURE AND PHYSIOLOGY. BY JUSTUS LIEBIG, M.D., 
 Ph.D., F.R.S., Professor of Chemistry in the University of Giessen. 
 Edited from the Manuscript of the Author, by LYOX PLAYFAIR, Ph.D., 
 and WILLIAM GREGORY, M.D. Fourth Edition, revised, with additions. 
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 correct principles." Loudan's Gardener's Magazine. 
 
 III. 
 
 FAMILIAR LETTERS ON CHEMISTRY, AND ITS 
 
 RELATIONS TO COMMERCE, PHYSIOLOGY, AND AGRICUL- 
 TURE. By JUSTUS LIEBIG, M.D., Professor of Chemistry in the 
 University of Giessen. Edited by JOHX GARDNER, M.D., Member of 
 the Chemical Society. Third Edition. Fcap. 8vo. 4s. 6d. 
 
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Professor Liebig's Works (continued). 
 
 IV. 
 
 ANIMAL CHEMISTRY; OR, CHEMISTRY IN ITS 
 
 APPLICATIONS TO PHYSIOLOGY AND PATHOLOGY. By 
 JUSTUS LIEBIG, M.D., Ph. D., Professor of Chemistry in the University 
 of Giessen. Edited from the Author's MS. by WILLIAM GREGORY, 
 M.D., Professor of Chemistry in the University of Edinburgh. Third 
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 work) Qs. Qd. cloth. 
 
 " Under the heads of animal heat ; of the nutrition of the carnivora andherbivora ; of the origin 
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 of the origin and use of the non-nitrogenized elements of food, and particularly of fat, and their 
 relative value as sources of heat ; of the effects of alcohol and fermented liquors ; of the effects 
 produced on the volume of the inspired air by the different articles of food ; and lastly, of the 
 true functions of the intestinal canal, and the origin, nature, and composition of the faeces, with 
 then- relation to the food, and to the supply of oxygen ; under all these heads, the reader will find 
 such an amount of new and interesting matter as must satisfy him that we have entered on the 
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 V. 
 
 FAMILIAR LETTERS ON CHEMISTRY, SECOND 
 
 SERIES. THE PHILOSOPHICAL PRINCIPLES AND GE- 
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 of vitality." Chambers' Journal. 
 
 TURNER'S CHEMISTRY. 
 
 Eighth Edition. Edited by JUSTUS LIEBIG, M.D., Professor of 
 
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