if. & ^ T&\b tt%t\ must Toe eonstlltid. i» the Boston Medical Librwy 8 Fenway PRISENTED TO THE ^1 ■ //<■<•/■/ r foM^iL^^o^yrnxfiAi^ SuMsr&Q) Mfi fsfij£ 4 Digitized by the Internet Archive in 2011 with funding from Open Knowledge Commons and Harvard Medical School http://www.archive.org/details/oninfluenceofphyOOedwa ON THE INFLUENCE OF PHYSICAL AGENTS ON LIFE, W. F. EDWARDS, M.D. F.R.S. MEMBER OF THE ROYAL ACADEMY OF SCIENCES, AND ROYAL ACADEMY OF MEDICINE OF PARIS, OF THE PHILOMATHIC SOCIETY OF THE SAME CITY, AND OF THE MEDICAL SOCIETY OF DUBLIN, ETC. Cramilatrtf from tije tfvmci), BY DR. HODGKIN AND DR. FISHER. TO WHICH ARE ADDED, IN THE APPENDIX, SOME OBSERVATIONS ON ELECTRICITY, BY DR. EDWARDS, M. POUILLET, AND LUKE HOWARD, F.R.S. ; ON ABSORPTION, AND THE USES OF THE SPLEEN, BY DR. HODGKIN ; ON THE MICROSCOPIC CHARACTERS OF THE ANIMAL TISSUES AND FLUIDS, BY J. J. LISTER, F.R.S. AND DR, HODGKIN ; AND SOME NOTES TO THE WORK OF DR. EDWARDS. LONDON: PRINTED FOR S. HIGHLEY, 32, FLEET STREET, AND WEBB STREET, MAZE POND, BOROUGH. 1832. DEC 5 1917 CT^^ LONDON : PRINTED ]i\ "STEWAUT AND CO. OLD JJAILEY, PREFACE. It does not appear necessary to say much to urge the importance of the investigation of the influence of a variety of physical agents on life, since it con- stitutes not only a most essential branch of phy- siology as a science, but is replete with practical points of vital importance and universal applica- tion ; seeing they are not less connected with the preservation of health, than with the cure of dis- ease. Many of the functions of life are con- fessedly veiled under an almost impenetrable ob- scurity. This indeed is so universally admitted, that the idea of reducing them to the rank of those phenomena which come within the province of physics (properly so called) or natural philosophy, and of applying to them those laws which we know to regulate operations in which inorganic or dead matter is concerned, is regarded as hopeless, and many physiologists, without reviving the auto- crateia of Stael, nevertheless refer to vitality with its vires conservatrices as so varying in its powers a 2 IV PREFACE. and operations, as to baffle every attempt to reduce to fixed principles many of those pheenomena of which it is an element. We cannot be surprised at this when we consider the almost infinite variety which life presents in the wide range of the animal kingdom, and observe how these varieties are mul- tiplied by those presented by a single species, nay, by a single individual under various circumstances of age, season, and situation. We must not, how- ever, too hastily adopt the idea, that this subject is really one which presents inherent obstacles of insurmountable difficulty. Many subjects which at first appear to be involved in inextricable con- fusion and perplexity, become clear and intelli- gible when once the proper clue or explanation is furnished. Some minds are so happily constituted as to have a remarkable readiness in perceiving the relations which connect facts and observations, which to others appear not merely isolated, but absolutely contradictory. This appears to be par- ticularly the case with Dr. Edwards. The labours of his predecessors had accumulated a vast collec- tion of invaluable facts and observations, many of which seemed to be almost annihilated by their standing in direct opposition to others supported by equally valid and respectable authority ; the labours of Dr. Edwards have explained many of these discrepances. It may be ill becoming in me to anticipate the judgment of the reader, but I PREFACE. T cannot refrain from expressing my admiration of the patient and clear induction with which the Doctor proceeds, step by step, through the great variety of subjects comprised in his work, so as to maintain the unity and connexion of the whole, and of the happy art with which he has both availed himself of the experiments and observa- tions of his predecessors, and supplied the breaks and deficiencies which he met with, by well con- trived simple and conclusive experiments of his own. It is at least presumptive evidence of the merit of the Doctor's work, that different parts of it presented at separate times to the Academy of Sciences of Paris, obtained for their Author, al- though a foreigner, the honourable distinction of the physiological prize. It is certainly to be re- gretted, that our philosophical countryman has not himself exhibited his instructive work in an English dress, that our medical literature might have the credit of possessing it as an original -ra- ther than as a translation. Translations are gene- rally inferior to original publications. In the pre- sent instance I have endeavoured to reduce the weight of this objection by submitting the trans- lation to the Author's perusal, and be has kindly supplied me with some fresh matter, which will be found in the Appendix. Whilst I feel justi- fied in expressing myself as I have done with VI PREFACE. respect to the original work, to which I have to acknowledge the obligation of much important assistance in practice, I must confess myself very differently circumstanced with regard to the trans- lation. To suit the convenience of English students, who have in general neither time nor inclination for voluminous reading, Dr. Fisher and myself have laboured, as far as possible, to compress the work without omitting a single experiment or conclusion. This, however, has been no easy task, as Dr. Edwards' own method of exposing the subjects of which he treats is in general too concise to admit of abbreviation, without incurring the risk of producing obscurity. I have thought it best, in publishing the transla- tion, to omit the copious tables, in which the Author has set forth the individual results of his very nu- merous experiments, to enable the reader to con- firm the conclusions which he has deduced from them. These form a valuable addition to the ori- ginal work, but as I conceive that the majority of readers will rarely if ever refer to the tables, I have judged that to reprint them would consi- derably and needlessly increase the price of the book. Those who are engaged in similar re- searches with Dr. Edwards, and are desirous of referring to the tables, may easily consult them in the original work, since, as they are almost PREFACE. VII purely numerical, they may be easily understood even by those who are unacquainted with the French language. The Appendix to the original work, relates to electricity in conjunction with the phenomena of life. It was furnished by Prevost and Dumas, and is principally devoted to their views respect- ing muscular contractions, on which subject I must confess myself under the necessity of dis- senting from those able physiologists. To the Appendix, in the translation, I have made some additions, in order to put the reader in posses- sion of subsequent researches regarding the re- lations between life and electricity ; yet it must be confessed, that this subject is still in a very imperfect state, and calls for further investiga- tion, which would doubtless well repay the la- bour of conducting it. Some other points relating to physical pheno- mena connected with life, are also briefly noticed in the Appendix, viz. : Dutrochet's views re- specting endosmosis and exosmosis — those of Dr. Stephens, which have thrown most important light on the chemical changes produced in re- spiration and circulation, and the labours of other experimenters on the same subject. I have likewise reprinted, with some additions and alterations, my Thesis on Absorption, a short paper on the Uses of the Spleen, and the micro- Vlll PREFACE. scopic observations of my friend Joseph J . Lister and myself, in relation to the tissues and fluids of animals. The obvious relation which they bear to the objects of Dr. Edward's work, will, I trust, be a sufficient apology for the introduction of them. The notes which are also given in the Appendix, are few and generally short. For the materials of the Appendix, I am greatly indebted to the kindness of my friends, and it gives me pleasure to embrace this opportunity of acknowledging my obligations in this respect to Sir Astley Cooper, Dr. Stephens, Dr. Marshall Hall, Dr. C. Thompson, my valued friend Luke Howard, C. Woodward and to my learned and accomplished friend A. R. Dusgate. I cannot conclude this preface without ex- pressing a hope, that the students and younger members of the profession may zealously pursue the investigation of the various interesting sub- jects which physiology presents, in the philoso- phical method of which Dr. Edwards has given so striking an example. CONTENTS. Page Introduction 1 PART I. THE BATRACHIAN REPTILES. CHAP. I.— On Asphyxia 7 Sect. 1. — Comparative Influence of Air and Water upon the nervous and muscular Systems 9 Sect. 2. — Asphyxia in Water 11 Sect. 3. — Strangulation . . 11 Sect. 4. — Cutaneous Respiration 12 Sect. 5.- — Animals inclosed in solid Bodies 13 CHAP. II. — On the Influence of Tempera- ture 16 Sect. 1 . — Influence of the Seasons ., 18 CHAP. III. — On the Influence of the Air CONTAINED IN WATER 22 Sect. 1. — On the Effects of limited quantities of Water... 25 Sect. 2. —Stagnant Water renewed at intervals, ....... 26 X CONTENTS. Sect. 3. — Action of Aerated Water upon the Skin. ..... 27 Sect. 4. — Running Water 29 Sect. 5. — Limits of this Mode of Life 30 Sect. 6. — Combined Action of Water, Air, and Tempera- ture 32 CHAP. IV. — On the vivifying Action of the Atmosphere 35 Sect. 1. — Influence of Cutaneous Respiration 35 Sect. 2. — Influence of Pulmonary Respiration 38 CHAP. V. — The Influence of the Atmosphere on Perspiration 42 Sect. I. — Loss by Perspiration in equal and successive Periods 42 Sect. 2. — Effect of Rest and of Motion in the Air .... 44 Sect. 3. — Respiration in Air of extreme Humidity .... 45 Sect. 4. — Perspiration in dry Air 46 Sect. 5. — Effects of Temperature 47 CHAP. VI. — Absorption and Perspiration .. 48 PART II FISHES AND REPTILES. CHAP. I.— Tadpoles 51 CHAP. II.— Fishes 56 Sect, I;—- Influence of Temperature on the Life of Fishes, In Water deprived of Air , ... , ,,.,,,.. . 50 CONTENTS. XI Sect. 2. — Influence of the Temperature of Aerated Wa- ter, in limited Quantities, in close Vessels.. 57 Sect. 3. — Influence of Temperature, and limited Quan- tities of Aerated Water, in contact with the Atmosphere 58 Sect. 4. — Respiration in the Air 9 59 Sect. 5. — Life of Fishes in the Air 59 CHAP. III. — Lizards, Serpents, and Tortoises 65 PART III. WARM-BLOODED ANIMALS. CHAP. I. — On the Heat of young Animals... 68 CHAP. II. — On the Heat of adult Animals.. 75 CHAP. III. — The Influence of the Seasons on the Production of Heat 81 CHAP. IV.— On Asphyxia 84 Sect. 1 . — Influence of External Temperature .......... 89 CHAP. V. — On Respiration in Youth and adult Age 91 CHAP. VI.— -On the Influence of the Sea- sons upon Respiration 98 CHAP. VII. — On Perspiration, or Exhalation 103 Sect. 1. — Loss by Perspiration in equal and successive Periods 103 Sect. 2. — Influence of the Hygrometric State of the Air 107 Sect. 3. — Influence of the Motion and Rest of the Air. . 110 Xll CONTENTS. PART IV. MAN AND VERTEBRAL ANIMALS. Page CHAP. I. — On the Modifications of Heat in Man, from Birth to adult Age.. 112 CHAP. II. — On the Influence of Cold on Mortality at different Periods of Life 117 CHAP. III. — Momentary Application of Cold 123 CHAP. IV. — Momentary Application of Heat 125 CHAP. V. — Influence of the Seasons in the Production of Heat 126 CHAP. VI.— Asphyxia 132 CHAP. VII. — On the Modifications of Respi- ration DEPENDING UPON SPECIES, Age, &c 141 CHAP. VIII. — Of the combined Action of Air and Temperature 145 CHAP. IX. — Effects of Temperature upon the Functions of Respiration and Circulation 151 CHAP. X. — Influence of the Respiratory Movements on the Production of Heat 157 CHAP. XL— On Perspiration 1 62 Sect. 1 . — Influence of Meals 1 64 Sect. 2. — Influence of Sleep . 1 67 CONTENTS, Xlll Page Sect. 3. — Influence of the Hygrometric State of the Air.. 168 Sect. 4. — Influence of the Motion and Rest of the Air . . 169 Sect. 5. — Influence of Atmospheric Pressure 170 Sect. 6. — Perspiration by Evaporation and by Transuda- tion .... 171 Sect. 7. — On the Influence of Temperature 176 Sect. 8. — Cutaneous and Pulmonary Perspiration .... 178 Sect. 9. — Perspiration in Water 180 CHAP. XII. — Absorption in Water 181 CHAP. XIII. — Absorption in Humid Air 186 CHAP. XIV.— On Temperature 190 Sect. 1. — On the Degree of Heat which Man and other Animals can endure 190 Sect. 2. — On the Influence of Excessive Heat upon the Temperature of the Body 195 Sect. 3. — Comparison of the Losses by Perspiration in Dry Air, Humid Air, and Water, at Tem- peratures inferior to that of the Body .... 198 Sect. 4. — On the Influence of Evaporation upon the Tem- perature of the Body when exposed to an excessive Heat 200 Sect. 5. — On Cooling in different Media, at Tempera- tures, inferior to that of the Body 202 Sect. 6. — On Refrigeration in Air at Rest, and in Air in Motion 204 CHAP. XV. — On the Influence of Light upon the Development of the Body. 206 XIV CONTENTS. CHAP. XVI. — On the Alterations in the Air from Respiration 212 Sect. 1. — Proportions of the Oxygen which disappears, and of the Carbonic Acid produced 216 Sect. 2. — On the Proportions of Azote in the Air inspired and expired 221 Sect. 3. — On the Exhalation and Absorption of Azote, . 225 Sect. 4. — On the Production of Carbonic Acid in Res- piration 22q Sect. 5. — General View of the Alterations of the Air in Respiration 242 CHAP. XV.— Applications 245 APPENDIX. On Electricity. By Prevost and Dmnas 285 On Muscular Contractions produced by bringing a solid body into contact with a Nerve without a Galvanic Circuit. By Dr. Edwards 307 On Atmospheric Electricity. By M. Pouillet 316 Extract from an Essay on some of thePhcenomena of Atmo- spheric Electricity, By Luke Howard, F.R.S., Sfc. . . 320 Remarks on the same subject by the Editor, and Experi- ments and Observations by C. Woodward and P. Smith 325 Be A bsorbendi Functione. By Dr. Hodgkin 342 Further Remarks on the same subject, and Notices of the Papers of L. Franchini, Fiscinus and Sexier, Dr. Barry and Fodera 382 CONTENTS. XV On the Phenomena to which the Names Endosmosis and Exosmosis have been qiven by H. Dutrochet 414 On the Microscopic Characters of some of the Animal Fluids and Tissues. By J. J. Lister and Dr. Hodgkin .... 424 On the Uses of the Spleen. By Dr. Hodgkin 448 NOTES. On Asphyxia 463 On the same subject. By Dr. M. Hall 464 On the Proteus 464 On the Existence of Fish, Sfc. in Water of High Temperature 465 On Hybernating Animals -» 467 On the Temperature of Hybernating Animals and of Young Animals. By Dr. M.Hall 469 On the Views of Dr. M. Hall and Dr. Holland on this sub- ject 470 Original Experiments on the Effects of Heat and Cold. By Sir Astley Cooper 472 Experiments on the same subject, tvith reference to Resto- ration from suspended Animation. By Thomas Nun- nelly 475 Observations on the Influence of Temperature on the Mor- tality of Children. By Dr. M. Edwards and Dr. Villerme 476 On Cutaneous Absorption. By Dr. Corden Thompson . . 476 Connexion of Rainy Seasons with Disease, exemplified in the Cases passing through an Hospital 479 On an Increase of the Weight of Atmospheric Air, noticed by Dr. Prout during the prevalence of Cholera 480 On the Changes effected in the Air by Respiration, with Notices of the Experiments of Dr. Stevens, S. D. Broughton, and Allen and Pepys 48 1 ERRATA. Page 9 line 8 from bottom for heart read hearts. 19 in note for preceding read succeeding. 24 line 9 from bottom for lugs read lungs. 245/or Chapter XV. read Chapter XVII. 331 line 10 from bottom for hogs read dogs. 334 5 from bottom for F. Smith read P. Smith. 448 12/or contribution read contributor. INTRODUCTION. The object of the present work is the examination of the effects of those agents by which we are surrounded, and whose influence is incessantly exerted upon us. They are called physical agents, as being the objects of that part of science which is denominated physics. They are to be distinguished from mechanical agents. These researches will relate to the Air in its several conditions of quantity, motion, or rest, density or rarity ; to Water in a liquid state, and in a state of vapour ; to Temperature, as modified both in degree and dura- tion ; to Light; and to Electricity. These agents operate simultaneously, and, in general, imperceptibly, on the animal economy. The impression produced is the result of their combined influence. Even when the intensity of any one of them is such, that we are enabled to distinguish the cause which is affecting us, it most frequently happens that the sensation alone is attended to, whilst the accompanying changes escape our notice. Hence, the most careful observation of phenomena, as presented by nature, cannot enable us to analyze the result of such combined actions," and to assign to each cause its peculiar effect, whilst those effects, which it is not in the province of sensation to detect, will re- main undiscovered. By means of experiments, we may, however, control external circumstances, and vary that Z INTRODUCTION. of which we wish to appreciate the action ; and thence, by observing the correspondence existing between such modi- fication, and the accompanying change which takes place in the animal economy, we may establish the relation of cause and effect. In order to derive advantage from this method, the intensity of the cause must be determined on the one hand, and the degree of effect on the other. In physics we may generally find means of accomplishing the first : the reader will judge how far I have succeeded with the second. I took, for the subjects of my experiments, various species of animals from all the four vertebrated classes, in order to give greater certainty to particular results, when an agent produced uniform effect on beings so differently con- stituted. Moreover, I hoped that the investigation of the very evident modifications, of which certain species are sus- ceptible, might lead to the discovery of similar modifica- tions in species in which they are too little marked to fix the attention in the first instance. I soon found the result to equal my expectation. In the detail of my researches I have adhered to the order in which they were conducted. I have divided the work into four parts. The first relates to the Batrachian Reptiles ; the second, to the other Cold-blooded Vertebrated Animals ; the third, to Warm-blooded Animals ; the fourth, to Man, and the other Vertebrated Animals.* In the outset of these inquiries I soon perceived that the science of electricity was too little advanced to supply me with the requisite means for placing the investigation of * I also made corresponding experiments with several families of invertebrated animals. M. Adoin,well known by his labours on the anatomy of insects, assisted me in conducting them. INTRODUCTION. 3 this on a par with that of other agents. The recent dis- covery of GErsted, by which the phenomena of electricity and magnetism are connected, forms, in conjunction with those of Ampere, and several other natural philosophers, a new epoch in the annals of this branch of science. The principles which they have established, and the instruments which they have invented for the appreciation of actions hitherto unknown, have furnished Prevost and Dumas with the means of making some very interesting researches on electricity, in connection with the animal economy. To their kindness I am indebted for the concise view of the present state of our knowledge on this subject, which is contained in the Appendix to this work. Tables are added, exhibiting the individual results of the principal experiments, in order that the reader may be better enabled to judge of the bases on which the con- clusions are founded. The examination of one fact always led me to that of another ; hence, the intimate connection between all the phenomena which I have detailed. The importance of the agent decided the point at which my researches were to commence. All the physical agents are indeed indis- pensable to the maintenance of life ; but as the air is that for which there is obviously the most pressing necessity, I began by examining the effects which result from the pri- vation of it. The choice of the animals for experiment followed as a consequence. Those which offered the widest scope for observation, with regard both to the duration of the phenomena, and to the facilities afforded for variation of the experiments, were the first to be examined, I therefore commenced with the family of the batrachians. They unite many other advantages, which render them peculiarly adapted to afford the first notions of the influence b 2 4 INTEODUOTrON. of physical agents. As they participate in the qualities of reptiles and of fishes, the knowledge obtained from the study of them renders it the more easy to pass rapidly to the other cold-blooded vertebrals. The minutiae of detail may be collected from the tables whenever the uniformity of the phenomena is obvious, whilst the attention is directed to the particular considera- tion of those instances which at first sight appear to be exceptions, the examination of which leads to further re- sults. The higher temperature of the mammalia and of birds, being the physiological fact which forms the strongest contrast between them and reptiles and fishes, I make it the first point to be considered in the study of warm- blooded animals ; and, regarding the development of heat as a function abstractedly, I endeavour to determine what are the variations to which it is subject, according to various circumstances with respect to organization on the one hand, and to external agents on the other. The results of this examination furnish the elements which enter into a great number of other phenomena, which are the subjects of sub- sequent researches. The commencement of the third part corresponds to the researches in the first, in which I examine the effects of the internal temperature on cold-blooded vertebral animals. I there make no allusion to the facts detailed in the pre- ceding parts, but confine myself in treating of warm- blooded animals to the independent consideration of them. It is only in the fourth part which relates to man, with the other vertebral animals, that I take an extended view of the phenomena, as well through the medium of the pre- viously detailed facts as of others, which serve as the com- plement to them, or lead to new considerations. It is this generalization which admits of our entering on the consi- INTRODUCTION. O deration of man. This is the end which I proposed to myself, and to which every thing that I have advanced leads and refers. The relations of the physical agents to the animal eco- nomy are infinite. It was necessary to make a selection. I have confined myself to those direct actions, which the present state of the physical sciences furnishes us with the means of appreciating, and to the examination of their combinations. In the choice of the circumstances, of which I sought to discover the influence, I have always been guided by the wish to establish principles capable of useful application. The agents which I have examined, having immediate relation to the nervous system, and to the organs of respir- ation, circulation, exhalation, and absorption, I have been led to the investigation of a great number of facts con- nected with hygeia and pathology, of which an idea will at once be formed, when it is considered that I have been particularly occupied with modifications dependent on con- stitution, and with the changes which constitution under- goes through the operation of external agents. The greater number of the facts which I have related, were first brought forward in various papers which I have read before the Royal Academy of Sciences of Paris, or presented to that body as subjects for the prize founded for the promotion of experimental physiology. # * Chap I. The part, On Asphyxia was read to the Academy of Sciences in 1817. and printed in the Annates de Physique el de Chimie for the same year, Vol. 5. Chap. IT. The first part, On the Influence of Temperature was read to the Academy in 1818, and published in the Annates de Phy- sique et de Chimie the same year, Vol. 8. Chap. III. The first part, On the Influence of Air, contained in 6 INTRODUCTION. I owe the acknowledgment of my obligations to my pupil M. Vavasseur, who assisted me in the course of my experiments. water, was read to the Academy in 1818, and inserted in the An- nates de Physique et de Chimie, Vol. 10. Chap. IV. The first part, On the Vivifying Influence of the At- mosphere— Chap. V. First part, On the Influence of the Atmosphere on Transpiration — Chap. VI. First part, On Absorption and Transpiration in Water, — were read to the Academy of Sciences in 1819. These three chapters united to the second part with a short state- ment of the facts contained in the third, were presented to the con- cours for the prize of experimental physiology in 1819, and were crowned by the Royal Academy of Sciences, together with the work of M. Serres sur les I'Osteogenie in 1820. Baron Cuvier gave an account of these memoirs in the Analysis of the Transactions of the Royal Academy of Sciences, published each year. The 1st and 2d sections of chap. 16. 4th part, are extracted from a paper which I read to the Academy, January 1821, On Respiration and the Influence of the Seasons on the Animal Economy ; and which, being presented to the concours, divided the prize for experimental physiology with M. Dutrochet's paper. On the Groioth and Repro- duction of Vegetables. The 3d section, On the Exhalation and Absorption of Azote, Chap. 16, 4th part, was read to the Academy in 1823, and printed in the Annales de Physique et de Chimie, and in Magendie's Jour- nal de Physiologie ; the 4th section, On the Production of Carbonic Acid in Respiration ; and the 5th section, A General View of the Changes in the Air in Respiration — were read to the Academy in the same year. It will be seen from several parts of this work that I did not originally intend here to treat of the changes of the air in respiration, this subject being designed for one of the parts of an- other work, On the Influence of the principal Chemical Agents. For reasons which I need not relate, I have concluded to publish these researches in this place, where they Avill serve as a supple- ment to those which precede them, PART I. THE BATRACHIAN REPTILES. CHAP. 1. ON ASPHYXIA. The action of Air in respiration, is one of the pheno- mena with the investigation of which physiology was the first engaged ; but it has been one of the last to be studied with advantage. The solution of this question depended on another science which, until latter times, did not furnish the requisite light. When Priestley had discovered oxygen gas, and its pro- perty of converting dark into red blood, and when Lavoisier had laid the foundation of the new chemical theory, Good- win made the application of it to asphyxia, and demon- strated by accurate and skilfully combined experiments that the exclusion of air, by preventing the conversion of dark into red blood, is the cause of the death of animals. Bichat again took up the subject, and has published a treatise on as- phyxia, under the title of " Researches on Life and Death." He took a wide view of the subject ; and, by a beautiful train of experiments, endeavoured to determine the triple relation of the nervous, respiratory and circulatory systems, O ASPHYXIA. He drew the conclusion, that venous blood penetrating the brain, causes its functions to cease, and that afterwards, the heart ceases to beat from the same cause. Legallois likewise treated of Asphyxia in his Researches on the Principle of Life, and made it appear that venous blood, acting on the spinal marrow, causes the movements of the heart to be stopped. It is to be observed, that these physiologists made their experiments almost exclusively on warm-blooded animals. The phenomena presented by cold-blooded animals merited particular attention. Spa- lanzani took them up in his Researches on the Relation which the Ah' bears to organized Beings, a work equally remarka- ble for the number and the importance of its facts. The alteration which the air undergoes from the organs, capa- ble of modifying it, was the principal object of his en- quiry. The relation between the three great functions, on which Bichat and Legallois have so much insisted, but little arrested his attention. At that time physiology had not made the progress which it has done since the labours of that celebrated experimental philosopher and naturalist ; and chemistry had not then perfected the process for the examination of gases. One of the philosophers, who has the most essentially contributed to this improvement, has also published a treatise on the respiration of fishes, which leaves nothing to be desired on this point.* The phenomena presented by cold-blooded animals are so wonderful, that it would seem impossible to bring them together with those exhibited by the other vertebrated ani- mals. It would not be believed, that they are united by a common chain, if the careful investigation of nature did not discover the uniformity of her laws. * Memoire sur la Respiration des Poissons, by Humboldt and Provencal, in tbe Memoirs of the Society of Arcueil. ASPHYXIA. 9 Sect. 1. — Comparative influence of Air and Water upon the nervous and muscular systems. Previous to our examination of the phenomena of as- phyxia, we shall first enquire whether the media in which it may take place have not a peculiar influence, independ- ent of that which is exerted over the lungs. Of these media, the most important are air and water. The singular power possessed by reptiles of living a considerable time after the excision of the heart, supplies us with the means of appreciating the respective influence of these media. By the removal of the heart the circulation of the blood, and, as a necessary consequence, respiration, are annihilated. A part of the blood escapes ; and that portion which remains may be regarded as a constituent part of the organs. The nervous and muscular system alone are left, and these are inseparably connected. If, after having cut out the hearts of reptiles, taking care to remove, also, the bulb of the aorta, an equal number be placed in air and in water, deprived of air, the difference in the duration of life, if any difference exist under these two circumstances, will indicate the respective influence of these media on the nervous and muscular systems, inde- pendently of that which it may exert on circulation and respiration. This experiment was performed on salaman- ders, frogs, and toads. I cut out the heart of four salamanders of the species Triton, removing, also, the bulb of the aorta. I exposed two to the air, and immersed the two others in water of the same temperature, which had been deprived of air by boiling. In about four or five hours the salamanders in the water appeared dead ; but that life still existed was rendered evident, when they were moved or pinched. One died in eight hours, the other in nine. Those in the air, 10 ASPHYXIA. however, lived from twenty-four to twenty-six hours. These experiments were afterwards repeated with the same pre- cautions upon six other salamanders, and similar results were obtained. Consequently air, in comparison with water, has a superior vivifying influence upon the system of these animals, independently of its action by means of circulation and respiration. The heart and bulb of the aorta were removed from twelve frogs (R. esculenta and R. temporaria) six of which were placed in water, deprived of air, and six in air. Those in the water lived two hours, and those in the air three. Their activity which continued to be considerable, after the excision of the heart, decreased far more rapidly in the water than in air, and stimulation produced much less effect. The same experiment succeeds equally well upon toads. If a frog, thus deprived of its heart, and immersed in water, be drawn out and exposed to the air, at the moment when all signs of life have disappeared, it immediately begins to recover. If it be again plunged in water all ap- pearance of life instantly ceases ; and it may thus be made, several times alternately, to lose and recover its motion and sensibility. This confirms, in a striking man- ner, the vivifying effect of air, and the deleterious influence of water on. the nervous system.* * Nasse has likewise shewn by experiment, that water has the effect of destroying the irritability of muscles, and has pointed out an application of this fact to some points of physiology and patho- logy. This property of water had already been noticed by Humboldt, and also by Pierson. Note of the Editor. ASPHYXIA. 11 Sect. 2. — Asphyxia in Water. In the preceding cases the functions of the nervous and muscular systems alone remained. In asphyxia, there is, in addition to these, the circulation of blood, which has been deprived of the influence of the air. I next attempted to ascertain the comparative duration of life under these two conditions, in order to discover the effect which the circu- lation of venous blood produces on the nervous system. With this view, frogs, whose hearts had been removed, and an equal number left entire, were placed in vessels containing water deprived of air. The result, in all cases, exhibited a marked difference, sometimes above twenty hours in favour of the latter. Similar results were ob- tained with toads and salamanders. The removal of the air in the lungs, by pressure or excision of the lungs them- selves occasions no difference in the effects. Hence the circulation, even of venous blood, is favourable to the action of the nervous and muscular systems, though incapable of maintaining life beyond a very limited period. Sect. 3. — Strangulation. It may be presumed, that the water which, from the experiments in sect. L, was shewn to exert a deleterious influence upon the nervous system, may have prevented the circulation of venous blood from prolonging life so much as it would have done in a less noxious medium. I strangled six frogs, by tying, very tightly, with a pack- thread round the neck, a piece of bladder fitted very closely to the head, so as to exclude the air. In fact, the ligature was sufficiently tight to effect this of itself. At first the frogs were paralysed, but they afterwards, to a great degree recovered, and lived from one to five days ; while 12 ASPHYXIA. the same number in water were dead in ten or twelve hours. The same experiment upon salamanders was at- tended with similar results. One of these animals lived twelve days, when the head became gangrenous ; it af- forded me an opportunity of making observations anala- gous to those of M. Dumeril, in his interesting experiments on a salamander, which survived decapitation a sufficient length of time for the neck to cicatrize. The phenomena in these cases being complicated with serious injury of the the nervous system, belong to a subsequent section. On comparing asphyxia by submersion with strangulation in the air, we see so marked a difference in the duration of life, as to lead to the inference, either that these animals can live for many days without any other action of the air than that which is exerted on the nervous system, or that that fluid acts also upon the blood through the skin. Sect. 4. — Cutaneous Respiration. Spallanzani concluded, from his investigation, that when the skin of these animals (frogs and other batrachians) is in contact with the air, carbonic acid is produced ; but he operated upon batrachians whose lungs had been cut out. In this case the blood from the wound, in contact with the air, -must necessarily produce carbonic acid. To obviate this objection M. Chevillot and myself placed frogs, strangled with bladder and a ligature, as in the preceding experiment, in receivers containing atmospheric air. We took them out alive an hour or two after, and having ex- amined the air of the vessel, we found in it a sensible quantity of carbonic acid. Hence it follows, that the length of time which reptiles, in the state of strangulation, can live in air, must in part be referred to the action of that fluid upon the skin. ASPHYXIA. 13 I defer, for the present, the consideration of the mode in which the carbonic acid was produced. Sect. 5. — Animals inclosed in solid Bodies. From the preceding facts and observations, it appears that animals asphyxiated under water perish sooner than the mere circulation of venous blood would cause them to do ; while the life of those in air is prolonged by the influ- ence of that fluid exerted through the skin. If, therefore, the animals could be incased in a solid material, which should exert no deleterious influence on the nervous sys- tem, the influence of the venous blood would be free from both these complications. Numerous instances are re- corded of toads having been found in blocks of stone, and other similar situations, in which they must have re- mained, without extinction of life, for an incalculable length of time. But in these cases there was probably- some crevice, forming a communication between the ex- ternal air and the cavity containing the animal.* In 1777 Herissant proved to the Academy of Sciences that toads could live eighteen months in boxes inclosed in plaster ; but as, even in this experiment, the animals were surrounded by the air in the boxes, it is not absolutely conclusive. I took, on the 24th of February 1817, five pasteboard boxes of three and a half inches diameter and two deep, and filled each of them with plaster, in which was imbed- ded a toad ; one of them was found alive on the nine- teenth day. The others were left for examination after a longer period. Similar experiments were tried upon sala- manders and frogs with the like results ; but these last do not live so long as the toads and salamanders. * We are inclined to think that at least in some of these instances such communications must have been altogether impossible. 14 ASPHYXIA. The foregoing facts appear still more remarkable, on comparing the duration of life of some of those animals exposed to air, with that of others buried in solid bodies. Four frogs were exposed to the air in a dry bottle. At the same time, an equal number were placed in dry sand of the temperature of the atmosphere. I examined them every twenty-four hours. On the third day all those in the air were dead, except one, while all those buried in the sand, with one exception, were perfectly alive. The life of the animals inclosed in plaster or sand ap- pears to be preserved by the air having still sufficient access to them to exert its vivifying influence through the skin. The permeability of sand is evident. In order to ascertain how far plaster possessed the same property, I took an open tube, five inches long and five or six lines in diameter ; closed one extremity with plaster to the extent of about an inch, and took care to cover it outside. I let it dry and again put plaster over it, in order to close the imperceptible openings which might exist in it. When the whole was sufficiently dry, the tube was filled, with mer- cury, and inverted over the same fluid : it was not long- before I perceived that the air penetrated and lowered the mercury. This experiment repeated several times had al- ways the same result, which shews that air freely pene- trates plaster. It might, however, have been the case, that the quantity of air which penetrates the plaster was insufficient to sup- port the life of these animals. I therefore inclosed frogs, salamanders, and toads in plaster, as in the preceding ex- periment, and placed some under water and others under mercury, to intercept the air, and found that they died almost as soon as when the water is in immediate contact with them. But it remains to be ascertained why the duration of ASPHYXIA. 15 the life of these animals is longer in the sand or plaster than in the air ? Frog's and salamanders waste rapidly in the air, and undergo desiccation. In the proportion that they waste, their motions are performed with increasing difficulty ; they move, however, until they have lost the quantity of water necessary to their existence. The pasteboard-boxes containing toads and salamanders, mentioned in p. 13, were opened at intervals of from six weeks to two months and a half from the commencement of those experiments. The animals were all dead, and in a state of complete desiccation. I observed the same of the frogs which had died in the sand. Hence I concluded, that in both cases death arose from the loss of the fluids by perspiration, and I presumed that the perspiration must be less in the plaster than in the air. This was afterwards proved by exposing some frogs to the air in dry vessels, and burying others in dry sand, and afterwards weighing them, at intervals of two, three, four, and five days, I uni- formly observed a greater loss in the air than in the sand. Comparative experiments were also made in air and plaster upon toads, and the difference was much more striking than in the sand. Hence the cause of the greater duration of life in sand or plaster than in air, is from the perspir- ation being more abundant in the air than in the solid substances. Under an exhausted receiver, in which the effects of rapid evaporation and absence of air are combined, death, as might be expected, takes place very speedily. Several experiments which I performed, in* conjunction with M. Chevillot, on frogs and salamanders, demonstrate this fact. CHAPTER II. ON THE INFLUENCE OF TEMPERATURE. The facts detailed in the preceding chapter may be modified by various circumstances, which have not yet been considered. One of the most important of these is temperature. In the months of July and September, 1816. I made forty-two experiments on the submersion of frogs, in glasses containing two-tenths of a litre * of aerated water inverted over saucers. The mean temperature of the atmosphere was 15.°6 of the centigrade thermometer, or 60° of Fahrenheit in July, in September it was 14.° 1 of the cent, or 58° of Fahr. the temperature of the water was from 17° cent, or 63° Fahr. to 15° cent, or 60° Fahr. The mean duration of life, or sensibility to ordinary stimuli was one hour and thirty- seven minutes in July, and one hour and forty-five minutes in September. At the same time I made the following experiments, in order that the only appreciable difference might be in the temperature. Spallanzani and some other naturalists had already observed, that frogs immersed in water lived longer in winter than in summer, but they had not investigated the subject. The temperature of the Seine water being 17° cent, or 63° Fahr. I cooled it by means of ice to 10° cent, or 50' Fahr., * A litre is equal to V76 pint, new measure. INFLUENCE OF TEMPERATURE. 17 and found that, of two frogs immersed in it, one lived oh. 50' and the other 6h. 15'. When the water was re- duced to 0° cent, or 32° Fahr. eight frogs were introduced into it, and they lived from 6h. 7' to 8h. 18'. When, in- stead of cooling the water, its temperature was raised to 22° cent, or 72 Fahr., that of the air being 20° cent, or 68° Fahr., the frogs only lived from Ih. 10' to 35'; when it was raised to 32° cent, or 90° Fahr. they died in from 32' to 12'; and when it was raised to 42° cent, or 108° Fahr., they scarcely lived a few seconds, and in no instance exceeded two minutes. Hence we may observe that as the temperature of the water is reduced, the duration of the life of the frogs im- mersed under it, is prolonged until at 32° Fahr., or 0° of the centigrade thermometer, it is more than tripled. On the other hand the elevation of the temperature produces a corresponding abbreviation of life, till, at 108° of Fahr. or 42° of the centigrade thermometer, death might almost be said to be immediate. It is worthy of remark that the de- gree of heat at which frogs cannot survive immersion in water, is about the natural temperature of warm-blooded animals. The temperature about zero appears then the most fa- vourable to the life of frogs plunged in water, but it must not be supposed that the prolongation of their life was oc- casioned by their becoming torpid. They are certainly less active at that temperature, but they perform the functions of voluntary motion and enjoy the use of their senses. On the other hand, the elevation of temperature is accompanied by a progressive and corresponding diminution in the dura- tion of life, and a proportional increase of agility. Analogous experiments on toads and salamanders pro- duced similar results. Tn warm climates, animals of this class may perhaps c 18 INFLUENCE OF TEMPERATURE. continue to live in water at 42° cent, or 108° Fahr., but since they would have full liberty of respiration, this fact, if proved, would not be an objection to the preceding ex- periments, which have reference to a state of asphyxia. The influence of temperature with freedom of respiration will be examined in the sequel. In reply to an objection which may be raised, that the speedy death of the frogs might be occasioned by the rapid transition from the temperature of 15° cent, or 60° Fahr. to that of 42° cent, or 108° Fahr., rather than to the eleva- tion of the latter, it may be observed that the transition was equally rapid in the descending scale. The considerations, to which the preceding researches conduct us, are by no means so simple as might at first be imagined. The influence of climates and seasons, the mode of life of these animals, the action of the air con- tained in the water, and the relation which it bears to tem- perature, and lastly the effect of habit are all accessory circumstances whose complicated elements exert their re- spective influences. Sect. 1. — Influence of the Seasons. It will be recollected that in the months of July and Sep- tember, the frogs lived from an hour to 2h. 27' in aerated water at 15° cent, or 60° Fahr. and at 17° cent, or 63° Fahr. On the 7th November, ten frogs similarly placed in water kept at the temperature of 17° cent, or (33° Fahr. lived from 2h. 5' to 5h. 35'. All the circumstances being the same in these cases, except the season, it is to this cause that the difference in the results must be referred. But in what way does the season produce this effect ? Is it by means of temperature, or the intensity of light, or the weight of the atmosphere, or its hygrometric or electric INFLUENCE OF TEMPERATURE. 19 states, or its degree of motion or rest ? Is any thing to be referred to changes in habits of the animals themselves ? The influence of light and electricity must be left out of the question, until we can appreciate the degree of their in- tensity. The pressure of the atmosphere which exerts an influence by affecting perspiration may be disregarded' since the difference of mean pressure in the two seasons in which the experiments were made was very inconsiderable.* The same may be said of the influence of the winds and of the hygro metric state of the air, since batrachians, though powerfully affected by these causes whilst living in the air, are wholly removed from their operation when immersed in water. The only circumstance, therefore, left for con- sideration is the influence of temperature, and as the water in which the animals were immersed was kept at the same degree in both the series of experiments, it is evident that the temperature of the atmosphere prevailing at the time could exert no influence upon the result. The case, how- ever, is different in regard to the temperature, during a cer- tain space of time previous to the experiment. The shallow waters which frogs inhabit, vary in temperature with the atmosphere and more or less approximate to it. The frogs submitted to the July experiments had been for the pre- ceding months under the influence of a mean temperature of 14°.8 cent, or 58°.6 Fahr., and those made use of in September had experienced during August, the effect of a mean temperature of 15°.5 cent, or 60° Fahr. while the frogs subjected to the November experiments had been for the previous month exposed to a temperature of 7°.3 cent, or 45° Fahr. Hence results the remarkable fact, that these animals were able to live in the latter season twice as long; * The effects of variation in the rapidity of perspiration, and of diminished atmospheric pressure in accelerating perspiration, are shewn in the preceding chapter. c 2 20 INFLUENCE OF TEMPERATURE. as in summer in water at the same temperature. Admitting this to be the uniform result, it necessarily supposes a con- siderable change in the constitution of these animals, which thus prolongs the duration of their existence in water. To ascertain the uniformity of this principle was the subject of the following experiments. On the 23d Nov. 1817, the air and water being at 10° cent, or 50° Fahr. and the mean temperature of the month being nearly the same ; five frogs were placed in water at the same degree. They lived from 5h. 10' to llh. 40' ; the latter period being about double the duration of life of these animals in water at the same degree in summer. On the 22d Dec. the thermometer having; been about 0° cent, or 32° Fahr. for twenty days, three frogs were put in water at 10° cent, or 50° Fahr. ; they lived from twenty to twenty- four hours. On the 23d Dec. the temperature being still 0° cent, or 32° Fahr. four frogs were placed in water at 0° cent, or 32° Fahr. the same apparatus being employed as in the preceding experiments. They lived from twenty- four to sixty hours. The experiments just related were frequently repeated with the same results, for two successive seasons, and can leave no doubt on the mind respecting, 1st, the in- fluence of the temperature of the water in which the animals were immersed, and 2d, the influence of the tem- perature of the air for some days previous to the experi- ment. When these causes are combined the effect is doubled. Hence, in the last-mentioned experiment the animals were placed in circumstances the most favourable to the prolongation of their life under water. The congela- tion of water fixes the limit of the descending scale. In a greater degree of cold, the conditions are altered, and belong to the question of asphyxia in solid bodies. Being desirous of ascertaining whether the influence INFLUENCE OF TEMPERATURE. 21 of previous temperature would extend itself to the case of batrachians immersed in water at a high temperature. I placed, on the 30th October, the mean temperature of the month having been 7° cent, or 45° Fahr., six frogs in water, kept at the temperature of 42° cent, or 107° 6' Fahr. the degree which proves instantly fatal to batra- chians in summer. But they lived about the same time as in the analogous experiments made in the summer, viz. from one to two minutes. I tried the same experiment on the 23d December, the temperature of the month having been near 0° cent, or 32° Fahr. and repeated it upon toads and salamanders with the same results. CHAPTER III. ON THE INFLUENCE OF THE AIR CONTAINED IN WATER. In entering on this subject, it will be necessary to direct our attention to the habits of the frog. Spallanzani, from observations made by himself in the neighbourhood of Pavia, states, that the frogs there leave the water in Oc- tober, and withdraw to the sand, in which they provide themselves with an aperture, called by the frog-catchers, il respiro della rana, the frog's breathing hole. French naturalists, however, assert that frogs make their winter retreat in the water from October till spring ; and M. Bosc, who has paid great attention to the habits of these animals, informs us that he has often found them under water during winter. But do they remain constantly in this situation? or do they come occasionally to the surface for the purpose of respiration? This is a question not easily decided by observation, for however narrowly we might watch them, we could scarcely be certain that they had not come to the surface without being observed. Be- sides, it has appeared, from one of the preceding experi- ments, that in winter they have lived in water for two days and a half. From direct observation, therefore, we can derive little assistance in our inquiry, whether frogs can during winter, dispense with respiration. The affirmative side of this question is somewhat supported by the fact, INFLUENCE OF AIR CONTAINED IN WATER. 23 that they are sometimes found alive in water which is covered with ice. But this is not decisive, unless it could also be ascertained how many days had elapsed since the formation of the ice, and whether it were free from any aperture. M. Bosc has informed me, that he has seen, in winter, frogs quit the water for several days in succession, at a certain hour, and take breath for a short time on land. In the numerous experiments which I made in the win- ters of 1816 and 1817, on the asphyxia of frogs in a limited quantity of aerated water, they have never lived longer than two days and a half, even at the temperatures most likely to prolong their existence during their submersion. Spallanzani, in one instance, found a frog live eight days under water, varying in temperature from half a degree to a degree above zero, cent, and one to two degrees above 32° Fahr. ; he adds, that a more elevated temperature would inevitably occasion death in the course of a day. But during the season of the retirement of these animals, the temperature varies considerably. It may, perhaps, be supposed that frogs remain torpid during their hibernation. Torpor, however, does not ex- empt animals from the necessity of respiration ; but even admitting the contrary, it has been ascertained by the ob- servations of M. Bosc and myself, that frogs, though less active in cold weather, are not torpid even at the tempera- ture of zero, cent, or 32° Fahr. Let us now proceed to investigate the influence of the -air contained in the water. I am acquainted with one ex- periment only, which has been made in reference to this subject. Spallanzani placed a frog in water, deprived of air, and another in a similar quantity of aerated water. The former was at the point of death in ten hours, but the latter not until twenty had elapsed. This insulated expe- 24 INFLUENCE OF THE rinicnt, however, proves nothing, since the difference in the duration of life might have been occasioned by the different constitution of the individuals. The influence of the air contained in water, on the life of fishes, has been examined with great care by Spallan- zani, Sylvester, Humboldt, and Provengal ; and their la- bours have brought to light some most interesting facts, in reference to the natural history of fishes, but the con- clusions are applicable to this class of animals only, their gills being especially designed for receiving the influence of the air contained in water. To be amphibious in the strictest sense of the word, an animal ought to be capable of performing respiration both in the atmosphere and by means of the air contained in water; a double faculty, hitherto ascribed to no adult reptile, except the proteus and the siren. The axolotl, as Cuvier has shewn, has precisely the organization of the larva of the salamander. If these singular animals, which have been united to the family of batrachians, possess, like tadpoles, the faculty of breathing the air of the atmo- sphere, as well as that of water, they have also, like them, the double apparatus of lugs and gills. But, with these exceptions, the adult batrachians have only lungs, organs exclusively adapted to atmospheric respiration. There is nothing, therefore, which should lead us to conclude a priori, that they are capable of performing both func- tions. By the following experiments 1 have endeavoured to discover how far they are influenced by the air contained in water. AIR CONTAINED IN WATER. 25 Sect. 1. — On the Effects of limited quantities of Water, Several glasses, holding about five ounces and a half, and filled with water, deprived of air by boiling, and then cooled to the temperature of the atmosphere, were inverted over saucers containing about the same quantity of similar water. An equal number of similar glasses were filled with aerated water at the same temperature. At the same time a frog was introduced into each of these vessels, and the dura- tion of their respective lives carefully noticed. The result was in favour of the frogs placed in the aerated water, but it was not very decisive, showing only that the small quan- tity of water made use of did not contain so much air as to produce marked and uniform differences. We might safely, therefore, conclude, that though Humboldt and Provencal have shewn that boiling in open vessels is not sufficient entirely to deprive water of the air contained in it, and that the small quantity which remains is capable of exerting a marked influence upon fishes ; yet, that in this instance, no sensible influence could have been produced from this cause, in consequence of which I judged it un- necessary to have recourse to the method which they em- ployed for entirely banishing air from the water which they used. I next endeavoured to render the difference more strik- ing, by increasing the quantity of aerated water. On the 10th of November, the air being at ll°cent. or 52° Fahr., and the water at 13° cent, or 55° 4' Fahr. six glasses similar to those used in the preceding experiments, 26 INFLUENCE OF THE were filled with aerated water, and inverted over the aper- ture perforated in the shelf of a pneumatic trough, contain- ing ninety-eight pints and a half of Seine water. A frog was placed in each glass. At the same time, the same number of frogs was put into similar glasses of boiled water of the same temperature, and inverted over saucers. The latter lived from three hours and forty minutes to five hours and thirty minutes; while those in the aerated water lived from six hours and forty-three minutes to ten hours and forty minutes. The result of these experiments, though satis- factorily shewing that aerated water has a decided in- fluence in prolonging the life of these animals, is yet far from proving that it is capable of doing so to an indefinite extent. Sect. 2. — Stagnant Water renewed at intervals. Although the want of organs specially constituted to act in the air contained in water, rendered it improbable that frocks could live in water like fishes, I thought I ought to leave nothing untried, in order to determine the in- fluence of aerated water upon their existence in that liquid. On the 4th of December, the temperature of the room being 6° cent, or 43° Fahr., a male frog of the species rana temporaria, was secured at the bottom of a glass vessel, holding seventeen pints and a half of Arcueil water, by means of a transverse wire grating. The next day the water was drawn off with a syphon till only a sufficient quantity was left to keep the animal covered, when the vessel was replenished with fresh water. This was repeated daily ; the frog not merely survived for eight days, the longest period for which Spallanzani had been able to keep AIR CONTAINED IN WATER. 27 a frog alive, in water at 1° or 0° 5., but continued to live to the 25th of February, that is, for more than two months and a half, during which period the temperature had varied from 0° cent, or 32° Fahr. to 11° cent, or 51° Fahr. An accidental neglect to renew the water occasioned the death of the animal. This experiment shows the remarkable fact, that frogs are really amphibious, since they can not only breathe the air of the atmosphere, but can also live exclusively by means of the air contained in water. Tadpoles, which are possessed of gills as well as lungs, can also live in water without coming to the surface; a fact which I proved by an experiment conducted in the same manner as that which has just been detailed. They cannot, however, live on land previous to the full development of their limbs. Sect. 3. — Action of aerated water upon the skin. Let us now inquire what is the organ through the me- dium of which the vivifying influence of the air contained in the water is exerted upon these animals. We shall first examine what foundation there may be for supposing that the water enters their lungs, which' would, in this case, perform the functions of gills. Inspiration in frogs is per- formed by a kind of deglutition, and is accompanied by very evident movements of the throat, and of the soft parts under the lower jaw. When the animal is breathing in the atmosphere, their movements are repeated from forty to one hundred times in a minute. If it be plunged in water they immediately cease, and whatever be the length of time during which the submersion is continued, it is very seldom that any movement of deglutition can be observed. In the numerous experiments which I have made upon the 28 INFLUENCE OF THE asphyxia of frogs in aerated water, I have observed these movements in only a very few instances, and Spallanzani never perceived them. Humboldt observed that the fre- quency of the inspiration of a frog in a limited quantity of atmospheric air was diminished by the introduction of azote, and that the rarity of inspiration was proportioned to the quantity of azote introduced ; but neither azote, hydrogen, nor carbonic acid, has so strong a tendency to suspend inspiration as water. These experiments might be deemed sufficient to prove that it is not through the medium of the lungs that these animals receive the influence of the air contained in water. The importance of the fact, however, induced me to make a careful examination of the lungs of frogs, which had been previously immersed in water for a considerable time, and in no instance could I detect any water in them. This is likewise confirmed by the experience of Spallanzani. The air contained in water, therefore, does not act upon the lungs of the frogs which are immersed in it. Its action must consequently be referred to the skin, the only other organ in contact with the fluid. The question whether this action on the skin is analogous to that on the gills of fishes, and the investigation of the changes which these organs effect in the air, belong to a subsequent part of this work. It will be sufficient here to state, that during the time in which the life of the animal was maintained by aerated water, the arteries in the webs of the feet evidently contained florid blood. AIR CONTAINED IN WATER. 29 Sect. 4. — Running water. In the foregoing experiment, the water in which the frog was placed was at rest. Would life have been equally maintained in running water? This query would certainly appear an idle one, had not Spallanzani been led to con- clude from his experiments, that the animals died sooner when submerged in running water, than in that which was at rest in vessels kept in his laboratory. On the 6th of November, a frog in a net to which a weight was attached, was sunk to the bottom of the Seine, at a part where there was about ten feet of water, and was retained in that situation. On the eleventh, the net was drawn up, and the frog being found alive and well, was again similarly sunk. He was afterwards examined on the seventeenth, when he was found equally lively. At the very same season, frogs placed in vessels holding five ounces and a half of water which was left unchanged, survived only a few hours. Water salamanders as well as frogs may have life sup- ported by the contact of aerated water with the skin. A crested salamander and a green salamander of Latreille, were confined by means of transverse septa of wire at the bottom of vessels, each containing four quarts of Arcueil water changed daily ; they lived about two months, and the latter died from neglect to change the water, on the same day that the frog mentioned above, suffered from the same cause. Both the above mentioned species of sala- mander bear submersion in water, at the temperature of zero, without becoming torpid. As conclusions deduced from experiments on frogs and water reptiles might not apply to the brown toad, which is altogether a land animal, an individual of this species was 30 INFLUENCE Of THE put into a net on the Gth of November, 1817, and sunk in the Seine. On the 17th he was still living ; but he had made his escape when the net was again examined a month after. At the season of this experiment, brown toads as well as frogs survived only a few hours when confined under the surface of limited qualities of unchanged water. Sect. 5. — Limits of this Mode of Life. The faculty of living by means of air dissolved in water being shewn to belong to the three genera of batrachians, which were made the subject of the preceding experiments, it is important to know the conditions which influence this mode of life. Are these animals capable of it at all seasons ? and what is the influence of temperature ? It might be supposed that when frogs quit their water retreats, they are no longer able to live under water, since at this season their constitution undergoes a remarkable change. They are in a state of the most lively excitation, and certain parts of their bodies become visibly altered : for example, the thumb of the male acquires a black colour, and a con- siderable increase of size. It is the period at which the species is propagated. In order to ascertain whether, at this time, frogs continued to retain the power of living under water, one of these animals was tied by the leg, and secured at the bottom of a vessel, containing forty-nine pints of Arcueil water. He lived twenty days, during which time the water had been changed every twenty-four hours, and its temperature had never exceeded 10° cent, or 50° Fahr. Frogs, then, may live under water for a long time after they are wont to quit it in the spring. Experi- ment further proved that they possess the same faculty in autumn. But is this mode of existence subjected to no limits ? Is AIR CONTAINED IN WATER. 31 it only necessary to attend to the quality of the aerated water ? Does temperature, which is productive of so great an influence when the water is limited in quantity, exercise none when the quantity is unlimited ? The frog before mentioned, immersed in aerated water, which was changed every twenty-four hours, died on the twentieth day, the temperature not being elevated above 10° cent, or 50° Fahr. This was in the spring of 1816. In October, 1817, a frog lived under water, in an earthen vessel, containing forty-nine pints, for eleven days. During this interval the temperature varied from 9° cent, or 48° Fahr. to 12° cent, or 53° 6' Fahr., and it was at the latter temperature when the animal died. These experiments induced me to attempt others, in order to determine whether so slight an elevation of temperature could affect the existence of these animals in aerated water, which was frequently changed. On the 12th of April 1 put a frog in a tub containing fifty-six litres (seven gallons and a half ) of Seine water, at 12° cent, or 53° 6' Fahr., and kept it at the bottom, by means of a packthread attached to a weight. I found it dead the next day. I repeated the same experiment for several successive days with the same result. The tempe- rature of the water had risen in this interval to 14° cent, or 57° Fahr. I repeated these experiments on toads and sala- manders, with the same result. In these experiments, the animals were kept in vessels containing water which was renewed every twenty-four hours. But would they experience the same fatal effect from this slight elevation of temperature, if they were kept under the water of ponds and rivers, so as not to be allowed to come to the surface to breathe ? To solve this question I tried the following experiment : — On the 12th of April I put seven frogs and two toads into 32 INFLUENCE OF THE an osier basket, which was immersed in the Seine ; the temperature of the river, at the surface, was 12° cent, or 53° 6' Fahr. On the 20th of the same month I drew them out, and of the seven frogs, four were dead, the two toads were still alive. The temperature continued at 12° cent, or 53° 6' Fahr. The running water was, therefore, much more favourable to the life of the fross than the water in the vessels. Could this be attributed to a difference of tem- perature at the surface and bottom ? To decide this, I filled a bottle with water, and corked it, I then sunk it where I had placed the basket, at the depth of five feet and a half. J drew it out twenty-four hours afterwards, and found the temperature of the water which it contained exactly the same as that at the surface. The same experiment, re- peated several times in this month, gave the same result. Of the two toads, one died on the 5th of May, the water at 16° cent, or 61° Fahr., the other on the 19th, the water at 17° cent, or 62° 6' Fahr. On the 13th of June one of the seven frogs was still living. During this interval of above two months, the temperature varied from 12° cent, or 53° 6' Fahr. to 22° cent, or 70° Fahr. In the first week more than half the frogs died, between 12° cent, or 53°. 6' Fahr. to 14° cent, or 57° Fahr. ; one only resisted the tem- perature of 22° cent, or 70° Fahr. Sect. 6. — Combined Action of Water, Air, and Tem- perature. In the life of frogs under water, there are then at least three conditions having a powerful influence on their exist- ence : — 1. the presence of air in the water; 2. the quan- tity, or the change of water ; and 3. its temperature. The relation of these three causes deserves particular notice. We have examined the first with great attention, CONTAINED IN WATER. 33 and have proved that the air in the water could maintain the life of batrachians immersed in that liquid. But how does the temperature act in this case ? Since the air is the principal condition for prolonging their existence, one might suppose that the elevation of temperature acts by diminish- ing the quantity of air. But Humboldt and Provencal, in their work on the Respiration of Fishes, have proved that the Seine water contained the same quantity of air, in the various analyses which they made of it, from the month of September to that of February. Now, its temperature varies in that interval, at least from 0° cent, or 32° Fahr. to 16° or 17° cent, or 61° or 62° Fahr., which last is higher than that at which the greater number of the frogs above mentioned died. Since it is the temperature, and not the quantity of air which varies, it is to the former that we must attribute the variation in the effects. The experiments related in the last chapter perfectly accord with those which have been just mentioned. By the former it was shewn, that when frogs are immersed in five ounces and a half of aerated water, the dura- tion of their life is inversely proportional to the eleva- tion of temperature from 0° to 42° cent, or 32° to 107°. 6 Fahr., at which point they die, almost suddenly ; and that through the whole range of this scale a small number of degrees is sufficient to produce a great difference in the duration of their life. It has now been shewn, that the air contained in the water has a contrary effect to the ele- vation of temperature. When they are immersed in about two gallons, changed every day, a temperature between 0° cent, or 32° Fahr., and 10° cent, or 50° Fahr. is not sufficiently high to counterbalance the vivifying effect of the air ; but when it rises to 10° or 12° cent, or 50° to 53° 6' Fahr., the former overcomes the latter, and the animals D 34 INFLUENCE OF AIR CONTAINED IN WATER. die, unless the quantity of air is increased. Now the quan- tity of air may be increased by furnishing, in a given time, a greater quantity of aerated water ; this was the cause of some of the frogs in running water resisting the tem- perature which would be fatal to them in the vessels with water changed only once in twenty-four hours. But the influence of the change of the water is very inconsiderable beyond certain limits ; for, as is well known, water contains but a small part of its bulk of air ; and according to Hum- boldt, that of the Seine only ^. These animals, then, have but one means of resisting the effects of temperature, and that is, by coming to the surface to breathe the air of the atmosphere, without which most frogs would die, in a tem- perature as low as 12° or 14° cent. 53°6. Fahr. or 57° Fahr. The small quantity of air contained in water under 10° cent, or 50° Fahr., which is sufficient to support the life of batrachians in that liquid, produces an extraordinary effect upon their mode of existence. The extreme activity of frogs is well known, and there is a striking contrast in this respect between them and toads ; but keeping them under aerated water destroys this characteristic. It does even more ; they become so sluggish in their movements as to resemble tortoises. The slightest noise, which in their state of liberty excites a panic among them, at that time makes no impression. Light, which, on other occa- sions calls them so easily to the surface, no longer induces them to rise, when the temperature is sufficiently low. They have, however, the faculties of sense and motion ; but in air of the same temperature they are extremely lively. CHAPTER IV. ON THE VIVIFYING ACTION OF THE ATMOSPHERE. Sect. 1. — Influence of Cutaneous Respiration. In order to appreciate the influence of the atmosphere on the skin, it is necessary to suspend the action of the lungs, by intercepting- the passage of the air to those organs. As the mouth of these animals, when they breathe, is necessarily shut, in order to introduce the air into the lungs by an act of deglutition, it has been thought that this mode of respiration could be suspended by keeping the mouth open. In order to determine, whether I could avail myself of this circumstance for the object which I had in view, I placed a piece of stick in the mouth of a frog to serve as a gag : it projected a little on each side ; and was fastened at its extremities by a thread which passed under the axillae. I tried this experiment on six frogs, which were placed under a glass, in a saucer; the edges of the glass were slightly raised to allow change of air, and a little water was also introduced into the saucer to supply the animal with the necessary degree of moisture. The tem- perature was then 24° cent, or 75° Fahr. In this state, five died the following day ; the sixth lived seven days. The state of constraint occasioned by the stick which kept the mouth open, and the slight compression of the limb by the thread could certainly not explain this rapidly fatal result. Respiration was evidently checked, but it was d 2 36 ON THE VIVIFYING ACTION not entirely suspended. The movements of deglutition, al- though less frequent, still took place ; the flanks at inter- vals contracted. These indications of respiration were suffi- cient to destroy my confidence in the experiment for the accuracy of which, a perfect suspension of the communica- tion between the lungs and the atmosphere was absolutely necessary. A ligature passed behind the head can be sufficiently tightened to completely intercept the passage of the air. I in this manner applied a ligature to six frogs, and took particular care to use the most rigid compression, and tied the ligature several times, so as altogether to exclude the atmospheric air. The temperature was 12° cent, or 53°.6 Fahr. in the room, and 6° cent, or 43° Fahr. out of doors. I placed the animals on wet sand. They lived a considerable time, one of them for twenty days. These animals would have died in the space of from one to three days, if I had placed them in five ounces and a half of water, as I proved at the same season in this and the preceding years. The influence of the atmosphere on the skin must then have been considerable, in order to obviate the effects of stran- gulation for so long a time. It may be here mentioned that the more rapid termination of life in the former experiment in which respiration was only imperfectly suspended, than in the present, is fully ex- plained by the higher temperature to which they were ex- posed. The important influence of this circumstance has already been shown. The violent operation, however, inflicted in this last ex- periment must have tended to shorten life; and conse- quently to set limits to the beneficial influence of the at- mosphere upon their skin. I, therefore, determined upon other more effective means of accomplishing my purpose; this was no less than the absolute removal of the lungs OF THE ATMOSPHERE. 37 which may be done by a very slight incision, and with the loss of very little blood. I performed this extirpation in the middle of December, 1818, on three frogs of mode- rate size. They did not appear to suffer much, and pre- sented, after the operation, the same activity as those which had not been touched. I placed them upon moist sand. The temperature of the room was 7° cent, or 45° Fahr., and it rose to 12° cent, or 53°.6' Fahr. on the 17th Jan. 1819. Two died at this time, having lived thirty- three days, and the third on the 24th, having lived forty. If we now call to mind the long duration of the life of these animals under aerated water which was continually renewed, and which acts only on the skin, we shall be in- clined to query, since air dissolved in water serves so well to maintain their life without the aid of their lungs, ought not they to find still greater resources in the atmosphere itself, if we only furnish them with sufficient moisture? To answer this in the affirmative would be a mere as- sumption. The comparative influence of the atmosphere and of aerated water is so little understood, that we can- not say why fishes live better in aerated water than in air. Yet the knowledge of this would be of considerable physiological interest. I wished to determine whether the operation itself, in the preceding experiment, did not tend to shorten life. With this view, on the 4th March 1819, I cut out the lungs of six frogs, and closed the incision by a suture. They were placed in a basket with six other frogs, which had not been mutilated, and immersed in the water of the Seine, which was then at 4° cent, or 39°.G, but in the space of a week, it progressively rose to 9° cent, or 48° Fahr. The greater number of the frogs without lungs died before the others ; but at the end of the experiment, one of the frogs deprived of lungs was found alive, with the only sur- 38 ON THE VIVIFYING ACTION vivor of those which possessed them. The season being- unfavourable to the life of these animals under water, ter- minated the experiment on the 15th of March. These frogs were in every respect similarly circum- stanced, with the single exception of the operation ; I therefore, felt myself warranted to conclude, from the re- sult of this experiment, that since the greater part of the frogs which had undergone the operation died before those which had not, the operation must have also contributed to terminate the lives of those which were placed in the at- mosphere, in the preceding experiment. Hence it may not have shewn the utmost duration of life in the batrachians, maintained by the influence of the air exerted on the skin alone, but for the present we admit the limit which it has given us, and proceed to further considerations respecting the action of the air. Sect. 2. — Influence of Pulmonary Respiration. ,We have now to resolve the converse of the question con- sidered in the last section, viz. would these animals live if permitted to breathe by the lungs alone, the atmosphere being altogether excluded from contact with the skin ? A frog was placed in a glass containing five ounces and a half of water. A wooden cover at the surface of the water prevented him from coming out, and an opening which was made in it gave him liberty to breathe the atmospheric air. The liquid, which he dirtied in a few hours, was changed every day. The temperature was 12° cent, or 53° 6' Fahr. and it was as high as 24° cent, or 75° Fahr. at the latter period of the experiment. This frog lived three months and a half, with no other nourish- ment than the small quantity of water in which it was immersed. In this situation, the animal has no other OF THE ATMOSPHERE. 39 direct communication with the atmosphere than by the lungs. Through the medium of the water, he can, it is true, receive the influence of the small quantity of air con- tained in this liquid ; but we have seen in former experi- ments that where these animals were immersed in the same quantity of aerated water without being allowed to breathe at the surface, this quantity of air did not sensibly prolong their existence. Still, however, there is some room to doubt, whether this small quantity, which under other circumstances, might be safely overlooked, may not be useful in this instance and contribute to aid the action of the lungs. The application of a coating to the surface of the body? naturally suggests itself as a ready method of cutting off the influence of the air on the skin ; but the moisture and continued secretion of the skin, renders it nearly or quite impracticable. The removal of the skin does not get rid of the difficulty, because none of the batrachians long sur- vive this severe operation, which is rather surprising, when we consider how much mutilation they are capable of en- during. Oil would answer the purpose of excluding the air if it were free from objection in other respects. If it be sub- stituted for water in the glasses with floating covers, as in the preceding experiments, the frogs die in a short space of time. The experiment was tried on ten frogs, six of them lived seven or eight hours, the other four died the following day. The temperature was at 21° cent, or 70° Fahr. as in the experiments with water. It was also found that this substance has a deleterious action on the skin. Some frogs were placed in glasses containing five ounces and a half of oil, and others in the same quantity of water, and not allowed to breathe. Those in the oil made extraordinary movements, and even many attempts 40 ON THE VIVIFYING ACTION at vomiting ; however they lived equally long in both liquids. If, in these two cases, instead of suppressing re- spiration it be left free, the difference becomes considerable. Water, which contains or absorbs a little air, has a ten- dency the reverse of that of the oil, and pulmonary respira- tion with this feeble assistance in the one case, and slight obstacle in the other, is found sufficient or insufficient to support life. If then we could confine these animals, in their relation to the atmosphere, to pulmonary respira- tion alone, they would be as it were, on the limits of life and death. This consideration induced me to inquire if there were not other animals of the same family, to the support of whose life pulmonary respiration would not be suffici- ent, notwithstanding the influence of the small quantity of air contained in the water. Tree-frogs are animals of this family ; they differ from common frogs and toads in having a little cushion at the end of their toes, which en- ables them to climb perpendicularly on trees, and even on smooth and flat walls. The species submitted to the ex- periment is that which is the most common in France. I made use of the same apparatus as in the preceding ex- periment, with the addition of a small but loose net, fixed over the opening in the floating cover. The frog put- ting its head under the net, breathed in the atmosphere without being able to escape from the water which sur- rounded him. Eight of these animals in succession were submitted to this experiment in the space of five days; the temperature varied from 17° cent, or 62° Fahr. to 20° cent, or 68° Fahr. ; there was in each glass only about five ounces and a half of water, which was changed several times a day. They did not live, however, beyond three or four days. Hence it is evident that pulmonary respiration is not OF THE ATMOSPHERE. 41 sufficient to support the life of tree-frogs without being accompanied by the atmospheric influence upon the skin. The case is the same with the rana obstetricans, on which the experiment was also tried, and we may conclude that the observation applies to all the batrachians. I put seventeen frogs into a vessel containing seven pints of Seine water permitting them to breathe at the surface j the temperature was the same as in the preceding experi- ments. Four days after, seven of them died. I repeated this experiment on twenty frogs placed in the same cir- cumstances, adopting the precaution of changing the water every day ; nine died in the space of three days ; while others, which were placed in glasses with five ounces and a half of water, all lived. The difference depended on the depth of the water. In the glasses, being supported by the bottom, they breathe ad libitum, but in vessels contain- ing seven pints, and having a foot in depth, although they may support themselves for some little time at the surface, yet, after having expelled a certain quantity of air from the lungs, their specific gravity being increased, sends them to the bottom, and they rise and sink alternately, till these intermissions of respiration, uncompensated by the action of well aerated water on the skin, puts an end to their existence. We may therefore conclude, that frogs would die in deep waters, if they could not occasionally come to the bank, or find support from time to time on other bodies. CHAPTER V. THE INFLUENCE OF THE ATMOSPHERE ON PERSPIRATION. The first very perceptible change which animals ex- perience when placed in the atmosphere, consists in a diminution of weight, from a vapour which is exhaled from, or a liquid which transudes through their skin, or escapes from the pulmonary surface, and is known under the name of sensible and insensible perspiration. It is this loss of weight that we are now to appreciate, as well as its variations, according to certain circumstances. Sect. 1. — Loss by Perspiration in equal and successive Periods. We shall first inquire, What is the relative quantity of perspiration in equal and successive periods ? Is it vari- able or uniform? Or, if variable, does it increase or di- minish according to any fixed law ? It was very necessary to make this preliminary enquiry, in order to ascertain the rate of the loss by perspiration, influenced only by changes depending on the animal itself, and consequently avoid confounding these variations with those which depend on external agents. With a view to determine the relation of the losses of weight sustained in equal times, I weighed a frog from INFLUENCE OF THE ATMOSPHERE, &C. 43 hour to hour in air, which appeared calm, the temperature was carefully noted, and remained sensibly the same during the course of the experiment. In comparing the successive losses of weight, a remarkable fluctuation was observed. The variations were very considerable, in some cases amounting to double or triple quantities in equal times : they were usually alternate, without, however, pre- senting equality in their increments and decrements. Repeated experiments proved that this phenomenon was not confined to an individual case, but appeared even in the different genera of the family which were examined. This irregularity not depending on any error in the mode of experimenting, supposes the action of various influential causes, which do not remain constant in the course of the experiment. This induced me to give a longer period to the duration of the experiments, and in weighing the animals at intervals of two hours, I found a marked ten- dency to diminution in the quantities lost in equal times. On comparing them afterwards at intervals of three hours, the tendency becomes indubitable ; three hours in most cases proved sufficient to render the diminution constant; but in a few instances, intervals of nine hours were neces- sary to arrive at such a result. This difference, doubtless, depends on a change in the state of the animal. Now the most remarkable change in its state is the progressive diminution of the mass of its fluids ; and in proportion as this is reduced by previous perspiration, ought the subsequent losses from this cause to be less considerable. In observing the degree of rapi- dity with which the loss by perspiration takes place, it deserves particular notice, that in the intervals of time employed in the experiments just related, the loss in the first period was often great in proportion to that in the subsequent periods, and that in these succeeding intervals 44 INFLUENCE OF THE ATMOSPHERE its rapidity progressively lessened. Taking the animal at the point of saturation at the commencement of the experi- ment, it may be said that it loses by perspiration less and less in proportion as it removes from this point. Hence it is obvious, that for a number of experiments to agree in these results, attention must be paid to the condition of the animals in respect of saturation. If we compare the weight of the animals, and the perspiration, without refer- ence to their state as to saturation, we shall obtain not only very different, but even contradictory results. We shall have to return to this subject in the sequel. Sect. 2. — Effect of Rest and of Motion in the Air. The fluctuations in the amount of loss by perspiration as observed from hour to hour, did not arise from any cir- cumstance dependent on the life of the animal, nor even on its peculiar organization, since they are found to take place in pieces of charcoal soaked in water, and exposed to the influence of spontaneous evaporation, under the same cir- cumstances, with respect to the atmosphere, as the frogs. We must, therefore, have recourse to external agents, to account for the variation. It is well known that the at- mosphere, even when it appears to us perfectly calm, is really sufficiently agitated to exercise a perceptible in- fluence on evaporation. We are, then, naturally led to ex- amine into the extent of that influence on the perspiration of animals. For this purpose I hung some frogs in the draft of an open window, and placed an equal number in the same room at another window which was shut. The animals exposed to the open window lost at least the double, and, according to the intensity of the wind, the triple, and quadruple of what was lost by those which were placed in the interior of the room. It was also found, that on sus- ON PERSPIRATION. 45 pending these animals in vessels, with a wide mouth, to allow the perspiration to dissipate itself freely in the at- mosphere, the hourly fluctuations either ceased altogether, or were very inconsiderable. Sect. 3. — Respiration in Air of extreme Humidity. We now come to examine the results arising from the hygrometric state of the atmosphere ; and in the first place to consider the question, whether perspiration can take place in air saturated with moisture ? To arrive at the solution of this question, it was of course necessary to remove, as much as possible, the influ- ence of the motion of the air, and all other disturbing causes. With this view the animal was suspended in a glass vessel, inverted over water ; which vessel had been ascertained, by experiment, to be sufficiently large to obvi- ate any effect from the alteration of the air by respiration on the duration of its life. The experiments were often repeated, the intervals of weighing were varied considerably, and a diminution of weight was uniformly observed. It is true, that the che- mical changes in the air, occasioned by respiration, would occasion a diminution of weight, in case of this loss not being repaired ; but particular experiments on the extent of the respiration of these animals, proved that the slight de- duction which this cause requires, leaves a greater loss, which can only be attributed to perspiration. It is true, that these animals have a temperature of their own, though it differs in general, but very little indeed, from that of the bodies which surround them ; and this may have a slight influence on perspiration in damp air. But it is the fact rather than its cause which I am here seeking, and we may conclude, that air saturated with moisture does 46 INFLUENCE OF THE ATMOSPHERE not prevent perspiration, though it reduces it to its mini- mum, relatively to all the other causes which we have hitherto examined. Sect. 4. — Perspiratiofi in dry Air. The effects of air as dry as could be procured were after- wards compared with those of air saturated with moisture. Several causes prevented the air of the vessel from attain- ing the point of extreme dryness ; in the first place, the necessity of commencing the experiment on perspiration at the same time with the drying of the air in a close vessel, in order to obviate the passing of the animal through the mercury into a .vessel containing air previously dried ; which circumstance might occasion such an increase of weight as to destroy the effect of the experiments ; add to this, the perspiration of the animal, which, in air perfectly dry, changes the hygrometric state of this fluid. An hygrometer placed in the vessel with the animal, and a good quantity of quick lime, marked the degree of dry- ness of the air. On the whole, the effects of calm air pro- gressively dried during the course of the experiment, was very remarkable. In the same space of time, all other cir- cumstances being the same, the perspiration in dry air was from five to ten times greater than in extreme humidity, according to the degree of dryness and the duration of the experiment. If we compare the influence of the hygrome- tric state of the air with that resulting from its motion, we shall find, that the agitation of the air, provided it is not at the point of extreme moisture, may increase the perspir- ation, as considerably as a drier air in a state of rest. ON PERSPIRATION. 47 Sect. 5. — Effects of Temperature. In order to appreciate the effects of mere temperature, it was of course necessary to reduce to a minimum the influ- ence of the two preceding causes. Hence, the experiments made with a view to this object, were performed in a still atmosphere saturated with moisture. I compared the influence of temperature between 0° and 40° cent, or 32° and 104° Fahr., which are the limits com- patible with life, and nearly those of the atmosphere itself. The general tendency of a rise of temperature was to equalise the losses in equal times, or in other words to di- minish the decrements in the quantities lost. As to the relative influence of different degrees of tem- perature upon the quantity of perspiration itself, it is much less than would have been anticipated. During five hours the quantity perspired at 20° cent, or 68° Fahr., was scarcely twice what it was at 0° cent, or 32° Fahr. ; that at 40° cent, or 1 04° Fahr. is seven times greater than that at 0° cent, or 32° Fahr. ; which resembles the effects obtained from a dry and still, compared with a humid atmosphere. CHAPTER VI. ABSORPTION AND PERSPIRATION. The present question is, how is the weight of the body influenced by the contact of water with its external sur- face ? To render this as sensible as possible in the case of frogs, they were first placed in air, until they had under- gone evident loss by perspiration, with the expectation, that if they absorbed water this absorption would be more strongly marked, according as they were removed from the point Of saturation, which was found to be the fact. These animals, having previously lost a considerable portion of their weight by perspiration, and being afterwards put in water of the same temperature as the air, increased in weight, while the absorption of the fluid was rendered evi- dent, by the sensible diminution of its quantity in the vessel in which the animals were placed. But to what extent does this absorption take place ? what is its rate of progress and what its limit ? what ensues when this limit is reached, if the animal be still kept in contact with the water, a condition to which all these animals may be exposed, and of which it is important to know the influence ? It results from the experiments which I made, that if perspiration in the atmosphere be not car- ried too far, water will be absorbed, until the loss incurred thereby shall be repaired. It does not, however, always cease at that point ; it may, indeed, go far beyond it, be- ABSORPTION AND PRESPIRATION. 49 fore it arrives at the point of saturation. The quantities absorbed in equal times, like those lost by perspiration in the atmosphere, diminish progressively, provided the tem- perature is not very high. This diminution is likewise more rapid, according as the animals approach the point of saturation. It appears, also, that the time required to repair by absorption the loss occasioned by perspiration, is shorter than the time during which the same loss is incurred. A question still remains. When the body has arrived at the point of saturation, does its weight remain stationary, or undergo any further variation ? In seeking for the so- lution of this question, I found that after the body has arrived at its point of saturation, there are alternate stages of diminution and of increase, but the increments do not pass beyond the point of saturation, at which the diminu- tion commences. This circumstance is explained by the fact, that in addition to the aqueous fluid exhaled from the skin, a portion of solid matter is also excreted. The loss occasioned by these excretions are at first compensated by the absorption of the water ; but after some time a real and progressive diminution is observed to take place. It is evident, from what has already been stated, that when one of these animals is placed in water, the weight of his body will increase or diminish according as either of the opposing functions of absorption and transudation predominates over the other. It is interesting to determine what is the influence of temperature upon the relations of these functions. It appeared from experiments, that at 0°. cent, or 32° Fahrenheit, the absorption predominates over the loss of weight ; while at 30° cent, or 86° Fahr. the losses are greater than the increase by absorption. It was also observed that elevation of temperature in water had a marked tendency to augment the animal excretions ; E 50 ABSORPTION AND PERSPIRATION. from which we seem authorized to conclude that an ana- logous effect would be produced upon perspiration in the air. On the other hand, the motion of the air, exercising little, if any chemical agency, would have less influence than temperature upon the excretion of animal materials, and consequently contribute more to the production of the aqueous portion of perspirable matter. The effects of dryness and moisture would also seem to have less influence than temperature on the loss of the animal matters. PART II. FISHES AND REPTILES. CHAPTER I. TADPOLES. In treating of the family of the Batrachians, the first stage of their lives, during which they have a peculiar form and distinct functions, has been slightly passed over. And since their mode of life at this period, in many re- spects, resembles that of fishes, I have reserved the exa- mination of it until I should come to treat of this class of cold-blooded animals. The most important peculiarity of tadpoles is not that which depends on their external con- formation, the absence of limbs, and the presence of a tail ; but that which results from their possessing two kinds of respiratory organs, lungs and gills. Tadpoles unite, in regard to respiration, the functions of reptiles with those of fishes; their use of them varies not only according to their deve- lopment, but also according to their physical conditions, under the influence of which we are now about to consider them. The tadpole has, in common with the adult animal, the power of supporting life through the medium of the skin, by means of the air contained in water. It has e 2 52 TADPOLES. already been shewn that the limits of temperature in which the adult animals are able to exist, are 32° and 50° F. or 0°. and 10° cent., and that beyond the higher limit, the greater part were obliged to have recourse to atmospheric respiration ; but tadpoles having an additional organ, by which they are enabled to avail themselves, in a higher degree, of the vivifying influence of the air contained in water, ought, one would imagine, to support, under water, a much greater elevation of temperature, without having recourse to the external air. That this is actually the case, is shewnby experiments, in which they were kept a long time in vessels with the water occasionally changed, and in running water, at the temperature of 25° cent, or 77° Fahr. The most important point in our enquiries respecting tad- poles, is the influence which physical agents may exert on their transformation. The action of these agents on the form of animals, is one of the most curious questions in physiology. One of the conditions which is best known, is the necessity of aliment for the development of forms. This is the reason that when we wish to hasten the metamorphosis of tadpoles, we take care to mix with the water in which they are kept a small quantity of nutritious substances, and to change the liquid, that the decomposition of these materials may not prove fatal to them. On the other hand, their transform- ation is retarded, when the supply of nourishment is scanty. Temperature is another condition, the influence of which is generally known. We are aware that tadpoles change in warm seasons : but it is a fact not so generally known, that in our climate a great many are not changed the same year. This happens to those which are produced late in the summer. The subsequent temperature not being sufficiently high, they pass the winter in the state of larva, and do not quit it until the return of warm weather. These TADPOLES. 53 are the only influences which have been hitherto ascer- tained with regard to the developement of these animals. There is another which I have endeavoured to determine, and to which I have been led by my experiments on the adults : it is, the effect which atmospheric, compared with aquatic respiration, exercises on the form of these animals in their earliest age. The difference which these two modes of respiration occasioned in the activity of the adult animal, induced me to conceive, that limiting the tadpole to aquatic respiration would tend to continue its original form. With this view I procured a tin box, divided into twelve compartments, each of which was numbered and pierced with holes, so that the water might readily pass through the box. A tadpole, (which had been previously weighed) was put into each compartment, and the box was then placed in the river Seine, some feet below the surface. A larger numbei was at the same time put into an earthen vessel, taining about four gallons of Seine water, which was hanged every day. These tadpoles were at liberty to rise to the surface and respire air, and they soon went through their metamorphosis. Of the twelve placed in the box under water ten preserved their form, without any progress in their transformation, although some had doubled, and others trebled their weight. It should be observed, that at the time when the experiment was begun, the tadpoles had acquired the size at which the change is about to take place. Two only were transformed, and this very much later than those which, in the earthen vessel, had the liberty of respiration in air. The want of atmospheric respiration appeared here to have a marked influence, but we had not the means of accurately informing ourselves of one very influential cir- cumstance, that is, the supply of nourishment. In the river the water is renewed incessantly ; and frequently ve- 54 TADPOLES. getable and animal substances must necessarily be more abundant in it, than in the water of a vessel which is changed only every twenty-four hours. Notwithstanding this difference in favour of the tadpoles deprived of atmo- spheric respiration, it had influence upon two only ; the other ten underwent no change. It would appear to result from these facts, that the young animals, with double respiration, would retain their original form under water, if their nutriment were not too abundant, and the temperature were not too high ; and that the difference of atmospheric respiration alone, joined to these circumstances, would determine the trans- formation. This conclusion, at first, appeared to me to be strictly correct ; but there was an element which I had not taken into account ; namely, the absence of light : for the tad- poles, which were in the tin box, were deprived of light as well as of atmospheric air. For the present, we will rest satisfied with the conclusion that, under these two priva- tions, tadpoles are retarded in their transformation ; but we shall return to the subject in another part of this work, in which the influence of light is considered. There are three remarkable animals, which have a strong affinity to tadpoles, and have been considered as belonging to the family of batrachians, these are the axolotl, the siren, and the proteus. We are indebted to Cuvier for some valuable investigations respecting the structure of these animals. According to him, the axolotl has the anatomical characters of the larva of the salamander ; and the siren and proteus are species of different genera from each other. In the proteus, the lungs, he says, are little more than ru- dimentary. These animals are all furnished with a double respiratory apparatus, lungs and gills ; but the pulmonary organ of the proteus is, as we have said, in an imperfect TADPOLES. 55 state. It is possible, that the result of the preceding re- searches might be applicable to these animals. It would be desirable to ascertain the effect of the united influence of increased nourishment, elevation of temperature, aerial respiration, and the presence of light, on the axolotl, and the siren ; and to examine whether the exercise of the lungs, by a frequent use of atmospheric respiration at the surface of the water, would not tend to suppress the bran- chiae, as happens to the young batrachians, when tempera- ture and nutrition are favorable. It may be remarked, that the proteus has been always found placed in those conditions as to temperature, darkness, and respiration, in which the branchiae remain. In fact, it inhabits the sub- terranean waters of the lakes of Carniola, in which it can- not perform atmospheric respiration, and where the tem- perature is, perhaps, sufficiently low to preserve the bran- chiae. The last point of view under which it remains to examine tadpoles, relates to their existence in air : but this subject being intimately connected with the life of fishes in the air, will be examined when I treat of that class of animals. 56 CHAPTER II. FISHES. The labours of Spallanzani, of Sylvestre, and of Humboldt and Provencal, have made us more accurately acquainted with the physiology of fishes than with that of any other cold-blooded animals. I shall not attempt to detail the result of their researches, most of which are foreign to my present subject. I have only to consider fishes in relation to those points which bear on the phenomena already pre- sented to us by the batrachian reptiles. I shall first examine the influence of temperature. Sect. 1. — Influence of Temperature on the Life of Fishes, in Water deprived of Air. To arrive at a correct result, we must firrst reduce the cir- cumstances of the experiment to their greatest simplicity. For this reason I shall commence by enquiring into the effect of temperature on fishes in water deprived of air. Comparative experiments were made on individuals of the same species, and with as close a resemblance as possible, at temperatures varying from 0° cent, or 32° F. to 40° cent, or 104° Fahr. The result was, that at the higher limit death was speedy as with the batrachians, and the duration of FISHES. 57 life progressively augmented in proportion as the tempera- ture was diminished to the lower limit. It is here seen that the effect of temperature (excluding all other influ- ences) is altogether analogous to what has been observed in the batrachians ; that the limits of the shortest and longest duration of life in the batrachians and fishes placed in water deprived of air, are alike in both ; and that in the same range of temperature, from 0° cent, or 32° F. to 40° cent, or 104° Fahr., the duration of their life goes on augment- ing or diminishing, according as the temperature falls or rises between these extremes. In regard to the differences which fishes of the same species present at the same degrees of temperature between these limits, size has a marked influence, the smallest as well as the youngest are those which are the least capable of bearing an elevation of temperature. However different may be the duration of the life of small fishes at low tem- peratures, at 40° cent, or 104 Fahr. it is almost uniform in all. They scarcely ever live more than two minutes ; but the larger fishes are able to survive several minutes longer. Sect. 2. — Influence of the Temperature of Aerated Water, in limited Quantities, in close Vessels. On varying, in a series of experiments, the temperature and quantities of aerated water, it appears, 1st, That the duration of life goes on increasing with an increase of the quantity of aerated water, the tempera- ture remaining the same. 2. That the same result takes place when, the quantity of water remaining the same, we lower the temperature. 3. That the duration of life remains the same, when, within certain limits, we increase or diminish, at the same time, both the temperature, and the quantity of aerated water. 58 FISHES. Sect. 3. — Influence of Temperature, and limited Quantities of Aerated Water, in contact with the Atmosphere. Sylvestre has ascertained that a limited quantity of aerated water, in which a fish is placed, absorbs the air in contact with its surface. It evidently follows from this fact, that the life of the animal, in a limited quantity of water, will, ceteris paribus, be the longer, the more fully the absorption of air by the water compensates for that which the animal consumes in the water. Add to this, that the fish, when free, is able to derive directly from the atmo- sphere fresh supplies of air, according to its wants. Let us now see the influence of temperature under these circumstances. Take for example a bleak (cyprinus albur- nus). If we put it into a vessel with a large mouth, con- taining five ounces and a half of aerated water at 20° cent, or 68° F. in summer, it dies within a few hours : but when the temperature is lowered to 10° or 12° cent., or 50° or 53° F., and is kept at that degree, the animal lives until its secretions are so abundant as to corrupt the water. If, to remedy this inconvenience, we merely renew the water every twenty-four hours, the animal lives in it almost inde- finitely. This is exactly what we have seen to take place with the batrachians. Between 0° cent, or 32 Fahr. and 10° or 12° cent, or 50" or 53° Fahr. they live an indefinite time in aerated water, provided it be renewed sufficiently often ; but they die for the most part as soon as the temperature rises above this limit. Let us now examine the general result of these facts, not- withstanding the different conditions in which the animals are placed. The more the temperature is raised beyond certain limits, the greater is the degree of the influence of the air required for the support of life. This influence, FISHES. 59 without reference to other causes, will be great in propor= tion to the quantity of this fluid. Here, however, there are limits depending on the organization of the animal. Sect. 4. — Respiration in the Air. As yet we have only considered the respiration of fishes in water : their respiration in air deserves particular atten- tion. When a fish, in a given quantity of aerated water, has reduced the proportion of air until its respiration has become difficult, it rises to the surface and takes in air from the atmosphere. In order to show that atmospheric re- spiration has an influence on the life of fishes, Sylvestre placed a diaphragm at the surface of the water, to prevent the fishes from taking air directly from the atmosphere. He observed that in this case fishes die sooner than when they had access to the atmosphere, which proves that they can breathe air, and that this mode of respiration tends to prolong their life in water. Sect. 5. — Life of Fishes in the Air. We now proceed to the examination of a new circum- stance in respect to the life of these animals ; viz. their existence in the atmosphere. This, as regards the influence of physical agents, is the most obscure point in the life of fishes. It is also a condition in which they present phe- nomena which do not appear in any way to accord with those presented by animals breathing air. When we take a fish out of the water, -we see it, according to its species, die in a few minutes, or in a few hours. It is not then surprising that fishes should have been considered inca- pable of living by atmospheric respiration, and that this should have been attributed to the greater density of the air existing as atmosphere, compared with that contained in solution in water. Air does, undoubtedly, act differently 60 FISHES. according to its density, on living beings. It is also true that the greater part of vertebrated animals quickly perish from the opposite transition, by passing from the atmosphere into aerated water ; but in this case it is evident, that they die because they have not sufficient air; and we might suppose that fishes die in the atmosphere because they have too much. Having already stated the proofs by which Sylvestre has shewn the influence which the respi- ration of air exerts in prolonging the life of fishes in water, I may proceed with these animals as with others in the examination of the changes which they undergo by ex- posure to the atmosphere. A chub, (cyprinus jeses) and a gudgeon, (cyprinus gobio) were first wiped, then weighed, and exposed to the air. Their gills continued to beat until death. The sur- face of their bodies gradually dried, and at the time of their death they were stiff, and dry. On weighing them again, I found that they had lost by perspiration, the one, one-fifteenth, and the other, one-fourteenth of its weight. This result is nearly the mean of experiments made on other species. Having in our researches on the batrachians seen the in- fluence of loss by perspiration from exposure to air, we shall now apply it to the case of fishes. To simplify the examination of this subject, let us here consider, as we have done in our researches on the batrachians, the losses by perspiration, as solely at the expence of the water con- tained in the animal. Capacity of saturation with water implies the quantity of this liquid which an animal is able to contain, between the point of greatest repletion, or satu- ration, and that of the greatest inanition, compared with the weight of its body. The means of carrying the body to the point of saturation when it is capable of absorbing- water, is to place it in that fluid, until the increase in FISHES. 61 weight has arrived at its maximum. This is exactly the condition in which fishes are found in their natural state, and on removing them from the water in which they live, we may regard them as saturated with this liquid, pro- vided they are in a state to absorb it. Now we shall take for the measure of their capacity of saturation with water, as we have hitherto done in regard to the batrachians, the loss which they experience by perspiration before death ; and we see it is sufficient to ensure the death of fishes, that they lose the fourteenth or fifteenth part of their weight. If this loss appear too inconsiderable for us to ascribe the death of these animals to it, let us compare this result with those which we obtained in our researches on the batrachians. They were not given in the preceding chapter, that they might be reserved for this occasion. It has been shewn that the point of saturation with water, in the case of batrachians, depends on the state of their nu- trition, and that it may vary within very considerable limits. Now the losses which they undergo by perspiration vary in the same manner. In conditions favourable to nu- trition, their capacity of saturation may equal the third of their weight ; but, in unfavourable conditions, it is so small, that the least appreciable loss is sufficient to cause death. On applying these results to fishes, whose capacity for water is small compared to that of batrachians, we shall see that the loss which they experience by evaporation is enough to cause their death in air. But the phenomena relative to this subject are not always so simple; they may be very complicated : one might be led to believe that at- mospheric respiration would keep fishes alive if we could devise means for obviating their loss of weight by evapo- ration. With this view, a fish which had been wiped and then weighed, was suspended in a limited quantity of aerated water, so that it had its head and gills above the 62 FISHES. surface ; it died in nine hours and twenty-one minutes. On then weighing it again, it appears that it had not sen- sibly diminished in weight, but on the contrary had slightly increased. This result would appear to be inde- pendent of the cause we have before assigned for the death of fishes, where the whole body is exposed to the action of the atmosphere. But before enquiring into the influence of a new cause which may be added to the first, let us more attentively examine the complicated case in which fishes are found in the circumstances of the experiment last related. The body is plunged in water, but the head and gills are exposed. On one hand absorption takes place in the water, on the other, perspiration in the air. The ab- sorption by the body plunged in water is proved by the slight increase of weight which takes place during the ex- periment, and the loss by perspiration from the part ex- posed to the air is demonstrated by the preceding experi- ments. Now it is evident, that the organ of respiration, which is exposed to the atmosphere, cannot continue its functions unless the losses by perspiration are repaired. It is true the rest of the body absorbs, and that, on the whole, it does not lose any of its weight ; but this condition is not sufficient for the continuance of respiration. It is also ne- cessary that the distribution of the fluid absorbed by the trunk, should be such, that the gills and muscles which move them should receive a proportion of it capable of re- pairing the loss which those organs experience by perspi- ration. Presuming it possible that this equilibrium might not take place, I made the following experiment to enquire into the relations of partial and simultaneous perspiration and absorption. I placed some fishes in the opposite position to that of the fish employed in the last experiment, that is, with the head and gills in water of the same quality and quantity, and the trunk, suspended in the air FISHES. 63 by a thread passed through the end of the taiL They lived in this state many days. I weighed them after that inter- val, and discovered that there was evidently, in this case, a slight increase of weight. But the drying of the surface of the part of the trunk exposed to the air was as marked as in the case where these animals were entirely exposed to the atmosphere, and where they died after a considerable diminution in weight. It is therefore evident that the fluid absorbed by the gills was not distributed to the rest of the body in a proportion sufficient to repair, in all parts of the trunk, the loss which it had sustained by perspiration in air. The following fact, relative to the physical conditions of fishes in air,is important in the consideration of the principal causes of their death when so placed. Some fishes, when exposed to the air, soon cease to move their gills, although they continue to live pretty long afterwards ; but they die much sooner than those of the same species whose gills beat to the last. Suspecting that this difference in the duration of life proceeded from the interception of the air, I remedied it by raising the gills by a small peg placed be- neath them. The branchiae were thus exposed to the air. This change of condition, in relation to the atmosphere, proved sufficient to protract life as long as in those cases in which the respiratory movements were continued spon- taneously. The effect of thus raising the gills is so con- siderable, that if the gills of a fish, out of water, have quickly ceased to beat, we may, by its means, restore, for a while, their spontaneous action, and even do so for several times in succession. We see, therefore, that the life of fishes in the atmosphere, depends on several conditions ; of which the principal are, temperature, the capacity of sa- turation with water, the corresponding loss by perspiration from the trunk and gills, the quickness of this loss, the ac- tion of the muscles which move the gills, and the use 64 FISHES. which they make of their muscles to avail themselves of the action of the air upon the gills. In short, they come under the general law, relative to the influence of the atmo- sphere on the life of vertebrated animals. As fishes seem to form an exception to this law, I have thought it neces- sary to shew that they are so only in appearance. What has been here stated relative to the life of fishes in the at- mosphere, is equally applicable to tadpoles, placed in the same circumstances. They die from the quantity of water which they lose by perspiration, and although their capa- city of saturation is, at least, equal to that of frogs, since it varies between one-third and one-fourth of their weight, yet, as their size is very small, and their perspiration rapid, on account of the delicacy of their skin, they soon lose that proportion of water, and in the experiments which I made, I found that thev did not live more than four hours. 65 CHAPTER III. LIZARDS, SERPENTS, AND TORTOISES. The cold-blooded animals which remain to be examined are the families of lizards, serpents, and tortoises ; in other words, the saurian, the ophidian, and the chelonian reptiles. The species employed in my experiments were the grey lizard, the ring-adder, and the rat-tailed and the mud tortoises, which served as types of their differ- ent families. The external covering of all these cold- blooded animals like that of the batrachians, receives a vivifying influence from the contact of the atmosphere, and thus concurs with the pulmonary respiration to support their existence, as connected with the influence of the air. The isolated influence of pulmonary respiration in lizards, serpents, and tortoises, presents the same differences as in the batrachians, i. e. in summer it is sufficient with some, and insufficient with others for the continuance of life. The families to which pulmonary respiration is in general sufficient are serpents, and tortoises. In lizards, on the con- trary, it does not, in summer, suffice to maintain life, The same experiments were made on these animals, as on the tree-frog, and the rana obstetricans, and with the same re- sult : but it was much more remarkable, in as much as their skin being scaly, would certainly not induce us to presume that the action of the air on that organ was so necessary for the preservation of their life. If we enquire into the general cause of these differences in the batrachians and 66 LIZARDS, ADDERS AND TORTOISES. other reptiles, we find it in the varied proportions of the lungs. I have proved that among the species submitted to this kind of experiment, those in whom pulmonary respira- tion is sufficient are the frog, and the brown toad, and that of Rcesel ; these are precisely the species in which the lungs are proportionally the largest. Now, as it has been shown by multiplied experiments that pulmonary respiration alone was scarcely sufficient in summer to maintain the life of these animals, and that it required only slight obstruc- tions to occasion their death, it follows that inferiority in the extent of the lungs, in other species, would produce the same effect when they are limited to pulmonary respiration. We see the same circumstance giving rise to the same re- sult in other reptiles. Tortoises and serpents are similarly circumstanced with the frog and common toad : pulmonary respiration alone appears sufficient for them, but lizards die in summer in a few hours if we confine them to pulmonary respiration, and suppress the vivifying action of the atmo- sphere on the skin. There is a marked difference in the proportionate extent of their lungs, and those of serpents and tortoises. We see then that, as respects the action of the atmosphere, the general results are the same with all cold-blooded animals. The modifications of the vivifying action of the atmosphere on the external surface of the body, all reduce themselves, on taking the phenomena in a general point of view, to the physical conditions of the ex- ternal covering. The same may be said of the physical agents which we have examined with reference to perspira- tion. We shall therefore consider the influence of the ex- ternal covering as respects its porosity and thickness, in relation both to the vivifying influence of the atmosphere, and to perspiration. We have seen that the batrachians can live in solid coverings surrounding them on all sides, provided these coverings are so porous as to admit a suffi- LIZARDS, ADDERS, AND TORTOISES. 67 cient quantity of air. I showed that these animals lived a long time in plaster exposed to the air, notwithstanding the thickness of the covering; but in pursuing these re- searches, I afterwards discovered that the quantity of air which they receive through plaster, is only under certain circumstances, sufficient for the maintenance of life. It is evident that through these coverings the proportion of air which they receive in a given time, is less than when the skin is exposed. For this reason they cannot live under running aerated water, when enclosed in solid bodies, although they do so very well without such a covering. In the same way, lizards, serpents, and tortoises, in the ex- periments which I have made on this subject, were unable, on account of the thickness of their natural coverings, to live under running aerated water. The same cause has an equal influence on perspiration. We have seen, in the first chapter, that when the animals are surrounded by a solid covering, they perspire much less than when the bare skin is exposed to the air. In like manner lizards, serpents, and tortoises, on account of the scales with which they are covered, perspire much less than the batrachians. From these differences dependent on the coverings of the body, arises the variety which we observe in the duration of the life of these animals when deprived of nourishment. This diversity depends on the rapidity or slowness of per- spiration, as is proved by the numerous and varied experi- ments which I have made on the duration of the life of batrachians, under different circumstances with respect to perspiration, among which the effect of solid coverings was the most remarkable. The influence of temperature on the duration of life in lizards, serpents, and tortoises, is analo- gous to that which I have already shown to be the case with batrachians and fishes. f2 PART III WARM-BLOODED ANIMALS. CHAPTER I. ON THE HEAT OF YOUNG ANIMALS. It is a general opinion, inferred from the circulation be- ing more rapid and the nutritive function more active in young animals, that their temperature is likewise more elevated than that of adults. But this opinion not being founded upon direct observation, I turned my attention to it at the commencement of my researches on animal heat. By means of a thermometer placed under the axilla, and the bulb applied so as to be on all sides in contact with the animal, I ascertained the temperature of some new- born puppies whilst in the act of sucking, and found it to be nearly equal to that of the mother, about a degree or two lower; but as this difference is not constant, and is ob- servable among adults also, it may be altogether disre- garded. We are therefore warranted in concluding that the temperature of the new-born animal, when placed near its mother, is not superior to that of adults. But if, at the temperature between 10° and 20° cent, or 50° and 68° Fahr., a new-born puppy be removed and kept ON THE HEAT OF YOUNG ANIMALS. 69 an hour or two from its mother, its temperature falls con- siderably, and continues falling until, in the course of three or four hours, it stops a very few degrees above that of the surrounding air. This effect cannot be occasioned by the want of food for so short a time ; and even though it were, the difference in this respect between young and adult animals would be no less remarkable. But the temperature begins to fall as soon as the separation takes place, and the diminution is not in the least retarded by furnishing the young animal with milk from time to time. The same phenomenon takes place with kittens and rabbits. It might be supposed that this difference is accountable from the difference in the natural coverings ; as rabbits, for example, are born almost naked, and certainly cool more rapidly than puppies and kittens, but, on the other hand : these, although well covered with hair, will cool down to the same degree, though more slowly, so that this circum- stance can have but a secondary effect. Besides, the sub- stitution of an artificial covering is found only to retard, not to prevent the lowering of the temperature to the same degree. We must therefore admit that, in the young animal, less heat is produced in a given time than in the adult. If we examine the change which the temperature under- goes in the process of life, we shall find at first but little alteration ; after a while the diminution will take place more slowly; then the limit to its descent will be gradually higher and higher in the scale, till, at the end of about a fortnight, it will maintain itself at a degree nearly equal to that of the adult animal. This remarkable change which takes place in the young of the mammalia, with respect to their temperature, makes them pass from the state of cold-blooded to that of warm- blooded animals- 70 ON THE HEAT OF YOUNG ANIMALS. The phenomena above mentioned are not, however, com- mon to the young of all the mammalia. The heat of young guinea-pigs, born when the temperature of the air is between 10° and 20° cent, or 50° and 68° Fahr. in the above expe- riments, will be found to be nearly as great as that of adults, and if they be separated under the same circumstances, it is not diminished. The same is true of many other ani- mals of this class. The young of mammalia appear to be distinguished into two groups in relation to animal heat. Some are born, as it were, cold-blooded ; others warm- blooded. Corresponding with this difference, is a distinc- tion deducible from the state of the eyes. Some are born with the eyes closed, others with the eyes open. The tem- perature of the former, according to the foregoing experi- ments, rises successively, and at the end of a fortnight, (which is the period when the eyes open), it is nearly equal to that of adults. Thus the state of the eyes, through hav- ing no immediate connection with the production of heat, may yet coincide with an internal structure influencing that function, and certainly furnishes signs which serve to indi- cate a remarkable change in this respect, since at the period of the opening of their eyes, all young mammalia have nearly the same temperature as adults. Birds are known to have in general a temperature two or three degrees above the mammalia. Wishing to know if this was the case in the early period of life, I procured some young sparrows about a week old. They were well fed and collected in their nest. I took them out one by one and ex- amined their temperature. It was between 35° and 36° cent, or 98° and 100 Fahr. which is sensibly less than that of adults. As their nest sheltered them, and they contributed by mutual contact to keep each other warm, I separated them, and although the air was mild (17° cent, or 62° 6' Fahr.) they cooled rapidly. In an hour they fell from 36° to 19° cent, or from 100° to 66° Fahr. ON THE HEAT Ol YOUNG ANIMALS. 71 Another series of experiments was made when the air was 22° cent. 71° 6' Fahr. Even at this high temperature sparrows of the same age cooled rapidly to within one de- gree of the atmospheric temperature. It is true that these birds are hatched without feathers, but feathers are merely a covering ; although they may retain, they cannot produce heat. It is from within alone that animal heat can origi- nate, however outward coverings may contribute to retard its dissipation. Now, if it is true that birds produce heat more than any other warm-blooded animals, the nakedness of their bodies ought not to prevent them from maintaining their temperature, especially when the external air is warm, since man, and other mammalia with bare skins, have this faculty. In a question so important as this, we should not be satisfied with such reasoning, however probable, but en- deavour to ascertain the truth by more direct experiments. I stripped an adult sparrow of its feathers, cutting them so as completely to expose its skin ; at the same time I exposed to the air, then at the temperature of 18° cent, or 64° Fahr. young birds of the same species, taken from their nest, where they had a suitable degree of warmth, which the feathers that they had begun to acquire, tended to preserve. Notwithstanding the advantage which this gave them, they cooled down to within one or two degrees of the external air, whilst the adult bird, though quite naked, preserved the temperature which he had before the expe- riment, being 20° cent, or 36° Fahr., above that of the at- mosphere ; his internal source of heat, unaided by covering or muscular exertion, being sufficient to counterbalance all his losses. Not to pass over any thing calculated to throw a doubt on the conclusion which would naturally be drawn from this experiment, viz. that the source of heat was less pow- erful in the young than in the adult animal, we must take 72 ON THE HEAT OF YOUNG ANIMALS. into account the circumstance of the smaller size of the former. It is evident, that a small body, c&teris paribus, will cool faster than a large one ; but in the case of its producing heat, and of its developing it in sufficient quan- tity, it will repair its loss, and retain its temperature, whatever be its size. Now this is just the case of adult warm-blooded animals. The greatest difference in their size does not affect their temperature. The wren preserves its warmth as well as the eagle, when the external temper- ature is not at an extreme point. On the other hand, young hawks, already covered with a thick down, and almost as large as pigeons, in an atmosphere at 17° cent, or 62° 6' Fahr. suffered a diminution of 14° or 15° cent, or 25° or 26° Fahr. All circumstances then unite in proving that young birds produce less heat than adults. They require, however, a degree of heat nearly equal to that of their parents, and we have seen that not only the mild warmth of spring, but the strong heat of summer is, of itself, in- sufficient. This want is supplied by the shelter of their nest, their mutual contact, and the assiduous care of their parents, who are employed in imparting to them the warmth of their own bodies during all the time that is not occupied in obtaining food. These subsidiary aids become less necessary with the growth of the young animals. Be- fore they have acquired all their plumage, and when they are still unable to take their food unassisted, they begin to develope sufficient heat to maintain in spring and summer, the degree which characterises warm-blooded animals. The phenomena, indicated by the foregoing experiments are not, however, common to all young birds. Some, as soon as they are hatched, can maintain an elevated tem- perature, if exposed to the air in a favourable reason. They come into the world in a more advanced state than other birds. When just hatched they can cat and run, and it is ON THE HEAT OF YOUNG ANIMALS. 73 when other birds can perform these functions that they also develope the same degree of heat. The }roung birds which are able to run about and pre- serve, their own temperature, are only convered with a to- lerably thick down, and not with feathers, which is another proof that the difference in the temperature of young ani- mals and adults does not essentially depend on the cover- ing with which their bodies are provided. We have seen that the mammalia born with closed eyes, and birds hatched without feathers, produce so little heat as to be, in relation to the air, in the state of cold-blooded animals. We have followed the changes which they un- dergo as they advance in life, and have pointed out the epoch at which they acquire the power of preserving a high temperature when exposed without shelter to the action of the air. Let us now examine the circumstances in which they enjoy this faculty. They usually come into the world in summer, when the external temperature is favourable to them; — but suppose an alteration in this respect, will young animals preserve their heat as well as adults ? To solve this question, I obtained, in spring, a winter-temperature, by immersing vessels in a mixture of salt and ice. They were in all respects alike ; and the air in these continued steady, at 4° c. or 39° F. In this cold atmosphere I placed some young magpies, and left them for a short time ; in twenty minutes one of them lost 14°c. or 25°F. The others were examined at different intervals, the longest not exceeding seventy minutes; they had cooled 14°c. or 25°F. and 1 6°c. or 29°F. ; this was a con- siderable and rapid loss of heat, which the animals could scarcely survive. An adult of the same species, placed in the same circumstances, sunk only 3° c. or 5° F., a loss not incompatible with a state of health. The cause of this difference must be looked for in the 74 ON THE HEAT OF YOUNG ANIMALS. animals themselves, the external circumstances being the same in both cases. By lengthening the duration of the cooling process in the adult bird, I more than compensated for the slight advantage which it might derive from its size and feathers. We can scarcely ascribe the inequality in the cooling of these birds to any other cause than a difference in the power of producing heat. The blackbird, the jay, the oriole, and the starling, were exposed to the same arti- ficial cold, at an age at which their temperature had risen and become stationary, with the same result as in the pre- ceding case. The rapid progress which they make in ac- quiring the power of producing heat is wonderful. But a few days after the preceding experiment, the young birds cooled much less when they were exposed to the same degree of cold, although their appearance was very little, if at all, altered. This influence of age is not confined to birds ; I have proved its existence with the mammalia also. Young guinea pigs at birth are able to walk and run, and take the same food as their mother. They do not require to be warmed by her, and appear to possess an equally steady and constant temperature, when the season is not severe ; but they have not the same power of maintaining their temperature against cold. These points were proved by means similar to those employed with birds, and it was made equally evident that the difference depended on an inferior power of producing heat. On the whole, therefore, we are warranted in the general conclusion, that the power of producing heat in warm- blooded animals is at its minimum at birth, and increases successively until adult age. /o CHAPTER II. ON THE HEAT OF ADULT ANIMALS. Among warm-blooded animals are to be found a small number, which from their undergoing a considerable loss of temperature, accompanied by a state of torpor during the winter months, have been denominated hibernating animals. The species which, in our climate, are universally allowed to merit this appellation are, the bat, the hedge- hog, the dormouse, the fat dormouse, the garden dormouse, and the marmot. There are other species which some naturalists suppose to be similarly circumstanced : of these I shall speak hereafter. The, animals above-mentioned, have all the characteristics of mammalia. They belong to various genera and families, and are not distinguished from other animals of the same class by any peculiarity of structure. It is during their hibernation only that they are in any manner to be distinguished from other mam- malia. At this period they appear to be converted, for the time, into cold-blooded animals; their temperature is scarcely above that of the surrounding atmosphere ; they are torpid like reptiles ; their respiratory movements are irregular, feeble, and at long intervals; and, what is very remarkable, this state continues several months, during which they take no nourishment. We can scarcely conceive two modes of existence more dissimilar than the summer and winter lives of these ani- 76 ON THE HEAT 0*F ADULT ANIMALS. mals. Does this depend, as some have supposed, on a change of structure, which modifies their mode of being? Or with the same organization at all seasons do they pre- sent different phenomena, because their temperament is subservient to changes in the atmosphere ? If we consider that it is only when the temperature sinks in autumn, that these animals retire into the holes in which they are afterwards found, cold and torpid, we may pre- sume that it is the operation of this cause which produces the effect ; and after all that we have related above re- specting the influence of external temperature on young warm-blooded animals, we shall have little difficulty in believing that it is so. If we suppose that in summer and spring the hibernating mammalia produce less heat than other adult warm-blooded animals, it is a necessary conse- quence that their temperature should sink with the fall of the year. It might however be supposed that deficiency of nourishment produced these effects ; that not being able to procure food in cold weather, their long fast threw them into a state of langour approaching to death, and that their coldness and insensibility, and their interrupted and almost imperceptible respiration were the consequences. Observation and experiment only can decide the question. These animals have been made the objects of numerous and important researches ; but they have been principally examined during hibernation. Spallanzani, Hunter, Man- gili, Prunelle, and De Saissy, have ascertained the pheno- mena which they present during the state of torpor, the means of recalling them to active life, and of again inducing torpidity, as well as several other facts connected with them. Of the numerous remarkable phenomena presented by the hibernating mammalia, those only need arrest our attention which relate to their temperature, since they belong to the subject with which we are now engaged. ON THE HEAT OF ADULT ANIMALS. 77 They are the more interesting because they seem to in- fluence all the other phenomena. Buffon thought that the temperature proper to the hibernating mammalia was 10° of Reaumur's thermometer, which is equal to 12° 5' cent, or 54° 5' Fahr. but the physiologists just mentioned have proved that it is from 35° cent, or 93° Fahr. to 37° cent, or 98° 6' Fahr. in spring and summer. Here then they do not essentially differ from other adult mammalia ; but if we wish to discover whether, notwithstanding this similarity of temperature, they really produce less heat, we must see how they bear the influence of natural or artificial cold. M. de Saissy has repeatedly examined these animals at different periods during their state of activity. On the sixth of August, the temperature of the air being 22° cent, or 73° Fahr. that of a marmot was 36° 5' cent, or almost 98° Fahr. in the axilla. On the twenty-third of September, the air was 18° cent, or 64° 5' Fahr. and the marmot 31° 25' cent, or 88° Fahr. and on the tenth of November, the air was 7° cent, .or 44° 6' Fahr. and the animal only 27° 25' cent, or 81° Fahr. which is 9° 25' cent, or 16° 6' Fahr. lower than its temperature in the month of August. A garden dormouse examined under the same circumstances had a warmth of 36° 5' cent, or 88 Fahr. on the third of August; of 31° cent, or 87° Fahr. on the twenty-third of September ; and only 21° cent, or 69° 8' Fahr. on the tenth of November, having lost 15° 5' cent, or almost 28° Fahr. since the first examination. The examination of a hedo-e- hog gave the following results. It was 37° cent, or 99° Fahr. on the third of August ; 35° cent, or 96° Fahr. in September ; and only 13° 75' cent, or 57° Fahr. having lost more than 20° cent, or 40° Fahr. The author of these observations has not informed us whether these animals were in the constant practice of taking food whilst undergoing this loss of temperature, a 78 ON THE HEAT OF ADULT ANIMALS. circumstance of some importance, to enable us to judge of its cause, and to draw a strict comparison between the hibernating and other mammalia. M. de Saissy succeeded in torpifying a marmot in the months of May and June. He had inclosed it with a little straw in a copper box, the lid of which was pierced with a hole about half an inch in diameter. After leaving it in an ice- house for twenty-four hours, he exposed it to an artificial cold of 10°c. or 18°F. below the freezing point. It fell into a profound torpor eleven hours after, and although its tempera- ture had fallen from 35°c. or 95°F. to 5°c. or 4l°F. ; yet its health did not appear more altered than in the ordinary circumstances of hibernation ; for, on being afterwards exposed to the warmth of the atmosphere, it recovered from its torpor, and resumed its wonted activity. This interesting; fact shews that hibernating- animals may become torpid at any season, and from other causes than the want of nourishment ; and also that the pheno- mena which take place in hibernation do not proceed from any change in the organization of the animal at the end of summer, as some have supposed. We may now compare the hibernating with the other mammalia, with reference to the external temperature during spring and summer, when both are in the enjoyment of the full activity and vigour of life. In the preceding experiment, the degree and duration of the cold to which the marmot was subjected, were such as might lead us to question whether non-hibernating animals would not have lost as much heat under the same circum- stances, enclosed in a box with so small an aperture, that respiration might have been impeded. We may also con- clude, from the following observation of the same author, that cold was not the only influential cause : — " The mar- mot which I reduced to a torpid state at two different ON THE HEAT OF ADULT ANIMALS, 79 times, only became so, I believe, in consequence of its oc- curring to me, to close the aperture in the lid at a time when its respiration was much enfeebled. It was only in this manner that I succeeded, for all my previous attempts had been vain." We have here, then, a combination of two causes — external cold, and diminished respiration ; without being able to distinguish the respective effects of each. I performed the following experiment, with a view to determine the influence of cold upon an hibernating animal, compared with other warm-blooded animals in similar cir- cumstances. In April, 1819. the air being 16°c. or 61°F. an adult bat, of the long-eared species, recently taken, in good condition, and at the temperature 34°c. or 93°F. was placed in an earthen vessel, which was cooled by a mixture of ice and salt, which surrounded it, till the air within was reduced to l°c. or 33° 8' F. It had a cover, which allowed a free communication with the external air. After the animal had been there for an hour, its temperature was reduced to 14°c. or 57°F., being a loss in this short space of time of 20c. or 36°F. Guinea pigs, and adult birds, placed in 4;he same circumstances, lost, at the utmost, no more than two or three degrees, although the influence of the cold was prolonged in this case, to compensate for the difference of size. We see from this, that bats are in the habit of producing less heat than animals which do not hibernate ; and it is to this cause that we must chiefly ascribe the reduction of their temperature during the cold season. If we compare this experiment on the bat, with those on young warm-blooded animals, we perceive a remarkable analogy, with this difference, however, that what is a transitory condition in the young of most warm- blooded animals, is permanent in the bat. We may safely extend the result of this experiment to 80 ON THE HEAT OF ADULT ANIMALS. the whole group of hibernating animals, — and draw this general conclusion respecting them, that whatever causes of a different nature may influence their temperature during hibernation, it is mainly to be attributed to a defi- ciency in the power of producing heat. 81 CHAPTER III. THE INFLUENCE OF THE SEASONS IN THE PRODUC- TION OF HEAT. Age, the influence of which we have just been considering, is certainly not the only cause common to warm-blooded animals which modifies the development of heat. We shall now examine the effect of the seasons in this respect. From reflecting on the remarkable change produced in the vertebrated cold-blooded animals, by the long-continued action of heat and cold, which has progressively modified their constitution, so that in summer and in winter, though placed, in other respects, in precisely the same circum- stances, they have a vitality so different that they would scarcely be known as the same beings, except from ob- serving their form and structure ; I was led to presume that the other classes of the vertebrata, though more ele- vated in the scale of beings, might also experience some constitutional change under the constant action of causes so powerful. As no inquiries appeared to have been instituted on this subject, I was induced to take it up, and I did so the more willingly, as it is obviously connected with the influence of climates. I proposed to examine whether, in the opposite seasons of winter and summer, warm-blooded animals, not hiber- nating, present any difference in respect of their power of 82 THE INFLUENCE OF THE SEASONS producing heat. This was to be ascertained by placing animals of the same species in the same conditions of refrigeration in winter and in summer, and observing if their temperature diminished unequally. In this case it would follow, that their power of producing heat is not the same at these two periods, supposing nothing to be omitted to render the experiments parallel. It is necessary, in the first place, that the animals se- lected should be as similar as possible, and that the expe- riments should be sufficiently numerous to obviate any considerable influence from individual diversities. In order that the mode of refrigeration should be the same, attention must be paid, not only to the temperature, but to the humidity of the atmosphere; for a difference in the hygrometric state of the air would produce a corresponding difference in the evaporation from the lungs and skin, and consequently in the quantity of heat lost. The apparatus consisted of glass vessels, of the capacity of two pints, placed in a freezing mixture of salt and ice. The air thus cooled, is at its point of saturation with mois- ture. When it is at zero cent, or 32° Fahr. the animal is introduced, and placed on a false bottom of gauze, to pre- vent the contact of the cold glass. A lid covered with ice is placed over the vessel, but so as to permit change of air for the free exercise of respiration ; and, in order more effectually to secure the purity of the air, a concentrated solution of caustic potass is placed at the bottom, to absorb the carbonic acid, which it readily does, through the gauze. The general results are as follows : — In the month of February the experiment was made, at the same time, upon five adult sparrows. In the course of an hour they lost, on an average, only 4° cent, or 72° Fahr. — some having lost none, others only 1° cent, or 1° 8' Fahr. Their temperature then remained stationary, until ON THE PRODUCTION OF HEAT. 83 the end of the experiment, which lasted three hours. In July, I tried the same experiment on four others. Their temperature, in the course of the first hour, sustained an average loss of 3° 62' cent, or 6° 5' Fahr. j at the end of the third hour the average reduction from their original temperature was 6° cent, or 10° Fahr. In another series of experiments on six sparrows, in the month of August, the mean loss of temperature at the end of the first hour was 1° 62' cent, or 2° 9' Fahr. ; and after three hours, 4s 87' cent, or 8° 76' Fahr. These experiments indicate a considerable change ef- fected in the constitution of these warm-blooded animals, by the influence of the seasons ; they shew that the con- tinued elevation of temperature diminishes the power of producing heat, and that the opposite state of the atmo- sphere, provided the cold is not too severe, increases it. g 2 84 CHAPTER IV. ON ASPHYXIA. Having examined the principal points connected with the influence of heat on the animal economy, we shall now pass to the consideration of the air, another physical agent no less important in its relation to life. The ancients were to a great degree, ignorant of the pro- perties of the atmosphere, and most of them have only been ascertained of late years. Whilst they remained unknown, it was impossible to understand the action of the air upon the animal economy. Already our knowledge of this agent has been advantageously applied : the subject, however, ad- mits of being carried considerably further, but the investi- gation requires much time. The earliest knowledge which was acquired respecting the relations of the air with the animal economy, was the most important fact of the necessity of this fluid for the support of life, a necessity so urgent, that man, and the animals which most resemble him in their structure, perish almost as soon as they are deprived of it. Three or four minutes suffice to do away with all appearance of sensation and motion, and though some feeble remains may yet exist in the interior of the body, these are quickly extinguished. The cessation of external sensation and motion is called apparent death, and in this case it is scarcely short of actual death. So powerfully docs the privation of air tend to destroy ASPHYXIA. 60 life, that animals of the largest size, and those possessed of the greatest muscular energy, sink under it almost as quickly as the smallest and the weakest. We might be inclined suppose that those warm-blooded animals, which are con- stantly obliged to plunge under water in pursuit of prey, or to elude their enemies, would acquire the power of resisting the effects of the privation of air longer than other animals. To ascertain this fact, a moor-hen was plunged in water : at the end of about three minutes, it had neither sense nor motion. Some birds, it is true, perish sooner, and others perhaps, will survive longer ; but this fact indicates of what slight avail on this occasion is habit, which, in general has so powerful an influence on the animal economy. The hope of producing such an alteration in animals as to enable them to support the privation of air, for a much longer term than is natural to them, led BufFon to a very important discovery with respect to young animals. He placed a greyhound bitch of the largest species, when on the point of giving birth to young in a tub of warm water, and secured her in such a manner that she was obliged to bring them forth under water. These were afterwards for the sake of nourishment transferred to a smaller tub of warm milk, but without giving them time to breathe. They remained there for above half an hour, after which they were taken out and all found alive. They began to breathe, which they were allowed to do for half an hour, and were then again plunged in the milk which had been warmed again in the mean time. There they remained for another half hour, and when they were again taken out, two were quite strong, and seemed not to have at all suffered: The third appeared drooping: but was carried to its mother, and soon recovered. The experiment was continued on the other two, they were allowed to breathe a second time for about an hour ; and were then plunged once more in 86 ASPHYXIA. the warm milk for half an hour, after which they appeared as strong as before. However, being taken to their mother one of them died the same day, whether by accident or from having suffered from the privation of air could not be ascertained. The other lived as well as the first, and both thrived as well as the other puppies produced after the bitch was removed from the water, and which had not undergone the ordeal. Le Gallois who does not appear to have been aware of what Buffon had done, made experiments upon rabbits with the same view. He undertook them, for the purpose of ascertaining how long a full grown foetus could survive without breathing, when separated from its communica- tion with the mother. He found that when he deprived them of respiration by immersing them in water, the mean duration of their life was twenty-eight minutes. But this power of resisting the want of air, rapidly diminishes with the progress of life. Le Gallois observed, that at the end of five days, young rabbits plunged in water, live only sixteen minutes. At the end of another five days, the time is re- duced to five minutes and a half, and when they are fifteen days old, they have then reached the limit which adult warm-blooded animals can rarely pass, when they are with- drawn from the influence of the air. The results of these experiments would favour the belief, that the duration of the life of new-born mammalia, under such circumstances, is about half an hour. I was much surprised, however to find that the guinea-pig, at birth, when plunged in water, lives only three or four minutes longer than the adult. I found other species also in which the difference was not greater. I therefore directed my attention to discover the cause of this remarkable difference. My researches upon cold-blooded animals had enabled me to perceive the g;rcat influence of temperature over this ASPHYXIA. 87 mode of existence. Having afterwards found that warm- blooded animals present among themselves marked diffe- rences in the production of heat, I concluded that these might give rise to modifications of their system, analogous to those produced by external temperature upon cold- blooded animals. Let us then compare together the species which have been just mentioned, in this point of view. On the one hand, new-born dogs, cats, and rabbits are similarly af- fected in asphyxia. They all give signs of life for half an hour, and sometimes longer : now these are the very species in which we have observed so feeble a production of heat. We formerly observed, that in this respect they bore a close resemblance to reptiles and fishes ; we see here that they also resemble them in the power of sustaining the priva- tion of the air, which implies an intimate connection be- tween these two phenomena. On the other hand guinea-pigs are in the class of those which produce most heat at birth ; and of these I have never seen one which lived above seven minutes under water, and frequently they do not attain even that limit. We shall be better enabled to perceive the cormexion between animal heat and this mode of vitality, by observ- ing their respective modifications in the progress of early life. We have seen, in the experiments of Le Gallois, that at the end of the fifth day the duration of life during as- phyxia is reduced one-half: now this reduction corresponds to a sensible elevation of their temperature. The same is the case after the second interval of five days; the heat is then much increased, and the power of living without respiration is considerably diminished. Lastly, when they have arrived at the fifteenth day, a period when they usually have a temperature nearly equal to that of adults, 88 ASPHYXIA. they scarcely differ from them in the duration of asphyxia. If, instead of passing at once from the first to the fifth day, we examine the young animals in the intervening days, we shall find, that during the first and second, and even, not unfrequently, the third, the duration of asphyxia is only very slightly altered. The production of heat cor- responds with this, and both phcenomena likewise concur in the more rapid and striking change that quickly after takes place. We see that the distinction formerly pointed out between young mammalia, founded in the production of heat, is applicable to them also in respect to the duration of life when deprived of respiration. This duration has its maxi- mum in the group of mammalia which produce the least heat at birth, and its minimum in those which produce the most. I have made similar researches respecting birds. I have exposed young sparrows separately to the action of the air to compare their rate of cooling. The temperature of the atmosphere was at 16° cent, or 61° Fahr. in the month of May. One of them, which had, in half an hour, cooled from 35° cent, to 19° cent, or 95° to 66° Fahr. was after- wards warmed, and when he had regained his original heat was immersed in water ; he lived in it eight minutes ; now adults live only a minute and a few seconds. The other, whose temperature was only reduced to 26° cent, or 79° Fahr. was in like manner warmed again and immersed in water ; he gave signs of life for only four minutes. Others, which lost little heat by exposure to the air, dif- fered equally little from adults in the duration of life under water. These facts are sufficient to shew the correspondence between animal heat and the power of living, excluded from the contact of the air ; but there is a limit at which ASPHYXIA. 89 this correspondence ceases, and animals soon arrive at it. The increments of heat taking place beyond this limit have no longer any sensible influence upon the duration of life in asphyxia. Sect. 1. — hiftuence of external Temperature. In the preceding experiments no notice is taken of the temperature of the water in which the submersion took place. This circumstance has a powerful influence on the cold-blooded vertebrata. Is it the same with the warm-blooded ? We shall examine the effects of temperature between 0° and 40° cent., including the range the most nearly related to the animal economy. I subjected some kittens a day or two old to compara- tive experiments. In water cooled to 0° cent, or 32° Fahr. they ceased to give signs of sensibility and motion, after four minutes and thirty-three seconds, taking the mean of nine experiments. At a temperature of 10° cent, or 50° Fahr. the duration of life extended to ten minutes and twenty-three seconds. At 20° cent, or 68° Fahr. it in- creased considerably, being on an average thirty-eight minutes and forty-five seconds ; at 30° cent, or 86° Fahr. a retrograde course commenced, as they lived but twenty- nine minutes ; lastly at 40° cent, or 104° Fahr. they lived ten minutes and twenty-seven seconds. It may be remarked, in the first place, that the degree most favourable to life, in the circumstances in which the kittens were placed, may, with reason, be considered as a cold temperature. A bath at this degree, commonly pro- duces upon our bodies a very lively sensation of cold ; and is 20° cent, or 36° Fahr. below the mean temperature of warm-blooded animals. The change of the external tem- perature either above or below this degree, produces dele- 90 ASPHYXIA. terious effects, but in different proportions. A rise from 20° cent, or 68° Fahr. to 40° cent, or 104° Fahr. is neces- sary to produce the same effect as a fall from 20° to 10° cent, or 68° to 50° Fahr. ; similar experiments upon pup- pies, &c. of the same age lead to the same results. This influence of external temperature is not confined to early age, it extends to every period of life ; and although the life of adult mammalia (and, yet more, that of birds) is so closely connected with the influence of the atmosphere, that when it is suspended death takes place so soon as to afford but a very limited field for observation, the fact is, notwithstanding, apparent. There are, then, two principal conditions which influence the life of warm-blooded animals when deprived of air. The one is the quantity of heat developed by the animals themselves, the other is the external temperature to which they are exposed. 91 CHAPTER V. ON RESPIRATION IN YOUTH AND ADULT AGE. After having observed what circumstances modify the duration of life, when animals are deprived of air, let us now examine the influence of this fluid upon the body. Air, in contact exteriorly with the skin, and interiorly with the lungs, exerts its vivifying influence much more power- fully on the latter than on the former. As soon as air is intercepted from the lungs of warm-blooded animals, al- though the whole external surface be still exposed to it, they experience the same distress, as if they were entirely plunged in water; and if this interception of the air be continued, asphyxia is produced as quickly as by submer- sion. If, on the contrary, the contact of air with the skin is prevented, whilst it has free access to the lungs, no in- convenience is found to arise from it. These facts have necessarily led to the lungs being re- garded as the only organ intended to support life by means of contact with the atmosphere. We will, for the present admit the correctness of this opinion, and shall, in the first place, consider the mutual relation of the lungs and air for the support of life ; we shall afterwards examine if the skin does not contribute to the same effect. The first relation of the air to the lungs, depends on the capacity of these organs, and the extent of surface which they present. The differenee in the size of warm-blooded 92 RESPIRATION IN YOUTH AND ADULT AGE. animals, indicates a corresponding difference in the capa- city of their lungs. But when we limit the respiration of animals of various sizes to the air contained in the lungs by placing a ligature upon the trachea, the small live al- most as long as the large. One might hence infer that the extent of surface of the lungs in animals of the same class is also proportioned to their size. We shall return to this subject. The air which supports life must be continually renewed. The necessity of this renewal is proved by the accidents which happen when it is suspended. The whole of the air in the lungs is not, however, renewed by an inspiration and expiration ; and it is the portion of air which enters and issues from the lungs when these acts are performed, which essentially contributes to the support of life. Although the will has a slight control over the respi- ratory motions, yet, on the whole, they may be considered as involuntary ; and in a state of health, and in a condition free from the influence of disturbing causes, they have a strong tendency to uniformity. The capacity of the lungs, as compared to the size of the trunk, is but little affected by age. If it is rather less in youth than in adult age, the succession of respiratory movements is, in general, more rapid, so that, in the same space of time, the quantity of air which comes in contact with the pulmonary surface of a young animal is propor- tionally equal, if not superior, to that which is inspired by an adult. From the necessity of the renewal of the air in respiration, it may be inferred that it undergoes some change. In two respects this change is evident. The expired portion has acquired an increase of temperature, and is charged with vapor. It is, however, an ascertained fact, that the most im- RESPIRATION TN YOUTH AND ADULT AGE. 93 portant alteration of the air during respiration is chemical, and consists principally in the substitution of carbonic acid for a part of its oxygen. When the quantity of air in which a warm-blooded animal respires, is limited, this alteration is progressive, and when it arives at a certain point, the animal dies as it does when altogether deprived of the contact of the air. All warm-blooded animals, when thus confined to a limited quantity of air, alter it to nearly the same degree, and though it still contains a small quantity of oxygen, it is as fatal to them, when placed in it, as submersion in water. The space of time which they live in a given quantity of air, is determined by the rapidity with which they consume the quantity of oxygen, which is susceptible of alteration by respiration. This subject merits particular attention. The difference between individuals in this respect does not wholly depend on the proportionate quantity of air admitted into the lungs, but in part on the constitution of the animals. I placed some sparrows, in every respect as much alike as possible, in vessels of the same form, and containing each a litre, or about a pint and three quarters of air, inverted over mercury. Still further to ensure equality in the con- dition of the experiments, I performed them simultane- ously, thereby avoiding differences in the temperature, pres- sure and humidity of the air. In a great number of ex- periments, I ascertained that there was sometimes a con- siderable difference in the duration of life with the same quantity of air, and that the shortest and the longest du- ration might differ by one-third. The air, however, was altered nearly to the same degree by all, so that the du- ration of life was principally affected by the comparative rapidity in the consumption of oxygen. Since the experiment was complicated by the presence of carbonic acid ; to the action of this gas, varying accord- 94 RESPIRATION IN YOUTH AND ADULT AGE. ing to the sensibility of the individuals, might perhaps be attributed a difference in the respiratory movements, which would affect the rapidity with which they consumed the air, and thus diminish the respective duration of their lives. The presence of carbonic acid does, it is true, influence the respiratory movements, but the differences above stated, equally existed when I employed means to absorb the car- bonic acid as it was formed. We must then admit other causes depending upon individual constitution which affect the rapidity with which the air is consumed. We shall now proceed to consider the changes in this respect, which the same individual undergoes in the pro- gress of life. In youth, all the functions seem to conspire to promote the development and growth of the body. Di- gestion is more rapid — the calls of appetite are more fre- quent and more pressing — respiration is more rapid, and when we consider the necessity of air for the continuance of life, we might be induced to presume, that the relative consumption of air was greatest in youth. Our reasoning may be deceptive ; experiment alone can decide the point. In this investigation there are several precautions neces- sary to arrive at accurate praetical results. We must avoid comparing those animals in which age occasions a great difference in size, as the question is to determine the influence derived from the constitution, and not from a difference in bulk. But as the increase of the body and the changes in the constitution are inseparable during a certain period of life, we ought to choose those species whose dimensions vary the least in the progress of life, and in which the other differences are more prominent. The species used in the preceding experiments combines these advantages. To simplify the comparison still more? we must absorb the carbonic acid as it is formed. The experiment was made with vessels containing a RESPIRATION IN YOUTH AND ADULT AGE. 95 pint and three quarters or sixty-one cubic inches of air, inverted over a solution of caustic potash. The animal was placed on a partition of gauze. The young sparrows which I employed were apparently from eight to ten days old : their bulk was about two cubic inches and a fifth, and that of the adults rather more than twice as much. This difference in size alone would occasion a more rapid consumption of air by the older birds, and it ought not to appear extraordinary that they died sooner. The mean duration of their life was 1 h. 30' 32" ; but the young sparrows prolonged their existence to so disproportionate an extent as to astonish me; their mean term was 14 h. 49' 40". Towards the close of the experiment, when they have altered the air until it is no longer capable of supporting life, we may suppose that they still live as long as they can when deprived of air. We have seen in the former chapter upon asphyxia, that this period is longer in young than in adult animals. But the maximum with sparrows is seven minutes. It is evident, therefore, that in allowing for all these differences, the young sparrows lived much the longest in the same quantity of air, and that conse- quently their consumption of it is comparatively less. What is the modification of the animal economy, de- pendant upon age, which corresponds with this difference in the consumption of air ? The most striking difference between the constitution of young animals and that of adults exists, as we have already shewn, in their production of heat. It is in the early steps of life that warm-blooded animals develop least heat. It is also in the early stages of life that the. sparrows consumed the air most slowly. In order to verify this relation under circumstances the most favourable to a satisfactory result, these experiments were continued on the same snecies at less distant ages. 96 RESPIRATION IN YOUTH AND ADULT AGE. Their growth is so rapid that they scarcely begin to feed themselves before their size is nearly equal to that of adults. Their temperature then supports itself in the open air. It was at this age that I compared them with adults. Five of these young animals, placed in sixty-one cubic inches of air, and supported by a gauze partition over a strong solution of caustic potass, lived, on an average 2h. 39', but adults, in the same circumstances, lived only lh. 32'. Here we have no correction to make either for volume, or for difference in the duration of life after the air has become unfit for respiration. These are alike in both these respects, or differ too slightly to deserve atten- tion ; but they differ essentially in the production of heat, and we see that the young birds, which produce much less heat, also consume air more slowly than adults. These researches, following a different method, were extended to mammalia, I placed over mercury, in ves- sels containing the same quantity of air as in the pre- ceding experiment, puppies a day or two old, and Guinea pigs about a fortnight old. The dogs were taken out at the end of four hours and fifty-nine minutes, and the Guinea pigs after an hour and forty-two minutes. By analysis of the air, the mean of the quantities of oxygen was found to be sensibly the same. Regarding only the difference of bulk, the consumption of air by the puppies ought to have been much more rapid, be- cause they were larger, but when we recollect the fact pre- viously established that young puppies at birth produce much less heat than Guinea pigs, we see here the same relation to exist between the consumption of air, and the production of heat, that we had determined in the case of the sparrows. These facts regarding the vital heat and respiration of young animals compared with adults, opposed, as they are, RESPIRATION IN YOUTH AND ADULT AGE. 97 to preconceived and general opinion will, on reflection, be seen to be in perfect accordance with the order of nature. Is it not the same relation which the cold-blooded have long been known to bear to the warm-blooded vertebrated animals, and does not the same relation exist between the mammalia and birds ? 98 CHAPTER VI. ON THE INFLUENCE OF THE SEASONS UPON RESPIRATION. In the course of trie seasons, several changes in the atmo- sphere occur, which may affect respiration. Such are variations in the temperature, pressure and density of the air. Let us consider the effects of different degrees of density of the air upon the consumption of this fluid in respiration, independently of other atmospheric changes. We know that we can quickly destroy warm-blooded animals placed under the receiver of an air-pump, by rarefying the air which they breathe. It is true, the rarefaction of the air does not produce one effect only; but whatever other effects it may produce, we can attribute the suddenness of the death only to the fact, that air when dilated is consumed so slowly as not to suffice for the maintenance of life.* From this condition, which we shall consider as simple, we shall proceed to another which is complicated. When the temperature of the air changes, its density changes also ; cold contracts it, heat dilates it. We have noticed the effects of the change of density, but what is the pecu- liar effect of temperature ? We here leave out of view its influence on the motions of respiration and those of the heart, as this exists in extreme cases only. The air being * See Legallois' Papers on Respiration. INFLUENCE OF THE SEASONS, &C. 99 rarer in summer and at the same time warmer, but to a de- gree which does not affect the motions of the respiratory muscles or of the heart, what is the effect of this elevation of temperature? Does it act conjointly with the rarefac- tion in diminishing the consumption of the air, or does it counteract such an effect ? The respective effects of ele- vation of temperature and rarefaction of the air do not ap- pear to have been ever examined. Their combined opera- tion has not been altogether neglected. Crawford made guinea-pigs breathe in air of different temperatures, and found by analysis that more carbonic acid was produced in air at the temperature of 8° cent, or 46 Fahr., which may be considered as cold, than in warm air of nearly 35° cent, or 95 Fahr. : but as the colder is likewise the denser air, this latter circumstance may have occasioned the difference no- ticed by Crawford. Analogous experiments performed by Delaroche, obtained variable and somewhat contradictory results. The subject must therefore be considered as un- decided, and I shall not enter upon it here, as it requires the employment of means which I have reserved for ano- ther occasion. I have devoted considerable attention to it, and I shall state the facts which I have proved, when I come to speak expressly of the changes effected in the air by respiration. But another important question remains : Does the change of seasons occasion modifications in the constitu- tion, such, that, supposing the density, temperature, &c. to remain the same, it would be consumed in different propor- tions at different periods ? The facts which we have already established lead us to form a very probable conjecture as to the result of the inquiry. In following the changes which take place with the progress of age in warm-blooded animals, we have seen, that at different periods from birth to maturity, the h 2 100 THE INFLUENCE OF THE SEASONS consumption of air increases, ceteris paribus, with the deve- lopment of heat. This connexion between respiration and the production of heat, is in accordance with the relation which we have observed that animals of different classes bear to each other, such as the cold-blooded to the warm- blooded vertebrata, and the mammalia to birds. We may therefore expect likewise to discover a corresponding rela- tion in cases like that which we are now to examine, in which it may not as yet have been observed. It has been shewn in one of the preceding chapters, that warm-blooded animals, if in full vigor, and possessed of constitutions adapted to the climate, possess the power of producing heat to a greater degree in winter than in sum- mer. There ought, then, circumstances being in other re- spects the same, to be a greater consumption of air in win- ter than in summer, if there really exist an intimate con- nexion between the two functions. With a view to determine this question, I made in Ja- nuary, 1819, a series of experiments on six yellow-hammers, ( Emberiza citrinella,) in separate receivers, each containing 71 cubic inches, or rather more than two pints of air, placed over mercury, with a gauze partition for the bird to rest on. I raised the temperature of the air to 20° and 21° cent, or 68° and 70° Fahr. in order to represent a moderate summer temperature. The average of the duration of their life in this quantity of air was lh. 2' 25". In August and September the same experiments were repeated at the same tempera- ture, upon 13 individuals of the same kind. The average duration of their life was then lh. 22'. In January of the same year, the same experiment was performed on four green-finches; (Loxia chloris.) They lived on an average lh. 9' 15". In August, for want of opportunity to procure a larger number, the experiment was tried upon only two ; one lived lh. 30', and the other UPON RESPIRATION. 101 lh. 36'. This is mentioned merely, as tending to confirm the preceding ; alone, the fact would be altogether insuffi- cient. The experiments, hitherto, had been made over mercury ; consequently, the carbonic acid formed during respiration remained in the receiver, and complicated the experiment. I proposed, in another series of comparative experiments in the two seasons, to suppress this cause of complication, by placing the receivers over a strong solution of caustic potass, capable of absorbing the carbonic acid gas which was produced. With this modification, I resolved to apply it to a great number of individuals. At the close of December and in January, it was tried upon 16 yellow-hammers. The mean duration of their life was lh. 7' 37". The following sum- mer, at the close of August and beginning of September, the temperature being at 20° cent, or 68 Fahr., and 21° cent, or 70 Fahr. ; the same experiment was made upon 12 yellow-hammers ; — they lived on an average lh. 23' 43" The concurrent evidence of these varied experiments leaves no doubt as to a change being produced in the constitu- tion of the animals by the influence of the seasons. I considered that the phenomena presented by animals respiring the same quantity of air, would likewise furnish some data calculated to throw light on the mode in which they consume air in the different seasons. When respiration is performed in a limited portion of air, that fluid loses its oxygen and receives an accession of carbonic acid. When this last is absorbed as it is formed, the diminution of the oxygen will still occasion the respi- ration to be oppressed. An unequivocal symptom of this oppressed respiration in birds is the opening of the beak, a symptom which is manifested sooner or later, according to the more or less rapid consumption of the oxygen. 102 THE INFLUENCE OF THE SEASONS. I noted in January, in the case of 10 yellow-hammers, the period at which they began to open their beaks, during an experiment similar to that above described, the carbo- nic acid being absorbed by a solution of potass. The aver- age period was 52' 53" from the commencement of the experiment. Similar observations made at the end of Au- gust and beginning of September, upon 12 yellow-ham- mers, in the same circumstances furnished an average of lh. 8' 55" from the beginning of the experiment. There could not be a more evident confirmation of the conclusion to which the former experiments likewise tended, that the consumption of oxygen is more rapid in winter than in summer. In order to obviate any objection which would attribute the result to a diminished quantity of air in the winter ex- periment, it may be mentioned, that the mean pressure was the same in both seasons ; but the air with which the vessels were filled was colder previously to raising it to the summer temperature, so that there was really more air used in the winter experiment. Hence, we mav conclude, that the differences in the phenomena of respiration depended on the change in the constitution, effected by the influence of the seasons. Such a conclusion might have been anticipated from the fact proved by former experiments, that the power of producing heat in warm-blooded animals is greater in winter than in summer, and from the evident relation subsisting between the consumption of air and the development of animal heat. 103 CHAP. VII. ON PERSPIRATION, OR EXHALATION, When on the subject of cold-blooded animals, we fully- treated the influence of different states of the atmosphere in increasing or diminishing the loss of weight occasioned by perspiration in that class of animals. We shall now resume the same series of researches, with respect to the perspiration of warm-blooded animals. Sect. 1. — Loss by Perspiration in equal and successive periods. We shall begin by determining what is the proportion between the successive quantities lost in equal times under the same external influence. Four young guinea-pigs were placed separately in small iron-wire cages. The temperature of the room was 14° cent. 57° Fahr., and the air was kept still, and free from draughts. They had been previously fed, that they might be in the best condition. They were weighed from hour to hour. A plate was placed under the cage to receive their urinary and alvine evacuations. Every excretion was weighed immediately, and the liquid part taken up with silver paper, the weight of which was determined both before and after the operation. The experiment lasted six 104 ON PERSPIRATION, OR EXHALATION. hours. The quantities lost, compared from hour to hour, were so various, that no tendeney to a regular course could be recognized. But on comparing them at intervals of two hours, the losses decreased successively in some, and a tendency to the same result was manifest in the others ; again, in comparing them at intervals of three hours, the diminution of the losses effected in three equal periods were evident in all, A similar experiment was tried upon another genus of mammalia. Four adult mice were placed in small wire cages, with the same precautions regarding the excretions. The temperature of the room was 19° cent, or 66° Fahr. The experiment was continued for six hours ; it was at- tended with the same results as that upon the guinea-pigs. Instead of pursuing these researches upon mammalia, I thought it preferable to take animals in the other class of warm-blooded vertebrata. The more the organization dif- fers in individuals which present the same phenomena, the more certain it is that these phenomena are common to a greater number of species. These experiments were therefore repeated upon birds. Four sparrows were exposed to the air in a room, at 19° cent. 66° Fahr. ; four others to a temperature of 20° cent. 68° Fahr., employing the same methods, and the same pre- cautions, and for the same space of time as in the foregoing experiments, and obtained the most complete confirmation of the former results. It did not seem expedient to prolong the duration of the experiment, lest the powers of the ani- mals should be reduced by too long abstinence. By stopping short at the irregularities which are observ- able in successive intervals of a single hour, we might be deceived as to the progress of perspiration, and not discover any certain tendency, and the fact might be united to many other anomalies in vital phenomena in support of the ON PERSPIRATION, OR EXHALATION. 105 opinion, that they are not susceptible of being reduced to laws. They may, however, be so examined, as that we may perceive in them a greater consistency than was ima- gined, of which the facts above stated are an instance. Notwithstanding the difference of the species employed in the experiments, they presented analogous results. They were similar, whether presented by mammalia or by birds. The facts being ascertained with animals of both classes, it is needless to multiply examples, and we are warranted in considering them common to warm-blooded animals. The results, stated generally, are as follows : That the successive losses by perspiration are subject to considera- ble variations and alterations of increase and diminution, when compared at short intervals, but constantly decrease when considered at longer periods. The periods during which the fluctuations take place in vertebrated animals generally, may be pretty accurately determined. We have always observed, in warm-blooded animals, the alterations to take place with intervals of an hour, and this term may be regarded as a general rule. On examining the whole series of experiments upon vertebrata of different classes, it was observed that the shortest intervals within which the successive diminution took place were those of two hours, and the longest, nine. In taking a mean of six, we may hope to include almost all the cases, for even when a longer space of time was necessary, three hours were suffi- cient to determine a diminution, if not constant, at least with little variation. In the greater number of cases, it took place in successive intervals of three hours. The first series of experiments upon the perspiration of warm-blooded animals, having yielded results perfectly con- formable to those which were obtained by corresponding re- searches respecting the cold-blooded, it is probable that we shall discover uniformity in others. 106 PERSPIRATION, OR EXHALTION. It is almost needless to observe, that with reference to temperature solely, the action of the air similarly influences the perspiration of both warm and cold-blooded animals. The same remark does not hold good with respect to dry and moist air. The testimony of our senses is not adequate to inform us of the effects of these two modifications of the atmosphere. A dry air, by its property of absorbing moisture, may cause perspiration to disappear, and a moist air by the opposite quality allows it to accumulate on the surface of the body. In the first case, it might be imagined, that dry air diminished perspiration, and in the second, that humid air increased it. May not sensibility, which in the higher order of animals is so exquisite, and has so powerful an in- fluence on their secretions, be so affected as to occasion very different results from those which are purely physical ? May not dry air produce such a constriction at the sur- face of the skin, and on the internal surface of the lungs as to diminish perspiration, and may not moist air occasion such a relaxation as to cause the opposite effect ? These considerations are sufficient to shew the uncer- tainty which must exist on this question, if we have not re- course to direct experiment, and are unwilling to follow the analogy drawn from the facts connected with the cold blooded vertebrata. It is surprising that the direct experi- mental enquiry should never have been made. Delaroche ascertained the comparative effects of dry and moist air upon man at high temperatures, but this condition ma- terially changes the effects of the agents. Other indivi- duals who have examined the subject of perspiration, have made experiments upon it at moderate temperatures, but under such complicated conditions, that the results may be attributable to other causes than those to which they have been assigned. PERSPIRATION, OR EXHALATION. 107 Sect. 2. — Influence of the Hygrometric state of the Air. In order to compare the effects of dry and humid air, all other conditions such as temperature, pressure, &c. must be equal. To succeed in this most easily, the ex- periments ought to be performed simultaneously. As to humid air, the vapour should be transparent, and not that which is termed vesicular, the state in which it is exhibited in fogs. The other state of the atmosphere is the most usual, and consequently the most important to be known. A guinea-pig was placed in a wire cage suspended in a glass vessel, the sides of which had been previously wetted and which was afterwards placed over water. The vessel contained about 12 litres, or 732*5 cubic inches. It had been previously ascertained that, under such circumstances, the air rapidly arrives at extreme humidity. At the same time, I suspended in a perfectly similar vessel, another guinea-pig of the same litter, and as nearly as possible of the same weight. The vessel was placed over two pounds of quick lime, to absorb the moisture, and tallow was used to intercept the air.# An hygrometer within, indicated the progressive desiccation of the air. The external tempera- ture was 1 5° cent, or 59° Fahr. Perfect dryness, although easily obtained, at the commencement of the experiment, could not be preserved during its continuance. The animal, if passed through mercury into the vessel might have ac- quired weight, and when introduced there, its perspiration would furnish moisture, perhaps, faster than it could be * The vessels or little chambers were not, however, perfectly air-tight, which would have interfered with the respiration of the animals, they were made of panes of glass, so put together as to allow the animals to breathe, yet sufficiently close to secure the requisite hygrometric state. 108 PERSPIRATION, OR EXHALATION. removed by the means employed to absorb it. By the means which I employed, a high degree of dryness may be ob- tained, equal to any met with in our climate, except at very great heights. The necessary conditions of the experiment, prevented us from ascertaining directly the losses occasioned by the alvine and urinary evacuations. We, however, sufficiently fulfilled the condition of equality in this respect, by mul- tiplying the experiments. Let us examine the results, which we shall afterwards submit to another test. Five guinea-pigs were placed in air of extreme humidity, and five others in air comparatively dry, and whose dry- ness went on increasing during the whole course of the experiments, which lasted six hours, except on one occa- sion which occupied eight. In all the cases, the losses in the dry air were much more considerable than in the humid. The influence of individual varieties did not fail to exhibit itself, but it was only in varying the amount of the difference. We see here a confirmation of the power- ful action of the hygrometric state of the air, since it pre- vails over all disturbing causes, originating from varied combinations of organization and sensibility in individuals of the same species. In order to obviate the objection that the difference in the losses arose from the difference in the weight of the animals, the largest were placed in the moist air, in which, from the experiments on cold-blooded animals, I concluded that the losses would be least. Since, then, the superiority in the weight of the larger animals, though counteracting, did not compensate for the inferiority in the quantity lost, the difference in the weight is only a fuller confirmation of the result of the experiment. It may likewise be objected, that the diminution of loss in damp air is occasioned, not by a diminution of perspira- PERSPIRATION, OR EXHALATION. 109 tion, but by that of the alvine and urinary evacuation. But we had occasion to observe, that their excretions were rather increased than diminished by the moisture of the atmosphere. In order to verify these results in the case of other warm- blooded animals, differing considerably in organization, eight adult sparrows were submitted to similar experiments with the same precautions. This species of animals has the advantage of exhibiting less difference in weight, and other particulars among individuals belonging to it, than many others. The results were similar to those of the pre- ceding experiments. The numbers representing the amount of loss in an- alogous cases were very similar, when the experiments were not unduly protracted ; but when they lasted above six hours, the want of food and other causes produced a degree of suffering, which, without disturbing the relation between the effects of dry and moist air, may increase per- spiration by hurrying the respiration and circulation. The state of respiration has a great influence in this respect. Hitherto we have considered merely the differences in the quantities lost, but we may approximate to the pro- portion which they bear to each other. I determined the average weight of the alvine and urinary evacuations of eight individuals of the same species, exposed to the open air of the room for six hours. This I subtracted from the loss sustained by those which were confined in dry and moist air for the same space of time ; the remainder fur- nished the amount of the respective losses by perspiration. Those in the dry air lost 1-04 grammes, or 15*9 grains : those in the moist air only Ol? grammes, or 2*6 grains. Hence, it follows, that the perspiration was six times greater in the dry than in the humid atmosphere. It is evident, however, that the properties might be rendered much greater, since the air was far from its extreme point of dryness. 110 PERSPIRATION, OR EXHALATION. These facts appear very simple, they are nevertheless very complicated. They will be explained in the fourth part of this work. Sect. 3. — Influence of the Motion and Rest of the Air. The effects of rest and motion in the atmosphere, have an intimate connexion with the preceding facts. The evaporation continually taking place from the bodies of animals in an atmosphere not saturated with moisture, creates for them a peculiar atmosphere more humid than the rest of the air. Now, currents of air tend to prevent this effect, by constantly renewing the air by which the bodies are surrounded, and consequently to increase per- spiration. Air at rest has the opposite effect. But in the present case, the effect of the motion of the air is not con- fined to this. The temperature of warm-blooded animals raises that of the fluid in contact with them. Inordinary circumstances, currents furnish supplies of colder air in place of that which is thus warmed, and consequently oc- casion a fall of temperature, which tends to diminish the perspiration. Now it remains to be ascertained, whether this last effect counterbalances the former. To ascertain this point, I compared the losses from per- spiration in the calmest air which could be procured, and in air moderately agitated. This was effected in the following- manner. The apparatus which were employed in the ex- periments on the hygrometric state of the air, served, at the same time, to prevent, as much as possible the agita- tion of this fluid. But since during confinement in a close vessel, the air is moistened by perspiration ; I compared the losses occasioned by perspiration in a vessel of dried' air, with the losses of animals of the same species, in the PERSPIRATION, OR EXHALATION. Ill open air of the room ; and I found that not only in mam- malia but in birds, the losses were greater in the latter case. Now, in consequence of the greater dryness of the air in the vessels, the perspiration ought to have been the more abundant ; but the slight agitation of the outer air was more than sufficient to counterbalance this effect. In comparing the foregoing results of experiments on the perspiration of warm-blooded animals with the correspond- ing cases of cold-blooded vertebrata, we observe a striking similarity in the effects produced by the same physical agents. This agreement tends to confirm both ; and the confirmation is the greater, as the animals which furnish them, present the greatest differences of structure in the scale of vertebrata. 112 PART IV. MAN AND VERTEBRAL ANIMALS. CHAPTER I. / ON THE MODIFICATIONS OF HEAT IN MAN, FROM \ BIRTH TO ADULT AGE. The results obtained in my experimental inquiries into the influence of physical agents on other warm-blooded ani- mals have been so uniform, that they may, by analogy, be extended to man, although he can scarcely be made the subject of the experiments themselves, and, for this reason, was not mentioned in the preceding part. Considered in reference to structure, man has been placed in the class Mammalia. Standing alone in the gift of intellect, he resembles other mammalia, in the effects produced on organization by phy- sical agents. His life, like theirs, may be endangered by mechanical forces, and his intellect merely enables him to resist those forces by means of others of the same kind. Like them, he suffers from the extremes of heat and cold, and would sink under them, if his intelligence had not discovered the means of setting their destructive influences in opposition to each other. He is not, less than they, subjected to the THE MODIFICATIONS OF HEAT IN MAN, &C 113 necessity of the constant contact and renewal of the air, without which, his life would be extinguished as promptly as that of other animals of the same class. He has no pri- vilege from his organization capable of removing him from the power of the physical laws which preside over the for- mation of vapours, and by virtue of which, a part of the water contained in his body is dissipated in the atmosphere. He has not a sensibility so peculiar, that the function by which the skin excretes upon its surface a part of the fluid, is uninfluenced, as in other mammalia, by the condition of the external temperature. As a species, man may be affected peculiarly as to de- gree, and in this respect he presents individual differences, or the same individual may vary at different periods of his life, but as to the manner in which he is affected, he comes within the group studied in the preceding division of this work, and the general truths there established must be equally applicable to him. We shall first consider how far the power of producing \ heat, is modified in man by the circumstance of age. y^ In treating of warm-blooded animals, we formerly ob- served, that those which are born with their eyes closed, when exposed to the air, in the spring or summer, lose their heat, almost as rapidly as cold-blooded vertebral animals ; while those whose eyes are open at birth, preserve, under similar circumstances, a high and constant temperature. In accordance with analogy, a new-born infant, born at the full time, will have the power of maintaining a pretty uniformly high temperature, during the warm seasons. If, however, birth takes place at the fifth or sixth month, the case is altered ; the pupil is in general covered by a membrane denominated membrana pupillaris; which cha- racter drawn, from the state of the eyes, may be considered equivalent to the closure of the lids. We should, from 114 THE MODIFICATIONS OF HEAT IN MAN, analogy, conclude that in such a child the power of pro- ducing heat would be very feeble. Let us now proceed to verify these conclusions by obser- vation. An infant born at the full period, and separated from its mother, if exposed to a moderate temperature, scarcely varies in its temperature. It is true that we cannot strip it of its clothes to judge of its power of maintaining warmth un- der a long exposure to the air, but I have already shown that this trial is unnecessary. Those new-born mammalia which cool in the air almost as cold-blooded animals would do, may in vain be well clothed. They cool, however, the more slowly for it. The new-born infant does not then belong to this group, confirming the conclusion drawn a priori from the state of the eyes. It remains still to be determined whether the human sub- ject at birth produces less heat than afterwards. We shall not, as in the case of inferior animals, expose individuals of different ages to an artificially reduced temperature, in order to ascertain their respective powers of producing heat, but, as substitutes for such experiments, shall employ observa- tions which will furnish satisfactory data. I have not considered slight differences in the temperature of animals as sufficient indication of a corresponding difference in their power of producing heat, and I have, therefore, had recourse, in the researches set forth in the third part, to the plan of artificially reducing the temperature. But, after having ascertained by this method that the young mammalia, which are born with open eyes, produce less heat than adults, we may take advantage of the observations made on their natural temperature. All the animals of this group, which I have examined, have at birth, and for some time after, a temperature inferior to that of their parents. I have observed in this respect a difference of one or two degrees centigrade, or from 1° 8 to 3° 6 of Fahrenheit. This, for FROM BIRTH TO ADULT AGE. 115 our present purpose, is an important index of the difference in the power of producing heat. If a similar difference exists in the human temperature at the two periods of life, we shall not hesitate to regard it as a proof of a difference in calorific power, like that which we have demonstrated with respect to other mammalia. The temperature of the adult man has frequently been taken, and as it varies in different individuals, it is impor- tant to ascertain its limits, and the average. It varies also in different parts of the body. In the mouth it is generally rather higher than in the external parts of the trunk, some- times to the extent of one degree (of the centigrade ther- mometer.) To establish, therefore, a comparison between the adult and the new-born infant, the thermometer should, in each, be applied to the same part of the body. In thus taking the temperature of twenty adults, it was found to vary from 35° 5 to 37° cent, or 96° to 98° Fahr., the mean being 36° 12 cent, or 97° Fahr., which agrees with the best observations. In ten healthy infants, from a few hours to two days old, in the wards of an hospital, under the care of my friend M. Breschet, the limits of variation were from 34° to 35° cent, or 93° to 95° Fahr. ; the mean of the whole number was 34° 75 cent, or 94° 55 Fahr. Their temperature is, therefore, inferior to that of adults ; a rela- tive difference rendered probable by analogy, and confirmed by observation. I should have laid no stress on so slight a disagreement, if numerous experiments on warm-blooded animals had not proved that this difference in natural tem- perature coincides with a difference in the power of produc- ing heat, at the different periods of life. Another analogical conclusion which I wished to verify related to the temperature of infants prematurely born. The facilities for doing so do not often occur, but through the kindness of Dr. Dagneau, who attended a lady who was i 2 116 THE MODIFICATIONS OF HEAT IN MAN, &C. my patient also, I had an opportunity of ascertaining the temperature of a healthy seven-months' child, within two or three hours after birth. It was well swathed, and near a good fire, but the temperature at the axilla did not ex- ceed 32° cent, or 89° 6 Fahr. Before the period when this child was born, the membrana papillaris usually disappears. If it had been born pretty long before the disappearance of the membrane, there can be no doubt from what has been above stated, that its power of producing heat would be so feeble, that it would scarcely differ from that of mammalia born with their eyes closed. 117 CHAPTER II. ON THE INFLUENCE OF COLD ON MORTALITY AT DIF- FERENT PERIODS OF LIFE. The preceding facts being established, let us now proceed to the consequences which flow from them. When the fa- culty of evolving heat is not the same, the vitality will be different. First, the relation to the external temperature will be changed. The need of warmth and the power of supporting cold cannot be the same where the internal source of heat has not the same activity. There is scarcely any agent which exerts a more powerful influence on life than the temperature of the atmosphere ; hence, its rela- tions are amongst those which it is the most important to know. There is, moreover, no agent which we have more in our power to modify and adapt to our necessities. When circumstances prevent our doing so, as when we are exposed to the open air, we have other resources to supply the deficiency. Hitherto our care in this respect has mere- ly been guided by instinct, or by that kind of observation which every body can make. But it requires a more inti- mate knowledge of our relation to the external temperature, properly to regulate the employment of means, expedient to protect us from the injurious influence of heat and cold. Let us first examine how far these relations vary accord- ing to the modifications dependent on age, as set forth in the preceding chapter. Instinct leads mothers to keep their in- fants warm. Philosophers by more or less specious reason- 118 THE INFLUENCE OF COLD ON MORTALITY ing, have, at different times and in different countries, in- duced them to abandon this guide, by persuading them that external cold would fortify the constitutions of their children, as it does those of adults. We will examine this question by the test of experience, in order to be governed by the observation of nature, rather than by the varying opinions of men. We shall begin with those young warm-blooded animals, which produce the least heat ; viz. mammalia, born with closed eyes, and birds hatched without feathers. They are, for the greater part of their time, secluded from the effects of external temperature, being warmed in their nests by contact with each other, and more especially with their mother. Under such circumstances, therefore, their heat cannot differ much from that of adults. But if ex- posed to the air in spring or summer, in the early stages of life, their temperature would not exceed that of the atmo- sphere by more than a very few degrees. This fact, though not amounting to proof, renders it probable, a priori, that the higher temperature occasioned by seclusion and con- tact with the mother is essential to the support of life. On 12th February 1819, a kitten, newly littered, re- moved from its mother, and exposed to the air, at the tem- perature of 14° cent, or 51° Fahr. being cooled down in nine hours to 18° cent, or 64° 4 Fahr. became stiff, and almost incapable of executing the slightest movements. The following month the air of the room being 10° cent, or 50° Fahr., I exposed two kittens, of one day old, and hav- ing a temperature of 37° cent. 98° 6 Fahr. In 2h. 25, the temperature of one was reduced to 17° cent, or 62° 6 Fahr. and that of the other to 18° cent, or 64° 4 Fahr. They had become stiff and almost insensible. In the month of January in the same year, four puppies, littered the day before, were of the temperature of 35° to 36° AT DIFFERENT PERIODS OF LIFE. 119 cent, or 95° to 97° Fahr. The air of the room was 1 1° cent, or 52° Fahr. The cooling which they underwent from nine in the morning till ten at night, lowered their temperature to 13° and 14° cent, or 55° 4 and 57° Fahr. They were then so enfeebled that they were almost motionless. The symptoms of weakness and suffering soon after the young animals are exposed to the air, increases as their temperature sinks. The same circumstances occur with those young birds which produce the least warmth when hatched. Although the diminution of temperature thus occasioned by exposure to the air, would ultimately prove fatal to these young animals, it is remarkable how long they are capable of enduring a considerable reduction of temperature. New- born puppies or kittens may live two or three days at a temperature of 20° cent, or 68° Fahr. and even 17° or 18° cent, or 62° 6 or 64° 4 Fahr. But the air must not be too cold, or they would soon be deprived of sense and motion, and in a short time this apparent death would become real. When they appeared on the point of expiring, I easily re- stored animation by placing them before the fire, or by im- mersion in a bath. These means, if promptly applied, may even prove effectual when they are quite motionless, and, to all appearance, dead. By the above facts we find that this group of young ani- mals, both birds and mammalia, support a considerable re- duction of their temperature, and may even be repeatedly exposed to this trial, provided that they be not left too long in the state of reduction, and that proper care be taken in the restoration of warmth. The exposure is, however, in- jurious to the animals, and if very often repeated, or too long continued, is fatal. This facility of recovery, after great reduction of tempera- ture, does not continue in the same degree with the progress 120 THE INFLUENCE OF COLD ON MORTALITY of life. I cooled artificially birds of various species, such as jays, magpies, orioles, &c. when they were almost entirely fledged. The temperature of some was reduced to 20° cent, or 68° Fahr., that of others to 18° cents, or 64° 4 Fahr. They had been exposed to the cold but for a short time. They were then very weak and seemed ready to ex- pire. However, they did not fail to recover as rapidly, and apparently as completely as younger birds, but this recovery was temporary ; they mostly died in one or two days. The reduction of the bodily temperature is, then, less injurious, in its permanent effects, in proportion to the youth of the animal. Now, there is here another relation which is deserving of notice ; we see that it is according as the power of developing heat increases, that of supporting a reduction of temperature diminishes ; and, to be con- vinced of the intimate connection between these two cir- cumstances, let us compare the adults of different groups of vertebral animals ; the cold-blooded animals, the hyber- nating mammalia, and other warm-blooded animals. In this arrangement they form a scale in which animal heat goes on increasing. Reptiles and fishes, at the bottom of the scale, are, as is well known, those which best support a reduction of temperature ; and the hibernating mammalia, inferior, with regard to temperature, to other warm-blooded animals, have, on the other hand, the advantage of being able to survive a reduction of temperature which would destroy the latter. In the same manner I have shewn that, in young warm- blooded animals, the capability of supporting reductions of temperature is inversely in proportion to their power of pro- ducing heat. I shall now point out the necessity for this. Whatever degree of care parents may take of their young, they cannot always remain with them in order to maintain their temperature at a high degree, if they are of that class AT DIFFERENT PERIODS OF LIFE. 121 of animals which are born with eyes closed, or without feathers. As soon as they leave them to provide subsis- tence, the temperature of their young begins to be reduced, and if this reduction were as injurious as it is to those animals which produce more heat, the greater part would perish. Other young warm-blooded animals are not exposed to similar reductions of temperature, because they are born with a more abundant source of heat. But if the external tem- perature were such that it lowered that of their bodies to the same degree, and as frequently, as with the groups of young animals above-mentioned, a much greater mortality would prevail among them. Hence the danger to which they would be exposed, if born in winter ; hence, also, may be perceived the end which nature had in view by generally avoiding their production in that inclement season. This is usually the case with wild animals which are born with the greatest development of heat. However considerable this may be, it would not enable them to support the cold of our climate in the early periods of life ; and as they are at the same time stronger, more active, and more indepen- dent, their mother could not secure them from the incle- mency of the air. They are usually born, therefore, in spring, or at the beginning of summer, during the fine weather. Their power of producing heat gradually in- creasing, they are more capable of resisting the severity of the succeeding winter. The following is a general review of the facts relative to the influence of cold, at the different periods of life. We must distinguish two things — the cooling of the body, and the temperature capable of producing it. The cooling of the body, without regard to its cause, is less in- jurious in proportion to the youth of the animal. Lower the temperature of two animals of the same spe- 122 THE INFLUENCE OF COLD ON MORTALITY, &C. cies an equal number of degrees, the younger will suffer less, and will recover more perfectly. But in order to lower the temperature of animals of dif- ferent ages, different degrees of external cold will be neces- sary, being lower, the nearer the animal is to adult age. If, on the one hand, young animals suffer less from the same reduction of warmth, on the other hand they cool more readily. It is on this last circumstance that the mortality in warm-blooded animals, at different periods of life, from birth to adult age, principally depends, so far as it is the result of the influence of external cold. 123 CHAPTER III. MOMENTARY APPLICATION OF COLD. Although animals previously exposed to cold may have regained their temperature, it does not follow that they still retain to the same degree the power of producing heat. If this be the case, on repeating the exposure to cold, about the same time will be sufficient to enable them to recover their temperature. But I have observed, in cool- ing and warming successively the same individuals, that the time required for the recovery of the original tempera- ture became longer by repetition, which proves that their power of producing heat was thereby diminished. With- out that knowledge of the facts which we have unfolded regarding animal heat, we might be tempted to attribute the continuance of the sensation of cold long after the cessation of its cause, merely to the natural duration of all strong sensations. But there is more than the prolon- gation of a strong impression, more than a simple affec- tion of the nervous system ; there is an alteration of func- tion, a diminution in the production of heat. In a severe winter, in which the Seine was frozen, a young man attempting to cross it, broke the ice and fell into the water, but being strong and active he succeeded in getting out. His health did not suffer, but for three days he had a continual sensation of cold. This case is analo- gous to those mentioned above. A potent chill acted on 124 MOMENTARY APPLICATION OF COLD. the faculty of generating heat, producing a sensible dimi- nution in it, greatly exceeding in duration the length of time in which the cold was applied. And even if the sensible heat were fully restored after such an exposure, its influence would not have been entirely at an end. The calorific function had not recovered all its lost power. We do not know at what interval one may again be ex- posed to a degree of cold, which might before have been tolerated without inconvenience. 125 CHAPTER IV. MOMENTARY APPLICATION OF HEAT. After an exposure to cold, sufficient to diminish the power of producing heat, continuance in a high tempera- ture tends to the recovery of this power ; for, in exposing animals to successive applications of cold, their temperature will fall the more slowly, the longer they shall have been subjected to the influence of warmth. It follows, therefore, that the effect of the application of a certain degree of heat is continued after the cessation of the cause, furnish- ing the counterpart of what we have stated with respect to the application of cold. Hence, we see that those who are liable to frequent ex- posure to severe cold, are rendered more capable of sup- porting it, by subjecting themselves, in the intervals, to a high temperature ; — a practice adopted by northern na- tions, and justified by the foregoing facts. Attention should be paid to this principle, that the transient applica- tion of heat occasions effects which are continued beyond the time of the application, and that it operates whenever the system stands in need of heat. Beyond this point other effects ensue which form the subject of the next chapter. 126 CHAPTER V. INFLUENCE OF THE SEASONS IN THE PRODUCTION OF HEAT. No phenomenon of heat discovered by the thermometer, has excited more astonishment than the uniformity of tem- perature maintained by man and the higher classes of auimals. — As soon as the formation of vapour was ascer- tained to be a cooling process, this principle was made use of, to explain the uniformity of animal heat. But although perspiration, by moderating the increase of heat has un- doubtedly some influence in maintaining a uniformity of temperature, yet there is another very important element which enters into the solution of the question. Warm-blooded animals may be divided into two classes, in regard to the influence of the seasons : viz. those whose constitution is perfectly in harmony with the cli- mate, and those whose constitutions are not adapted to it. The first undergo changes corresponding to the season, which allow them the free use of their powers, and that enjoyment of life which constitutes health. According as the temperature falls, their internal source of heat increases, until it attains its maximum in winter, and afterwards de- clines with the elevation and duration of the external tem- perature. Here, then, is a new element which should enter into the explanation of the uniformity of animal tem- perature. A balance is thus maintained between the heat INFLUENCE OF THE SEASONS, &C 127 coming* from without and that which is developed within, the excess of the one supplies the deficiency of the other. But the system only acquires this power of accommo- dating itself to the external temperature with the slow pro- gress of the seasons ; at least it is only thus that it is acquired in the highest degree. In summer, a degree of cold which we bear in winter, would take the body as it were by surprise and unprepared. The power of produc- ing heat being then reduced to its minimum, the loss would be insufficiently repaired. In this respect, our states in summer and winter differ in the same manner, though not in the same degree as young animals differ from adults. In the former, the increase of the power of producing heat takes place through the progress of organization whilst under the influence of a mild temperature ; in the latter by the influence of cold in degree and duration suited to their constitution. In the same way, the winter state being acquired, a transient elevation of the external temperature, if it be not excessive, has but little effect on the power of produc- ing heat, which continues to be developed in abundance. To reduce this power, without injury to the health, the heat must be raised slowly, and maintained during a long period. These changes do not however take place in all animals. There are some whose constitution is not adapted to so great a range of the external temperature. The cold which they can sustain without inconvenience is much less, be- cause they have not the same resources for repairing the loss of heat. When reduced below this limit a fall of tem- perature produces an effect the reverse of what has been above described ; instead of increasing the production of heat, it diminishes it. The type of such constitutions is exhibited in young warm-blooded animals and in hiberna- 128 INFLUENCE OF THE SEASONS IN ting mammalia. They present its operations in the most marked degree, but traces of them, whether found in man or in other warm-blooded animals, though more feeble, are not less truly of the same nature. When we look at the hiber- nating mammalia, with reference to their peculiarity of becoming torpid, it appears to separate them by an im- mense interval from other animals of their class, but when we consider them with reference to the function with which we are now occupied, and which seems to be ultimately connected with that peculiarity, we pass by insensible degrees to those mammalia which are in appearance the furthest removed from them. We have shewn that the hibernating mammalia occupy the lowest ranks in the scale of the production of heat amongst adult warm- blooded animals. We have made one group of them without distinction, because they present phcenomena in common — a like diminution in temperature, and a long- continued and profound torpor. — But they do not all exhibit these conditions to the same degree under similar circumstances. The unequal effects which the same de- gree of external temperature produces on the warmth of their bodies shew that the different species differ consider- ably in their power of producing heat. Amongst the spe- cies which I have mentioned, bats on the one hand, and marmots on the other, may be placed at the two extremes of the scale. Bats cool the most readily, they differ much from the species which immediately follow them, and a considerable interval exists between them and the marmots. There are some adult species of the class mammalia, which, though not passing the winter in a torpid state, closely resemble hibernating animals, in their feeble power of producing heat. Mice are of this number. On ex- posing these animals to a moderate cold in winter, I have been surprised at the reduction of their temperature, and THE PRODUCTION OF HEAT. 129 this circumstance served to explain to me the use of a very, singular habit among them. They make nests at all times, not for their young only, but for themselves. It is known that confined in small cages they do not propagate. I kept in this way some of both sexes and various ages, and observed them, in seasons when I should not have suspect- ed that they required much heat, carefully forming nests like those of birds. I placed near them bits of straw and flocks of cotton, which they pulled through the bars of the cage for this purpose. Thus we see that they seek to pre- serve the little heat which they develope, and which is ne- cessary to their existence, for, when exposed to the air they often perish from a degree of cold which, to us, would ap- pear moderate. In taking up their residence with man, they have not only the advantage of more abundant food, but also additional facility for guarding against the effects of cold. This fact leads us to recognise the group of warm-blood- ed adult non-hibernating animals, comprehending the species the least adapted to increase their calorific power, under the influence of the gradual reduction of the external temperature. Most of those animals which burrow or inhabit caverns, and crevices in rocks or holes, in walls or trees, are of this class. Other causes, doubtless, concur to in- duce the choice of these retreats, as the necessity of avoid- ing surprise and of finding a place of refuge, or for a store of provisions against a scarcity. And if they are sometimes chosen only as a magazine, they likewise serve as a pro- tection from the cold, which many of these animals cannot bear with impunity. This is particularly evident with those animals which carefully line their dwellings with materials suited for the retention of warmth. A similar difference of constitution prevails among men inhabiting the same climate. Some, and these constitute K 130. INFLUENCE OF THE SEASONS TN the majority, experience, a salutary effect from the gra- dual reduction of temperature, not from blunted sensibility, but from increased power of producing warmth. Others, not having the same resources in themselves to counteract the loss of cold which they undergo in winter, are obliged to have recourse to auxiliary means of protection from the effects of winter. There are some who regain their heat with difficulty, even when the cold is moderate, and they require a greater elevation of temperature in their rooms. This class is more numerous than is suspected. It is not confined to chilly persons; for the injurious effect of cold does not always manifest itself by the "painful sensation to which we give the same name : it may be indicated by very different sensations ; by various states of indisposition, pain and uneasiness, differing from the peculiar sensation gene- rally produced by exposure to cold. The absence of this sensation makes us mistake the cause, and consequently fail in applying the remedy. We have seen, from the experiments on warm-blooded animals, that the temporary application of cold acts upon constitutions of this kind, by diminishing the power of pro- ducing heat, and that this influence extends beyond the period of the cooling process. When, therefore, the ex- posure to cold is lengthened, the effects of each portion of time are added to those of the succeeding portions. Thus, individuals of this class, by the very duration of the same degree of cold, undergo a progressive diminution in their power of producing heat. This observation applies to a very remarkable pheno- menon presented by hibernating mammalia. Pallas informs us, in his excellent work on some new species of the family of dormice, that, the external temperature remaining the same, the torpor of these animals went on increasing with the du- ration of the cold. M. de Saissy has made the same ob- THE PRODUCTION OF HEAT. 13l servation, which I have also had an opportunity of verify- ing; but this effect is not unlimited. In like manner, the continuance of the same slight cold increases the power of producing heat in constitutions adapted to the climate, but this increase is necessarily limited. K2 132 CHAPTER VI. ASPHYXIA. We have already shown, by repeated observations, the in- timate connexion which subsists between the power of living for a time with a suspension of respiration and the power of producing heat. Accordingly we divided the young mammalia into two classes. First, Those which produce so little heat that they have, as it were, no temperature of their own. And second, those which produce enough to maintain a high temperature when the air is not too cold. The first live the longest without air ; the others for a short time. The ex- ternal character serving to indicate the class to which any given species ought to be referred, is derived, as has been observed, from the state of the eyes. Now the infant is born with its eyes open, and belongs to that class which produces most heat, from which we may conclude that it will, when deprived of air, live a much shorter time than animals of the first class. When we speak of the duration of life in asphyxia, it is important to recollect that we only judge by the outward signs which are manifested during the experiment. These signs consist in movements voluntary or involuntary; and when the animal no longer moves spontaneously, we try to excite these motions by pinching it. As soon as this means is ineffectual, we put an end to the experiment. There still, however, exist internal movements ; the heart ASPHYXIA. 133 continues to beat, but as we cannot excite visible move- ments and the animal does not spontaneously perform them, it is then in the state of apparent death. I shall not here treat of the duration of this state, nor of the conditions which limit it. It is a question connected with an other order of phenomena requiring distinct re- search, and must be reserved for another occasion. We shall confine our attention to apparent death in- duced by submersion in water. Whether the water be aerated or not, the effects upon mammalia are the same. The phenomena which they present are very different according to the period of the ex- periment. In the first moments, the motions are varied, repeated, continuous, and evidently voluntary ; the animals endeavour to rescue themselves from their painful situation; but soon voluntary motion ceases, and then there is evi- dently loss of consciousness. Up to this time the mouth remains shut, oris only accidentally opened. But after the animal has lost consciousness, the motions become involun- tary; at first suspended for a short interval, they are after- wards performed in an automatic manner, with a certain regularity in their motion and their action. Every part of the body participates ; the mouth opens wide, the chest ex- pands, the trunk bends forward, the limbs approach each other, the muscles relax, and the body becomes motionless. These motions are repeated in nearly the same manner till towards the close of the experiment. Then the trunk gradually ceases to bend, the limbs to be drawn together, the chest to be expanded, at least to a perceptible degree, but the mouth continues at intervals to open, though less widely than before, and this motion is the last to cease. It is remarkable that the voluntary motions are always of short duration, even in individuals which live the longest in asphyxia- Thus puppies, kittens, and rabbits, recently 134 ASPHYXIA. brought forth, although they live in that state for half an hour, commonly lose voluntary motion and consciousness in three or four minutes. The fact has repeatedly arrested my attention. Buffon was then deceived in his experiments on the sub- mersion of puppies, when he thought that they did not suf- fer from the suspension of respiration for half an hour. As they were in milk he was unable to see the phenomena which they presented. This celebrated naturalist was de- ceived by the facility with which the puppies were restored. The fact was, that involuntary movements not having ceased, respiration immediately went on in air ; yet one of the puppies which had been three times subjected to the trial died, not indeed immediately after the experiment, but the same day. We must here observe that puppies will exhibit signs of life during more than half an hour's submer- sion. I have seen them live under water fifty-four minutes, but this case is rare. If left in water until they no longer move, either of themselves or when excited, they would not be restored by exposure to the air ; at least I have never seen this take place either with them or any other species of mammalia. I offer this observation only incidentally, for it relates to the possibility of recalling life after appa- rent death ; a subject which I do not propose to treat of here. I shall merely add that man possesses one of the most favourable conditions for restoration by exposure to the air. From the description which I have given of the pheno- mena of life during submersion, we may easily judge whe- ther the means proposed by Buffon in the following pas- sage could obtain the end which he had in view in the repetition of the experiment. " I have not," he says, " pursued these experiments fur- ther, but I have seen enough in them to persuade me that ASPHYXIA. 135 respiration is not so absolutely necessary to the new-born animal as to the adult, and that it might perhaps be possi- ble, by proceeding carefully, to prevent, by these means, the closure of the foramen ovale, and produce excellent divers ; and species of amphibious animals, equally capable of living in air and in water." Let us suppose that the frequent repetition of submer- sion, commenced at birth, could preserve to the adult, the same mode of vitality which it possessed in infancy, and by which it was enabled to live a long time without breathing, it must have, to be a good diver, the use of its senses and voluntary motion : now, we have seen that the newly born mammalia generally lose consciousness in three or four mi- nutes, and that they have, in this respect, but little advan- tage over adults. I have often ascertained, at the swim- ming schools of Paris, the length of time that the best divers can remain under water, and have found three mi- nutes to be the utmost. There are, indeed, few men who are able to dive for so long a time. We have seen from the considerable power of producing heat which the infant possesses, that it belongs to that class which at birth are unable long to bear submersion in water. Warmth, whether produced in the system or derived from without, produces the same effects on the mode of vitality. There is no physiological character which more emi- nently distinguishes the cold-blooded from the warm- blooded vertebrata, than the great difference in the dura- tion of their life when deprived of air, but this character depends less on their own nature, than on the circumstances in which they are placed. We have seen that the batrachian reptiles can live two or three days in water deprived of air ; but under what circumstances does this happen ? This 136 asphyxia. long duration of life depends on two external conditions: 1st, That the water in which they are placed is at 0° cent, or 32° Fahr. or a very little above it ; and, 2dly, That the air shall have been, for a long time before the experiment, at nearly the same temperature, in order that the constitu- tions of the animals may have undergone a modification, dependent on this long duration of cold. (See the First Part, Chap. II.) If the same experiment be made in summer, and with water at 20° cent, or 68° Fahr. they live about an hour only, varying more or less, according to the degree of preceding warmth. We may see from this that they scarcely differ from some of the new-born warm-blooded animals, such as puppies, which, as I have shewn above, may live fifty-four minutes in water of the same tempera- ture. If instead of this degree, we raise the water to 40° cent, or 104° Fahr., the mean temperature of warm- blooded animals, batrachian reptiles plunged in it will not live longer than the adult mammalia. The same is the case with fishes, especially with those of small species. With others the difference amounts merely to a few minutes. Grey lizards, in the same circumstances, lived about six minutes. Hence we see that heat, whether internally or externally produced, has the same influence on the duration of life in asphyxia. With reference to the influence of cold, it is evident, that in experiments upon warm-blooded animals we cannot ob- tain results equally decisive with those derived from the cold-blooded vertebrata. In the first place, the mammalia and birds cannot, whatever may be their age, endure so great a reduction of temperature as reptiles and fishes ; and secondly, at an equal reduction of temperature, warm- blooded animals cannot, in general, remain the same length of time. From these considerations we should be led to conclude, that the hibernating mammalia which are sus- ASPHYXIA, 137 ceptible of a considerable reduction of temperature, and are also capable of living a long time in this state under the influence of a cold air, would bear a strong resemblance to reptiles and fishes in the power of living a long time with- out the contact of air. It is easy to foresee the probable duration of their life when they are deprived of air by sub- mersion in summer. Let .us recollect that in this season they have a high temperature like other mammalia, and that they have been subjected to the influence of this tem- perature for the whole course of the preceding fine weather. They will, therefore, be in the condition most conformable to the duration of life in asphyxia. I asphyxiated bats in water at 20° cent, or 68° Fahr., at a period when they were not torpid ; they lived only four or five minutes. Let us now change the conditions of the ex- periment ; let some hybernating animal have undergone the greatest reduction of temperature of which it is capable ; let it have lived a long time in this state, under the influ- ence of cold air ; it is easy to foresee that, participating then in the winter mode of vitality of the cold-blooded ver- tebrata, it will present analogous phenomena in the dura- tion of life, when deprived of air. Spallanzani furnishes us with some interesting facts, shewing the correctness of this conclusion. He placed in a receiver containing carbonic acid, at the temperature of 12° cent, or 53° 6' Fahr., a marmot completely torpid. It shewed no sign of uneasi- ness during the whole course of the experiment. Spallan- zani took it out at the end of four hours, without its having appeared to suffer from the ordeal, and certainly it would have lived longer if left in the gas. We may remark, in addition, that this gas is very deleterious, that it acts not merely by depriving the animal of the contact of atmo- spheric air, but also by a property tending to extinguish life. 138 ASPHYXIA. The facts just mentioned prove that temperature has a similar influence upon all the vertebrata, in prolonging or shortening the duration of life in asphyxia. The range of temperature at which these observations were made lies between 0° and 40° cent, or 32° and 104° Fahr. At the higher limit there is a remarkably slight difference in the times that the animals can live without breathing. It is at the lower degrees only that the differences become more decided, according to the species, and increase in proportion as we approach the inferior limit. Although the general influence of temperature as above stated, may be considered as demonstrated, it is by no means pretended that, amongst the complicated phenomena of life, other causes do not concur to modify the duration of life under privation of air. When an animal is cut off from communication with the air, as in submersion, the circulation continues, but the blood loses its arterial quality, and becomes venous. Does the circulation of this venous blood contribute to the sup- port of life ? In the first chapter of this work, this ques- tion has been decided in the affirmative, with regard to rep- tiles. Is it also the case in warm-blooded animals ? I made, with kittens, experiments similar to those related in the first chapter upon reptiles, and found that the kittens, whose circulation was prevented by cutting out the heart, when plunged in water, lived in general but a quarter of an hour ; whilst others, whose circulating system was left entire, gave in water, at the same temperature, signs of life for about half an hour.* In experiments upon adult warm-blooded animals, the influence of the circulation of venous blood cannot easily be seen, on account of the rapidity with which the privation of air causes apparent death, and renders it * Some experiments made on young rabbits by Le Gallois tend to the same conclusion. ASPHYXIA. 139 useless to endeavour to determine minute differences, which perhaps cannot be made perceptible ; but there can be no doubt that the circulation of venous blood contributes to maintain the life of those animals after the cessation of ex- ternal motion, and during that state which we call apparent death. These observations lead us to examine the function upon which temperature acts, according to its degree, so as to prolong or shorten life during asphyxia. We may suppose that temperature between 0° and 40° cent, or 32° and 94° Fahr. acts, either directly or indirectly, on the motion of the heart of asphyxiated animals. As we have proved that circulation contributes materially to pro- long the life of those animals which live long without air, it follows that the different degrees of activity of the heart may exercise different degrees of influence upon the duration of life. It is a fact that the rapidity of the heart is very differ- ent in animals plunged under water, according to the tem- perature of that liquid. In reptiles, as in young mammalia, it is slowest at 0° cent, or 32° Fahr. and very rapid at 40° cent, or 104° Fahr. We shall suppose that the degree of rapidity of the heart which is the best adapted to prolong the life of asphyxi- ated animals, is that which is determined by the tempera- ture at which they live the longest, and we shall inquire if this same temperature has not a special action upon the nervous system favourable to its functions ? I convinced myself of this in the following manner. Towards the end of December, the previous temperature having been very low, the hearts were taken from eight frogs. Four were placed in water at 20° cent, or 68° Fahr., and four others in water at the freezing point. The first set lived on an aver- age an hour and three minutes, the second eight hours and fifty-five minutes. Temperature, therefore, acts upon the 140 ASPHYXIA. frogs when circulation is destroyed, and which are, as it were, reduced to the exclusive action of the nervous system, in the same manner as in those whose circulation is in full activity. The hearts were cut out of three new-born kit- tens ; one was put in water at 20° cent, or 68° Fahr., ano- ther in water at 40° cent. 104° Fahr., and the third in water at 0° cent, or 32° Fahr. The first lived thirteen minutes and thirty seconds ; the second seven minutes; and the third i:ve minutes. Now these animals lived only by the nervous and muscular systems, and if we com- pare the result of these experiments with those related in Part III. Chap. IV. performed on animals of the same species, whose circulation was not destroyed, and which were placed in the same circumstances, it will be seen that the temperature exercised upon both an analogous influence. For it was in water at 20° cent, or 68° Fahr. that they lived the longest, much shorter at 40° cent, or 104° Fahr., and the shortest at 0° cent, or 32° Fahr. Temperature, there- fore, within these limits, exerts a direct influence on the vitality of the nervous system. 141 CHAPTER VII. ON THE MODIFICATIONS OF RESPIRATION DEPENDING UPON SPECIES, AGE, &C. If animals differ much in the duration of life, when the contact of air is cut off, they differ no less in their commu- nications with air by respiration. This pabulum vita is far from being consumed by all in the same proportion. We have given several examples of this in the Third Part of this wort, when treating of warm-blooded animals ; but the comparison of these vertebrata with others which breathe in air, presents differences much more considerable. Let us select them of about the same size, and at the period when the cold-blooded vertebrata enjoy all their activity. Place a frog upon an open-work partition, in a receiver containing a litre, or 61 cubic inches, of air, over a strong solution of pure potass, to absorb the carbonic acid produced by re- spiration ; do the same with a yellow-hammer of the same size ; the latter will live about an hour, the frog from three to four days. This great difference does not arise from the frog's being able, after having consumed all the air which can support respiration, to live long without that function. It breathes continually, as long as the air is respirable, and quickly dies, after it ceases to be so. It was shewn in the first part of this work, that these animals when de- 142 THE MODIFICATIONS OF RESPIRATION prived of the contact of air in summer, could not live above one or two hours. Neither does the great difference in the duration of life depend on the frog's being able to derive greater advantage from the air, by depriving it of its last particles of oxygen. . When the experiment is made, as mentioned above, by absorbing the carbonic acid as it is formed, the bird has the power of consuming a greater quan- tity of oxygen. So little of it remains at the end of the ex- periment, when the air is no longer capable of supporting life, that the proportions scarcely differ in the two cases. The enormous disproportion in the duration of life of the reptile and the bird, in equal quantities of air, essentially depends on the comparative rapidity with which they con- sume the air, that is admitted : but it may be well to fix our attention on some of the conditions of this difference. To consider only the lungs : it is manifest that the sur- face in contact with the air is more extended in the bird, not because the lungs are larger, but because the air-cells are more numerous. The extent and frequency of the re- spiratory motions are also an indication of the great quan- tity of air which enters the lungs of birds. Besides, it is known that their lungs contain much more blood, and it is principally to the blood that we attribute the power of alter- ing the air. All these conditions in favour of birds are to be referred essentially to multiplied communication with the air. They may be considered as physical data, since they consist in relations of quantity, but there are undoubtedly others of a different kind, which are of no less importance. If the blood have a great influence by its quantity, will it not likewise have by its quality ? Simple inspection may satisfy us that the blood of the frog is more watery than that of the bird. From this single difference must arise a different relation between the blood and the air, for no one will attribute the alteration of the air to the watery part of DEPENDING UPON SPECIES, AGE, &C. 143 the blood, but rather to the animal matter which it contains. Of this the proportion is necessarily less in the reptile. There is still another difference which is quite fundamental. The blood to the naked eye appears void of organization, but by the help of the microscope it has been long known to contain particles of a regular figure. According to the last researches of Sir Everard Home in England, and of Pre- vost and Dumas at Geneva, these particles always consist of a colourless spheroid, with a red covering.* Although these particles are elliptical both in the reptile and in the bird, they are of very different dimensions, being much larger in the former. Prevost and Dumas have given the measurements in their excellent treatise on the blood. Thus, the quality of the blood in the two species mentioned, differs essentially both in the number and the dimensions of the particles. The same conditions of organization which retard the consumption of air in the frog, as compared with the bird, exist in all reptiles and fishes. Mammalia clearly resemble birds in the quantity of air which they consume. This difference in the extent of re- spiration constitutes a remarkable distinction between the vertebrata, and distributes them into four groups ; one in- cluding reptiles and fishes, the other mammalia and birds. This division is also founded on another characteristic,which has given to the former the epithet of cold-blooded, and to the latter that of warm-blooded ; a confirmation of the * Prevost and Dumas have certainly given the best statement of the compara- tive dimensions of the particles of the blood in different animals, but their views as regards their form and structure are not confirmed by later observations made under far more favourable circumstances as respects the instrument employed. As far as the above remarks of Dr. Edwards are concerned, the correction is of no importance. Some account of the physical constitution of the blood will be found in the Appendix. 144 THE MODIFICATIONS OF RESPIRATION. opinion that there exists an intimate connection between the phenomena of the production of heat and the consumption of air. The following; facts tend to the same conclusion. Having ascertained that the mammalia which are born with eyes closed, and the birds which are hatched without feathers, bear a strong resemblance, in the early periods of life, to cold-blooded vertebrata, in the phenomena of animal heat, I was led by analogy to extend this resemblance to the consumption of air. Experiment has confirmed this opinion, and has shewn that the developement of heat in mammalia and birds goes on increasing with the consump- tion of air from birth to adult ao-e. Afterwards both these functions undergo variations according to the influence of the seasons. Those individuals which, by the successive reduction of external temperature, acquire the faculty of producing more heat, undergo, at the same time, a change of constitution which occasions them to consume more air. This is not the result of a difference in the rapidity of the movements of respiration, nor of variations in the density of the air, but of a change inherent in the animal economy. The contrary effect is produced by the slow but progressive elevation of the external temperature. There is a diminu- tion in the production of heat, and also in the consumption of air. These observations are only applicable to those indi- viduals which, among warm-blooded animals including man, support well the vicissitudes of heat and cold in the opposite seasons of summer and winter. The other individuals which we have pointed out as not seasoned to the climate, because their production of heat diminishes by the influence of the cold, would present the contrary phenomena. This is actually the case with the hibernating mammalia. M. De Saissy compared the respiration of the marmot, the hedgehog, the dormouse, and the bat in the waking state, in August and November. They consumed less air in the latter. 145 CHAPTER VIIL OF THE COMBINED ACTION OF AIR AND TEMPERATURE, It is easy, with some animals, greatly to vary their rela- tions with the air, without destroying their life, provided they are placed under favourable circumstances. We may avail ourselves of this in examining the influence which temperature exerts on life in those cases in which we vary the extent of respiration. In the first part of this work, many facts are stated upon which may be founded a knowledge of this influence. I shall here briefly reca- pitulate them, and add several others, that we may judge of its generality. We have demonstrated that several species of batrachian reptiles, such as the frog, the toad, and the salamander, can live under water by means of the air contained in it, and which acts solely on the skin. There is then no pulmonary respiration. The animal is reduced to cutaneous respiration, and even this is at its minimum, because of the very small proportion of air contained in the water. The air in this case must have a very feeble vivifying power, yet it suffices to maintain the life of the animal, so long as the temperature is be- tween 0° cent, or 32° Fahr. and 10° cent, or 50° Fahr. ; but if the temperature of the water be raised higher whilst the animals are restricted to the same limited respiration, the majority perish. To counteract the deleterious effects of this low degree of warmth, their relation with the air must be increased, its vivifying power will be augmented, L 146 Or THE COMBINED ACTION OF and life will be preserved. The animals cannot increase their relation with the air except by coming to the surface to exercise pulmonary respiration. It is by this means that they preserve the equilibrium between the effects of warmth and the influence of the air. When they are at liberty in the marshes, pools, and small streams, they can keep below the surface so long as the temperature of the water does not exceed 10° cent, or 50° Fahr. as is generally the case in autumn, winter, and the commencement of spring, but however little it exceeds this point, they are obliged to rise in order to draw air from the atmosphere. Having received its vivifying influence by an increase of respiration, they are again in a state to live under water, and this for so much the longer time as the water is less above 10° cent, or 50° Fahr., but in proportion as the tem- perature is raised their tarriance under water is shortened, and they come more and more frequently to the surface until a point is arrived at, at which they can scarcely sup- port the suspension of pulmonary respiration. There is another mode of respiration to which these animals are obliged to have recourse during the greatest heat of summer. Pulmonary respiration aided by cuta- neous respiration in water, is then unable to counteract the effect of the high temperature. They are obliged to quit the water to bring the skin into contact with the atmo- sphere. Without this resource they would die in great numbers. This is a necessary consequence of the relation between the effect of heat and the influence of the atmo- sphere. The following fact communicated to me by M. Bosc confirms what I have advanced. In one of our re- cent summers, remarkable for its long continued and in- tense heat, many frogs died in a pool in his nursery. The sides of the bason were too steep to allow of the frogs coming out of the water, and during the great heat they AIR AND TEMPERATURE. 147 were unable to counteract its influence either by cutaneous respiration in air, or by the cooling power of evaporation. The combined effects of temperature and air are the same with fishes. Fish in winter can live under water without coming to the surface to breathe. Different species, according to their sensibility to heat, are obliged, as the temperature rises in spring and summer, to increase their relation with the air, by coming frequently to the surface, to breathe the atmosphere. As this is generally the limit of their respiration, they die in great numbers if the heat of the season be intense. But those species which suffer the least by evaporation in air, find the means of support- ing this heat, by for a time exposing the skin and bronchiae to the vivifying action of the air. Thus we may sometimes see certain species keep in the shade, with the greater part of their bodies out of water, resting on the leaves and stalks of $he water-lilly, or quitting their own element to throw themselves on the banks. They are then entirely exposed to the action of the air, and breathe like land animals. The preceding cases are complicated with the substitu- tion of another medium, the influence of which upon the animal economy, may at equal temperatures be very dif- ferent ; and in fact it is so, independently of the effect of evaporation in air, but it will be seen, by the following ex- periments in which this complication does not exist, that this effect is only an accessory. The batrachians can live in air with the action of the lungs suppressed. It has been shown in a preceding part of this work, that frogs deprived of their lungs have survived a long time in air, by cutaneous respiration alone, provided the necessary precautions are taken to preserve their humidity. They live in this way in winter, and when the temperature is low; but if the action of the lungs l 2 148 OF THE COMBINED ACTION OF is suppressed in this way in summer, they die almost as quickly as when entirely deprived of the action of the air by submersion in water. The vivifying action of the atmosphere, on the skin is too feeble to counteract the deleterious influence of the summer heat. Observe too that they have the assistance of a more active evaporation to cool them ; but this advantage is insufficient. It is essential that they should increase their relation with the air, by means of the lungs, in order to bear this high temperature. The same relation between the combined effects of heat and air is observed when different means are employed to limit respiration. A solid but porous envelop lessens the contact with the air, yet frogs have lived for a considerable time buried in plaster, (see Part I. Chap. 1.) Those expe- riments were made in winter, and the animals bore this limited respiration, because the temperature was low. The case is different in summer ; I have then known them die when similarly enclosed, almost as quickly as if they had been plunged under water. If at this season sand be used instead of plaster, they can live a much longer time, because the sand admits more air. There can be no doubt that the relation between heat and respiration extends to warm-blooded animals. An observation of Legallois furnishes a proof that it holds in the case of young mammalia. The cutting of the eighth pair of nerves produces, along with other phenomena, a considerable diminution in the opening of the glottis, so that in puppies recently born, or one or two days old, so little air enters the lungs, that when the experiment is made in ordinary circumstances, the animal perishes as quickly as if it was entirely deprived of air ; it lives about half an hour. But if the same operation be performed upon puppies of the same age benumbed with cold, they AIR AND TEMPERATURE. 149 will live a whole day, In the first case, the small quantity of air is insufficient to counteract the effect of the heat, but in the other it is sufficient to prolong life considerably. We shall now apply this principle to adult age, and particularly to man. A person is asphyxiated by an ex- cessive quantity of carbonic acid, in the air which he breathes ; the beating of the pulse is no longer sensible, the respiratory movements are not seen, his temperature how- ever is still elevated. How should we act, to recal life? Although the action of the respiratory organs is no longer visible, all communication with the air is not cut off. The air is in contact with the skin, upon which it exerts a vivifying influence ; it is also in contact with the lungs, in which it is renewed by the agitation which is constantly taking place in the atmosphere, and by the heat of the body which rarifies it. The heart continues to beat, and maintains a certain degree of circulation, although not perceptible by the pulse. The temperature of the body is too high to allow the feeble respiration to produce upon the system all the effect of which it is susceptible. The tem- perature must then be reduced, the patient must be with- drawn from the deleterious atmosphere, stripped of his clothes, that the air may have a more extended action upon his skin, exposed to the cold, although it be winter, and cold water thrown upon his face until the respiratory movements reappear. This is precisely the treatment adopted in practice to revive an individual in a state of asphyxia. If instead of cold, continued warmth were to be applied, it would be one of the most effectual means of extinguishing life. This consequence like the former, is confirmed by experience. In sudden faintings, when the pulse is weak or imper- ceptible, the action of the respiratory organs diminished, and sensation and voluntary motion suspended, persons 150 OF THE COMBINED ACTION OF AIR, &C. the most ignorant of medicine are aware that means of re- frigeration must be employed, such as exposure to air, ventilation, sprinkling with cold water. The efiicacy of this plan of treatment is explained on the principle before laid down. Likewise in violent attacks of asthma, when the extent of respiration is so reduced that the patient experiences suffocation, he courts the cold even in the most severe weather, he opens the windows, breathes a frosty air, and finds himself relieved. 151 CHAPTER IX. EFFECTS OF TEMPERATURE UPON THE FUNCTIONS OF RESPIRATION AND CIRCULATION. The organization of the vertebrated animals which breathe in the atmosphere furnishes them with several means of quickly modifying their communications with the air. These consist principally, in the first place, in the move- ments of the thorax and abdomen, and in the second place, in those of the heart and blood-vessels. The former are the movements concerned in respiration, the latter in cir- culation. It is rare that one set is accelerated or retarded without being accompanied by a corresponding change in the other. Every body knows that the will can retard, accelerate, or stop the respiratory movements, but it rarely takes any part in them. They are determined by another force which keeps up and controls them. Throughout life they pro- ceed, except under particular circumstances, without our being conscious of them, and when the will occasionally interferes, it only does so for a few moments. They habit- ually proceed at a regular rate, the same number of move- ments being produced in certain intervals. This rhythm is maintained with very little variation so long as the system and external circumstances remain the same. This observation is applicable to all the vertebrata which breathe air. 152 EFFECTS OF TEMPERATURE UPON THE Let us study the relations according to which the respiratory movements are affected by external tempe- rature. We know that elevation of temperature accelerates their movements. It is a general phenomenon, but the degree of temperature necessary to produce this effect is not the same for all. From what has been already said, we may comprehend the advantage of this acceleration, which rarely takes place to a very sensible degree, except when the heat is oppressive or very distressing. We then extend our re- lations with the air, and increase its vivifying influence. The respiratory movements become more rapid or more ex- tensive, and thus more air comes in contact with the lungs in a given time, and reanimates what the heat depresses. From this increase of the respiratory movements necessary to counteract, at least for a time, the effects of external temperature, arises an order of phenomena different from those of health, and which characterize a peculiar type of fever. There is a certain range of moderate temperature within which the respiratory movements vary but little. This range is of greater or less extent according to the constitu- tion of the individual. We have shewn the effects of tem- perature exceeding the superior limit ; we shall now pass to the effects of temperature reduced below the inferior limit. These effects are not, as in the preceding case, uni- form in all the vertebrata. Cold, when it influences the respiratory movements of reptiles, retards them progres- sively, according to its intensity, until it arrests them. Life then is ready to be extinguished. If, whilst respira- tion is diminished by the cold, the heat of those animals could maintain itself, life, with the greater part, would soon be extinguished. But reptiles conform very closely to the external temperature ; and the diminution of their FUNCTIONS OF RESPIRATION AND CIRCULATION. 153 heat co-operates with that of their respiration for the pre- servation of their life. When the cold descends below the point at which respi- ration ceases, it becomes destructive. To prevent death without changing the external temperature, it is necessary to increase the action of the air, which cannot be done but by increasing the respiratory movements. Reptiles, how- ever, do not appear to have such a resource in themselves, though we shall see that there are animals which have. Among mammalia, the hibernating animals present such a series of phenomena. In spring and summer their tem- perature is high and their respiratory movements lively, as in other animals of their class ; in the decline of the year, their temperature and motions are observed sensibly to di- minish, provided the observations are made at sufficiently long intervals. This simultaneous decrease may go on until the cessation of the respiratory movements, without putting a stop to life. But if the cold becomes more in- tense, the animal must perish, or extend its relations with the air. The intensity of the cold, under which it is ready to sink, excites the respiratory movements ; the air inspired maintains them, at least for a time, and counteracts the destructive influence of the temperature. Thus, cold may either retard or accelerate the respiratory movements, according to its intensity and the constitution of the animals. We have just seen that it is the most in- tense cold which produces this last effect upon hibernating mammalia. However slightly the young of warm-blooded animals may be exposed to cold, it accelerates the respiratory movements or increases their extent. This phenomenon is very remarkable in those which are born without the power of maintaining their temperature in the open air. They, but more especially young birds of this description, are no 154 EFFECTS OF TEMPERATURE UPON THE sooner exposed to cold than their respiration increases in rapidity or extent, and their temperature begins to fall. No doubt they experience a lively sensation of cold, not- withstanding the warmth of the season — their whole being- indicates it. They present the phenomena of an attack of febris algida, and this state is quickly fatal if not remedied by renewing the heat of the body. Although the acceleration of respiration is a powerful means of coun- teracting the effects of cold, by extending the contact of the air with the organs best adapted to feel its vivifying influence, this acceleration has its limits ; it may diminish, but cannot compensate for the effects of excessive cold. In this case it retards, but does not prevent, death. In other circumstances, when the cold is more moderate, this vis conservatrix may prove effectual. The word cold is here used in its strictest sense, but refers to temperatures to which do not ordinarily suggest that idea. The words heat and cold, as is well seen in this instance, are com- pletely relative when applied to the animal economy. Let us follow these young animals in the progress of life. The same temperature less and less affects the respiratory movements, until at length it has no influence over them : consequently, in adult age, the rapidity of their movements is much less subject to the influence of external tempera- ture. But whatever be the extent of the range in which the movements of the thorax preserve the characteristic type of health, there is a degree of cold which alters them. In all the experiments which I have made upon the refri- geration of adult warm-blooded animals which are not sub- ject to hibernation, I have remarked an acceleration of the respiratory movements until, the powers being exhausted, these movements, like all the others, languish and fail. I do not doubt that there are cases in which an abatement of respiration takes place with these as with the hi- FUNCTIONS OF RESPIRATION AND CIRCULATION. 155 bernating mammalia, but we cannot now enter into this enquiry. We have said that there is a range of temperature within which variations scarcely influence the rapidity of the re- spiratory movements, and that this latitude is greater or less according to the constitution of the animal. Now this is a relation which it is of importance to understand with the greatest possible precision, because, if we know the kind of constitution which in the variations of external temperature more or less preserves that rhythm of the re- spiratory movements which characterizes health, we should be better able to maintain it, or when it is deranged by this cause, to re-establish it. We have seen that mammalia and birds are more affected in this respect by external temperature, in proportion to their youth. Now the most important modifications of functions which characterize the differences of age in the animals of these two classes, are those of the production of heat and the extent of respi- ration. It is with the development of these two functions that we see a diminution of the influence of external tem- perature upon the respiratory movements. This corre- spondence exists even in those cases where there is no difference of age. We may be convinced of this by com- paring, at their birth, the mammalia which are born with closed eyes to those which are born with their eyes open. It is the same in adult age : thus the hibernating mam- malia, which produce less heat and consume less air than the other mammalia, experience a sensible alteration in their respiratory movements, from a degree of cold which would have no effect upon the rhythm of respiration in others. It follows from these facts, that when an individual ex- periences a change of constitution which diminishes his production of heat or consumption of air, he cannot endure 156 EFFECTS OF TEMPERATURE, &C. that degree of cold which previously would have been salu- tary to him, without experiencing sooner or later an altera- tion in the rate of his respiratory movements. Hence the necessity, when these two functions have experienced this alteration, as in cases of organic affection of the heart and lungs, of placing the patient in communication with a milder temperature, either artificially or by change of climate. 157 CHAPTER X. INFLUENCE OF THE RESPIRATORY MOVEMENTS ON THE PRODUCTION OF HEAT. In studying the influence of the respiratory movements on the production of heat, we must confine ourselves to the mammalia and birds; because reptiles produce too little heat to enable us easily to appreciate the causes which modify it. When we see the diminution of the temperature and of the respiratory movements of hibernating animals take place at the same time under the influence of cold, we can draw no conclusion from it in reference to the subject be- fore us, since the cold is the cause of both phenomena. In like manner, when we remove one of those animals from the place where he has been benumbed into a warmer situ- ation, his respiration is accelerated, and his temperature rises, under the same influence of external heat. But there are other facts relative to those animals, in which we recognize the influence of the respiratory movements in the elevation of heat. I shall quote the experiments of M. de Saissy. The air of the room was 1° 5 cent, or 3° 7 Fahr. below the freezing point. The temperature of a bat profoundly torpid was at 4° cent, or 39° Fahr. M. de Saissy irritated it by mechanical means, and left it exposed to the same temperature at which it had become torpid. It was an 158 INFLUENCE OF THE RESPIRATORY MOVEMENTS hour in awaking; thirty minutes after, its temperature was 15° cent, or 59° Fahr., and in thirty minutes more 27° cent, or 80° 6 Fahr., but it could not pass this limit. A hedge-hog, equally benumbed, in the same place was only 3 cent, or 37° 4 Fahr. He was excited in the same manner. lie did not awake for two hours. His tempera- ture was then 12° 5 cent. 54° 5 Fahr. ; an hour after, 30° cent. 86° Fahr. : it rose afterwards only 2° cent. 3° 6 Fahr. in the same interval, and then remained stationary. In the same circumstances, a dormouse cooled to the same degree was stimulated in the same manner. In an hour, its temperature was 25° cent. 77° Fahr., and in the same space of time, the animal had recovered its natural heat, 36° cent. 97° Fahr. In these experiments, the external temperature had no- thing to do with the restoration of the animal heat, and we shall see by the following experiments of the same author that the means of mechanical excitation had no perceptible share in its production, except by exciting respiration and circulation, thereby showing that the increased respiratory movements and the restoration of heat stand related as cause and effect. On the same day and hour when M. de Saissy performed the experiments above mentioned, he placed in a window exposed to the north, with the precautions necessary not to arouse them, another hedge-hog and dormouse, whose tem- perature was 4° cent. 39° Fahr.,while that of the atmosphere was 4° below zero cent. 25° Fahr. The respiratory move- ments were very feeble. The dormouse awoke a little more slowly than in the preceding experiment, and ran into his cage with agility. In the first hour from his exposure to the cold, his temperature, like that of the other dormouse, rose to 25° cent. 77° Fahr., and at the end of the second, to 36° cent. 97° Fahr. The hedge-hog awoke two hours and ON THE PRODUCTION OF HEAT. 159 a half after the commencement of the experiment, when his heat had only risen to 12° cent. 54° Fahr. At the end of five hours, it was 28° cent. 82° Fahr. In this new set of experiments, it is evident that the cause which produced the awakening was not of a nature to contribute directly to the production of heat. If a mo- derate cold may favour it, as we have shown elsewhere, a more severe cold has a contrary tendency. In this instance the intense cold produced an impression sufficiently power- ful to be perceived in spite of the torpor, and excited to more extended respiration. We recognize in this chain of phenomena a striking ex- ample of that vis conservatrix of which so much has been said, and which in general has been perceived rather than distinguished. We shall have on more than one occasion to specify the means which nature employs to contend against the agents which threaten life. But the cause which has excited the movements of these animals is not adequate to maintain them. They pro- duce too little heat, even in expending all their resources, to resist for any length of time the temperature which has momentarily stimulated them. The cold which has roused them withdraws too rapidly the heat springing up under the influence of respiration and circulation, to allow the play of these functions to continue ; their temperature quickly sinks, and they relapse into a lethargy which be- comes fatal from the intensity of the cold. This is not the case when, in a moderate cold, they are excited by mechanical means : after having recovered more or less heat, according to their power of producing it, they return to their original state, from which they may again be excited. In these observations on hibernating animals, the respi- ratory movements, at first very feeble and scarcely percep- 160 INFLUENCE OF THE RESPIRATORY MOVEMENTS tible, progressively increase to the degree of rapidity and extent which they have in the natural state.* The ques- tion now is, what is the influence of these movements on the temperature of the body, when they are raised beyond the rate of health ? We cannot answer this enquiry by observations made on the sick. The circumstances are then too complicated to admit of even drawing conclusions from them : we must seek our examples amongst healthy animals, whose consti- tutions and the modifications which they undergo from the circumstances in which they are placed, are not unknown to us. We have said that young birds collected in their nest have a high temperature, although they have then few, if any, feathers, but that their temperature falls as soon as they are exposed to the air. In the first days after they are hatched, their cooling in such a case is constantly pro- gressive until the limit at which the cold benumbs them. Whatever be the modifications of their respiratory move- ments, this effect always takes place, and it is not at this period that we can discern the influence of respiration upon temperature : they then produce so little heat, that no ef- fort of their organization can rescue them from the succes- sive reduction of their temperature ; but some days later, when they develope more heat, we frequently recognize by unequivocal indications that the acceleration of respiration beyond the rate of health is a salutary re-action to increase the heat of the body, and counteract the influence of the cooling process. The following experiments will show the result of observations on several individuals very near the age at which they can maintain their own temperature in * The acceleration of the respiratory movements does not always stop at this limit ; but in these irregular movements, we cannot distinguish the phenomenon which we have next to examine. ON THE PRODUCTION OF HEAT. 161 the air. One of them had a temperature of 40° cent. 104° Fahr. and 97 inspirations per minute. Taken from the nest, and exposed to the air of the room, which was at 18° cent. 64° Fahr., he lost 3° cent. 5° 4 Fahr. in a quarter of an hour : his respiration, however, had been accelerated. They rose to 120 inspirations per minute, which rate was maintained for twenty minutes. He was then warmed half a degree ; some time after he cooled again, but his respira- tion, which had become a little less frequent, acquired ex- tension ; his heat was restored to the same degree, and continued so for some time. Another had a temperature of 38° cent. 66° Fahr. and 84 inspirations per minute ; a quarter of an hour after his exposure to the air, he lost three quarters of a degree cent. 1° 3 Fahr., his respiration had risen to 108 inspirations, and continued at this rate; examined at the end of an hour, he had recovered his ori- ginal temperature. Lastly, in another, the respiration was accelerated, and his temperature, instead of falling, rose one degree. Here, then, are several cases in which the acceleration of respiration above the type of health may have a sensible ef- fect upon animal heat. In the first, the temperature of the body falls under the influence of the cooling cause ; but by the re-action in question, it rises a little, without, how- ever, being restored, and may afterwards fall lower, pre- senting fluctuations. In the second it diminishes, and af- terwards returns to the point of departure. Lastly, in the third, it does not fall, and can not only support itself, but even rise above what it was at first. From the foregoing facts, it follows, that in the cases in which the temperature of the body progressively falls, not- withstanding the acceleration of respiration, the effect of this acceleration is limited to a retardation of the cooling process. M 162 CHAPTER XL ON PERSPIRATION. Perspiration in the human subject has long been an object of multiplied researches. Sanctorius was occupied with it when experimental philosophy was yet in its in- fancy. From the small quantity which sensibly escapes in the form of sweat, no conception could be formed of the considerable amount actually lost by perspiration in the condition of imperceptible vapour. It was this quantity which Sanctorius determined, and when he announced that five-eighths of our ingesta escape in this form, he must doubtless have excited either astonishment or incredulity. He occupied himself during many years in determining, by the help of scales, the variations in the quantity of per- spired matter and the relations which they bear to the food, the alvine and urinary evacuations and other percep- tible secretions ; to the states of sleeping and waking, of exercise and rest, of ease and of suffering, of sickness and health ; to the passions, and to the periods of day and night. These are relations which, with proper precautions, he might determine with precision ; but from the state of science at the time when he lived, he had not equal facili- ties with respect to the action of external agents ; he has therefore said little on the subject, and that little is either vague or erroneous. It is more surprising that, as the in- ventor of statical researches, he has furnished so few ON PEKSPIRATION. 163 numerical reports, and still more wonderful that many of his aphorisms are founded on reasoning rather than on the use of the scales, even in those cases in which the informa- tion could only be obtained by weighing. Sanctorius, however, opened the path, and for this he deserves the tri- bute of our gratitude. His successors have furnished more positive data. Keill, Lining, Rye, Robinson, &c, have published their results in the form of tables, the only sure mode of enabling us justly to appreciate general proposi- tions by shewing what is founded on fact and what merely the produce of the imagination. All these labours princi- pally relate to some of the subjects mentioned above, in speaking of the researches of Sanctorius. Our object, on the other hand, has been to examine the influence of most of the external agents on the perspiration of vertebrated animals. We shall apply to man the general facts which result from these experiments ; we shall compare them with the statements of those who have been engaged in statical researches on perspiration ; and we shall enter into the de- velopment of several points which we have reserved for this (the fourth) part. We found it necessary to begin by determining the rate of perspiration in equal and successive periods, first examining them from hour to hour, whilst ex- ternal circumstances continued sensibly the same. It was shown by experiments on both cold and warm blooded vertebrata, that the losses varied considerably from hour to hour. The statical experimenters have paid little atten- tion to this subject, but the fact is supported by the fol- lowing remark of Sanctorius, " Non qualibet hora corpus eodem modo perspirat." We have seen, that with the inferior animals this fluctu- ation disappears when longer intervals of time are em- ployed, and that a successive diminution of the loss by perspiration takes place at intervals of two, six, or nine m 2 164 ON PERSPIRATION. hours. If a diminution is effected in the shorter interval, a fortiori it must take place in the longer. The average of six hours will include almost all cases. The uniformity of this phenomenon in the vertebrata is a sufficient ground for admitting it in man, even though no observations had been made on this point. Thus, taking man, on getting up, in the state of health, and in circumstances exercising no sensible influence on his perspiration, whatever may be the fluctuations from time to time, we may regard them as uniformly diminish- ing in each succeeding period of six hours. In some it may be presumed that longer periods will be necessary ; nine hours ought to admit few exceptions. In some indi- viduals again, successive diminution of perspiration may be observed in periods of three hours ; this I should con- sider as the minimum. We shall infer, from what has been said, that the period of the greatest perspiration, when no obstructing cause exists, is, in general, from the hour of rising in the morning, say six o'clock, till noon, and that the losses are successively less in similar intervals for the remainder of the twenty-four hours. To secure this regular course, it will readily be imagined that it is necessary not only to remain quiet, but also to abstain from food and sleep ; a condition which was pro- bably not fulfilled by those who have hitherto made sta- tical observations upon man. Nevertheless, it may be in- ferred from these experiments that periods of six hours are as applicable to men as to other animals. Section I. — Influence of Meals. The influence of meals requires particular examination, the more so because it has rendered complicated the inves- ON PERSPIRATION. 165 tigations of Sanctorius, Gorter, Keill, and others, as to the period of most abundant perspiration. But for this com- plication their results would, there is no doubt, have been more accordant. In taking food, new materials for perspiration are fur- nished : but when does the food begin to have this effect so as to augment the perspiration ? I shall propose ano- ther question, which may appear strange to those who have not had their attention turned to the subject. For some hours after the meal, would not perspiration be di- minished ? Sanctorius, in one of his axioms, has asserted that perspiration is very slight for three hours after a meal, but it is probable that the theoretical reason which he as- signs for it, viz., that nature is too much occupied with digestion to be engaged with perspiration, misled his judg- ment, and induced him to generalize too hastily ; for we may infer, from other parts of his work, that he had fre- quently ascertained perspiration in such cases to be very abundant. I shall content myself with a single aphorism, Hord dormitionis meridiona. a cibo corpora aliquando libram aliquando selibram excrementorum occulte perspirabilium ex- cernere solent. Keill, who has made comparative observations upon per- spiration before and after dinner, has given us numerical results, from which it appears that it was not less abundant during the process of digestion. The experiments of Do- dart and others confirm these conclusions, and even go beyond them. I do not, however, maintain that perspiration is necessa- rily more abundant, but only that it is not necessarily di- minished, and that if, as I have no doubt, it is sometimes less at this period, it must be attributed to the fluctuation which takes place when the periods of comparison are too short. 166 ON PERSPIRATION. There must, however, be limits within which we may observe an increase of perspiration from the influence of food. The following are the conditions necessary to render the experiments comparative and the results conclusive : 1st. They ought to be made at the same hour, that the system may be as much as possible in the same disposition to perspire. 2dly. The space of time during which the perspiration goes on ought to be sufficiently long to obviate the influ- ence of the fluctuations so often referred to : it ought to be six hours. These conditions appear sufficiently united in the researches of Sanctorius to allow us to receive his data. He expresses them in a general manner, in the 326th aphorism : Qui vacuo ventriculo it cubitum, ea node tertiam partem minus more solito cir titer per spir at. We may be certain that this is not a hasty conclusion from two small a number of experiments. He recurs to the same subject in different places in which he gives the quantities lost in both cases. The numbers and the pro- portions differ, which evinces that he made repeated ex- periments, and that the desire of uniformity did not in this instance hurry him into premature generalization : in- stead of a third, he frequently found more than twice that difference. In some instances the quantity lost by perspiration after supper was not greater than when the individual retired supperless. We must, however, conclude from the aver- age, and remember that there are other causes which affect the perspiration. The night, in the researches of Sanctorius, is a period of seven hours ; and as the increase of perspiration from the influence of food was considerable, we may reduce to the limit of six hours, the interval in which we shall recognize ON PERSPIRATION. 167 this effect. We cannot appreciate this influence by ob- serving the amount in similar periods before and after a meal. Section II. — Influence of Sleep. In order to judge of the influence of sleep we must com- pare it with the state of watchfulness during the same period. It is only in Sanctorius and Keill that we find obser- vations which can furnish data on this point. Both in- form us in their aphorisms that perspiration is diminished during restless nights spent in frequent tossing in bed. It is evident that they compare a night of wakefulness with a night of sleep. Sanctorius returns so frequently to this subject, that he must frequently have observed the relative influence of sleep and sleeplessness. We may draw the same conclusion from the aphorisms in which he speaks of perspiration during the day-sleep or siesta. I have had sufficient occasion to observe this tendency of sleep to increase perspiration, though I have not ascertained it by statical experiment ; I have frequently observed upon children of different ages, in good health, and fast asleep, a degree of perspiration which astonished me when com- pared with the temperature of the air or the thickness of the bed-clothes. I am satisfied that it was not an acci- dental effect, but an habitual tendency of sleep. We may at any rate consider it as certain that perspiration during sleep and in a state of health may be increased indepen- dently of the action of external causes. It is necessary to be aware of the natural variations in perspiration during the twenty-four hours, and of the manner in which they are influenced by food and sleep, in order to estimate the power of other causes which operate on the perspiration. 168 ON PERSPIRATION. Section III. — Influence of the Hygrometric State of the Air. In applying to man the results of the experiments made on the vertebrata, we should say that the relative condi- tions of dryness compared to extreme humidity, consider- ably increases the perspiration within certain limits of temperature. This qualification is indispensable to ren- der the proposition correct. We shall afterwards see the reason, and the facts upon which it rests. I may add that the individual ought to be in health and in that ordi- nary state of perspiration in which it is insensible ; in this case, moderate degrees of dryness may render the losses of weight by perspiration six or seven times greater than in the cases of extreme humidity, and even go much farther. The temperature at which these experiments were made did not exceed 20° cent, or 68° Fahr. The greater amount of perspiration in dry than in damp air does not take place at all temperatures. The phenomena are reversed at a high external temperature. We may see from this that perspiration is a complex function, partly physical and partly vital. There is one circumstance accompanying the increase of perspiration in dry air which deserves examination. It is well known that evaporation cannot be increased without producing cold ; all water which is converted into vapour requires a certain quantity of heat proportionate to the quantity evaporated. We learn that cold tends to dimi- nish the loss occasioned by perspiration. Now, notwith- standing the refrigeration caused by evaporation, the losses by perspiration do not fail, with the qualification respecting external temperature above referred to, to be greater in dry than in damp air. The authors who have made re- ON PERSPIRATION 169 searches respecting the perspiration of man have no diffi- culty in admitting that it is increased by the dryness of the air ; notwithstanding the complication of circumstances in which their observations have been made, they have re- cognised this effect. Section IV. — Influence of the Motion and Rest of the Air. Gorter, although he has paid more attention than other observers to the hygrometric state of the air, and has at- tributed the increase of perspiration in dry air to increased evaporation, has by no means fully appreciated the power of this cause. Where the states of motion and rest are concerned, he only considers the cooling effect produced by the successive changes of the air heated by the body, and concurs with the aphorisms of Sanctorius respecting the diminution of perspiration by the movement of the air. This is evidently not the result of experiment but of erro- neous reasoning. The atmosphere which surrounds the body is not only warm, but humid. That which replaces it is colder, but at the same time drier. It is well known that a current of air, independently of any other difference, may in proportion to its rapidity produce an almost indefi- nite increase in evaporation. In other parts of this work, it has been established, by direct experiments, that the motion of the air uniformly tends to increase insensible perspiration. This cause is so power- ful, that differences in the motion of the air, which appear very slight, and which are sometimes imperceptible, occa- sion very great differences in the losses from perspiration ; so much do the physical conditions under which evapora- tion takes place, influence the results of that function. 170 ON PERSPIRATION. We have examined two of them, the hygrometric state, and the motion of the air. It is necessary here to re- collect, that this effect of the motion of the air is appli- cable only to those circumstances in which there is not a marked tendency to sensible perspiration or sweat. Section V. — Influence of Atmospheric Pressure. On this subject previous observers have left us nothing but conjecture. Sanctorius, although the contemporary of Galileo, the discoverer of the weight of the atmosphere, had not the instruments necessary for this kind of observation. Keill, although he carefully noted the state of the barome- ter during his observations could discover no relation be- tween the losses by perspiration and the changes in the pressure of the atmosphere. It is only within a short period that natural philosophers have succeeded in determining the influence of the weight of the atmosphere upon evaporation. They have taught us that the diminution of pressure upon liquids accelerates their conversion into vapour. After all the proof that we have adduced of the influence exercised by physical causes of this kind upon perspiration, we could scarcely doubt that those which we have just mentioned act in like man- ner on the animal economy. I have, however, attempted to ascertain this by direct proof. I have compared the perspiration of animals placed under the receiver of an air- pump, containing rarefied air with that of individuals of the same species exposed at the same time to the open air. Cold-blooded animals are the best adapted for this kind of experiments. They suffer little from the degree of rare- faction to which the air must be reduced in order to ob- tain quick and sensible effects ; the causes of complication ON PERSPIRATION. 171 which would throw a doubt over the results of such expe- riments upon warm-blooded animals, are thus excluded, and it is found that in air which has been rarefied, the losses by perspiration are increased. These experiments are detailed in the first chapter of this work, and I have no hesitation in applying the result to warm-blooded ani- mals, including man. Section VI. — Perspiration by Evaporation and by Trans- udation. There are three conditions which have a notable influ- ence upon perspiration, viz. the hygrometric state, the motion, and the pressure of the atmosphere. They act only upon the insensible perspiration ; it is that which is increased by the dryness, the agitation, and the rarefaction of the atmosphere. These causes do not produce sweat, at least directly, and the reason is evident, because they act in a physical manner, they diminish the mass of li- quids by causing a part to be converted into vapour. Sweat, on the contrary, is a loss ordinarily produced by a vital action, in the form of a liquid which transudes. This leads us to distinguish two modes of perspiration, one by evaporation, and the other by transudation. They would appear at first synonymous with insensible perspiration and sweat; but these terms, although they can sometimes be substituted for each other, are not synonymous. The dis- tinction is easy ; all that is lost by insensible perspiration ought not to be considered as the result of perspiration by evaporation. Is not the skin an excretory organ capable of eliminating from the body a certain quantity of liquid, independently of the co-operation of external agents, in like manner as the urinary organs separate and reject a part of the materials of the blood ? All that the skin 172 ON TERSPIRATION. loses in virtue of this power is by transudation. The quantity of liquid which issues in this way may be so small, or if abundant may be so rapidly dissipated in va- pour as to be insensible, and we commonly give the name of sweat only to visible transudation. We may on the other hand apply this term to the product of perspiration by evaporation, when from any cause it happens to be con- densed and precipitated upon the skin in the form of a liquid. All losses by perspiration are referable to these two modes of action. They belong either to evaporation which is a physical process, or to transudation, which is most fre- quently a vital action. Perspiration by evaporation takes place in the dead as well as the living body. It is independent of every species of transudation. It is a consequence of that porosity of organized bodies, by which the liquids near surfaces in contact with the air would diminish in quantity by being converted into vapour, even though the pores should be such as not to give passage to a single drop of liquid ; but living bodies have the power of eliminating by their ex- ternal surface a certain quantity of liquid ; a function which appears to be always in operation, although vary- ing in activity, which may be modified by external agents, but which essentially depends upon causes inherent in the living economy : it is in this view only that perspiration is a secretion resembling the other secretions of the body. We have already said that if this secretion did not exist, perspiration by evaporation would notwithstanding go for- ward ; on the other hand transudation takes place inde- pendently of the other mode of perspiration. As they are ordinarily combined, it would be interesting to determine their relative shares ; we should then know what we owe to physical processes and what we owe to ON PERSPIRATION. 173 vital functions. Nothing appears easier in theory than to establish this distinction. We have only to suppress the physical conditions which permit evaporation, and if losses are still produced by perspiration they will proceed from transudation. We should then obtain the proportion under given conditions, between perspiration by evapora- tion and that by transudation. But in order to render this method applicable we must pay attention to the fol- lowing considerations. Observe that, wholly to suppress perspiration by evapo- ration, the air must not only be of extreme humidity, but also at a temperature not inferior to that of the animal. If the air were colder it would be warmed by the contact of the body, it would then cease to be at its extreme of hu- midity, and would permit an evaporation proportionate to the degree to which it had been warmed. By making use of the cold-blooded vertebrata, we may almost entirely sup- press the loss by evaporation. Their temperature is not, as is generally imagined, always superior to that of the at- mosphere ; it is sometimes even lower ; and when it does rise above it, it is usually only to a fraction of a degree, and never more than one or two degrees (centigrade.) The average of the differences is a little above the temperature of the atmosphere, but this is so trifling that it may be dis- regarded altogether. In order to find the relative proportions of the losses by transudation and evaporation in dry air, we must subtract from the total that portion which has been incurred in hu- mid air. It appeared from numerous experiments with several species of cold-blooded vertebrata, that the propor- tion in these modifications of the air is, in the generality of cases, as seven to one. Since the second term represents the quantity lost by transudation, if it be subtracted from the first, the re- 174 ON PERSPIRATION. mainder is equal to the loss by evaporation. Perspiration by evaporation is then, in these cases, to that by transuda- tion, as six to one. By a series of experiments and inductions we have now been enabled to determine that in ordinary circumstances, in which perspiration is insensible, the losses by transu- dation form but a small portion of the whole. This serves to explain a great number of phenomena. We can thus conceive how the physical conditions which are favourable to evaporation, notwithstanding the diminution of transu- dation occasioned by the cold which they produce, do not fail, in ordinary circumstances, to increase the total loss. We may also imagine how much the continual variation in the motion of the air must contribute to produce these variations of perspiration which we have observed to take place with cold-blooded animals in successive intervals of an hour. All that we have hitherto shewn on the subject of per- spiration will considerably facilitate our examination of a question which naturally presents itself. Is perspiration susceptible of being suppressed? It is easier to resolve this question with regard to man and other warm-blooded animals, than with respect to the cold-blooded vertebra ta. Let us see what is the result of a very low temperature upon warm-blooded animals. We know, by the effect of cold upon the sweat, that it diminishes transudation. Now let us suppose that it may, by its intensity, suppress it al- together, there will remain perspiration by evaporation, which will always take place however humid the air may be. The high temperature of man and other warm-blooded animals, warms the air in contact with the body, and changes its hygrometric state by removing it from its ex- treme of humidity, and consequently occasions evapora- tion. If, on the other hand, the temperature of the air ON PERSPIRATION. 175 be raised to an equality with that of the body, at the time that it is saturated with humidity in order to suppress eva- poration, then perspiration by transudation is excited, and takes place to such an extent in man and other warm- blooded animals, that the sweat will stream from all parts of the body. We can then in no case suppress their per- spiration ; it will be performed either by evaporation or by transudation. We ought therefore to be careful how we take literally what we find in medical books respecting suppressed perspiration. There can be no such thing. That there may be suppression of sweat, is evident to every one ; but it does not follow that even in these cases there is no transudation. Since it is difficult to assure ourselves directly whether transudation is ever entirely suppressed in man and other warm-blooded animals, let us see what the cold-blooded vertebrata will offer on this point. The batrachians are the best adapted to this kind of re- searches, on account of the nakedness of their skin, of the fineness of its texture, of the copious loss which may be incurred through its medium, and consequently of the re- lation which their perspiration bears to that of man. On exposing frogs to the temperature of 0° cent. 32° Fahr. in humid air, in order to suppress perspiration by evaporation, they have lost by transudation, in different experiments, the 30th part of their weight. Transuda- tion is more abundant in these animals than in man, though the latter be placed in circumstanees much more favourable. When we consider how sensible these creatures are to cold, how much the activity of all their functions is diminished at a low temperature, and how much they may even then lose by transudation, it is not to be supposed that cold suppresses this mode of perspiration in man, and the less so from his having a temperature of his own which varies 176 ON PERSPIRATION. very little with the changes of the atmosphere, a condition which has a powerful tendency to maintain transudation. It may be very much diminished by the action of cold, but it appears that it cannot be altogether suppressed. It is a remarkable, but well known fact, that when life is sinking, and to appearance nearly extinct, the body is covered with sweat — so strong is the tendency to continue this function. Since we can scarcely determine by direct experiment on man and other warm-blooded animals the variations in the amount of transudation at temperatures below that of the body, because the losses by this mode of perspiration are confounded with those by evaporation, we must have re- course to the indirect means which have already served us under similar circumstances. Section VII. — On the Influence of Temperature. In studying the influence of temperature upon the trans- udation of batrachians at different degrees from 0° to 40° cent. 32° to 104° Fahr. in air saturated with humidity, in order to suppress perspiration by evaporation, we have ob- served that the increase of loss by transudation between 0° and 10° 32° and 50° Fahr. was very slight ; that it was similar between 10 and 20° cent. 50° and 68° Fahr. but that at 40° cent. 104° Fahr. the increase was considerable ; that on comparing the total of the losses in the space of six hours at the temperature of 0° cent. 32° Fahr. and that which took place at 40° cent. 104° Fahr. they were nearly as 1 to 55. By raising the temperature of the humid air to 40° cent- 104° Fahr. we may occasion as great loss from transuda- tion, as that which results from perspiration by evapora- ON PERSPIRATION. 177 tion solely in a dry atmosphere at a temperature not ex- ceeding 20° cent. 38° Fahr. What inference can we draw from these facts relating to cold-blooded animals which will be applicable to man and other warm-blooded animals? It is probable from what has just been shewn, that transudation in them, undergoes but a slight increase from elevations of tempe- rature to different degrees between 0° and 20° cent. 32° and 68° Fahr. If we endeavour to verify this application by the indications which simple observation furnishes, in the impossibility of exact appreciation we shall find this presumption confirmed. Every one has had occasion to observe that between the limits of temperature which we have mentioned, sweat is scarcely observable in man, when he is at rest, is in perfect health, and is free from all agi- tation of mind ; but when the temperature rises only 5° or 6° cent. 9° or 10° Fahr. above this limit, transudation be- comes evident on a great number of persons in the most tranquil state of body and mind, provided that the air be neither too dry nor too agitated. However little the tem- perature may be raised, the sweat increases in a proportion which appears much greater than that of the increase of temperature. There will then be a degree at which the loss by transudation may equal that resulting from per- spiration by evaporation in a very dry air, at or below 20° cent. 68° Fahr. Let us follow the modification of perspiration in an at- mosphere of a progressively rising temperature. Two ef- fects would result, which we shall now compare. The in- crease of heat above 20° cent. 68° Fahr. would increase transudation rapidly ; on the other hand the air becoming- warmer, would increase evaporation in an increasing pro- gression ; but the perspiration by evaporation would not necessarily follow the same rate ; and for this reason : ac- N 178 ON PERSPIRATION. cording as the sweat becomes abundant, it spreads over the body, and forms there an external layer more or less extended. In this space in which the sweat intercepts the contact of air with the skin, there is no perspiration by evaporation ; there is evaporation at the expence of the layer of sweat always supplied by transudation, but from these parts no fluid evaporates from within through the pores, and so far no perspiration by evaporation. This suppression will be general when the sweat universally covers the skin. Evaporation will always take place, but it will not be by perspiration. In order that this progressive diminution of perspiration by evaporation should take place in a dry air of a rising temperature, it is evident that the atmosphere ought to be calm or but little agitated ; for the motion of the air, in proportion to its rapidity, increases evaporation almost indefinitely ; whence it follows that sweat may be so quickly taken off in an atmosphere which is dry, warm, and sufficiently agitated, that the two modes of perspira- tion, by evaporation and by transudation, may take place at the same time as they do at lower temperatures. Section VIII. — Cutaneous and Pulmonary Perspiration. Sanctorius and Gorter were not ignorant of the pulmo- nary perspiration, but the means which they employed to estimate it were so imperfect that it would be useless to give their results. Hales employed more exact processes, but we shall pass them over and proceed to a period at which chemistry and experimental philosophy were much further advanced. Lavoisier and Seguin estimated the average loss by per- spiration from the skin and lungs in twenty-four hours, at 2 lbs. 13 ounces, of which 1 lb. 14 ounces is dissipated by ON PEKSPJRATloN. 179 the skin, and 15 ounces by the lungs, which gives the pro- portion of two to one.# Of this loss a portion is owing to the evaporation of water from the lungs, and another to the chemical changes of the air in respiration ; but it is certain that the water is the predominant portion. The difference in the manner in which this fluid is dissipated by the lungs and by the skin deserves particular attention. Whatever transudation there may be within the lungs, no liquid can issue from them but in the form of vapour. A new portion of air enters at each inspiration ; it becomes warm, and remains there until the whole mass rises nearly to the temperature of the body : in virtue of this acquired elevation, whatever may have been its previous hygrome- tric state, it converts into vapour the liquid with which it is in contact, and in respiration carries it into the atmo- sphere. It brings with it no water in a liquid state, nor any other substance in this form. There is then no loss by pulmonary transudation. All the perspiration, as far as water is concerned, takes place by evaporation ; making a considerable difference between the lungs and the skin, where the two modes of perspiration are united. This de- pends on their structure, one of their organs being a cavity which does not permit the flowing out of a liquid ; the other a surface so disposed, as to allow its escape at all parts. Here then is one reason for which, in man, the losses by cutaneous perspiration are more abundant than those oc- casioned by pulmonary perspiration. From this double source of perspiration at the skin, it is subject, as we have shewn, to great variations. From its greater simplicity, the pulmonary perspiration is much more regular, and con- sequently the losses are much more nearly equal in differ- ent periods. However, the loss of water by the lungs is See Lavoisier's Traite elementaire de Chimie, 3d edit. p. 228. N 2 180 ON PERSPIRATION. capable of being suppressed, because, being performed by a physical process, it may be stopped by the physical con- ditions which prevent evaporation. In an atmosphei'e sa- turated with moisture, if the temperature were equal to or above that of the body, there would be no watery perspi- ration from the lungs, because there would be no evapora- tions ; whilst the cutaneous perspiration would take place, not by evaporation, but by transudation, and that to a very large amount. Section IX. — Perspiration in Water. Supposing that water, in contact with the skin, had no physiological action upon that organ, it would merely pre- vent the contact of the air, and consequently suppress per- spiration by evaporation from the skin. There would then remain the loss by cutaneous transudation, which must be added to that which takes place by the lungs. 181 CHAPTER XII. ABSORPTION IN WATER. We have hitherto proceeded on the supposition that water exerted no special influence on the skin, and that it only acted by intercepting the contact of the air. We shall now enquire whether the presence of water produces any other effects which complicate the results. Does any absorption take place when water is in contact with the human skin ? Seguin,* after examining the changes in the weight of the body, both immersed in water and out of it, was induced to reject the idea of absorption. The result of these experi- ments may, however, admit of being differently viewed. We have proved in that part of this work which treats of the cold-blooded vertebrata, that the batrachians, whether smooth like the frog, or thick and rough like the toad, are capable of absorbing much water by their external surface, and that the quantity absorbed not merely soaks into the tis- sue of the skin, but spreads through the system, and is distri- buted to the different parts. These animals, like man, have the skin naked ; a condition the most favourable to absorp- tion. It is true that the skin of man, from the nature of its epidermis, is less disposed to absorption ; it nevertheless possesses this property to a very great degree. We cannot doubt it, when we observe what takes place in animals, * See Memoires sur les Vaisseaux Absorbans, and which, moreover, would not directly lead to the object which I had in view. The question in fact, as before stated, was to determine whether in the preceding experiments, the muscular con- tractions were occasioned by an agent altogether unknown to us, or whether they were effected by electricity, which is developed every time one body exerts a mechanical action on another. APPENDIX. 311 If electricity produced by the contact of the exciter with the nerve, were really the cause of the contractions, we might by greatly diminishing the quantity of electricity in the nerve, either sensibly diminish, or altogether suspend, muscular contractions. Now, these effects may be pro- duced by varying the conducting power of the substance placed under the nerve. Thus, when the nerve maintains its natural relations, it rests on muscle, which is an excel- lent conductor of electricity. If, whilst the nerve is so situated, it be acted upon by a given quantity of electric fluid, this will be divided between the nerve and the mus- cle, and thus there will be a diminution of the excitation of the nerve, and of the intensity of the phenomena resulting from it. If, on the contrary, we place under the nerve which we wish to excite, a non-conducting body, the whole of the electricity will be concentrated upon the nerve, and we shall obtain from the fluid the full effect which we are desirous of producing. This precaution is had recourse to in galvanic experiments, when it is wished to excite muscu- lar contractions by very small quantities of electricity ; such for instance, as are produced by the contact of two metals. To ascertain the respective influence of the insulation, and non-insulation of the nerve, the comparison must not be made without giving attention to the state of the ani- mal. If the animal be very fresh and excitable, the contrac- tions will, in both cases, be so strong that the difference will not be perceptible : for no conclusions can be drawn from the comparison, if motion takes place in the limb, under circumstances the most unfavourable, since we should then be commencing almost where gradation ceases. On this account, it is proper to wait till the animal is so 3J2 APPENDIX. far exhausted, that no muscular contractions, sufficient to move the limb, can be excited by the action of two metals on the nerve whilst it is resting on muscle. We may thus obtain the simple contraction of the muscle without loco- motion, or even suffer muscular contraction to cease. If, in this state of things we place a non-conducting body, as a piece of glass or oiled silk, under the nerve, and then establish the circuit by means of two different metals, we immediately cause the agitation of the limb. This fact, and the principle on which it depends, being well established, the next step was to ascertain, whether in the preceding experiments, in which the nerve was touched with only one body, and no circuit was formed, the muscular contractions were to be referred to the action of the same cause. It will be remembered, that a slip of oiled silk was placed under the portion of denuded nerve. A comparison was now to be made between an animal so prepared, and another in which the nerves, instead of being insulated, reposed on the subjacent flesh. I made use of small rods, with which I easily excited contractions, when I drew them from above to below, along the portion of de- nuded nerve, which was supported by the oiled silk ; but I was unable to excite them when I passed them along the nerve of the other animal, in which they were not insu- lated. Frequent repetitions assured me, that the want of effect did not depend on difference in the degree of con- tact ; I tried the experiment on many animals of the same species, lest there might be anything in individual pecu- liarity. As in the one case the nerves were brought farther into view, and kept somewhat tense and even with the sacrum, by means of the slip of oiled silk, whilst in the other they had no such support, I restored the parity of position, by placing under the unsupported nerves, a portion APPENDIX. 313 of muscle, corresponding to the slip of oiled silk, as well in size as mode of insertion, and still was unable to produce contractions by treating the uninsulated nerve, whatever was the material of the rod employed as the exciter. The difference was rendered still more striking, when instead of making the comparison between two individuals, it was made upon the same animal. After having in vain at- tempted to produce contractions by contact of a nerve rest- ing upon muscle, I found that they might still be induced, •if the oiled silk were had recourse to, and I was able to command their alternate appearance and disappearance, by using sometimes a non-conductor, and at others, a con- ductor for the support of the nerve. The manipulations which cannot be avoided, in making these trials, exhaust the nerve if they are too often re- peated. The difference is here as marked as possible. So decided a contrast as this was not necessary ; a less, would have sufficed, provided it were really manifest. The reason is not obvious, why contractions should not sometimes be produced when the nerve is not insulated, since in galvanic experiments, the quantity of electricity, elicited by the con- tact of two metals, will or will not produce contractions, according to the state of vitality of the animal, which not merely differs in different individuals, but varies in the same individual at different moments. This extreme of contrast in the effects, at first very satisfactory, as more strongly exhibiting the influence of the respective states, and throwing light on the nature of the cause, seemed, on a closer view, to prove too much, by uniformly exhibiting the same difference. I wished to be able sometimes to produce contractions by touching the uninsulated nerve, as happens in ordinary 314 APPENDIX. galvanic experiments, in which the contact of two metals is employed, though they might be expected to be less marked than in the latter case, since my method of excita- tion was one of inferior energy. I at length succeeded in this point. In observing the difference of effect in touch- ing an insulated nerve, more or less rapidly, T discovered that contractions were the most constantly produced by a quick and light touch. Having found that I produced contractions more easily by increasing the rapidity of the taction, I made trial on an animal whose nerve was not insulated, and frequently ob- tained slight contractions. In the preceding experiments, choice has been made of the extremes from amongst the good and the bad conductors, suitable to be placed under the nerves, for it is necessary that they should lie on a soft material, in order not to be irritated, and compressed between two hard bodies. Thus, the slip of muscle, and the piece of oiled silk, are both soft and flexible, but the one is the best conductor, and the other the best calculated to insulate ; they, therefore, offer the most favourable conditions for obtaining distinctly, marked, but opposite results. Notwithstanding the diffi- culty of obtaining appreciable differences, when employing substances of intermediate properties, I did not restrict myself to the two before-mentioned. Having prepared a frog, in the manner already described, I placed under the sciatic nerves, a piece of the skin of the animal, and under those of another, I introduced a slip of moistened paper, and perceived a marked difference j when, in the same manner, and with moderate quickness, I alternately touch- ed the nerves, first of the one, and then of the other. The frog, whose sciatic nerves were supported by the piece of skin, remained motionless, whilst the same degree of tac- APPENDIX. 315 tion applied to the nerve, resting on moistened paper, pro- duced contractions of the muscles. To find out whether the difference of effect was referable to the different con- ducting power of the slips placed under the nerves, I in- stituted by means of galvanic experiments, in which I employed two metals, a comparison between the conduct- ing power of the skin of the frog, and that of the moistened paper, and ascertained that they differed essentially. The frog's skin conducted much better than the moisten- ed paper, which is but an imperfect conductor. It is need- less to enter into the detail of these experiments, M. de Humboldt having already established the fact, that the conducting power of animal substances, is superior to that of vegetable matter in its recent state, and having shewn that this difference does not depend on the water which they contain, but on the nature of the organized structures themselves. These experiments are easily conducted ; they are founded on well known principles, and they appear sa- tisfactorily to prove that, cseteris paribus, the muscular contractions, produced by the contact of a solid body with a nerve, are much less considerable, or even wholly ab- sent, when the nerve, instead of being insulated, is in communication with a good conductor, and it would seem to follow as a legitimate conclusion, that these contractions are dependent on electricity. ON ATMOSPHERIC ELECTRICITY. BY M. POUILLET. Various theories have been formed by meteorologists to ac- count for the electricity sensibly present in the atmosphere. Of these, Volta's was, perhaps, the only plausible one. That philosopher was induced to believe, that bodies, in passing from one state to another, undergo a change in their electric condition, and supposed that the electricity lost in storms, was constantly being renewed by that pro- duced by evaporation perpetually going on from the surface, as well of the land as of the water. The recent and interesting researches of Pouillet, were instituted, not merely to ascertain the truth of the Italian Professor's hypothesis ; he was also desirous of discovering the efficacy of another cause, which he believed to be of no small importance in the production of electricity, and of bringing to proof a theory of his own, relative to the dis- tribution and accumulation of this principle in the atmo- sphere. Numerous and various experiments have brought him to the conclusion, that the mere passage [of a body, from the solid form to a state of vapour, is unaccompanied by the development of electricity, that the result is similar, when vapour is condensed into the liquid, or solid form. He conceived that Volta, though too accurate an observer to be mistaken as to the fact of the presence of electricity in his experiments, was, nevertheless, deceived as to the cause of its production, by the formation of carbonic acid, which mixed with the vapour of water, and complicated his experiments. In 1782, Volta, Lavoisier, and Laplace, shewed, that electricity was developed during chemical action, but as APPENDIX. 317 experiments relating to this point, are liable to afford dif- ferent and contradictory results, from slight differences of circumstances, the question has been regarded as undecided. It became, on this account, an object of special attention with M. Pouillet. He finds that in the combustion of charcoal, there is an unequivocal production of electricity, that the acid produced is in the positive state, whilst the charcoal always becomes negative. It is necessary, in order uniformly to obtain the same result, that the combustion should take place only at the upper part of the piece of charcoal, and by no means extend over the whole of it ; otherwise the contact, both of the charcoal and of the car- bonic acid, with the plate of metal destined to receive the electricity, will render the experiment irregular. To dis- cover whether the electricity, rendered evident in the pre- ceding experiment, was to be attributed to chemical action, or to the conversion of the charcoal from the solid to the gaseous, he examined the flame produced by the combus- tion of hydrogen. The external part of the flame con- stantly exhibits vitreous, and the interior resinous elec- tricity. Thus, by the act of combustion, the combustible becomes electrified negatively, and the body which is ac- tually burning, becomes positively electrified, whilst a trans- fer of electricity is taking place between the molecules, which are combining, and those which are about to do so. This fact is supported by a great number of experiments on the combustion of phosphorus, sulphur, the metals, alkohol, ether, fat substances, and vegetable matter. As plants during vegegation exert a chemical action on the atmosphere, sometimes converting its oxygen into car bonic acid, and at others, decomposing the carbonic acid already existing in it, the idea suggested itself, that if electricity were developed in the process of vegetation, their very extensive operation would warrant one in attri- 318 APPENDIX. buting to them a considerable portion of the electricity of the atmosphere. To investigate this subject, Pouillet examined the vege- tation of seeds in an insulated situation, having a condenser connected with the soil. Till the germs appeared at the surface, no signs of electricity could be detected, but as vegetation advanced, it became very evident. For the success of this experiment, it is necessary that the air should be in a state of considerable dryness; when this does not happen to be the case, the apartment must be ar- tificially dried by quick lime or some absorbent. It is obvious, that the soil could not acquire one electric state, without the opposite state, in a corresponding degree being communicated to the atmosphere. If, then, a languid vegetation, on a surface of five or six square feet, be capable of producing very decided effects, may we not reasonably conclude, that the influence of the same cause, operating over a large portion of the surface of the earth, is fully adequate to the production of many of the phsenoniena, which we observe. A second memoir, by the same author, carries this subject still further, and exhibits other causes besides the process of vegetation, which contribute to supply the atmosphere with electricity. In the first memoir he had shewn, that when two bodies combine, electricity is developed ; in the second he proves, that similar phsenomena attend the sepa- ration of bodies which were previously combined, and he applies this fact to the numerous instances of decomposition which nature is spontaneously producing on the surface of our terraqueous globe. Pouillet, in his experiments connected with this inquiry, employed two processes — the first resembles that adopted by Saussure, in his experiments on evaporation, and consists in connecting one of the disks of the condenser with the APPENDIX. 319 heated vessel, in which the subject of the experiment is to be placed. By the other process, the heated vessel is dis- pensed with, and he makes use of one of Fresnel's large lenses, to heat the body whilst it rests on a plate of platina. It should be remarked, that when vessels of copper, iron, or of other materials, on which the substance under exami- nation can act chemically are employed, the result will be a complication of effect, by which the phenomena will some- times be heightened, and at others neutralized. The results of these experiments are, 1. That by mere evaporation, whether rapid or short, no signs of electricity are produced. 2. That evaporation from an alkaline solution, however recent, whether it be of soda, potass, baryta, or strontian, leaves the alkali electrified positively. 3. That when other solutions, either saline or acid, are employed, evaporation leaves the body which was combined with the water, electrified negatively. Of the numerous saline solutions which were essayed, that of muriate of soda was naturally the one which excited the greatest interest. It formed no exception to the rule. Hence it can hardly be doubted, that evaporation from the surface of the sea forms one of the most important sources of atmospheric elec- tricity. Even lakes and rivers must have their influence, since their waters are never perfectly pure. 320 EXTRACT FROM AN ESSAY ON SOME OF THE PHENOMENA OF ATMOSPHERIC ELECTRICITY. BY LUKE HOWARD, F.R.S., &c. Read before the Askesian Society in 1800. From an attentive examination of Read's observations, I have been able to deduce the following general results. 1. The positive electricity common to fair weather often disappears, and yields to a negative state before rain. 2. In general the rain that first falls .after a depression of the barometer is negative. 3. Above 40 cases of rain in 100 give negative electricity, although the state of the atmosphere is positive before and afterwards. 4. Positive rain in a positive atmosphere occurs more rarely ; perhaps 15 times in 100. 5. Snow and hail unmixed with rain are positive almost without exception. 6. Nearly 40 cases of rain in 100 affected the apparatus with both kinds of electricity ; sometimes with an interval in which no rain fell, so that a positive shower was suc- ceeded by a negative, and vice versa; at others the two kinds alternately took place during the same shower, and it should seem with a space of non-electric rain between them. The regularity with which the latter phenomena some- times occurred, seem to furnish a clue for explaining some of the preceding cases, and indeed for constructing a hy- pothesis of local rain. I shall submit to the consideration ' APPENDIX. 321 of the Society my conjectures, in the confidence of their meeting with a candid examination, and on this account I ought to add, that the latter part of my investigation of Read's Journal has been performed with this supposed clue in my hands ; that I have met with some facts to which it is not applicable, and am, therefore, willing to distrust its guidance, except on those points were it applies directly to the phsenomena. The members may do well to compare what I shall advance with the Journal at large, since ob- jections may occur to them which escaped me. Let fig. 1. represent the area on which a local shower falls ; a. being a certain portion in the centre in which the rain is charged positive ; b. b. a surrounding portion in which the positive charge terminates, and which may be considered as occupied by non-electric rain ; c. c. the re- mainder of the area surrounding the two former portions, and occupied by a negative charge, which also extends into the surrounding atmosphere, e. e. to a distance propor- tioned to the intensity of the central positive charge. The non-electric boundary of the negative charge is represented by the line, d.d. d. d. Without this line, the atmosphere is supposed positive as usual when free from clouds. In a shower so constituted, the electric signs obtained by obser- vations made in a single and fixed station, (as Read's were,) would be subject to the following variations. 1. The central area remaining the whole time over the instrument, the observation would be positive ; and 2. The circumferential area doing the same, it would be negative. Many cases in Read will be thus explained, and it is favourable to the hypothesis, that the positive observations are to the negative nearly as 1 to 3 ; but, on the other hand, this does not account for the fact of several showers being negative in succession, nor for the relation Y 322 APPENDIX. which seems to obtain between depressions of the barometer and negative rain. 3. The rain beginning with the central area over the instrument, and ending with the circumferential, the obser- vation would be first positive, then negative after an inter- mission of the electric signs. 4. The circumference being first examined, and the rain ceasing by expenditure during the charge from the centre ; the order would be the reverse of 3. 5. The. cloud passing over in the zenith of the appara- tus, and the latter describing under it the line f. f., all the appearances would agree with those cases in which a shower commencing with negative electricity, shews itself to be positive in the middle and terminates as it began, with negative. 6. But the line which the apparatus may be considered as describing under the cloud, in consequence of irregu- larities either in the motion or form of the latter, may re- semble the curve, g. f. ; and after having entered the shower or commenced within it, may pass and repass the non-electric boundary several times during its continuance. It may also happen to commence or to terminate in the latter. This will serve to explain some of the most irregu- lar cases in the Journal. 7. It frequently happens, that the apparatus is charged in consequence of rain falling at such a distance, that not even the skirts of the shower come over it. This is par- ticularly the case in thunder storms, and the phsenomena are such as ought to take place, according to the hypothesis, when the centre of the mass of clouds and rain (which elec- trically considered form one aggregate) passes at a certain distance from and parallel to the line, f. k., on which we now suppose the apparatus to be. The latter then loses its positive charge at i., and presently acquires a negative, which APPENDIX. 323 becomes more intense as the rod enters further into the ne- gative area, and dies away as it quits it, till at k. it be- comes extinct. 8. If the station of the observer, during a thunder storm, happened to be in any part of the circle, d. d. d. d., he might be unable, if the time devoted to the observation were short, to obtain any signs whatsoever from his apparatus, although he might both see and hear the successive discharges in the horizon. I have witnessed such an occurrence myself, and I sus- pect that what Read has noted under June 22, 1790, is from the same cause. The centre of the storm in this case, appears to have been about Salisbury, distant 80 miles. When we consider the elevation which was necessary to render even the extremity of this storm visible at Knights- bridge, we shall not find this distance too great for the semidiameter of the total area in which its effects might be sensible with a good instrument. To some of the cases these explanations seem clearly appli- cable ; in others there is room for correction by future observa- tions, which would be far the most instructive if conducted in concert, by several persons at different stations, within the compass of a few square miles. It will be readily seen, that I have made the accumulation of positive electricity in a certain portion of the atmosphere, the basis of the whole system. The remainder follows as a necessary consequence from the known laws of electricity. But the production of positive electricity is not necessarily confined to the centre of an aggregate of clouds, nor its effects to a lateral direction only. Cases may occur in which one extremity of the ag- gregate may be positive, and the other in consequence, negative ; there may be positive electricity in a certain stra- tum of the atmosphere, and from hence may result a ne- v2 324 APPEN D1X. gative counter-charge in a contiguous stratum above or below. In continued rain such a distribution most pro- bably obtains, but we must have more observations to be able to prove it. Our present object is to shew how a local shower is organized, and if possible to trace its immediate origin to electrical causes; for it is in vain that the principles of chemistry alone are appealed to in this case. Let us see therefore how it happens, that the centre of a shower is often strongly positive. The clouds originate from vapour, which is first formed in contact with the earth. It is not therefore then electrified, except the surface on which it is formed be at the time super-induced. But the latter is the proper effect of impending clouds, and although a truly electrised vapour may be thus formed, and being condensed, may constitute a part of the system of clouds in a thunder storm, yet our present enquiry goes further : we want to account for the super-inducing charge. It would be a difficult undertaking to ascertain by expe- riment the electrical state of vapour, and of the surface on which it originates in the natural process. Experiments have been made on insulated substances at high tempera- tures, the results of which, even if more conclusive, would be quite inapplicable to this case. I shall therefore offer some conjectures on the origin of atmospheric electricity, which will in the first instance proceed on the supposition that vapour is originally non-electrised. A body in order to be charged must be first insulated, and the charge will continue during perfect insulation, but the latter seems unattainable. There is always a small degree of conduct- ing power in the very atmosphere when at the maximum of dryness, and this is greatly augmented by what is called moisture, by which I understand, diffused and suspended (not elastic and gaseous) water. We can scarcely imagine a body more perfectly insulated APPENDIX. 325 than the first particle of water which, separating- from va- pour that has ascended into the higher atmosphere, begins to obey the law of gravity. There are two sources from whence such a particle may obtain an electric charge, viz., the surrounding air, and the vapour out of which it was formed, and which may, though in itself non-electrified, afford to the water, now reduced many hundred-fold in vo- lume, a real positive charge. Appearances, likewise, are much in favour of the opinion, that the precipitation of water in the higher atmosphere is sometimes effected by a double affinity, in which electric air and gaseous water are mutually decomposed, the former seizing the caloric, the latter the electric fluid. At all events we are certain of the fact, that clouds are insulated and charged conductors. Franklin supposed, that clouds arising from the sea were positive, those from the land negative, and that their rencounters in the air were the cause of thunder storms. Kirwan, and others, go a little further, and say, that a positive cloud (become such in the way I have stated) may affect another with a negative state by its approach, and thus attract it to form rain. But all these explanations fall short of the phse- nomena. Had this been all the process, we should have known nothing of the electricity of rain, for a negative and positive cloud would unite in those proportions only, which should form non-electric rain. *#'.*■# The reader who may be curious further to pursue these highly interesting meteorological considerations, is referred to a new edition of Luke Howard's work on the Climate of London, now in the press, and in which will be found the whole of the paper of which the preceding is an extract, together with much new and important matter on collateral subjects. I have been induced to give the preceding extracts, from 326 APPENDIX. the idea that they may tend to throw some light on the very interesting, but still imperfectly understood subject of the influence of electricity upon vital phenomena. The observations of Prevost and Dumas, contained in the Appendix, relate to the supposed operations of electri- city, as an agent in some of the functions carried on within the body, and more especially in conjunction with muscu- lar contraction. The views which they contain are ex- tremely ingenious and interesting, but I must confess my- self unable fully to adopt them. The experiments and operations of Pouillet, respecting the development of electricity by the process of vegetation, led me to conclude, that a similar development must take place in the production of carbonic acid by the respiration of animals, and also by the vinous fermentation of fluids. My attempts to demonstrate the correctness of this sus- picion have not yet been successful. I hope hereafter to pursue the enquiry, and in the mean time I shall relate a few facts which seem to bear on the subject. It has long been observed that individuals of highly sensitive consti- tutions are concious of uneasiness, sometimes amounting to absolute pain, or the disturbance of function during the existence of a thunder storm ; this is by no means neces- sarily connected with fear, or other mental emotions, pro- duced by the loud sound and vivid light, or any other phenomenon cognizable to our senses. The influence of which I am speaking is frequently felt before the storm has commenced, and has occasionally been experienced by in- dividuals so far removed from the skirts of the storm, as not to be conscious of its existence at the time, except by the intimations afforded through the symptoms in question. Such cases seem to be analogous to the instance alluded to in the paper of Luke Howard, in which Read's appa- APPENDIX. 327 ratus, set up at Knightsbridge, for the examination of aerial electricity, was influenced by a storm supposed to have passed over Salisbury. Persons who watch the habits of leeches, have frequently remarked their peculiar agitation when the electric state of the air is disturbed by storms, and it is believed by persons accustomed to the rearing of poultry, that storms sometimes have an injurious, and even a fatal influence upon eggs undergoing incubation* It is a generally admitted fact, that liquors undergoing the vinous fermentation, suffer a great disturbance in this process during the existence of a thunder storm. These facts taken together, led me to question, whether the negatively induced electricity may not have a tendency to disturb the production of carbonic acid, which Pouillet has shewn to escape in a negatively electric state. We have as yet but few well-conducted and satisfactory observations, respecting the influence of an artificially dis- turbed electric state upon living organized beings. Some observations have been made with reference to vegetable physiology, and as this may often be appealed to for as- sistance, in our attempts to elucidate the more difficult subject of the physiology of animals, it may not be amiss briefly to relate them. With respect to dead animal and vegetable matter, the experiments of electricians completely tally with what has been observed to be the effect of the electric disturbance of the atmosphere. The observations of Achard of Berlin support this assertion. They are briefly noticed in the Encyclopaedia Metropolitana, from which the following short statement is extracted. It is a well known observation, that after a storm, flesh, either raw or boiled, acquires a putrid smell, which, in the latter, is particularly acid. It is known, also, that grain 328 APPENDIX. suffered to ferment for the purposes of brewing or distilling, undergoes, during stormy weather, very sudden and per- ceptible changes. On such occasions, it is often extremely difficult to observe where the first degree of fermentation ceases. It passes so speedily that the second degree, or the acetous fermentation, takes place before one is aware of it. To ascertain, therefore, whether the electric matter, which, during stormy weather, is so abundant in the atmosphere, has any share in these phaenomena, the following experi- ments were made. A piece of raw beef was cut into three parts. One of these parts was electrified positively for ten hours without any shock ; a second was electrified negatively for a similar time ; and the third was not electrified at all. The three pieces were left in the same apartment, exposed to the same degree of heat. When examined next day, both the pieces which had been electrified appeared to be tender, but were free from the least bad smell. On the fourth day, the elec- trified flesh had an intolerably foetid smell, and that which had not been electrified began to smell a little. M. Achard repeated these experiments with boiled veal. That which was electrified had, the next day, an acid smell, and an unpleasant taste ; but that which had not been elec- trified, continued sweet for three days, and only on the fourth day began to have an acid smell. Several birds were killed by electric shocks, and others were deprived of life, by sticking a needle through their heads, and then placing all in the same temperature, they were covered with glass receivers in order to preserve them from insects. Observing the gradual progress of corrup- tion in both sets, M. Achard plainly perceived, that it took place much sooner, and advanced more rapidly in those killed by electric shocks, than in those deprived of life by APPENDIX. 329 the needle. . In those also, to which a stronger shock had been given, the degree of corruption was far greater than in the others. Van Marum made a similar observation with respect to the rapid decomposition of eels, which had been killed by electricity. It clearly follows from these experiments, that electricity accelerates corruption, and that the putrefaction of flesh after a storm, must be ascribed solely to the more abundant accumulation of the electric matter at that time. M. Achard saw that this was the case in regard to several persons killed by lightning. The body of a farmer, who lost his life in this manner, between five and six o'clock in the evening, emitted next morning a very perceptible foetid smell, which in the evening was totally insupportable. Having stated these effects of electricity on dead vege- table and animal matter, which are sufficient to shew its power in modifying and accelerating chemical changes, we may now inquire after what is known of its influence when life is present. We shall commence with vegetables, in which the direct physical effects are less complicated, from their not being mixed up with what may be regarded as its moral effect on a highly sensitive nervous system. It is well known that trees may be killed by lightning, but in these instances there is so much violence and de- struction of texture, that we can draw no conclusion from them as to the influence of electricity. Cavallo, though he disputes the correctness of the statements of some elec- tricians, with respect to the influence of electricity on plants, has shewn that the bahandna impatiens is killed by shocks which are too slight to impair the structure. A branch of this plant died the day after receiving the shock — the branches of other plants survived longer. A laurel branch lived fifteen days and that of a myrtle a whole month. 330 APPENDIX. VanMarura and Nairne confirm the deleterious effects of electric shocks, shewing that they kill some plants and pre- vent slips from taking root and budding. If electricity in the form of shocks has the power of de- stroying vegetable life, we may reasonably presume, that a less violent application of this agent would produce some sensible modifying effect. The first experiments upon the application of electricity to living vegetables, appear to have been made by Mainbry, in Edinburgh, in the year 1746. In the autumn of that year, he subjected two myr- tles to gentle electric action during one month, and ob- served that they subsequently put forth leaves earlier than similar trees which had not been electrified. The Abbe Nollet, Jallabert, Boze, Menon, Dr. Carmoy, the Abbes D'Ormoy and Bartholon, maintain the power of electricity as a stimulant to vegetables ; the last named experimenter, in particular, has been extremely zealous in this enquiry. He regarded electricity as a most powerful stimulant to ve- getation, and recommended its practical application in hor- ticulture, for which purpose he contrived an apparatus, called electro-vegetometer, with which he employed artifi- cial excitation. He proposed the direction of atmospheric electricity to the same object, and believed that he pro- duced some good effect by watering plants with water charged with electricity. Although there can be little doubt, that the Abbe's enthusiasm in his subject led his imagination to the over-straining of facts, yet it is by no means improbable, that there is more truth in his observa- tions than Cavallo and Ingenhouse are disposed to admit. It has been asserted, that plants grow with encreased vigour in the neighbourhood of thunder rods. It might have been supposed, that if plants in general are influenced by elec- tricity, those plants which offer the most striking proofs of sensibility would be the most signally excited by it. Van APPENDIX. 331 Marum was, therefore, led to try its effects on the mimosa pudica, and on the hedysarum gyrans, but he could not detect that their movements were positively affected by it. It will be well to bear this fact in mind, when considering the motions of animals and vegetables. The fatal effects which violent discharges of electricity produce on animal life, are more notorious than in the case of vegetables. Scarcely a summer passes without nu- merous instances occurring in which man and other animals are killed by lightning. The discharge of an ordinary bat- tery is sufficient to kill insects and worms, and the shock from a tolerably large one will kill mice. It is truly sur- prising to see how instantaneously some of the lower ani- mals, which are remarkably tenacious of life, are completely deprived of it by the electric shock. I once discharged a battery of considerable size through a common earth-worm, which would in all probability have shewn signs of life long after minute division. Its death was as sudden as the shock, and the semi-transparent substance of the animal was changed like albumen which has been exposed to heat. The artificial accumulation of electricity in batteries of very large size, has been found sufficient to kill not only rabbits, but even large and vigorous hogs, a fact which was completely proved by my friend Charles Woodward in the presence of Dr. Scudamore. It may now be interesting to notice some of the pheno- mena induced by electricity, within those limits which are compatible with life. With the hope that this short expo- sition may tend to assist, either in the extension or appli- cation of our present knowledge of the subject, I shall endeavour to class these phenomena under the following heads. 332 APPENDIX. Electric tension — its effects on the system generally — - difference of the positive and negative charge — its effects on particular functions, such as circulation, exhalation, and secretion and respiration — the effects of the transmission of shocks — of a continuous stream — sparks — aura — appli- cation. It is well known, that that state of the atmosphere which is unfavourable to electrical experiments from its being ad- verse to the insulation, and consequently to the electric tension of bodies, is also ungrateful and oppressive to our feelings; and that precisely the opposite effect is ex- perienced in clear and frosty weather, and in other states of the atmosphere which facilitate the working of electri- cal machines. We might regard these as coincident, rather than connected facts, if it had not been observed that an artificial repletion with electric fluid produced a similar effect in exhilarating the spirits, a fact for which, with many others here related, I am indebted to my friend Charles Woodward of Islington, a gentleman who has long and successfully devoted his attention to electricity. This fact conducts us to the enquiry, whether there is any difference, as far as the influence on the animal eco- nomy is concerned, between a positive and a negative charge. Here, I regret to say, that I have very little of a decisive character to bring forward, yet I may state on the same valuable authority which I have just given, that a negative charge continued for about half-an-hour, has caused an unequivocal perception of languor and oppression. Do we not find an obvious parallel to this experiment in the power- fully oppressive and sometimes distressing influence of which highly sensitive individuals are conscious on the approach of a thunder storm, or during the prevalence of a north-east wind, which is characterized as peculiarly un- APPENDIX. 333 healthy and productive of a sensation of dryness and cold, unaccompanied by a corresponding depression of the ther- mometer? It was shewn, in the preceding article on Atmo- spheric Electricity by Luke Howard, that a highly electri- fied thundercloud is surrounded to a considerable extent by atmosphere which is in a negative or neutral state. The north-east and east winds are often in a similar condition. Except in cases of the transmission of a strong electric current through some part of the nervous system, which produces an instantaneous disagreeable, or even fatal effect, it would seem that a considerable portion of time is neces- sary for the production of anything like a sensible effect from disturbance of the electric equilibrium. Leeches, as I before observed, are said to be highly susceptible to very slight alterations in this respect. I was, therefore, led to enquire what would be the result of a great, but sudden and transient encrease of their electric tension. I was careful to avoid subjecting their bodies to the direct effect of a spark or shock. I placed several active healthy leeches in a glass vessel containing water, which being thus insulated, I kept for a little while strongly electrified positively, but without producing any sensible effect. Precisely the same result attended a negative charge. I next tried what would be the effect of converting the vessel containing water into a Leyden jar, by applying a partial coating of tin-foil out- side. Having given a moderate charge, I suddenly restored the equilibrium by discharging the jar, but I could not perceive any unequivocal appearance of uneasiness in the leeches, which remained perfectly healthy for several days, after which they were no longer watched. Although the statements which are made respecting the effects of increased electric tension upon the circulation at first appear contradictory, a little consideration will satisfy us, that these decrepancies are analogous to such as attend the \e[3u)i>." APPENDIX. 353 Hie, et in sequentibus excerptis non tantum actionem, sed instrumenta quoque indicat. 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