wa^^H ' ϋ-ΐ'^η- mm•-:. mM'^•''• ..' ^ .^„;.Lfeiirf«:iLr_' ... Q fri tri ^^omm^ "i^ ^ ^(aojiwDjo"^ ^.OFCAllFO% > V/ _ I i^ > ^OFCAllFOfiV WavHaiii^ ^i^Aavaan•^ iFOi?^ ^OFCAllFOfi•^ \WEUNIVERS/A ^>:lOSANCElfX> Ο ^mmyi^^ ^nxmmw "^aaAiNnawv' aweuniver% ^lOSANCElfj^. ο ^^^ " -5^lLlBRARYGc. ^;^l•UBRARYQ<. vsoi^ "^isaaAiNiiay^^ '^aojiivjjo''^ '^aojiwojo^ ■;), ^lOSANCEl^^ ^FCAIIF0%. ^OFCAIIF0%, -τ» ο m %JI1V3J0>^ .<.0F CAIIF0% > ^^i'Aavaan^ ^WE υΝίνΕΡΛ'^Λί. ^lOSANCElfj> ^lOSANCElij> ο -s^lUBRARYQ^ -s^lUBRARYO/C. ^aaAiNnawv** '^«iojiivDjo'i^ "^ojitvdjo^ 7- AWEUNIVERi//) Ο ^/5«3ΛΙΝη•3Λν ^OFCAUFOfti^ ^OFCAIIFO^^ ^ommit^ ^mi\m//;_ iS^I i ^iiAavaan-^- ^tujonyso^ "^ ^^lllBRARYi?/: u3 1 li— ^ ^ AWEUNIVERVa ^lOSANCElir^ ^iodiivjjo'^ "^JiiijDNvsoi^ %89ΛΐΝη•3\\ν^ ^^ojnvjjo•^ ^^ ^OFCAIIFO/?^ - ^' - 'δ C-1 ,^WEϋNIVER% ^>;lOSANCElfj> ^O^CAllFOί'^ %Ην«8Ι1•# Χΐ\\•^ ARISTOTLE ON LIFE AND DEATH ARISTOTLE ON THE PARTS OF ANIMALS. Translated, with Introduction and Notes, by W. Ogle, M.A., M.D., F.K.C.P. KEGAN PAUL, TRENCH, & CO. 1882. ARISTOTLE ON YOUTH & OLD AGE, LIFE & DEATH AND RESPn>lATION TRANSLATED, WITH INTRODUCTION AND NOTES, BY W. OGLE, M.A., M.D., F.R.C.P. SOMETIME FELLuVV OF CUKI'LS CIIiaSTI COLLliGI•., OXFORD LONGMANS, GREEN, AND CO. 39 rATIiRNOSTER ROW, LONDON NEW YORK AND I?OMUAY 1897 All ri({hM reserved iS> A7&3 /??7 PREFACE The treatise, of which a translation is contained in the following pages, is represented in all editions of Aristotle's works as consisting of two or more distinct opuscula, but without any perfect agree- ment among editors as to its precise subdivision. According to Bekker, the first six chapters form a treatise on Life and Death, Youth and Old Age, while according to Weise and the Tauchnitz edition the heading of this part should be only Youth and Old Age. All the remainder is held by Bekker to be a treatise on Respiration, while Weise cuts off the last four chapters and makes them form a separate opusculum on Life and Death. There seems, however, no adequate reason for any sub- division whatsoever of the treatise, and it appears more consistent with its internal structure to regard it as a single work dealing with several closely connected topics. For convenience, however, of reference, Bekker's subdivision and chaptering have been followed in this translation, while at the bottom of each page is given the reference to the page, cc)lumn, and line of the Berlin edition. :>.,' .Lic^i^^'^z Vl rUDFACI•: ΊΊκ• text of th(! ircatisc, which was apparently ihc last of those written by Aristotle on the phenomena of animal life,' is far from being in a satisfactory condition, and it is much to be wished that some competent scholar should undertake its thoroucrh revision. There are numerous obvious A'erbal errors, for some of which the necessary amendments can be supplied with much confidence, while in other cases it is not difficult to suggest new readings, which, if more uncertain, are yet fairly probable ; but there are also no few passages where the corruption has spread more widely, and where 3. translator must content himself with giving what appears to be the general drift of meaning, while he altogether ignores some unintelligible detail. The text is also much marred by frequent and annoying repetition, and the idea irresistibly sug- gests itself that the transcriber had two somewhat different versions before him ; and that, instead of simply selecting the better of these, he attempted to combine the two, and did this so unskilfully as to cause much iteration and confusion. Throughout his task, the translator has had the benefit of frequent and valuable assistance from his friend, Mr. Poste of Oriel College, Oxford, to whom he is glad to have this opportunity of expressing his gratitude. ' 467, b, 8. Be Long, et Brcv. Vit. 6, 8. CONTENTS ΡΑπ:: INTRODUCTION ι ON YOUTH AND OLD AGE, AND ON LIFE AND DEATH 6i ON RESPIRATION η ι NOTES 107 INTRODUCTION I Life is ascribed by Aristotle to the presence of a soul, of whose activity it is the manifestation. There is a soul in all living things, whether plants or animals, but in different degrees of complexity. In plants it is purely nutritive ; ' in animals, even of the lowest grade, it is at oncXi nutritive and sensory ; in higher animals, nutritive, sensory, and locomotive ; and, in the highest of all, not only such but also intellectual. This soul, or vital principle, is not itself corporeal, but yet is inseparable from the body ; and the first question that presents itself is, in what region of the body is it located. It is, says Aristotle, to be found to some extent in every part. In plants the phenomena of cuttings and grafts clearly show this to be the case ; for each such detached piece can reproduce the entire parent-form. In some of the lower animals, such as centipedes, the fact is also apparent enough ; for, if such an animal be cut in two, each part retains sensibility and power of motion.' But, as we get higher in the scale of life, this diffusion of the soul to all parts of the body becomes less and less ' Aristollc includes reproduction under nutrition. The distinction drawn \)y him between plants and animals is of course identical with that embodied in the often-quoted formula of Linnrcus : ' Vegetalia crcscunt ct vivunt. Ani- malia crescunt, vivunt et sentiunt.' - .See note 17. H 2 INTRODUCTION apparent — being still noticeable, however, in such an animal as the tortoise,' which shows signs of life even after removal of the heart — and it altogether vanishes in the highest animals, where centralisation has been carried to the utmost extent. Such an insect as a centipede is, says Aristotle, to be regarded as though it were an aggregate of individuals fused together - by growth, and each, of course, with its separate soul. Consequently each segment of a divided centi- pede can live independently for a space, and would indeed live on indefinitely were it not that it wants the necessary organs of nutrition, such as mouth, stomach, and the rest. Even in such insects, however, there is a certain amount of centralisation./ The soul in some centrally placed indi- vidual of the aggregate — to carry on the parallel — is more powerful than the souls of the remainder ; and, as we rise from insects higher and higher in the scale of life, its predominance becomes more and more marked, and the other souls more and more subordinate, until finally they are all merged in it. What part then of the body is it that in the lower animals forms the main scat, and in the higher animals the exclusive seat, of the vital principle or soul ? Aristotle adduces many arguments to show that the organ must be somewhere in the central region of the body. This, he says, would be the most advantageous position, for by it the dominating power and the several parts which it governs would be brought into the most convenient relation with each other ; and of all possible courses nature invariably selects that which is most advantageous, a dictum which, if for nature we read God, finds re-expres- sion in the axiom of Leibnitz that of all available plans supreme wisdom combined with equally supreme goodness cannot possibly but select the best.^ To this a prioi'i ' 479, a, 5. De Resp. 17, 4, and 468, b, 15. De Juv. et Sen. 2, 7. Cf. note 139. - 468, b, 9. Dejnv. et Sen. 2, 7. ^ 'Jam suprcma ista sapientia, bonitati nnn minus infinite adjuncta, non INTRODUCTION 3 argument he adds others drawn from observation. The body of an animal, he says, consists of three divisions, the head, the thorax, and the abdomen. Now you may cut off the head of a bee or wasp, and the united thorax and abdomen will still retain vitality ; and, similarly, you may cut off the abdomen, and this will die while the thorax with the head will remain alive. In each case that extremity which is in conjunction with the thorax is the one that survives, while the part not so conjoined perishes ; from which it is clear that it is the central part that determines the survival.' Again, when a seed is germinating, it is from the point where the two cotyledons are connected with each other, that is from the most central point, that both root and stem are given off.'•^ Having thus, to his satisfaction, located the soul in the central region of the body, he proceeds to inquire more precisely in what organ of this central region it is placed. The sensory soul, he says, cannot be elsewhere than in the heart ; for all the organs of sense are connected with this heart, while among them there are at any rate two that have no connection with the brain,'' which is some- times considered to be the sensoriuin commune} But if tlie sensory principle be in the heart, there also must be the nutritive principle ; for though the soul may be capable of multiplication, as is to be concluded from the phenomena already mentioned of plants and insects, it is indivisible, in the .sense that its parts or faculties cannot be dissociated.'' The soul in each surviving segment of the divided centi- pede represents not a part of the soul of the undivided parent, but the soul in its integrity. Of the other arguments advanced by Aristotle, cither in this treatise or elsewhere, for the localisation of the soul in the heart, the most notable are that disease of this organ potuit non cliycrc optimum,' — Toil. 'J'hcoil. 8. This is llic doctrine ridiculed l)y Voliairc in his Candidc. ' Cf. note 10. " Cf. note 22. ^ Cf. note 27. ' Cf. nolo 29. '■> ( i. nolc- 3. li 2 4 INTRODUCTION is more certainly .ind more rapidly fatal than that of any other ; ' that psychical affections, such as hope and fear, cause commotion not in the brain but in the heart,- which they set in violent action ; and, chief argument of all, that the heart is the first part that is distinctly formed in the embryo, making its appearance in the chick after three days' incubation, as a red spot — thepuitciuvi saliens of later writers — which palpitates and moves as though endowed with life.' To those who held with Aristotle, and the physiologists of a long series of centuries after him, that the soul or principle of life was localised in some special and limited portion of the body, this last argument must have seemed irresistible. For the principle to which was due, among other vital activities, the successive development of all the organs of the body, could manifestly not be lodged in any other part than that which preceded the rest in its appear- ance. The only question, therefore, open to discussion would be as to the part to which this precedence should be ascribed. Had those who were inclined to place the seat of the soul in the brain recognised the primitive groove, which is the first embryonic structure to appear in the fecundated ovum, and known that this was the rudiment of the future brain and spinal cord, they would without doubt have seized on this fact to support their doctrine ; but, as things then were, the only possible competitors for the place of prece- dence were the blood or the heart and vessels in which this is contained. The appearance of the heart is in fact slightly posterior to that of certain vessels, but this was unknown to Aristotle, and is indeed expressly denied by him.^ There remained then only the heart itself and the blood between which to choose. These are, in fact, formed simultaneously, as Aristotle himself appears in some passages to recognise.^ ' 667, a, 33. De Part. iii. 4, 31. * 666, a, II. De Pa7t. iii. 4, 12. ' 561, a, II. Hist. An. vi. 3, 2 ; and 665, a, 33. De Part. iii. 4, 14. See also note 24. * 480, a, 8. De Resp. 20, 6 5 Cf. note 148. INTRODUCTION 5 Still, the striking activity of the heart, visibly throbbing in the scarcely formed embryo, as contrasted with the passive character of its contents, and not perhaps impossibly the fact that these contents when first formed are colourless ^ and therefore scarcely to be looked on as true blood, led Aristotle to assign priority to the heart — which is indeed the first organ to enter into functional activity — and to place in this the local habitation of the soul. Some twenty centuries later our own Harvey, believing equally with Aristotle in the localisation of the soul, and holding, equally with him, that such localisation must of necessity be in the first-formed part of the embryo, held that such primary part was the blood, and that this fluid was therefore the seat of the principle of life. ' There appears at first,' he says, ' a red-coloured pulsating point or vesicle, with lines or canals extending from it containing blood in their interior, and in so far as we are able to per- ceive from the most careful examination, the blood is produced before the pimctuvi saliens is formed, and is further endowed with vital heat before it is put in motion by a pulse,' and ' I hold it as consonant with reason to believe that the blood is prior to its recipient, the thing contained to wit to its container, inasmuch as this is made subservient to that ; ' "^ and again : ' From this it clearly appears that the blood is the generative part, the fountain of life, the first to live, the last to die, the primary seat of the soul, the element in which, as in a fountain-head, the heat first and most abounds and flourishes.'^ Aristotle's localisation of the soul of the higher animals in the heart, and also Harvey's localisation of it in the blood, have long gone to join many another ingenious hypothesis ; but in Aristotle's remarks, already cited on an earlier page, as to the multiplicity of life -centres in the lower ' • For we see, while the chick is in the egg, the heart beating, and it ilicn contains a transiarcnt fluid before any red globules are formed, which fluid we may suppose to be the serum and the lymjih. '—/<'//« JIuitlcr's H'orks, iii. 66. - .Sydcnlian» edit. p. 374. ' Syd. ed. p. 377. 6 ΙΧΤΚΟΙΗ'ΓΤΙΟΝ' animals, and their liiadual centralisation as one mounts the scale of animal life, is clearly to be recoc^nised the germ of the mtxlern doctrine, according to which every compound organism, however complex its structure, is to be regarded as consisting fundamentally of a number of distinct units, each endowed with its own individual vitality and capable of maintaining its existence inde- pendently of its fellows. In the lower forms these units arc precisely similar to each other, and the only bond between them is that of simple aggregation ; but soon such aggregate becomes an association, in which the units, more or less differentiated in form and function, sacrifice some part of their independence to minister to the common weal. The higher we mount in the scale of life, the greater the differentiation of the units, the more complex their mutual relations, the less prominent their independence, and the more subordinate their separate vitalities to that of tin; whole of which they arc members, until eventually the individualities of the component units are so merged in the individuality of the aggregate organism, that they are apt to be lost sight of to general observation, though it requires but slight attention to show that they are still there. In those imperfect organisms in which the component imits are little differentiated, division is merely loss of size, and the divided parts live as well as before ; but, the greater the differentiation and mutual interdependence, the less is such retention of life possible. When, for instance, the units, or groups of units, that in the division of labour have undertaken for the rest the duty of the reduction of the food, are removed or fail to perform their work, the remaining units that have abandoned this office must of necessity succumb. The reason why they do not continue to live is, as Aristotle justly observes ' of such segments of a divided insect or centipede as are without mouth or ' 468, b, 7. De Juv. et Sen. 2, 6, and 411, b, 23. De An. i. 5, 30. INTRODUCTION 7 Other such part, that they have not got the organs requisite for their nutrition ; were these present they would sur- vive. If, then, the soul be lodged in the heart, in what shape or condition is it there present ? As an immaterial prin- ciple or essence, or as an actual substance, or as an essence embodied in some material substratum ? The vivifying in- fluence of the sun was of course as conspicuous to the ancients as to ourselves. Every year, as the sun mounted in the heavens, they saw the earth waken from its winter torpor, plants and trees burst into bud and leaf, and the life of animals assume increased energy. As the sun's heat waxed greater, so also did the activity and exube- rance of life, again to subside in autumn with the fall of temperature, and to relapse in the cold of winter to its former state of suspended animation. Year after year this striking cycle repeated itself with unbroken continuity. Moreover in the living body of man himself, as of all other mammals and all birds, the most notable feature was its constant heat. The body in life was warm to the touch, and became cold on death. Excessive cold put an end to life, and cold of less intensity brought numbness to the part affected, diminishing its sensibility and power of motion, and generally checking its vital activity. With such phenomena constantly before them, it could not but be that many philosophers should identify the soul with heat, and amongst those who did so was Democritus, whose views we shall have to consider later on. This doctrine, however, did not commend itself to Aristotle. That the soul was actually heat or fire seemed to him impossible ; his reason being, if I understand him aright, that, were the soul of fire or of air or of any other homogeneous sub- stance, it must of necessity be itself homogeneous,' and not contain, as it did, distinct parts or faculties. The soul, moreover, would be alike, saving in degree, in all living ' 41 1, 1). Di• Alt. i. 5, 22-4 8 1ΝΤΚ(1Ι)Γ( ΊΊΟΝ Ihiir^s, whether plants or animals, whereas it tliffercd larijel}' in kind in the different groups. But though the soul was not itself fire, fire was its necessary agent, being indeed the material substratum in which the soul was incorporate, and without which it could not exist. ' Birth corresponds to the first embodiment of the soul in fire ; life to the persistence of this association ; death to its dissolution.' ' This fire or vital heat, in which the soul was embodied, was not ordinary fire nor ordinary heat, nor any derivative thereof, but something of nobler origin and higher powder, akin to, if not identical with, that divine substance of which the sun and heavenly bodies were made ; and it was to the presence of this celestial spark, imparted to the germ b}' the male parent at the time of fecundation, that the heat constantly developed in the heart owed its efficacy, and was enabled to produce results of nutrition and reproduction, that were quite unattainable by the action of terrestrial elements.^ That there is some special force — be it called soul, arche, entelechie, vital force, vital principle, or what it may — existing in living beings and in them alone ; a force antecedent to their structural development, and that de- termines this and all their later vital activities, has ever been and still is the creed of some philosophers and physiologists. Those who deny or dispute its existence argue that force has no existence independently of matter, and that consequently the supposed vital force must be something inherent in the constituent material of the hving body. But the living body is entirely made up of oxygen, hydrogen, carbon, nitrogen, and other similar elements. The vital force then can be no special force, but must be some force derived from those inorganic elements, manifesting itself in a special way, because the combina- ' 479, a, 29. De Resp. 18, i. Cf. notes 141, 142. ' 73^> h. De Gencr. ii. 3, 11-13. INTRODUCTION 9 tion of conditions required for its manifestation is only to be found in organic compounds. This argument, says Milne Edwards, whose statement ' of it is here follo\ved, is unanswerable, if it be once admitted that the living body is in reality entirely made up, as affirmed, of molecules of known and ponderable matter, but falls to the ground if we suppose the presumed vital force to be the property of some more subtle and intangible substance, analogous to that imponderable matter, the existence of which is assumed by physicists, and to which they give the name of ether. This hypothesis, to which Milne Edwards apparently inclines, though without perfectly distinct acceptation, approximates very closely to Aristotle's doctrine of a soul incorporate in some non-terrestrial substance, akin to, if not identical with, that ethereal element of which he conceives the celestial luminaries to be made. Before going further in our analysis of Aristotle's doctrine, it will be well to point out that his attribution of natural heat to plants and to cold-blooded animals was a pure assumption, and one for which he advances no scrap of direct evidence.^ In the higher animals the asso- ciation of life with heat is obvious, and from this Aristotle inferred without proof the universality of such association. \Vc know nowadays that in all living things, whether plants or animals, a combination of oxygen with carbon occurs in ' The argument, as stated by M. Edwards (Lcfons sur ία Phys. xiv. 261), is as follows : ' Une force n'est rien independamment de la maticrc, cllecn est line propriete, et ne saurait exister sans clle. Les principes d'aclion qui existent dans un corps vivant sont, par consequent, inlierents i la niaticre con- stitutive de ces corps. Or, la maticre dont ces corps sont formes provicnt du regne mineral ct y rctourne. II faut done que les forces en question vienncnt aussi de la matiere non-vivante et, par consequent, qu'clles soient des forces generales (ou forces inorganitjues) non des forces speciales ; seulement, pour sc manifcslcr, il faut que cette matire soit placee dans des conditions qui nc sc trowvent rcunies que chez les composes organises.' - Menestor is said by Tlieoi)liraslus {Dc Causis Plant, i. 21, 6) to have found evidence of the heat of certain water-plants in their not being frozen in' winter, and of certain trees in the melting away of snow from their leaves. ΙΟ INTROI)UCTK~)Isr the tissues, and that this combination must of necessity be accompanied by the disengagement of heat ; but this gcncrahsation is one of our own days, and even in the earlier part of the present century we find physiologists of high repute, such as Trcviranus, altogether rejecting the idea that plants, reptiles, amphibia, fishes, and inverte- brates, when in their usual condition, possess any power of generating heat.' There are exceptional occasions when the warmth developed by a plant or a cold-blooded animal may become more or less readily perceptible, as in the spathe of a flowering arum or the body of an incubating serpent ; but under ordinary circumstances the heat developed is so slight as to be quite inappreciable without delicate instrumental appliances, and indeed in plants is usually counterbalanced, or overbalanced, by the re- frigerating effects of transpiration and the fixation of carbon. Whether the soul was identical with fire, as Democritus had taught, or whether fire was merely the substratum in which the soul was incorporate and the instrument of its activity, as Aristotle maintained, fire was equally of abso- lute necessity ; for without it life was impossible. But the body was incessantly parting with its heat, as was obvious to sense, and there must clearly be some means of repla- cing the loss. This replacement was brought about by the food, which after a primary concoction in the stomach passed to the heart and there underwent a second elaboration, accompanied by the development of vital heat. That the food is the fuel by which the heat of the animal body is maintained is of course true, the greater part of it being used simply for that end ; and if Aristotle thought that the production of heat at its expense took place in the heart, we may remember that Lavoisier, ' ' Eben so wenig als die Pflanzen besitzen im Allgemeinen die siimmtlichen Thicre, nur die Sauglhicre und Vcigcl ausgcnommcn, ein Vermogen Warme zu cnlwickcln.^— β ιοί. v. 20 (iSiS). INTRODUCTION I I with his later knowledge of the nature of combustion, not less erroneously located that production in the lungs. The doctrine that the heart was the source and centre of vital heat, and that this heat was something of nobler quality and greater efficacy than ordinary fire, appears to have been universally accepted as indisputable truth for many centuries after it had been laid down by Aristotle. It was fully held, at one period of his life, by Harvey, who borrows Aristotle's own language to describe the celestial nature of the vital heat,' and who in his Prelections, written in 1616, speaks of the heart as the /ons totius caloris and its arx ct dojn{ciliu7n. At a later period, however, Harvey changed his views in this matter.^ He had, as mentioned on an earlier page (p. 5), transferred the seat of the soul from the heart to the blood, and with the soul he naturally also transferred the vital heat with which it was associated ; and we now find him maintaining, in contra- diction with his former views, that ' the blood, instead of receiving, rather gives heat to the heart, as it does to all parts of the body,' and that ' the blood is the element in which, as in a fountain-head,^ the heat first and most abounds and flourishes.' Van Helmont had already in some degree dissented from Aristotle's doctrine, but this later teaching of Harvey appears to have been the first serious departure from it. The doctrine, however, once called in question, its assail- ants soon became numerous. The existence of any special kind of heat, whether in the heart or elsewhere in the body, was contested, and the vital heat declared to differ in no respect from that which is developed during fermentation, or which can be produced by friction ; and while some, as Descartes,'* attributed it to the former cause, others, as ' Harvey's Exerc. de Gen. An. 70, and Arist. De Gen. ii. 3, I1-13• * This change in Harvey's views as to Ihc localisation o( vital boat has been noted by Dr. Church in his interesting Ilarvcian Oration for 1S95 (p. .50). ' Sec passages f|uoted at p. 5. * Works ^ iv. 437 (Cuusiii's ed.) 12 INTKOnUCTION Ilallcr,' ascribed it to the latter, the particles of the blood being rubbed during its circulation against the walls of the heart and vessels. Descartes, it is true, while he thought that vital heat was no more than ordinary heat, imagined that the fermentation to which it was due occurred within the heart, and so far still held to the Aristotelian doctrine. But this partial adherence ceased to be possible when Borclli, introducing a thermometer into the body of a living stag, showed that the heart was in no degree hotter than any other of the viscera.- This experi- ment, repeated by others with similar results, gave its death-blow to the ancient doctrine, which fell to the ground never to rise again. Some dim vestige of its past exis- tence still, however, apparently lingers in our language, when we speak of men as warm-hearted or the contrary. But life not only was threatened with extinction from loss of heat, but also was in constant danger from its excess. Very excessive heat was as fatal to both plants and animals as excessive cold ; and that minor excess was also injurious, if not fatal, to animals was shown by the malaise and the fever it produced in them. Now the fire in the heart, fed by fuel from the stomach, was always tending to produce such excess ; and as there was provision for maintaining the fire, so also must there be provision for keeping it in bounds. This provision Aristotle finds in respiration for such animals as have lungs, and for other animals in the bathing of their gills or the general surface of the body in a medium colder than themselves. He is thus brought to deal with Respiration, and to this he devotes the chief part of his treatise. The exposition of his views and those of his predecessors on this subject, and the fate of their various speculations in later ages, will occupy the remaining sections of this introduction. ' ' Hactenus certe maxime probabile videtur, utique a motu sangiiinem in- calescere ; etsi nondum constat, quare magis quam aqua, ct quare non super cerium gradum incalcscere possit.' — El. Phys. ii. 307. ^ De Motu Atiini. (Rome, 16S1) ii. 1S9. INTRODUCTION 1 3 We must first, however, deal with another subject. It has been seen what were Aristotle's views as to life : it remains to consider what were his notions regarding death. Death he very properly divides into violent and natural ; meaning of course by the former not merely death from those coarser external forces to which we usually limit the term ' violence,' but death from disease, or such adventitious cause as is not inherent in the normal consti- tution of the body ; while natural death is that termination which, independently of disease or violence, comes inevi- tably in due course of time to every living thing.• To what is this natural death attributable ? In what does its necessity consist, and what is it that prevents a living thing, when it has once come into being, from living on indefinitely .■* In answer to this difficult question, modern writers tell us that there is in the body a something, which may be spoken of as life-force or life-material, that is constantly being consumed and as constantly reformed ; and that, while in the earlier stages of life the formation is in excess of the consumption, so that at that period accumulation occurs, and while in middle life production and consumption balance each other, in the later period of age expenditure becomes excessive, so that the stock gradually diminishes, shrinking, to borrow a simile from Huxley, like Balzac's pcau de chagrin with each vital act, until at last it is used up and life comes to an end.- This something was held by Aristotle to be vital heat. In youth this was at its maximum, and the mechanism for its regulation being as yet imperfect, inasmuch as the lung had not yet acquired its full develop- ment, there was excessive expenditure, as manifested by the energy of growth. In the prime of life, when the organ of regulation had acquired its full power, the c.\[)cn(.liture was ' 478, b, 24. De Resp. 17, i. ' Bacon, in his His/oria Vila et Mortis, ascrihcs natural rlcath to the gradual dissipation of the animal or vital spirit to which all the jihcnonicna of life arc due ; and the purjjosc of his treatise is to teach physicians hy wJiat means the escape of this spirit can he retarded. 14 INTRODUCTION brought under control, and growth ceased with the exception of that form oi it which consists in reproduction. Heat, how- ever, was still being lost, and by this gradual dissipation the amount remaining in old age became so small that it was comparable to ' a flickering flame, which the slightest casual disturbance would put out.' ' Such disturbance, moreover, could not but come, inasmuch as the lung had now become hardened by gradual evaporation of its fluid, and so unable adequately to perform its office of heat-regulation.•^ Such appears to have been Aristotle's explanation of natural or inherent death ; and it seemingly implies the belief that, though heat was constantly being developed in the heart, the amount thus produced was always somewhat less than that which was given off, and that the deficiency had to be made good out of the stock with which the organism started originally, that is, from the innate heat in which the soul was incorporate ; and that this eventually was so reduced by the constant drafts made on it that it became insufficient to support the soul. Natural death, then, being inevitable, after what lapse of time does it come .-* The natural span of life, says Aristotle, differs greatly in length in different species. These differences must depend ultimately upon radical differences in the material constitution and its degree of harmony with the environment.^ But, nevertheless, there are certain characters that, as a general but by no means universal rule, stand in close connection with specific longevity. As a rule big animals or plants are longer-lived than the smaller kinds ; sanguineous animals, or vertebrates, than exsanguineous animals, or invertebrates ; and, gene- rally, the more perfect animals than the less perfect ; and, lastly, a long gestation period goes, in most cases, with long duration of life. These views as to specific longevity are in strict ac- ' 479, a, 19. Dc Resp. 17, 7. - Cf. note 35. ^ 777i 1J) 7• ^^c Gen. iv. 10. INTRODUCTION 1 5 cordance with those of modern physiology. Bulk, degree of organisation, period of gestation are to a great extent correlated ; for great size is habitually associated with high organisation, and this with lengthy gestation ; and that these three factors should conduce to length of life is not only shown to be probable by the deductive reasonings of philosophical biologists,' but is a conclusion supported by the results of actual observation.^ II The external phenomena of human respiration, namely, the alternate inhalation and expulsion of air through the mouth and nostrils, with the accompanying rise and fall of the walls of the thorax, must have been familiar to man from the time when he first appeared on the earth. Nor can we suppose that there ever was a period when the continuance of this respiratory process was not regarded by him as a sure token of life, and its permanent cessation as an equally sure token of death. But between the familiar recognition of a phenomenon and the first speculation as to its cause and meaning centuries may intervene ; and we have no reason to suppose that in all the long ages that preceded the days of the early Greek physicists one single mind was led to investigate the phenomenon in question. Even when Greek speculation began, although this was strictly confined to the phenomena of Nature, to the exclusion of those other branches of knowledge which were comprised in Greek philosophy at a later period, very few of the physicists, as this first school of philosophers were called, turned their attention to the subject of respiration ; which, engaged as their minds were in attempts to fathom the inscrutable mystery of the nature and composition of ' See n. Spencer, Princ. of Biol. i. Ch. on Growth, and Kay Lankcslcr, Comp. Loiii^cvity, pp. 30-60. ^ See note 81. l6 INTRODUCTION^ the universe, must have seemed to most of them but a trivial and humble subject. Still, there were some few among them who found time to consider the phenomena in question, at any rate to a certain extent ; though we can but suppose, if the scanty accounts of their views that have been preserved fairly represent the results of such consideration, that the time devoted to the problem must have been extremely limited. It is true that we scarcely know more of the views of these speculators on respiration than has been preserved for us by Aristotle, who was in this matter their antagonist, and that the views and arguments of a writer are rarely put forth in the best and most favourable form by an antagonist, however desirous he may be to do them justice. Not only, however, was Aristotle manifestly a man of truth, but, prompted apparently by the fear that the strangeness of his predecessors' doctrines might leave his account of them open to suspicion, he protests difectly against being supposed to have misrepresented men who were no longer present to defend themselves, and avers that in stating their views he has practically used their own words. Be this, however, as it may, we have no choice but to accept his account of the matter, and in sketching the ancient theories of respiration we must of necessity take him as our chief guide. The aspect of respiration to which these earliest writers mainly devoted their attention was the mechanism of the process ; to which some further added the question of its universality in the animal kingdom, and some few the purpose to which it was subservient. Strangely enough, as it appears to us, and, indeed, as it appeared to Aristotle, who makes complaint of it, this last question, that of its utility, was one to which scarcely any of them attempted to give an answer. They seem, as a rule, to have been content to regard respiration as no more than an INTRODUCTION 17 inseparable accident of life (σύμπτωμα), though a moment's reflection would have shown them, as Aristotle points out, that this position was untenable, and that respiration was absolutely essential to its maintenance. Democritus, it is true, formed an exception to this rule, nor was he the only- exception, as will be seen later on ; but at present it will be best to confine ourselves to the various views as to the mechanism of respiration, reserving the question of its utility for later consideration. The earliest philosophers, then, of whose views as to the mechanism of respiration any record has come down to us, are Anaxagoras and his contemporary Diogenes of Apollonia. Aristotle tells us that these philosophers held that all animals respire, and he has preserved for us a scanty account of the mode in which they supposed the process to be carried on in fishes. They imagined that, when a fish discharges water through the gills from the oral cavity, air passes in from the surrounding water so as to fill up the otherwise vacant space in the mouth, and that the air thus abstracted from the water is then inhaled by the animal. Aristotle does not tell us how they accounted for air rather than water passing in through the mouth so as to fill up the vacant space, but we may plausibly suppose that their notion was that, when the water is being expelled through the gills, the fish closes its mouth — as, indeed, is to a great extent the case — but so closes it as to leave apertures large enough to admit the particles of air, but not large enough to allow the passage of water ; for Galen who some centuries later also held that water contains air, and that this air is utilised by fishes for respiratory purposes, supposed that in the gills there were minute openings of similarly nicely adjusted calibre.' ' ' Earum, quas liranchias nuncupamus, construclio ijisis vice pulmonis est ; cum cnim crcbris ac tcnuilnis foraminihus sint branciiix• haj interceptiv, acri quidcm ct v;i])ori pcrviis, subtilioribus quam pro mole aqua•, banc quidcm extra r<.'pcllunt, ilia autem promjite intromilUmt.'— Galon, De Usn Part. vi. 9, C 1 8 INTRODUCTION That ordinary water docs in fact contain air, and that this air serves for the respiration of fishes, we now know to be perfectly true. But it was not for very many cen- turies after the time of Anaxagoras or of Galen that the fact was established.' And in Aristotle's days the objec- tion made by him - that if there were air in water it would of necessity rise to the surface and escape must have seemed quite unanswerable. ' It had been noticed by divers authors,' says Boyle,•'' who, however, does not apparently accept the statement as certainly true, ' that fishes soon die in ponds and glasses quite filled with water, if the one be so frozen over and the other so closely stopped that the fishes cannot enjoy the benefit of the air ; ' but this clearly pointed rather to the necessity of the air outside the water than to the necessity of air in the water itself; and, whatever suspicions may have been entertained from more or less imperfect observations, it was not until Jean Bernoulli,^ writing in 1090, and following out the previous experiments and observations of Boyle'' and ' In the spurious Hippocratean treatise De Flatibus (ch. v.) is the fol- lowing passage : ' Moreover, that the sea is not entirely void of air is manifest. For such creatures as swim could not possibly live if they had no supply of air. And how can they be supplied except by means of the water, and by drawing air from it ? ' - 443, a, 4. De Sensu et Sensili, 5, 2. ' Boyle's Works, i. 109. ■• • Videmus si aqua vel alius liquor super igne coquatur bullulas excitari, manifesto certe aeris intro latentis indicio, qui ope ignis dilatatur, omniaque vincula quibus retinebatur solvit, et ob levitatem ad superficiem usque fertur, ubi tales bullulas format ; hinc fit ut pisces in aqua quae semel ebuUiit vivere non possint, ob defectum nempe aeris qui in ebullitione omnis exhalavit ; aerem enim et pisces haurire seque necesse est ac csetera animalia. In hunc finem eorum branchiae condita sunt, ut illarum ope aerem, qui ad vitam sustinendam necessarius est, ab aqua secernant, ut de hac re recte sensit CI. Majowius. Similiter liquoribus aerem inesse experimenta Boyliana confirmant ; si enim in vase recipiente liquor aliquis includatur, ex quo deinde ope antliae pneumatics aer extrahatur, statim videbimus innumeras bullullas (sicut in aquas ebullitione) ex liquore prorumpere.' — J. Bernoulli, Disseft. de Effei-vescetitia, ch. xiv. * Boyle {Phil. Tr. 1670, and Works, iii. 361), after showing that there was ' air lalitant in water,' and even attempting to determine its amount, had INTRODUCTION I9 Mayow, showed that bubbles of air are given off from water when it is heated over the fire, and that fishes are unable to exist in water that has been boiled, and thereby altogether freed from its contained air, that either the presence of air in water or its utilisation by fishes can be said to have been definitely established, or even to have had the support of any very serious argument. Aristotle, then, was perfectly justified in rejecting as he did the notion that fishes breathe air contained in water as a baseless fancy. He had, however, other weighty argu- ments to urge against Anaxagoras and Diogenes ; and of these the most telling, in the then state of knowledge, must have been that, if a fish inspires air, it must give this out again in expiration, and that in that case bubbles should be visible when a fish is kept under water, as is the case when a tortoise is so treated, but that nothing of the kind can be detected on experiment.' He asks further— and not without pertinence — seeing that, according to Mr. Lewes,"^ even in these days it is not easy to give a thoroughly satisfactory answer to the question — how comes it about, if a fish breathes air, that, when it is taken from the water and put. in the air itself, it dies with every appearance of suffocation ; for, says he, the answer of Diogenes that it dies under such circumstances because it has too much air is foolish, seeing that no other animal that breathes air is ever injured by excess of it. The difficulty propoundctl by Aristotle is a real difficulty, and, as already mentioned, is held by some modern writers to remain as yet unsolved. There are, however, experiments that appear to supply a fairly adequate explanation. For Spallanzani showctl furtlicr propounded the ' quccrc : whether in common water tlicre may not In- concealed air enough to be of use to such cold animals as fishes ; and whetlicr it may be separable from the water that strains through their gills.' ' It was by observing that bubbles of air arc given off from the sligmata of insects when kcpl under water that Malpighi demonstrated the rcspiralury function of their tracheal system. ' Immersis bombycibus prajcipuc in ardcnle aqua multum aeris sub bullarum specie ascendit ' {/)e Hombyc. p. 13). ■-' Lewes' Aristotle, p. 176. C 2 20 INTRODUCTION iong ago that the gills of a fish act in air no less than in water ; and more recently Mourcns and Bert have shown that the reason why such action in the air is in most cases insufficient for the maintenance of life is to be found in the collapse of the gills when no longer floating in water of practically the same density as themselves, and the conse- quent enormous reduction of their exposed and acting surface. The next philosopher, so far as is known, to handle the mechanism of respiration was Empedocles. This writer unfortunately chose to clothe his utterances in the garb of sonorous but very obscure verse, with the result, possibly with the intention, that, while the general outlines of his conceptions are fairly displayed, all detail is con- cealed from view. The twenty-five lines in which he dealt with respiration have been preserved by Aristotle, and are interpreted by him as follows : ' There are certain vessels which contain blood, but not in such amount as to fill them. These vessels communicate with the external air by pores, which are too small to admit the particles of blood, but large enough to give passage to those of air.' Now it is the nature of blood to move backwards and forwards, and, when it moves backwards, the air flows in through the pores and inspiration occurs, but when it moves forwards the air is driven out, and expira- tion is produced.' Aristotle, as his criticisms show, supposes Empedocles to have been speaking of respiration through the nostrils, and such is by far the most probable explana- tion.^ But it is the belief of some authorities, and not per- haps altogether impossible, that in this Aristotle is mistaken, and that Empedocles was in reality speaking of a supposed respiration by the general cutaneous surface ; and, supposing ' Much in the same way Aristotle supposed that the sweat was discharged on the surface by passages which were continuations of the blood-vessels, but were too narrow to give passage to the blood itself. Cf. 668, b, 3. De Part. iii. 5, 13. It was indeed by the existence of such pores of various calil)re in connection with the blood-vessels that all secretion was explained. 2 Cf note 66. INTRODUCTION 21 this to be the case, the conjecture may be hazarded that the terminal pores of the vessels, which alternately admit and discharge air with the ebb and flow of the blood- tide, were the orifices of the sweat-glands, visible at times to the naked eye in the palms of the hands, where they are both exceptionally numerous and exceptionally large. On this supposition there would be a curious kind of agreement between the teaching of Empedocles and that of modern physiology ; for that there is a general cutaneous respiration is undoubted, and it is probable that the orifices of the sweat-glands are the main channels through which the gaseous exchange between blood and air is brought about. Such agreement, however, supposing it to exist, would of course be merely accidental, and there can be no doubt that the speculations of Empedocles as to respiration were no more than speculations, and stood on no basis of observed fact or of anatomical investigation. There remains but one other pre-Aristotelian attempt to explain the respiratory mechanism, but this one is, for our present purpose, the most important of all ; for it is that of Plato, who, as Galen ' tells us, borrowed his phy- siology from Hippocrates, so that this explanation of the process must be taken to represent the views of the fore- most minds at the time when Aristotle took the subject in hand, and so, by giving the point from which he started, enables us to measure any advance he may have made. The account, then, of respiration as given by Plato in the ' Timaeus,' ^ and as summarised fairly by Aristotle, is as follows : 'When the hot air is discharged by the mouth, the surrounding air is thrust forwards by it, and being carried on by the impulse is made to pass through the porous surface of the body, until it occupies the sclfsainc space as that from which the hot air had issued, the ' Plato * cum Ilippocratis imitalor, si qiiis alius uni|uani, fuciil, ct al) iIId dogmata mutuatus bit maxima.'— /λ• Usu Purl. i. S. * Cf. note s6. 22 INTRODUCTION replacement being determined by the impossibility of a vacuum ; and this air in its turn, when it has become heated, passes out again by the same channels as gave it admission, and, impinging on the air that was previously discharged in a hot condition through the mouth, drives this back again through that orifice to the interior space, and thus a continuous alternation of inspiration and ex- piration is kept up.' This strange attempt to account for the visible phe- nomena of respiration manifestly can have had no pretence of being based on observed facts or on anatomical structure. It was a mere creation of the imagination, and is properly stigmatised by Aristotle as a baseless fiction. Strange, however, as the account is, and curious as is the light it throws on w^hat was held to be adequate explanation of natural phenomena in the pre-Aristotelian period, it is perhaps no less strange and curious to find its ghost still walking the earth as late as in the seventeenth century. At that period it had long been thoroughly recognised that the expansion of the thoracic cavity during inspiration was due to muscular action, and notably to the action of the diaphragm, and neither, as Plato had supposed, to the pressure of incoming air, nor, as Aristotle supposed, to heat ; but it was still a matter of dispute what caused the air to enter the expanded cavity, and whether the lungs were active or passive in the process. To this question, says Boyle,• writing in 1660, 'some of the best modern philosophers answer, that by dilatation of the chest the contiguous air is thrust away, and that pressing upon the next air to it, and so inwards, the propulsion is continued until the air is driven into the lungs and so dilates them.' To this view, as Boyle goes on to state, it was objected by Bartholin that, if a large glass vessel be taken with a narrow neck, a man, on applying his mouth to the orifice, can suck in air from the vessel, though clearly its walls must prevent ' Boyle's Works, i. lOO. INTRODUCTION 23 all pressure from without. One would have supposed that this objection would at once have put an end to the supposed explanation ; but ghosts are hard to lay, and it was answered to Bartholin's objections, as we are told by John Mayow,' that, though air is unable to pass through glass, yet there may be some more subtle matter that can do so, and that it may be that this matter, propelled by the compressed air without, passes through the walls of the vessel and is driven into the thorax. But if this be so, says Mayow, how comes it about that if a bird or other animal be shut in a glass vessel, and the air be extracted by the then recently invented air-pump,- the animal is unable to breathe, although the glass walls form no impediment to the passage of the particles required for respiration ? This seems at last to have administered an effectual quietus ; at any rate I have been unable to find any further appearance of the ' Tima^us ' doctrine in later writers. Such, then, were the notions, so far as they have come down to us, entertained by Aristotle's predecessors in regard to the mechanism of respiration ; it remains to con- sider what were their views as to its utility. Very few of them, says Aristotle, troubled themselves about this. They looked on the process as something incidentally associated with life but as in no way essential to its maintenance. There were, however, some exceptions. Thus there is a ' 'Alii vero existimant, aerem circumambientem proximum sil)i vicissim [iropellere, et ita continuari propulsionem, ut acr tandem ori vicinior in pulmoncs impellatur.' But he says, ' certo experimento constat posse aerem e vitro satis amplo, cum tenui tamen collo, quamquam naribus arete obturatis, per os hauriri et inspirari. Enimvcro in hoc casu ])ropulsio ilia per vitrum ori, uti supponimus, adaptatum continuari non potest. Contra allalum experimentum nonnulli respondent, subtiliorcm quandam materiam, ab aerc comprcsso propulsam, vitrum permearc et in thoraccm im|)clli. At qui fit ergo, quod animal quodvis, veluti avis, vitro inclusa, ex quo aer postca extrahilur, rcspirare non possit, si particulae respirationi idonccc vitrum illud etiamnum pertranseant ? ' — Mayow, De Kespiralione (Oxon. 1669), p. 3. ^ The first air-pump was made by Otto von (jiicricke and exhibited by liim at Ratisbon in 1654. Improvements were made in it by I'oyic. J 4 INTRODUCTION passage in tlic ' Dc Partibus ' ' from which it appears that there were among Aristotle's predecessors or contem- poraries some who held that it was to respiration that the action of the heart was due. What was their precise meaning we can but conjecture. The action of the heart is undoubtedly, in a sense, due to respiration, for if this latter process be stopped, as when an animal is strangled, the blood is unable to pass through the lungs, and this arrest of the pulmonary circulation acts backwards upon the heart and soon brings its motion also to an end. But it is scarcely necessary to say that this cannot possibly have been the meaning of those who, in the days of Aristotle, attributed the heart's action to respiration. It must have been to the mechanical process of respiration, to the alternate expansion and contraction of thorax and lung, and not to the utterly unsuspected chemical changes, that they attributed its influence upon the heart ; and the view is therefore worth a passing notice, as being the starting-point of a similar doctrine held by certain iatro-mechanical physio- logists in the seventeenth century, when Hook,^ by one of those noble and decisive experiments that from time to time clear away the mists from the path of science, gave it its death-blow. He contrived an arrangement by which a constant current of air was kept passing through the lungs of a dog without any motion occurring either in lung or thorax, and showed that under such circumstances life was maintained, and the action of the heart continued as before without check or hindrance ; so that the heart's action was in no way dependent upon the lungs' motion. We have next to consider the views of Democritus, who is the only philosopher mentioned by Aristotle by name, as having attributed any use in the animal economy to respiration. According, then, to Democritus, the universe consists of ' ' It has been stated, but incorrectly, that it is to the lung that the throb- bing of the heart is due.'— 669, a, 18. De Part. iii. 6, 5. ^ Phil. Trans. 1 667, Abridgement, i. 194. INTRODUCTION 25 plenum and vacuum, or, in other words, of matter and empty space. Besides these there is nothing else, nor does soul or mind form an exception. Space is unbounded, infinite ; matter is reducible to an infinity of indivisible particles or atoms, that present endless variety of form and size, though they are all precisely alike in substance. All things are aggregates of these atoms, and, though such aggregates may break up, and their constituent atoms enter into new combinations, and though these changes may go on in endless succession, yet the atoms themselves remain unchanged ; they are uncreated and imperishable. The differences, then, between substances — mind and soul included — depend on differences of their constituent atoms, and these, as already stated, are differences of form and size, and, it may be added, of position. Now the soul is identical with fire, as is indicated by the palpable coincidence of life with heat ; and as the soul is the cause of all vital motion, thought itself being a kind of motion, the atoms that con- stitute the soul or fire must be those whose form and size are most suitable for rapid motion. Such are the finest spherical atoms. The soul, then, that is the animating principle which is the source of vital heat and of all vital activities, is made of these ; and these fine spherical atoms are diffused throughout the body, alternating with the grosser and less mobile atoms that constitute its bulk. These spherical or soul atoms, in virtue of their essential mobility, and in consequence of the pressure of the environing air, are always escaping from the body. The escape of a certain small proportion, if unreplaced, causes sleep ; of more, causes swooning or apparent death ; of still more, causes actual death ; and, as the atoms are always escaping, death would soon ensue, were it not that the loss is constantly replaced by new spherical atoms inhaled with the air from outside. For the air is charged with such mobile spheroids, aggregates of them being visible as dancing motes in the sunbeam. Inspiration, moreover, not only thus replaces the lost soul-atoms, but 20 INTRODUCTION hinders their ready escape ; for the inhaled air counteracts b)' its opposing action the pressure of the air without.' This doctrine of Democritus, as to the replacement of soul-atoms by inspiration, would appear from a fragment preserved in the ' De Anima' (i. 5, 13) to have been to a certain extent ^ anticipated by the author of the so-called Orphic poems, when he wrote that ' the soul, borne by the winds, enters from the universe into animals during inspira- tion ; ' and may also be regarded as the lineal predecessor of the doctrine of the obscure vitalists of later ages, who even up to the time of Hallcr were teaching that the inspired air contains a number of active, spirituous, and ethereal particles, which pass from the lungs to the heart and arteries ' inque his organis in spiritum vitalcm forma- tur, in reticulo vero mirabili cerebri in animalem spiritum abeat. Neque inter nuperos desunt, qui banc animalium spirituum ex acre generationem tuentur.' ^ Limiting our view, to the physiological aspect of his doctrines, we see that Democritus assigned to respiration the all-important office of maintaining the heat of the body, replacing by a continuously fresh supply that \vhich was being as continuously given off from the surface ; and this fresh supply he supposed to be con- tained, already as heat, in the inspired air. There were, however, others whose names have un- fortunately not been preserved for us by Aristotle, but among whom was not impossibly to be reckoned Hippo- crates,'' who, while they agreed with Democritus that the end of respiration was the maintenance of heat, parted company from him when he said that this heat was introduced as such by inspiration, and held that the ' See, for a fuller exposition of the doctrines of Democritus, Zeller, Pre- Socratic Phil. vol. ii. ^ Asclepiades also, according to Galen, ascribed to respiration ' animse ipsius generatio ; ' while Protagoras followed his master Democritus in attri- buting to it not the ' generatio ' but ' corroboratio qucedam animse.' De Util. Resp. ch. I. ^ Ilaller, El. Phys. iii. 333. ■• Cf. notes 57, 59. INTRODUCTION 27 inspired air acted in the body as the air acts in a stove, and served as a kind of fuel. This view, of high interest in the history of physiology, as being the starting-point of the modern theory of respiration, was rejected by Aristotle with scanty con- sideration ; and, though a much nearer approximation to the truth than his own later doctrine, was, it must be admitted, justly rejected by him. The air that was given out in expiration was, so far as was then known or believed, precisely similar, save in temperature, to the air that had been taken in, and the suggestion that it served as fuel was therefore quite unmeaning. The one fact on which it rested was the manifest necessity of air for the maintenance of fire. This necessity was, of course, I)erfectly well known to Aristotle, who points out that, if the air be excluded from the coals in a chafing-pan by shutting down the cover, the fire is extinguished.^ But for this fact he had, as he thought, an adequate explanation. For, he believed, as did others for centuries after him, that fire could be extinguished, among other agencies, by excess of heat ; and that the reason why air prevented such extinction was that it tempered this excess, and kept the heat within necessary limits ; a doctrine of which, curiously enough, a remnant still survives in the popular belief that a fire will go out if exposed to the blazing rays of sunshine, the soils ardoribus, as Galen said.^ Another equally fatal objection in Aristotle's mind to the suggested use of respiration was that, while all animals required their vital heat to be maintained, it was only by a limited number of them that air was inspired. The suggested explanation was, therefore, inadequate to cover ' 470, a, 8. Dejuv. et Sen. 5, 5. * De Ulil. Resp. ch. 3, where Galen enumerates the various agencies by which fire can be extinguished. So also Aristotle (Prohl. iii. 23, and xxxiii. 2), ' Λ small fire can be put out by a large fire or by the sun ; ' so also Eacon, ' Flame likewise, as Aristotle well observed, is extinguished and over- powered by a greater and more powerful flame ; much more the spirit ' (Spcdding's ed. v. jit). 28 INTRODUCTION the facts, whereas his own, to which wc shall come presently, as he supposed took them all in. There remains for mention the view entertained by Plato, which, strangely enough, is not noticed by Aristotle, although, so far as it went, it bore a close resemblance to his own theory. Plato does not appear to have ascribed any use to respiration under ordinary circumstances,' but to have supposed that its beneficial effects were limited to certain occasions, when it served to check the ebullition caused by fear or passion. It will be best, however, to state his views in his own words as given in the ' Timaeus.' ' But the gods, foreknowing that the palpitation of the heart in the expectation of danger and the swelling and excitement of passion, was caused by fire, formed and im- planted as a supporter to the heart the lung, which was in the first place soft and bloodless, and also had within hollows like the pores of a sponge, in order that by receiv- ing the breath and the, drink it might give coolness and the power of respiration and alleviate the heat. Where- fore they cut the air channels leading to the lung, and placed the lung about the heart as a soft spring, that, when passion was rife within, the heart beating against a yielding body might be cooled and suffer less, and might thus become more ready to join with passion in the service of reason.' ^ III Such were the notions as to respiration that had been promulgated by the foremost minds in Greece when Aris- totle turned his attention to the subject. It was at once apparent to him that the mode in which his predecessors had approached the question was not such as could possibly give a satisfactory answer. If you would under- stand the working of a machine you must first study its structure ; nor will even such study be effectual, unless it be guided by the belief that the machine is made to sub- ' See, however, note 57. ^ Jowctl's Trans, iii. 492. INTRODUCTION 29 serve some purpose or other, to which its structure is adap- ted. ' The main cause/ says Aristotle, ' of these erroneous statements was the ignorance these writers were in as to the internal organs, and the fact that they had not grasped the truth that nature in all her works has a final cause in view. For had they put the question to themselves, what is the purpose for which respiration exists, and had they sought for an ansv/er by investigating the parts of the animal body, such as the gills and the lungs, they would soon have hit upon the right explanation.' ' That the study of function must be preceded by the study of structure, or, in other \vords, that physiology must be based upon anatomy, seems to us nowadays so trivial and so self-evident a statement, that we can hardly realise that there was a time when its truth was not recognised, and are, in consequence, likely to overlook or underrate the enormous value attaching to its first distinct enuncia- tion. We have, however, only to consider the accounts of the process of respiration given by Aristotle's prede- cessors, and discussed in the preceding pages, to see that what to us is so self-evident was to them absolutely hidden ; and, reflecting on this, we shall scarcely be dis- posed to join with those who, finding many strange blun- ders in Aristotle's physiological conclusions, express as- toni.shment at the rcnovvn he has enjoyed for ages as a biologist, and shall admit that, howe\cr unsuccessful he may have been at times in the practical ai)plication of his method of inquiry, its simple enunciation was in itself an ample justification for the perpetual niche allotted to him in the temple of fame. liy insisting on the absolute necessity of anatomical observation, he carried biology at one step from the world of dreams into the world of realities ; he set the science on a substantial basis, and may indeed be said to have been its founder, for the vain imaginings of his predecessors can hardly be dignified with the name of science. 471, 1), 23. /V AVr/•. iii. 8. 30 INTRODUCTION Doubtless, Aristotle thouciht that his new instrument of research was a much more powerful instrument than is in realit}' the case. We know now that simple observation will carry us but a little way if unsupported by experiment. That was a truth which had not revealed itself to Aristotle ; and though Galen made not inconsiderable use of experi- mentation, especially in his inquiries into the nervous system, it was not till after nearly seventeen centuries had passed away that its paramount importance in scientific research was distinctly recognised by Roger Bacon, and set forth in such forcible terms as the following : — ' Sed priEter has scientias est una perfectior omnibus, cui omnes famulantur, et quae omnes miro modo certificat ; et ha;c vocatur scientia expcrimentalis, quae negligit argu- menta, quoniam non certificant, quantumque sint fortia, nisi simul adsit experientia conclusionis . . . et haec pars hujus scientiai extendit se ad cognitionem futurorum et ad operationem mirabilium operum naturae et artis.' ^ Of this paramount necessity of experiment and the inadequacy of mere observation for the solution of mo.st problems, Aristotle had no conception. He thought that the functions of the several bodily organs could be deduced from simple observation of their structure ; and, with this conviction, he set himself zealously at work to examine the anatomy — internal and external — of all animals that came within his reach. The large number of species of whose organisation notice is to be found in his treatises shows how indefatigable was his industry in this work, though we may assume as highly probable that there Avere followers and students who aided him in his task. Doubtless his dissections — of which he wrote an illustrated ^ treatise, now unhappily lost — were of a somewhat rough character. He was contented with the coarser anatomy of the parts, the importance of more delicate investigation being neither ' Opus TertiutJi, ch. xiii. p. 44 (Rolls edit.) '^ Hist. An. i. 17, 19, iv. i, 25, vi. W, τ,; De Gen. ii. 7, 6, 497, a, 32, 525, a, 8, 566, a, 15, 746, a, 14. INTRODUCTION 3 1 recognised, nor its prosecution practically possible with such imperfect instruments as were then procurable. The scalpels, whether of iron, copper, or bronze,' must have been but clumsy articles, and quite unsuited for following out the course of a nerve or small vessel ; the injection of veins and arteries with coloured size had not as yet been devised ; there were no magnifying glasses, and no spirits of wine or other fluids to preserve the soft parts or harden them for careful examination, even if such had been thought necessary. Still, to speak of Aristotle's dissections as ' carving-knife ' dissections, as some have done, appears to me an unwarranted exaggeration, as any candid person will, I think, allow, if he read the description given of the heart and blood-vessels or of the lung in the ' Historia Animalium.' There are minds to which the mistakes and shortcomings of great men apparently present greater at- traction than their achievements. To them Bacon is but a man who believed in the spontaneous generation of mistle- toe ; Cuvier, an upholder of the fixity of species ; Kepler, one who thought that the huge volcanos in the moon were artificial structures built by its inhabitants ; Descartes, an assertor of the immediate transmission of light ; and Newton himself an advocate of the emission theory. To such persons Aristotle's anatomical statements will doubt- lessly supply much desirable pabulum. Ikit those more genial critics, who prefer to dwell upon what a man has done well rather than upon that which he has left undone or done amiss, and who bear in mind, firstly, that the detailed anatomical treatises of Aristotle have been entirely lost, and that consequently our knowledge of his work is based upon such imperfect glimpses as can be obtained from chance extracts in his other writings ; and, secondly, that this branch of science and this method of investigation was entirely new, and that the results obtained are therefore to ' A large proportion of the surgical instruments found at I'dinptii wire apparently made of copper, the rest of iron. See Smith's Diet, suh 'Clii- rurgia.' -2 INTRODUCTION be jiulcicd with much indulgence — such critics, I say, will admit that never has a science been started on its career b\• its originator with so large an equipment of facts and ideas as that with which Comparative Anatomy left the hands of Aristotle. We may apply to his work in this department the words in which he speaks of his labours in another field of knowledge. ' I found,' he says, ' no basis prepared, no models to copy. . . . Mine is the first step, and therefore a small one, though worked out with rriuch thought and hard labour. It must be looked on as a first step, and judged with indulgence. You, my readers or hearers of my lectures, if you think I have done as much as can fairly be required for an initiatory start, compared with other more advanced departments of theory, will acknow- ledge what I have achieved, and pardon what I have left for others to accomplish.' ^ We can well imagine with what contemptuous sur- prise the followers of the old a priori school must have regarded the new departure. To minds engrossed in specu- lation as to celestial phenomena, or as to the ultimate nature of things and the cosmos, the study of the struc- ture and offices of the organs of the body must have seemed an ignoble pursuit, beneath the dignity of a philosopher ; and especially so, when it was seen that such study could only be prosecuted by the repulsive handling of the viscera of the lower animals, the internal parts of man himself, owing to the religious feelings of the Greeks, being quite inacccessible to the anatomist. Their attitude and their arguments may be inferred from the following stately passage in the ' De Partibus,' in which Aristotle answers this class of objectors : — ' Some members of the universe are ungenerated, imperishable and eternal, while others are subject to generation and decay. The former are excellent beyond compare and divine, but less accessible to knowledge. The evidence that might throw light on them, and on the problems which \\