m I ' ' \ z. ^Mm > rigs Vfi f5TT .Wl ^•^' IK JH6 rsa?i; ---** *s^£ w #**?SWl m* 5^? E™6 ©tftumMa WLuivzxsxty in tto ©its of Hew ^orfe ® ^xkxuxvj COLUMBIA UNIVERSITY THE LIBRARIES Medical Library AN ESSAY ON mm ©iiiaifif OF ANIMATED MATTER. BY JOHN PATTEN EMMET. " Bene scire, est per causas scire. NEW- YORK: PRINTED BY C. S. VAN WINKLE, Printer to the uuiversity. 1322. M* COLLECTION /P£Z ay i CD an 2 Kif*tt0tttr*l Wiftmvmitm ON THE CHEMISTRY OF SUBMITTBD TO THE PUBLIC EXAMINATION OF THE TRUSTEES OF THE COLLEGE OF PHYSICIANS AND SURGEONS OF THE UNIVERSITY OE NEW-YORK, WRIGHT POST, M. D. PRESIDENT, FOR THE Degree of Doctor of Medicine, On the 2d day of April, 1822. TO WILLIAM J. MACJVEVEJV, M, U>» PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF THE STATE OF NEW-YORK. Dear Sir, It is with pleasure I avail myself of this opportunity to express my gratitude for the steady interest which you have always shown in my behalf. Prompted by your example, and guided by your instructions, I have enjoyed opportunities of which very few indeed can boast ; and it shall ever be my study to profit by them. Accept, dear sir, the dedication of this essay, and regard it, though inadequate, as a pledge of sincere esteem. THE AUTHOR. 288804 THE CHEMISTRY OF ANIMATED MATTER / DIVISIONS. I. Introduction, . From page 9 to 14 II. Chemical Agents, . . . . 14 to 73 Influence of Vital Functions, (page 32) Fluidity, (34) Temperature, (36) Galvanism, (38) Light, (55) Atmospheric Air, [Oxygen,] (60) Alteratives in General, (67) III. Sanguification, 73 to 94 Digestion, (74) Respiration, (90) IV. Assimilation, 94 to 125 Composition and Figure, (95) Animation, (HI) Digitized by the Internet Archive in 2011 with funding from Open Knowledge Commons http://www.archive.org/details/essayonchemistryOOemme THE ©MaffiiMmT OF ANIMATED MATTES. FIRST DIVISION INTRODUCTION. There is no subject for reflection so interesting to man as the principle of his existence. Whether we regard it in a moral point of view, or in connexion with the healing art, the most important advantages must follow the inqui- ry into life. Yet it is a singular truth, that no subject has met with a less candid investigation. Whatever may have been the sources of this neglect, there seems to be abundant proof that no more designed mystery is thrown around this form of creation, than any other. We have seen the lightning of Heaven subdued, Heaven itself scrutinized by the astronomer, and the infinite spaces of its planetary orbs brought to the level of a school boy's eye. Earth has been dissected by the busy hand of man ; her magnitude is measurable, her stores tan- gible and her general economy visible. Even man, who proudly raises his head above the range of creation and styles himself its lord, meets with as humble an analysis. 3 10 His life is sustained by the same principles as that of the brute or plant ; and the fabric which gives him his supe- riority moulders into the common stock of matter which has served him and others since creation. All created beings are members of one and the same family, and every day's examinanation teaches us, that distinction is but in degree. " The more the phenomena of the universe are studied, the more distinct their connexion appears, the more simple their causes, the more magnificent their design, and the more wonderful the wisdom and power of their author." How does it happen, then, that with all this similarity and connexion throughout creation, the principles of animation should be pressed down, as it were, into darkness ? It has often been asserted, that to inquire into the na- ture of our vitality is to go much farther than ever the Crea- tor of life intended. This conjecture (for so it is at best) has gained too easy a reception. Man is a rational being, and stands pre-eminently distinguished above all other animals. This superiority, at first sight, seems to leave between him and them nothing in common, and has hastily led to the conclusion that the principles of his existence are of another nature, and too refined to be com- pared with that of the brute. A review of animated be- ings shows how ill founded such an opinion is. It may be just as to man's superiority in the complication of his living powers, but cannot give any thing like a founda- tion for supposing a peculiarity of principle. It will be found, that the perfection of organization is always fol- lowed by a proportional perfection of life, in all animals alike, and that in man himself its progress is intimately dependent upon the state of his structure, during every period from his infancy upward. In what other light 11 can we consider the life of an infant than as animal life s such as the offspring of animals are universally endow- ed with ? If intellect at the same period of existence is to be considered as a just criterion, surely we cannot place the infant in comparison with the chicken or the calf. Metaphysical reasoners, who have built their ar- guments upon a subsequent superiority of mental faculty, have overlooked the formations of education. It is no less absurd to suppose that the human faculties previously existed, and were only developed by age, than to suppose that all the infinite number of human forms which have appeared since the creation, and are to appear hereafter, were originally incarcerated together in the same original ovarium. No argument can be drawn from the mental faculties without consulting their origin. Abstract ideas s and the force of recollection, are by no means more in- conceivable than the operation of will, in consequence of those ideas ; yet the brute has this last faculty, in some degree, as well as man. A cow, for instance, whose head is turned away from the barn, will sometimes suddenly rise up and go directly toward it, though the place she has left should be covered with provender, and external impressions, as the weather, &c, apparently more favoura- ble to her remaining where she was. In this case, the abstract idea seems to occur in the same manner as with ourselves. So, also, we find watch dogs suddenly spring from their sleep and bark furiously, when there is no ex- ternal impresssion given to the ear or other parts of the body : other dogs, of the hunting kind, will, also, during sleep, howl as they are used to do in the chase. We can- not attribute these acts to any other than abstract ideas ; we know we frequently have such passing within our- selves during sleep; and we cannot attribute their ap- 12 pearance to habit. If habit could make the dogs bark, the more powerful one of walking should prevent them from lying still any length of time. Numerous instances of abstract ideas could be pointed out among the inferior animals ; but a few are sufficient to show the probability of more. Now, the conclusion fairly to be drawn from such facts is, that where there are abstract ideas, there must be reason ; depending, as to its perfection, upon their number. Here we must observe a similar constitution between man and brutes. Memory also has the same foundation in one case as the other. The power of re- cognition is even more manifest in some brutes, and the faculty of committing to memory is as strikingly illustra- ted in the instances of birds, when they whistle without interruption the tune which they first heard from a hand- organ, as it is in man under similar circumstances. It is gratuitous, to suppose a difference of principle ; and man, though towering in his wisdom, may yet go through the fields, and receive a lesson from the ant or bee. Whatever may have been the feeling which dictated the distinction between reason and instinct, we cannot but perceive their resemblance, and acknowledge, that their difference lies only in degree, and is dependent upon or- ganization. Another consideration leads us to view the principle of life as similar in both, and as depending for its existence upon the body, without possessing a separate character. Man and brutes receive their original ideas from external impressions ; such are those of light, colour, figure, taste, smell, dimension, hardness, warmth, &c. ; their combination which afterwards helps to inform the mind, must therefore be considered as dependent upon the material organs, which first gave the impression. Fur- ther, the capacity to receive these ideas follows the per- 13 fection of organization through all its varieties. When th£ bodj suffers from disease, the mind fluctuates, and when the corporeal fabric ceases to exist, so must the principle of life, whether its maturity be instinct or reason. Where then do we see any superiority over the brutes, as to a difference of vital principle ? I cannot perceive a single circumstance to make the inquiry into man's existence or generation in the least degree more improper than one into that of the oyster, sea-nettle, or fungus. The com- mencement of animation is as wonderful in one part of creation as in another ; all show an invariable dependence upon the same principle, and are equally the works of one Creator. It is singular how much is overlooked in trying to hold the veil over life, and particularly over that of man. We give it independence without being able to strike off its weakest shackle ; and have, in the end, to leave it as our conformation requires it to be — a consequent of ma- terial composition. If the inquiry be improper, why is not the practice of physic considered as an audacious at- tempt to pry into forbidden secrets? Why are not anato- my and physiology ? The last, in particular, aspires to develop the sources of life. We even applaud the ingenuity of physiologists, when they attempt to introduce physical laws into the economy of the animated body. The reason plainly is, that the view of life, as generally entertained, is unfounded ; for what is considered as a distinct principle is nothing more than an effect, and its regeneration takes place, day after day, in as- similated nutriment. For these reasons, I shall con- sider the production of all organized matter (whether animal or vegetable) under the same light, and as I can- not see any assignable difference in their principles of life, I shall not assume one ; but enter upon my subject, trusting 14 that all knowledge, which is founded upon observation and experiment, must be proper ; since otherwise I conceive the light for investigation would have been withheld. SECOND DIVISION. I. THE POWER OF LIFE. Man has been early taught, by observing the uniform results of putrefaction, that the living structure is com- posed of the same materials as constitute the inanimate world, or, in other words, that he is literally formed from the sod under foot. This humiliating analysis of nature has been invariably corroborated by the more limited power of art. After such a lesson, it appears astonishing how it could be denied, that physical laws have given us birth. It is true, the production of living matter, as we daily see it, is accompanied with the ener- gy of life in the whole body; and this close connec- tion has given rise to a confusion between the cause and effect. When, however, we consider that no power of life could draw together the particles of matter, or make ihem cohere or change their properties, we must inevita- bly come to the conclusion, that the animated matter de- rives its distinguishing character altogether from physical laws, and that life is but a consequent. To illustrate this, let us examine the vital power as it appears after such formation. " The idea of life," as Cuvier remarks, " is one of those general and obscure ideas produced in us by observing a certain series of phenomena possessing mutual relations, and succeeding each other in a constant order. We know not, indeed, the nature of the link that unites these phenomena ; but we are sensible that a connexion 15 must exist, and this conviction is sufficient to induce us to give it a name, which the vulgar are apt to regard as the sign of a particular principle, though in fact that name can only indicate the totality of the phenomena which have occasioned its formation." According to this correct view, whenever we consider life, we shall find its investi- gation inseparable from the corporeal system in which it exists. We know that it depends upon the mutual exer- cise of material organs, which are liable to be acted upon by external agents, or decomposed like other matter. The metaphysician and divine may show its importance, by connecting it, in their discussions, with the soul ; but the little knowledge that we have on that subject bewilders the conception, though it may not shake the faith. Life, as we have it before our eyes, is nothing else than the aggregate effect of numerous material organs, endowed with an irritability which subjects them to be constantly- stimulated into peculiar and appropriate actions. The physician who wishes to support or recruit life, must give all his skill to the disordered organs ; for the affections of these alone are found to be the sole causes of disease. In no instance is life found to exist without the organization of matter, and all its varieties are referri- ble to the same state. When a member of the body re- ceives an extensive injury, it may mortify ; and there is sufficient reason why it falls off, or has a line of separation between it and the uninjured part, without supposing a vital repulsion. When an extraneous substance is lodged in any part of the body, what can be more unmeaning than to say, that the consequent inflammation is an effort of nature to throw it off? The reason why these expres- sions are improper is, that they give the opportunity for supposing life a peculiar intangible spirit and because 16 they do not sufficiently imply how much the vital organs are susceptible of being affected like inanimate matter. The great distinctive character seems to be the irritability which the former possesses in such an eminent degree. But this property, so far from acting the guardian part of a medicatrix upon all occasions, very often leaves the li- ving fibre exposed to the worst of dangers from decompo- sition, as may be seen in all cases of inflammation. When we examine the living body, we will find that one prin- ciple characterizes all its parts : this principle is irritabili- ty, which is as peculiar in its nature as the texture to which it belongs. Thus we know, that every part of the body can be stimulated to inflammation, although the irritability of muscular fibre cannot be made manifest to the sight. We will find that connecting organs are placed in every living part, for the purpose of concentrating their powers of life, and nourishing them. The first office is performed by nerves ; the second by arteries and veins. From both we learn a plain fact, namely, that the life of any single part, though the true type of animation, is nothing by it- self, and that its power is insufficient to its own support. The parts of the body thus intimately connected together, readily co-operate, and constitute, by their amount of ac- tion, the phenomena of life. But even after taking the most favourable survey of this complicated machine, we cannot avoid concluding, that its life is but a physical effect. The property of irritability has no existence, unless when a stimulus be present ; consequently, although any part should be capable of this excitement, yet, where no stimu- lus is concerned, it is completely dead ; and further, when this property is manifested, it must always be the result of action between two inanimate substances — the organ to be affected, and the stimulus. For this opinion there is 17 direct evidence ; we know that the corporeal organs are kept in motion during life, by the direct action of stimuli ; and we know further, that after death, the action of many may be revived by the same means. What agency, then, can such irritable matter have in the regeneration of itself, when the strongest character which it possesses proves liow very subject it is to be affected by the action of in- animate substances ? This irritability is the true life ; and it is in vain to try to establish any other principle be- cause the living power seems more complex. We cannot deny life to plants, and yet the most fanciful inquirer has never been able to allow them more than an irritable pro- perty. To lower the vegetable power of life beyond this point is not requisite, though it has been attempted more than once. This power of life, in plants, is even more distinct than in the polypus and other inferior animals, as the following instances will show. " The stamina of the cistus helianthemwn are seen to move in various directions, when the sun shines upon them ; the leaves of the mimosa pudica (sensitive plant) when touched by the hand, or when irritated by the alight- ing of an insect on them, immediately contract; dionea muscipula, (Venus' fly trap,) when a fly touches its leaves, closes the thorny fringes with which they are beset on the presumptuous insect, and crushes it to death ; but the motions of the hedysarum gyrans are the most re- markable of all those that take place in plants. The leaves of this extraordinary vegetable are seen in con- stant motion through the greater part of the day, without the intervention of any apparent external impulse ; and even when a branch is cut off, and kept in water, the mo- tion of the leaves continues for many hours together. All the plants which grow above the earth expose their 3 18 leaves and flowers to the warm sunshine, and when situa- ted in a place which is supplied by light only from one quarter, they gradually direct their branches toward that part by which the light enters. In stormy weather, they retract their leaves and fold up their flowers ; and when confined in the dark, their branches retain the position which they had when exposed to the light."* We surely cannot compare with such vegetable life that of the oyster, which is equally rooted to the mud or ground ; or of the polypus, which is washed about by the troubled water without manifesting the least exertion of will. In these examples, we perceive that life is nothing more than irritability diffused through the corporeal structure. In the higher classes, as among testacise, quadrupeds, birds, and mankind, irritability is equally the principle of life; but the organization is so much more complicated that that principle becomes multiplied. Thus we say they have sensibility as well as irritability. Physiologists have endeavoured to impress the idea of a great difference be- tween these two characteristics. They appear, however, in the end to be constituted by the same principle, and differ only in their mode of application. Nerves are ne- cessary for sensibility, whereas irritability is possessed by organic matter, wherein nerves have never been traced. So far there is a manifest difference. But what principle constitutes the power of action in nerves ? It must ulti- mately be dependent upon irritability, which, as I have remarked, is life in every form. The following example will show their similarity of principle, as well as an osten- sible difference in their results. When a muscular part meets with a violent injury, it, in the first place, inflames in consequence of the irritability residing in its compo- * Encyc. Brit, Physiol. 19 nent parts, which are all injured ; but if mania or sympa- thetic inflammation (as generally understood^ supervene elsewhere, it is because the nerves and other connecting organs, by the first impression, have been irritated, and they are endowed with the power of transferring the ex- citement. From similar arguments we must be led to the conclusion, that there is but one vital principle, whe- ther with or without nerves ; that such irritability is pecu- liar to every part of the living matter, independent of the system at large ; and that the nervous extension is for the purpose of concentrating this diffused animation, as well as for transferring internal and external stimuli to each part, without which, though thoroughly organized, they would be inanimate: furthermore, all this co-operating structure is constantly wasting away, though endowed with vitality ; hence another system of organization be- comes necessary, which, while diffused through all parts, makes up the full power of life, not by connecting those parts together, but by bringing to each a supply of blood, which preserves the irritable composition. Having thus examined the true form of life, and found it to be irrita- bility, let us now view this property more particularly, that thus we may estimate the vital power in the formation of animated matter. Baron Haller was of opinion, that irritability existed independent of a nervous connection, and therefore called it a vis insita of the part itself. We have seen in vegeta- bles, that nerves are not necessary for life ; the polypus seems an instance among animals. The umbilical cord has never shown the least trace of a nervous texture ; and accordingly, when divided, occasions no sensation of pain to the female, and apparently none to the foetus : yet we cannot but allow it has life. If nerves were necessary for 20 vitality in this part, it is highly probable, that they would at least be as manifest as those of the foetus, which are neces- sarily supplied with nutriment after the cord. The fibrine of the blood, which we can scarcely suppose to be affected by the nervous power when taken out of the body, is still susceptible of irritation. This curious fact was first stated by Circaud, and afterwards confirmed by Delametherie.* The difficulty of succeeding in such experiments must evidently be very great ; for when we consider how very soon irritability is destroyed by the least change of com- position, we cannot be surprised at failing to illustrate the power in fibrine. But it is of little consequence to prove the absence of nerves ; since in these also irritability may be considered as a vis insita. The term itself is far more questionable ; for irritability is not, strictly speaking, any thing else than a property of matter. Common language, it is true, gives sanction to such an application ; but it is evidently incorrect to style that a power which absolutely depends for its existence upon something else. In this case particularly, it becomes necessary to preserve this view, in as much as it points to the common error, of thinking life a cause, instead of an effect. There is no such thing known as irritability, without the influence of a stimulus, and when this property is made manifest, we can only consider it as a secondary existence. We say a body is sweet or sour, but we know that such qualities are dependent upon the gustatory nerves, as much as on the body itself. So it is precisely with life, which is a quality generated by stimulus upon the organic matter. This truth, when we conjoin the mode of action by stimu- li, must lead us to consider irritability as much a material property as those which we daily call so. It depends * Bostock's History of Galvanism. 21 upon the chemical composition more than shape or mag- nitude ; and is therefore very analogous to a chemical property. Such a conclusion may seem too hasty, and perhaps is, since experiments to the point are very few in number. Elsewhere I shall endeavour to do more justice to this subject, when treating of irritability, as re- sulting immediately from the composition of organic mat- ter, and as being in truth a part of the assimilating pro- cess. Persons who are unwilling to suppose life any thing else than a perfect archeus, making the body his home until death turns him out, have supposed that wherever this principle has been revived, it must have existed throughout, only in a latent state. The moment, however, this opinion is examined, its truth becomes questionable, at least, as to the application in many cases. Irritability, we know, can be manifest only as long as a stimulus is present. How then can we suppose a vital action, or even a latent vital power, when no stimulus is concerned ? Wharever may be the appearance, we may conclude, that whenever life appears, the organization must have remain- ed unimpaired ; consequently, in all such cases, life may really be destroyed and restored. If an egg, for instance, can after any lapse of time produce a chicken, the foetal structure must through that lapse have remained unalter- ed as to its chemical composition, as well as arrangement. Hence, then, the appearance of life in this case may be re- conciled with observation upon the living body itself - r in which we know the vital power has no existence, without a proper stimulus, and where we see that its regeneration depends upon that stimulus. The heart, for instance, con- tracts violently, as long as the lungs inhale the atmospheric oxygen, but when hydrogen is breathed, or any other gas which cannot readily unite to the carbon of the blood, the 22 heart languishes, and approaches true death. For the same reason we see why a seed appears to be dead (and really is so when without a stimulus) for many years ; but when exposed to the influence of heat, air, moisture, &c. acquires life. The structure is capable of being excited at any time before decomposition takes place. In Smith's work on Botany, we find an instance where a plant, after being kept twelve or fourteeen months, as a dry specimen, ob- tained life upon being planted. Now, in this case all kind of nutriment had been withheld ; and not only this, but the stimuli, which at other times are found to be absolutely necessary for life. Here then I think the subsequent growth plainly shows that the oganization (which in plants is always more permanent than in animals) remained so little impaired, that the natural stimuli of warmth, air, and moisture, were enabled to excite its actions, or, in other words, to create life. Whenever the structure is simple, irritability will remain longest ; for decomposition is then slowest in its effects. For this reason, it is so difficult to preserve the life in animal substances, after they have been exposed to injury, which almost always is followed by a decomposition. An egg is rendered unfit for hatching by a few shakes ; whereas the same will not affect a seed. By keeping in view that irritability is a property of mat- ter, and not a separate power, we will be enabled to value its influence over the formation of animated matter. As such, it must be confined to the substance possessing it, and in no case can effect a change of composition in adjoining matter. We might as well suppose that the sweetness of sugar could convert things of an opposite nature into sugar by mere contact. Before our food becomes assi- milated, it must be totally changed in composition and properties ; it generally also passes from the solid to the 25 fluid state. Now, it is an unsupported supposition that vitality can affect cohesion, or a change of chemical con- stitution, and it becomes apparently impossible, when we consider that this vital power must, under such circum- stances, be supposed to exist in tubes and cavities, where there is no animated matter. No part of the living econo- my has been more mistaken than that of regeneration. In spite of daily observation, that chemical phenomena take place in some of the vital functions, and the still more imperious truth, that no process in nature is known to be capable of altering the composition of matter, except that resulting from chemical affinity, yet every subterfuge is grasped at to limit this universal law. We can behold the arm move with mechanical advantages ; the eye regu- lated by the laws of optics, and the ear by those of ac- coustics, and yet though the laws of chemistry equally bespeak wisdom and design, we take upon ourselves to disturb a harmony which pervades the whole created world. It is doing no less if we deny the power of chemi- cal affinity in the composition of matter, merely because it is, or is to be animated, and that too while we confess a total ignorance of the vital power. The undeniable truth is, that the living system is made and supported by physi- cal laws, and that the only power of life consists in making them co-operate. All the changes which take place in the body must be affected by these laws ; even to the acquisition of vitality. They are all absolutely necessary, and those of chemistry the most extensive. Let our prejudices be what they may, we should be open to conviction. If we cannot conceive the mode, we should rather set it down to ignorance, which will long be the case as to our extent of chemical knowledge. Besides, it should be borne in mind that the misdoubt is, after all, about a 24 trifle. The application of physical principles to the phe- nomena of life, cannot make the nature of either more in- significant to the eye of philosophy. On the contrary, it completes that chain which binds the universe, and con- nects the gradations of its substances, from the simple atom to the most complicated form of organization and life. Can the wisdom of God's works be less divine because they exhibit connexion and uniformity ; or does the wis- dom displayed in them appear more limited because it be- comes more manifest ? Certainly not. And the individual who shuns or neglects the examination of His works, is far more likely, from ignorance, to err. than he who aspires to trace their symmetry and connexion. Whatever may be our doctrines, it never can derogate from the divine stamp of life, to prove that it derives advantages, or even exist- ence, from regulations which we all must feel were framed by the same wisdom. But now it may be asked, if there is no power of life in the organized compound to protect it from the laws of che- mistry, how does it happen that the structure is able to resist decomposition ? This I shall attempt to illustrate upon principles which, in my opinion, lead to the true vital economy; since they show that chemical changes can take place at all times upon a living solid, but that our functions are regulated so that the circumstances un- der which they occur shall not be long injurious. Phy- siologists who deny the power of this action, evidently draw their conclusions from the life of the body at large. Let them take the whole to pieces, and then value the in- herent power of life. If the corporeal structure does not perish by every local decomposition or injury, it is be- cause that derangement is adjusted before it extends to the most important organs. This surely is not to be con- 25 sidered in the light of a contra-chemical power ! The in- jury really takes place, and the wisdom of our conforma- tion consists in making amends for the action of laws which cannot be subdued as long as matter exists. Take the mortifying leg of an animal ; do we not there see the true life diminishing ? It is a portion of the general stock, which evidently is insufficient in its nature to prevent che- mical decomposition. Here, also, we may value the power ofhfe, which consists in the arrangement of parts, and not in giving them magic. As long as the blood vessels, nerves, and other connecting organs remain undecomposed, they will possess perfect irritability, and so long will be enabled, by the increased stimulus, to bring a share of blood to the mortifying limb, sufficient to re-compose its parts. The absorbents at the same time, and by the same means, take up and separate the detached portions ; thus preventing their further reaction on the limb. But if all this beauti- ful connexion looses the capacity for life or irritability, in consequence of being involved in the decomposition, no power or spirit can support the limb. Chemical changes progress as they did from the beginning, but the structure which they destroy is not rebuilt, and the whole sloughs away. It may indeed be removed by fluids secreted from the living extremities, as well as by those which result from the decomposition. These terminations generally prove successful in preserving the life of a portion, and indicate the most perfect design. Very few will have it in their power to disprove the true character of the chemical changes which take place in the forgoing example; but it may happen that the liv- ing texture shall meet with a similar exposure, and yet no fatal results follow. Whatever may be the appearance, we are justified in applying to all such instances the foregoing 4 26 principles ; since the organic arrangement being still the same, the mode can only differ in extent. The parts exposed, even if they should suffer incipient decomposition, are immediately roused where life (or as we consider it, irritability) yet remains, in proportion to the complexity of structure • fluids are thrown out on the li- ving surface, which they shield from decomposition, by re- moving the chemical agent beyond the sphere of its action. Here we see no proof that the life of the parts exposed resisted the chemical tendencies. That which follows being a proof that the animated matter has not the slight- est power of defending itself, but that it melts with all its success in consequence of connexion and arrangement. If the chemical agent be small and light, it becomes washed away, in a similar manner to what takes place when a grain of sand or dust enters the eye. This may be done before even the fluid which is employed, can suffer decomposition from the same substance. But when this agent is lodged to any depth, or is too heavy to be washed away, a chemical action always takes place independent of mechanical irritation. If a small quantity of white arse- nic (arsenious acid) be swallowed, it enters one of the most vital organs of the body; yet it may pass through the whole course of the stomach and intestines, without producing more than a trifling inflammation, wherever it meets with detention. The reason is obvious, and shows how very feeble any specific life (or that which belongs to a single part,) must be. We find that a fluid is always necessary to bear away the foreign material, and from this we conclude, that the provision has been made, not to destroy the tendency towards action, but by interposi- tion, to remove the materials from each other, and they prevent a result which otherwise would as soon take place in the body as out of it. Such an arrangement, instead of 27 diminishing the wisdom of our construction, infinitely ex- alts it. It shows a consistency with the rest of matter, without having to suppose that the life changes properties which are immutable elsewhere. Persons who deny the power of chemistry over anima- ted matter, contend that the absence of gaseous matter is a proof. But here again, the system at large is considered instead of any single part ; we all know that when chemi- cal action takes place to any extent in a limb, in the intes- tines, or, in short, in any other portion, that gases are abundantly formed. But the objection, when even appli- cable to the whole system is unsupported. What else can we consider respiration but a chemical function ? It is idle to object to this example, because respiration is not per- formed within the substance of the body 5 but merely on the pulmonary surfaces. Are we to dispute about trifles, when the principle is unimpeached ? Surely, if respiration be necessary to life, so must the chemical changes; which may therefore, as to principle, take place as well in the body as out of it. If we expect gases to be liberated in any quantity during the exercise of the functions, we are evidently going too far ; since, after all, chemical changes of the most varied nature may take place with- out the production of any gas. We know that all corpo- real changes during life are in appearance very gradual ; and therefore, although gases should be formed, they must pass away unobservable in magnitude, by the circulating blood. As long as the decomposition subtracts only one ingredient at a time, as carbon, and as long as health re- mains to re-establish the original compound, by speedily furnishing new, but similar matter, so long it must follow, that little or no gas will be manifest. The chemical changes of the living body need not, of necessity, be the same as those which take place in the cadaverous mass, 28 where all the constituents are liberated nearly at the same time, and where it would indeed be singular if gaseous products were not formed. But after all, if nothing can satisfy such doubters but facts, I need only refer to Pro- fesssor Brande's experiments, as related by Sir Everard Home, where two cubic inches of carbonic acid gas were obtained from every ounce of fresh-drawn blood. This, it may be remarked, is the gas which always results from organic decomposition, and agrees, in quantity, with the gradual changes of the living body. Another objection has been advanced, which at first sight appears forcible. One of the great phenomena of chemical affinities is, that the more complex a substance is in composition, the sooner it yields to spontaneous changes. Thus, when a body has two constituents, it is more firmly constituted than when one of these becomes multiplied, or where a third ingredient exists. During life, however, such parts which are always the most vital seem the least prone to decomposition ; and it is said that life must be the cause, since when such parts are dead, they readily obey the common law. I have already said, that the laws of matter have all their force in the living body as well as in the universe. This, 1 feel persuaded, is infi- nitely more consistent than to suppose that matter can exist any where without them. The present subject fur- nishes a demonstration which, to me, appears capable of upholding such an opinion. It is impossible, by any process of reasoning, to devest ourselves of the conviction, that the living substance has most of its properties in common with the dead. In com- position it certainly is similar, (as, for instance, the dead and living muscle,) consequently, although the decomposi- tion may be more manifest in one than in the other, we 29 must suppose its principles alike for both. This general, though correct consideration, leads us to expect the fore- going law of composition should hold true in vital and highly organized parts of the body; accordingly the ap- pearance which such parts have of resisting chemical changes admits of an explanation agreeable both to the phenomena of life, and the general law of matter. All parts of the body which are most complex are also most vital ; or, in other words, they are most largely sup- plied with blood-vessels, nerves, and other connecting organs. These are considered, in vague language, merely as characteristics of life ; but I conceive the design of our conformation can be traced much farther. They appear as constituting an arrangment, not to subvert chemical af- finities, (without which no organized substance can exist,) but to make amends for their undeviating sway. To the complex structure we may apply the general law, and by the living properties, which seem in opposition, prove its truth. We may say that the complex vital structure un- dergoes decomposition quicker or more readily than the simple one ; and for this reason it is furnished with a much greater supply of blood, that thus it maybe rebuilt without the whole system being injured. Other parts, as the nails and hair, are of uniform composition, and are well known to resist chemical decomposition • they, therefore, need not be furnished with blood throughout, and are in- animate when compared with the foregoing. This de- struction, previous to absorption, is not a mere conjecture ; the cohesion which could take place at the mouths of the absorbents must evidently be too powerful, subsequently, for those mouths to eat down, as Mr. Hunter supposed, or to be nibbled as by the mouth of a worm. " A mere conjecture, and most improbable. The solids are raised 30 by the agency of the vessels on the chemical affinities of the circulating fluids. They must be resolved by a pro- cess reducing them again to the state of, fluids, or the se- creting vessels throw out fluids which dissolve them ; an operation anterior to their absorption."* The brain is an instance of a very vital part, so is the womb ; accordingly we find, as John Bell remarks, that they " are the most liberally supplied with blood." Again, as the brain is the least firm of the two, we should conclude that it must, also, be most liable to decomposition ; and, as if to make amends for this state, we find that it has " two great arte- ries on each side ; it has two carotid, and two vertebral arteries ; they far surpass those of the womb ; their inos- culations are so particular that there are no others like them in all the body. The injection of any one artery easily fills the whole ; the preservation of but one artery saves the life of the creature when the others are stop- ped." What can be more reasonable than to suppose that this singular inosculation is for the purpose of supplying, under the worst of circumstances, a ready stock of blood to obviate the fatal effects of rapid decomposition ? " The brain, which weighs not a fortieth part of the whole body, receives one tenth of all the blood : a proportion which must occasion surprise." Every person who has made repeated dissections of this organ must have observed^how very soon it becomes destroyed after death has taken place •, and the same tendency cannot but exist during life. The spinal marrow is also well supplied with blood from the anterior spinal artery, which descends along the medullary column in a furrow formed for itself, and sends innumerable branches into its substance. * J. Bell's Anat 31 Thus are obviated some of the principle objections against the anti-chemical power of life peculiar to the solids. If there be any truth in the position, how shall we deny the tendency to chemical changes among our "various kinds of food and the fluids generally, which are within cavities, and appear to have no permanent con- nexion with the solid structure ? If changes in them are not fatal to the whole system, it is because they are kept in progressive motion through these cavities and canals, until they receive suitable changes of composition, from chemical agents placed in their way, being then separated from the mass by absorption, or expelled from the body before injurious accidents can take place. Another rea- son why the body escapes chemical injuries during its pro- gress is, that the substances which enter by the mouth, are in general mild nutritives, which readily submit to the changes of assimilation. When by accident or design, chemical agents of a more powerful nature are made use of, we see too clearly that life is either prostrated or ex- tinguished. As to fluids, a few remarks will show why they in par- ticular undergo ready changes of composition. Let us take the blood as an example, since this gives evidence of possessing irritability. This fluid is of a compound nature, not only by its own constitution, but by the continual intermixture of foreign materials. Its con- tact with the vital texture, is incessantly changing ; it has no diffused organs through its substance, for the purpose of repairing chemical changes, and without the slightest arrangement to concentrate its vital property. What then has it to make amends, but this simple quality of irritabi- lity ? We have already seen how poor a protection this is to the solid texture ; how much less, then, must it be to the blood, which, as a fluid, has not even a percepti- 32 ble affinity of aggregation, to oppose decomposition ; its fluidity not only assists its own destruction, but gives the same power to the intermixed matter. We accordingly iind that the blood does meet with such changes to a cer- tain extent. They are always made more manifest in diseases with languid circulation; and would un- doubtedly have a fatal issue, were it not that a pro- vision is made to separate these foreign substances, and to purify the blood itself, at the end ot every round. Circulation has this for one of its important objects. Each part of this fluid undergoes a complete review, as it were, in the lungs ; and before the course of circulation becomes complete, a great part of the blood itself, as well as its admixtures, are timely disposed of, in the form of secretion and excretion. Similar exposure and provision may be observed for all the other fluids. In this way, injury is prevented ; not by destroying chemical action, but by withdrawing the materials from each other, which other- wise would display their affinities, nowithstanding the sup- posed check of an inherent vital principle. CHEMICAL AGENTS IN THE FORMATION OF ANIMATED MATTER, AND ITS FUNCTIONS. We have already anticipated a great deal of the part which chemistry performs in the vital functions. The more these are examined the more one must be convinced, that the proximate cause of all organic formation is che- mical affinity. It is not reasonable to expect a detail of operations, so varied and unobservable in their nature ; neither is it neccessary. But we have general rules which are sufficient to establish the truth, without requiring that every ambiguous point should be cleared up by experi- ments. The laws of chemistry, are the only ones capable of effecting a change of composition : its agents are not 33 only surrounding the living structure 5 but they pervade its most important organs, and must of necessity charac- terize every material production within the system. Irri- tability which is the true type of life in the parts them- selves, cannot prevent decomposition, as has been shown, but, on the contrary, must always be the proof of action, no matter how indefinite. The phenomena of life when connected from part to part, cannot be regarded as show- ing that chemical affinities are subdued, since they admit of an explanation perfectly agreeable to both. When ex- amined, the true vital economy is found not to consist in destroying such laws, but interposing materials which have the power of acting chemically, and these, by the uniformity of their nature are generally attended with the designed end. Hence, then, we can safely say that, whate- ver be the form of structure employed, the changes of composition which take place during life are of a true chemical nature, as well as the agents employed. Our want of power to imitate or illustrate these, argues only our ignorance of the science. Every practical chemist knows how much difficulty he has in managing the few articles which may be placed in a crucible or retort ; and every new compound which he encounter requires the same kind of labour before he can presume to announce its nature. It would be the height of presumption to take up a few simple minerals, and say these constitute the living fabric ; but it never can be, to suppose that chemi- cal affinity is employed as much for one as the other. Neither is it to be supposed that analysis will enable us to succeed in the composition. It is easy to consume the brilliant by a burning glass and to prove that it consists of carbon ; but this success gives no power to form it anew. Though possessed of the materials, and perfectly convin- 5 34 ced, that they still have the same chemical tendency as at other times, the only constant result is, to be convinced that it is much easier to destroy than constitute, notwith- standing the similarity of principle for both processes. When we confine our attention to the higher range of ani- mals we are inclined to consider that life effects all their phenomena, and so it does remotely ; since it is the result of organic arrangement, and operates by presenting mate- rials. So does the chemist, when he pours sulphuric acid from one glass into another of carbonate of soda, remote- ly produce the sulphate. But we must not confound the operation of his hands with the affinity which constituted the salt, or occasioned the effervescence. The life of a plant is considered as a very humble one ; and if such, so must be its power. Yet the secretions formed under such circumstances have as much constitutional difference as those of the most perfect animals, Here, then, there is infinitely less opportunity to intoduce this mysterious in- fluence ; and turn where we may, the same outline is ob- servable. With this we should be satisfied, without trying to oppose laws which we can not alter. MOISTURE AND FLUIDITY. This state of cohesion is observable all through the living stucture, and is so important in promoting chemi- cal action, as to give rise to the rule " corpora non agunt nisi sint soluta." I am not to be understood as implying that such is their most important use in the body ; on the contrary, when intermixed, or in contact with solids, they are of the most obvious use in facilitating motion, defend- ing surfaces from chemical action by interposition, in pre- venting, as well as sometimes in effecting adhesions. It is 35 t equally true, however, that where they effect a solution they give a greater opportunity for chemical changes ; and this result is always independent of the fluid. Further- more, we may say, that all the important combinations are effected by the agency of solution. Even supposing, with Mr. Hunter, that the " modelling absorbents" eat down the solid parts, still their solution must be effected before, or shortly after their being swallowed. Such is the state at least when they are examined in the thoracic duct, and such must be their state before they can circulate with the blood. Every part of the solid texture has a moist or liquid matter pervading it ; hence it is but reasonable to suppose that this is a means employed to render the differ- ent parts fit for being absorbed, as soon as their texture looses its aggregation. As the fluids are not united to the system at large by interwoven nerves or blood vessels, we cannot suppose them capable of resisting chemical changes, or of making amends for themselves, after such have taken place. With them, as with every other part of the body, extensive and uninterrupted connexion is necessary. Fluids, therefore, are absorbed, and thus brought into new ranges of affinities, suitable to the general economy, or are by the same act checked in their tendency, by divid- ing the mass before it can take place. Another arrange- ment, also, effects the same end. The slowest motion among the particles of a fluid, unless they possess a very powerful affinity for each other, tends to prevent their re- maining in contact long enough to combine. This is also aided by the water which constitutes so large a portion of their bulk ; as a solvent it separates the particles be- yond the sphere of action. But with all these provisions, there can be no doubt but that the fluids are proximately the field wherein all the organic formations and destruc- 36 tions take place. In their arrangement we behold a con- stant view towards their chemicai and physical quality. The mucous fluids are generally secreted upon surfaces which have outlets through the body ; because, as they have the property of coagulating under circumstances, they would often prove injurious by occasioning improper adhesions, unless there were means of expelling them. The serous fluids, since they have not the chemical pro- perty of the other are deposited upon the surfaces of en- closed cavities, as within the peritoneum, pleura, or the capsules of joints. There are other fluids secreted for the express purpose of chemical action; such are the gas- tric and pancreatic juices, the bile, saliva, and various others, but it is not necessary to consider them in this place more minutely, since their chemical agency de- pends upon their composition rather than their state of cohesion. ANIMAL HEAT. This is also an auxiliary. We find it nearly equally dif- fused throughout the body ; and its presence is sufficient to promote chemical changes, without inquiring into its origin. It is the degree of temperature which seems most active in giving bodies their solid, fluid, and gaseous forms. As such, it must be regarded as similar, in its agency, to the foregoing ; that is, in influencing the aggregation upon which chemical action in a great measure depends. It must be confessed, however, that it seems more useful in keeping up a constant excitement in the irritable texture. We feel how completely sensation ceases when the hands or feet become cold ; or when the whole body is labouring under a shivering fit. As to its origin, there has been a great diversity of opinion ; and the general failing arises in 3? making it too particular. No doubt I think should be entertained, as to its resulting from chemical changes, when the same can produce it out of the body. But we cannot suppose that these are the only sources, A flush of confusion, or anger, will throw the face and neck into a glow ; but here it is absurd to introduce chemi- cal changes. Such phenomena seem more referrible to the nerves, or rather their irritability. This excitement may even depend upon physical causes, without entitling us to draw such conclusions. It is the property of alcohol, when tasted to act on the nerves so as to produce a sen- sation of heat ; the same is felt in the stomach, and no doubt can be entertained but that the same physical pro- perty afterwards affects the nerves of the heart and arte- rial system so as to occasion the fever from intoxication. We may even suppose that all exciters have this power over the nerves, in consequence of their chemical compo- sition ; yet it does not follow that they should always have chemical action. The two branches of a pine tree, for instence, though constituted upon these principles, do not, when rubbed together, produce heat by chemical action. Most of the animal temperature seems occasioned in a similar manner. When we rub a benumbed limb it becomes very soon glowing with heat ; our muscular motions always produce the same ; so must the incessant action of ths heart and arteries. And when we consider that the same hap- pens when two pieces of wood or stones are rubbed to- gether, we should view the result as depending, not upon life or chemical combinations, but upon one of the most common material properties. The observation of Craw- ford, upon the difference of capacity for caloric, between venous and arterial blood, is no doubt illustrative of a uni- form supply, but cannot be considered as sufficient to establish a theory on animal heat. S3 GALVANISM, ELECTRICITY, &2C. The process of secretion has long been a subject of in- vestigation; but manifest as its effects are, and notwithstand- ing the great importance which the nervous system appears to have during its complicated stages, no facts have been brought to light sufficient to illustrate its nature. We find the greatest variety of these products among vegetables, yet few have been willing to credit the existence of nerves in plants. The polypus, also, is an instance among animals where the process of assimilation takes place most perfectly, and to all appearance without a nervous system. To these we may add the formation of the um- bilical chord, and some examples of foetuses. M. Le Gal- lois mentions, in his treatise, several where neither brain nor spinal marrow were to be found. Clark (I think) re- lates in the early part of the Philos. Trans, an example where not a single trace of nerves could be found, al- though bones, flesh, cartalage, membranes, &c, were dis- tinctly formed. These considerations lead us to view the nerves merely as constituting an apparatus for the secreting agent; but without which that agent may, in some in- stances, be effectual. Several difficulties will occur if we regard the nervous, or even any other division of the vas- cular system as necessary for the formation of animated matter, and therefore most probably for all secretions. We find, for instance, that all the corporeal texture which is concerned in such offices have blood vessels which supply materials for secretion as well as others which support the organ itself; now, whether nerves be necessary for the last or not, we must suppose such a mi- 39 nuteness of vascular structure, by continuing this arrange- ment downwards, as will evidently be absurd, or else we must draw the conclusion, that the formation of animated matter does take place upon principles independent of the vascular arrangement. Let us illustrate the idea by an example, which will at once be allowed applicable to all the rest. When a nerve is injected, its substance is found to be interwoven with minute blood vessels.* These are for its support ; and, according to the general economy, should be accompanied with nerves for the pur- pose of secreting freshnervous matter; but, be this as it may the coats of these minute blood-vessels must be support- ed. How is this effected ? If by another and minuter vas- cular apparatus, how is the substance of this last secreted ? Thus we will be driven to fancy the existence of blood vessels and nerves as small as it is possible to divide mat- ter ; and even here the dilemma cannot cease, since for the very last, secretion of substance will be as requisite as for the first and largest set. On the other hand, we are led to think that secretions can proceed from the blood by the influence of an agent not necessarily limited to the nervous apparatus. This J really conceive is best sup- ported ; for if the foregoing descending series of vascular arrangement be inadmissible, then there appears no alter* native but to suppose that the smallest set of nerves and blood vessels had their solid texture formed from the blood without further apparatus. At a subsequent part of this essay it will be in place to state experiments which go to prove that arterial tubes with their ramifications can be formed directly from the blood by its chemical or physical properties. At present I shall rely on the foregoing, and ♦Bell's Anat. 2d vol. 40 consider nerves and vascular structure as established for convenience more than from absolute necessity in the pro- cess of converting the blood into organized matter. Sup- posing then that the nerves are mostly for the purpose of forming a perfect conducting apparatus, we must approxi- mate nearer to the true nature of the agent transmitted, when we experimentally become acquainted with any which has the property of readily passing through the same medium. The similarity is much farther heightened when we learn that this last is a powerful chemical agent. Such a one is galvanism, (including its modifications of electricity and magnetism.) It is not my attention to pre- sent a history of this very extensive agent, but merely to examine some of its greatest claims to being considered the nervous principle, and that employed in the formation of animated matter. Dr. Galvani of Bologna, as early as 1791, published his discovery, that the muscular fibre of frogs could be instant- ly excited by transmitting through its nerves the minutest quantities of electricity. He also proved, that this muscu- lar excitement would take place without any external sup- ply of electricity, when a conductor was made use of to connect the nerve and muscle, but that no such result ever occurred when new conductors were substituted. This discovery was clearly sufficient to prove, that nerves are among the best conductors of electricity. After that time inquiry was set on foot, with the most unreasonable ex- pectations, and was in turn as rapidly abandoned because, unfortunately, experiments did not warrant every scheme of the investigator. Without considering that the functions of life depended upon numerous co-operating principles, it was idly hoped, that they might be regenerated in the inanimate structure, where every other principle was ex- 41 tinct, except the fictitious one. It is not necessary, how- ever, that all such anticipations should be satisfied, in order to show the similarity between galvanism or electricity and the nervous agent. There are no less than four kinds of fish, which have a natural apparatus in their bodies, capable of imparting shocks, not only similar to those from a Leyden jar, but upon similar principles. These are the torpedo, the gymnotus electricus, the silurus electricus, and another found at the Comoro Islands, which seems of the genus Tetrodon. In each of these, there seems to be a distinct organization, for the purpose of accumulating and transmitting electrical power. In the torpedo this struc- ture consists of perpendicular columns, reaching from the under to the upper surface of the body. Hence on the prin- ciples applicable to the opposite poles of a galvanic bat- tery, this fish must be touched so as to make a circuit between its under and upper surface. Then a strong shock will be felt throughout the connection ; but only a chilliness, when either one is singly touched ; here we perceive a perfect coincidence as to principle. In a very large torpedo one electric organ was found to consist of eleven hundred and eighty-two columns, each with a diam- eter of one fifth of an inch. The shock which is given by the torpedo, when standing in the air, is about four times as strong as when standing in water. This fact shows an- other similarity •, for water is a much better conductor of electricity than air, consequently, in the latter position, more will be transmitted by a conductor. The torpedo shock is interrupted by nonconductors of electricity, and transmitted through those that have the power. Even though the circuit should be formed by several persons joining, the shock will be felt by them all at the same time.* * Walsh's paper, Phil. Trans, vol. 63. G 42 Dr. G. W. Schilling, in 1764, made experiments upon a torpedo about six inches long and one thick. The account, though it seems extravagant, cannot but be considered as demonstrating a very close resemblance between the power accumulated by this fish, and magnetism, which appears to be a modification of electricity. He put it into a vessel of water when its vigour was greatest. A magnet with a power of four ounces was then applied near the fish, which immediately began to move about with violence, though not touched. The desire to escape seemed greatly to increase, as the magnet was brought nearer. The magnet was then placed in contact with the water, and the torpedo, after slowly approaching, and at times endeavouring to escape, at last adhered to it, like a piece of iron. After being cautiously removed to some distance, it recovered the power of motion, but was totally incapable of giving a shock. The magnet again attracted it, where it adhered for half an hour, and then spontaneously fell off, evidently debilitated and without the power of giving shocks. It is also stated, that after the immersed magnet had destroyed that power, iron filings, when thrown into the basin, occasioned its restoration. Something analogous to this may be seen in the human body, during the paroxysms of neuralgia. It is a fact well authenticated, that when this nervous affection attacks the cheeks, a magnet, by being kept in the mouth, has the power of allaying the pain. A very intelligent physician, who had long suffered from this excruciating disease, re- marks, that he relied upon a magnet which he kept in his mouth next to the affected cheek, and found it capable, for a time, of affording him perfect rest, but that afterwards when that influence had ceased, being led by analogy to try a more powerful magnet, the result proved of a most 45 contrary nature ; the pain returned with such violence upon every application, as to render the attempt almost insup- portable.* With the view of checking this nervous disease, physicians have effectually recommended the use of mag- netic belts. From some experiments performed by Mr. Todd, it is shown that the shock of the torpedo passes from the elec- tric organs through its connecting nerves. An incision was made round the circumference of both organs, so as to leave no attachment between these organs and the animab except by nerves ; under such circumstances shocks were received as powerful as before the operation.! In this fish, therefore, we see that a power very similar to the electric, is naturally accumulated and transmitted through nerves as conductors. The gymnotus electricus in my opinion establishes their identity. Cavallo remarks, that " the strongest shocks of the gymnoti, which were exhibited in London, would pass through a very short interruption of continuity in the cir- cuit. They could be conveyed by a short chain when stretched so as to bring the links into a more perfect con- tact. When the interruption was formed by the incision made with a penknife, on a slip of tinfoil that was pasted upon glass, the shock in passing through that interruption showed a small but vivid spark, plainly visible in a dark room. This animal showed a peculiar property, namely, that of knowing when he could, and when he could not, give the shock 5 for if non-conductors or interrupted cir- cuits were placed in the water, he would not approach them ; but as soon as the circuit was completed, he would approach the extremities of that circuit, and immediately * Dr. Jones' letter to Dr. Rush. t Phil. Trans, for 1817. 44 give the shock."* In other respects this animal resembles the torpedo ; so also do the remaining two, the silurus and that from the Comoro Islands ; but less is known of them. I have been particular in describing these facts, because the j furnish the most manifest exhibition of the nervous energy, and prove, at the same time, that it is the same as the electric, galvanic, or magnetic. We can hardly have a more beautiful illustration of physical phenomena sub- servient to the vital economy. They do not result from fortuitous circumstances, but depend upon a separate struc- ture well adapted and apparently acting upon as definite principles as a galvanic battery. On this subject Sir Eve- rard Home remarked, in his paper on secretion, that these arrangements prove, " that a voltaic battery can be formed in a living animal, and that nerves are essential for its management, for in these fish, the nerves connected with the electrical organs exceed those that go to all the other parts of the fish in the proportion of twenty to one. The nerves are made up of an infinite number of small fibres, a structure so different from that of the electrical organ, that they are evidently not fitted to form a voltaic battery of high power; but their structure appears to Mr. Davy to adapt them to receive and preserve a small electrical power.'' In the same paper an experiment is stated which shows that the animal structure when detached has the power of accumulating nervous energy, or in other words of forming a voltaic battery. When the two hind legs of a live frog have been recently cut off from the body, the muscles of both will be excited to contractions if the cir- cuit be completed by making each crural nerve pass across from its own limb, and touch the muscular part of the other leg.t * Elements of Philos. ) Phil. Trans, for 1819. 45 Lagrave states, that by placing alternate layers of brain and muscular fibre together, and separating them by a porous body soaked in salt water, a galvanic pile will be formed, having the usual effects.* Here we see that the composition of animated matter qualifies it to accumu- late, under certain circumstances, the galvanic influence, and although the arrangement of the parts is not natu- rally so regular as this of Lagrave, the experiment just mentioned, of the frog's legs, shows that the natural one is sufficient. We thus learn that galvanism is accumulated by the structure alone, both during and after life ; we are also aware that its power is able, according to its extent, to effect the most varied chemical changes ; what then, I would ask, can authorize us to consider that this power, when excited during life, does not occasion new chemical compounds whenever materials are presented ? Many circumstances lead us to give credit to this power as a secreting agent. We know its influence over compounds, out of the body ; we know that it can be accumulated in the living system, and though there should not be nerves to transmit it, yet any organic compound, as the animal fluids, which by their position can direct it, or concentrate its power by forming circuits, must lead as directly to changes of composition. Nerves, however, are almost always present in the greatest abundance. Whatever may be the apparent use of this structure, we know that whether for secretion, motion, or sense, all are open to the galvanic influence. But it may be asked, if such is the arrangement, why are not the nerves of sense and motion constantly giving rise to secretions ? To this it may be answered, that one circumstance can always prevent them, even when galvanism is excited in their * Bostock's History of Galvanism, 46 neighbourhood. Under all circumstances its course will be through the shortest circuit, and for this reason most of its power will be confined to the same extent. This we know from experiment. If the knob and outer surface of a Leyden jar be touched by the thumb and fore finger, the violence of a shock will be confined to their extent, but if the two hands be substituted for the thumb and fore finger, we will feel the shock in the arms and shoulders. To confirm this further, let a person standing behind, place his hands, one on either arm, or either shoulder, so as to form a second circuit, and although his is connected with the first, yet as it is the longest of the two, he will feel no shock. Hence we see, that if one or more anastamo- sing branches of nerves intervene between the accumula- ted galvanism and the nerves of sense or motion, little or none of its influence can extend to them. If, however, these nerves of sense are include d within the circuit, they transmit galvanism with perfect freedom ; and what is still more singular, as Fourcroy observes, impart the sensations of smell, flavour, pain, warmth and vision.* Ritter, also, states, that the electricity of the positive pole augments the actions of life, while that of the negative diminishes them. Tumefaction is produced by the former, depres- sion by the latter. The pulse of one hand in contact with the positive pole for a few minutes is strengthened, and gives the sensation of heat ; that in contact with the nega- tive, is enfeebled and gives the feeling of coldness. When the eye is positively electrified, objects appear larger, brighter, and real ; while, to one negatively electrified, objects seem smaller, less distinct, and bluish. f Even the smallest galvanic action has the power of strongly affect- f Connais. CUem. f Ure's Dictionary. 47 ing these nerves. When a piece of silver is placed be- tween the upper lip and gums, and a piece of zinc un- der the tongue, this simple apparatus is capable, when- ever the mouth is closed so as to bring the metals in con- tact, of giving a sour taste to the tongue, and a flash of light to the eye, perceptible in a dark room. Other, and more familiar ones have been noticed ; but it is not my object to enumerate them. The influence of galvanism on muscular motion, through the connecting nerves, is far more striking. Small pieces of zinc and silver are sufficient to convulse the limbs of a frog, or other small animal, so as even to throw them from place to place ; but the magnitude and intensity of such effects have never been illustrated so forcibly as upon the human body. Few can read and credit Dr. Ure's experi- ments upon the executed convict without allowing that even if our vital motions are regulated by an unknown agent, none better need be sought after than that of galvanism. With his battery he made the dead chest heave as in re- spiration — the eyes open and shut with the motions of life, but the ghastliness of death ; — the mouth and lips ran into distortions as true and impressive as when prompted by the strongest or worst passions, and the whole face be- came impressed with characters so energetic as to sicken the bystanders, and force them to withdraw. The hands, arms, and legs, were also thrown into motion far beyond the natural power, and so violent as to baffle all muscular resistance. Dr. Ure concludes his experiments by sta- ting his belief, that if blood had been present and pro- perly arranged, he could have succeeded in establishing circulation.* We may not accede to his conjecture, since * Ure's Chem. Dictionary. 48 more parts than he could command would require to be set in motion; but we cannot doubt about the galvanic in- fluence being capable of exciting their actions. Many other conditions beside motion are requisite for life, and even this one might prove too imperfect for circulation, since it has been remarked by Bichat* and others that the voluntary muscles are thus excited, beyond comparison, much more than those which are not under the will. When persons are attacked with nervousness, one of the most singular symptoms is the erratic muscular motion ; the fingers twitch irregularly, and the impulse shoots from part to part like the coursing of lightning. This, in effect, is what would result from electricity constantly accumula- ting and diffusing itself through multiplied conductors. Galvanism seems to act as a stimulus to the muscular fibre, and its effects are too manifest to require any further de- tail. I shall now consider its agency in secretion. Dr. Wilson Philip on this subject makes the following observation : " I cannot help regarding it as almost ascer- tained, that in those diseases in which the derangement is in the nervous power alone, where the sensorial functions are entire and the vessels healthy, and merely the power of secretion, which seems immediately to depend on the ner- vous system, is in fault, galvanism will often prove a valu- able means of relief."! With this view he administered it in cases of habitual asthma, and, according to his own words, " it failed to give considerable relief only in about one tenth." It may, however, be supposed that such ap- plication only restored the muscular motions necessary for respiration without otherwise promoting the involved se- * Treatise on Life. t Philos. Trans, for 1S17. 49 cretions. In other experiments, related by the same au- thor,* digestion was accomplished by the galvanic influ- ence ; but, if we regard analogy from man, the extensive connection of the par vagum and fact that the coeliac plexus sends off branches to the stomach, render it uncer- tain whether the gastric secretion was directly effected by passing the galvanic influence through the par vagum or branch of the eighth pair. However, Dr. Philip as justly remarks, the " identity of galvanic electricity and nervous influence is established by these experiments." He divi- ded the par vagum, which is distributed to the stomach and subservient to digestion, by incision in the necks of seve- ral rabbits. After the operation, it was found that the parsley, which they had previously eaten, remained in the stomach without alteration, and after a longer time the animals died apparently from suffocation. Other animals underwent a similar division of the par vagum ; but the galvanic influence was applied to the portion below the division, or to that which was connected with the stomach. This was done by touching one wire to the divided end, and the other to a silver dish or plate, placed closely in contact with the skin of the animal opposite to its sto- mach. In this last case no difficulty of breathing took place, and after the galvanic influence had been continued twenty-six hours, the parsley was found to be as perfectly digested as that in healthy rabbits fed at the same^time. Their stomach also gave the peculiar smell which those of healthy rabbits have during healthy digestion. Until a more definite knowledge is obtained concerning the desti- nation of nerves connected with the stomach of a rabbit, these interesting experiments can only be considered as relating generally to the functions of the stomach, in* * Inquiry into the Laws of Vital Functions. 7 50 eluding its muscular motions, (which seem much more con- siderable in herbiverous than camiverous animals,*) as well as its office of secretion, &c. Experiments have been made upon blood and its com- ponents in order to imitate by galvanism the secreting pro- cess, but the range has hitherto been very limited. This is what might be expected when we consider how very unfavourable any arrangement must be. By subjecting blood to galvanism scarcely more than one product can result, since it is but reasonable to suppose that whatever compound is produced from any of its serum, the same must be produced from all of it. Probably, if any thing can promote a variety of products, it will be more likely to follow when that first formed from blood is taken and exposed by itself to the galvanic agency, repeating the same operation for all as they may occur. Dr. Philipt states, that galvanism changes arterial blood to a dark venous colour, and prevents the formation of a coagulum, or at least dissolves it when formed. The same kind of blood at the same time, and under all similar cir- cumstances, except that of galvanism, retained its florid colour, and coagulated. Galvanism also produces caloric, by its action upon arterial blood, but none when operating on venous blood. It is also remarked by the same writer, that venous blood suffers no* visible alteration. Whether this be strictly correct or not, we should be inclined to suppose that arterial blood has much more matter to un- dergo changes than that found in veins ; and any such anal- ogy between the galvanic and nervous agency is of the utmost importance to be known. When we consider their obvious similarity we feel inclined to illustrate one by the other. May it not, therefore, be supposed, that the gal- * J. Bell's Anat. vol. 3. t Inquiry into the Vital Functions, 51 vanic influence in the body over arterial blood, during the time of secretion, impoverished it agreeable to the gal- vanic analysis, giving out caloric, as Mr. Philip has shown it does, and changing its colour from florid to a dark one, leaving it thus characterized to enter the veins ? The resemblance is certainly close, for, according to these ex- periments, galvanism could effect no more changes on the venous blood. It is to be observed, however, that Sir Everard Home, in his paper, entitled " Hints on the sub- ject of animal secretions,"* details changes effected by galvanism or venous blood. Some of these I shall now mention. They were performed by Mr. William Brande. He immersed the conductors of a four-inch double plate battery, into four ounces of fresh drawn venous blood, keeping up its natural temperature all the time. The bath was composed of a very weak solution of muriatic acid. The galvanic influence seemed to cease at the termination of a quarter of an hour. When examined, " the^lood which had surrounded the negative wire, was of a deep red co- lour and extremely alcaline ; that surrounding the positive wire, was slightly acid, and of a brighter hue. In this experiment, the coagulation of the blood was not materi- ally affected by the electrical power alluded to." Dr. Philip, states, that venous blood undergoes no visible change ; but Brande observed, that its colour became brighter. Hare, in his work on the stomach, mentions that electricity prevents the blood from coagulating after death ; in tBe foregoing experiment, as well as in another performed by Mr. Brande on the venous blood of a deer pithed for the express purpose of preventing coagula- tion, we find that this property of blood manifested itself, Phi los. Trans, for 1809 52 although under the influence of galvanism. There is this difference however, that Hare alludes to a shock power- fully and rapidly pervading the system, as when struck hy lightning, whereas the blood in Mr. Brande's experiments was exposed to a current $ so that the fluid might by the latter mode manifest its property previous to any exten- sive changes. One of the most interesting discoveries, by transmitting galvanism through the animal fluids, is that they all con- tain albumen which is soluble, when united to an alkali^ and that their coagulation depends upon that union being destroyed. Mr. Brande in his paper on albumen* has ex- amined this property in several fluids ; and finds that a very small galvanic power is sufficient to effect a perfect coagulation at the negative pole, even where the albumen is diluted with so large a quantity of water as not to be detected by the usual tests. By the experiments mentioned in Sir Everard Home's paper, before alluded to, it appears that galvanism has the power of separating albumen from the blood, or its serum; by one degree of power it is sepa- rated in a solid form, and by a less degree, in & fluid form. Hence then, there seems reasonable ground for presuming that this agent is extensively employed in producing the different animal solids and fluids from the blood, since ac- cording to Mr. Hachett's experiments, albumen is the principal material of which animal bodies are composed.! Mr. Home, remarks "that the structure of the nerves may fit them to have a low electrical power, which can be em- ployed for that purpose, and as such low powers are not influenced by imperfect conductors, as animal fluids, the nerves will not be robbed of their electricity by surround- *Philos, Trans, for 1809. tPhilos. Trans, for 1800. 53 ing parts." We have also noticed that a low power is best adapted for effecting the separation of albumen. This power will even be effectual when the most delicate elec- trometer is incapable of affording the least indication.* I have already remarked, that animated matter is occasion- ally formed where nothing like a nervous structure has been detected; (see commencement of this section;) there are instances also, when this structure seems too minute and imperfect, to perform such a function. All embryos are of this nature. In eggs the evanescent structure can hardly be supposed to work all the diversity of animated compounds, which are found to accumulate so very rapidly. Its condition is isolated, and without any more maternal assistance than can be obtained from a common baking oven ; we find moreover, that the vital action is for a long time confined to a mere speck. The condition of em- bryos matured in the womb is scarcely better ; they all have a rapid secretion of animated matter, while their most favourable connexion with the mother seems merely for the purpose of affording blood. Even if we suppose (as is most probable) that this blood does not circulate through both, but that the mother affords nutriment which enters elaborated into the foetal circulation,! still all the peculiar products constituting true secretion must be effected, exclusively in the embryo. Plants of the most perfect nature are not supposed to have nerves ; how much less reason, then, must there be for denying the ex- istence of such a system in the circumscribed seed ? yet the energy of an acorn sends forth the gigantic oak. We find the secreting power as prominent in the millet seed as in the garden bean, and limits far below the microsco- *Mr. Home's paper on secretion. t Chapman on foetal circulation. 54 pic power, include hundreds of such systems. When we consider these facts, we must come to the conclusion, not only that secretions whether animated or not, can occur without a nervous structure, but that in the early stages of corporeal existence, there is a universal and diffusable agent employed for its advancement. Two reasons in particular induce us to consider this agent as electricity or galvanism. It is qualified to produce compounds of the most varied kind, and its supply is constant throughout nature; open to the minutest assemblage of organized substances, without requiring any vital action on their part. Dr. Philip, in his work on vital functions, suggests the agen- cy of galvanism at such times. " If the nervous influence be galvanism," he remarks, " there may be some appara- tus in the uterine system for collecting and applying this agent, which is every where diffused, till the brain and spinal marrow can perform their functions ; and which may continue to supply their place where they never exist. We have seen that galvanism is capable of performing all the functions of the nervous system, properly so called. In combination with the powers of circulation, it can, therefore, perform all the functions essential to the life of the perfect animal, except respiration, for which, we have seen the sensorial power (residing almost entirely in the brain) is necessary." Elsewhere this writer continues: " we must regard the rudiments of life as confined to the circulation, from which, by the power of galvanism col- lected by some means external to the foatus, all other parts are gradually evolved ; till within the foetus itself, a gal- vanic apparatus of sufficient power for the performance of the nervous functions is produced."* However we 55 may revolt from terms and expressions which give the vital functions the appearance of depending upon combi- nations, which we can only accomplish by mechanism ; we should always recollect that the principle is distinct from the workmanship ; and, I must confess, I am aware of no illustration so apt on the present occasion as galvan- ism; no matter whether the womb be the apparatus or the embryo, or, indeed, the universe itself. LIGHT. The agency of this principle over the vital functions, and of course over the animated productions, is in a num- ber of instances very obvious and important. It is proba- ble, however, that its extensive influence depends upon its being a compound of two of the most active ones before mentioned. The solar light is the form alluded to in the present consideration ; and we learn from the prismatic analysis, that the sunbeam is composed of rays of colour? heat, and electricity. The first does not seem capable of effecting chemical changes, and the two latter have already been noticed. But as the action of sunshine is very re- markable, and as, in the present state^of knowledge, it is impossible to explain its peculiarities by the properties of any constituent alone y I have assigned a separate considera- tion for the agency of life. Sir Humphry Davy* remarks, that, " in general, in na- ture the effects of the solar rays are very compounded* Healthy vegetation depends upon the ^presence of the solar beams, or of light ; and whilst the heat gives fluidity and mobility to the vegetable juices, chemical effects like- wise are occasioned, oxygen is separated from them, and * Elements of Cbem. Philos-. 56 inflammable compounds formed. Plants deprived of light become white, and contain an excess of saccharine and aqueous particles ; and flowers owe the variety of their hues to the influence of the solar beams. Even animals require the presence of the rays of the sun ; and their colours seem materially to depend upon the chemical in- fluence of these rays. A comparison between the polar and tropical animals, and between the parts of their bodies exposed, and those not exposed to light, shows the correct- ness of this opinion." In the animal creation, brilliancy of co- lour and gaudy plumage belong to the tropical climates ; more sombrous tints distinguish thepolarinhabitants j and dull co- lours characterize nocturnal animals, and those who chiefly abide below the surface.* In detailing the properties of light on the living system, I shall be compelled to neg- lect all arrangement or connexion ; the subject does not admit of it. The effects of light are moreover of such a general nature, that it will be impossible to point out its immediate agency in the production of animated substances. Indeed, there is reason to suppose that it has none, since their formation generally takes place within the corporeal system. But its importance in many of the functions con- ducive to such formations, cannot be overlooked. The action of light on animals is not so well understood as upon vegetables. We find that oviparous animals gene- rally deposit their eggs or spawns, where they will be ex- posed to the sunshine. One great source of vitality re- sulting from this arrangement is the warmth induced. Indeed, we may suppose this to be the prominent advan- tage, since we find birds, as the ostrich, deposit their eggs in sand banks, which as well as the egg shell itself has the power of reflecting light ; and in the night time the agency * Brande*s Chem. 57 of light seems withdrawn, whereas that of warmth still re- mains Besides, the hen and other birds which set on their eggs so great a portion of time, must prevent the access of light, while at the same time they accumulate the range of temperature. In vegetables the advantange of sunsnineis very manifest. Plants growing in hot houses wih expose their leaves to the sunshine, although the quality of the circumambient air cannot be materially altered, sinr-.e the light enters by glass casements ; neither does its tempera- ture require any farther increase. This appetence is in some instances very remarkable. Light acts beneficently upon the upper surface of leaves and hurtfully upon the under side. This at least applies to most plants, What- ever be their situation, either nailed up against a north or south wall, impending, or in a hot house, they will invaria- bly turn to light the side of the leaf that (m a perpendi- cular position of the plant) is uppermost ; even when by such motion less heat comes to them, as in a hot house. So great is this power, that though repeatedly checked by forcible retrograde motion, the leaves will constantly turn back again, until the plant becomes weak as it were by exertion. The misletoe and some others, both sides of whose leaves are alike in appearance ; or the upright sword-shaped leaves, both sides of which seem to perform the same function with light, are indifferently exposed, and do not alter in consequence of any variation of the light, or of the position among the stem and branch- es. A familiar example of leaves following the sun and its beams, may be observed in a clover field. The Helia- anthus anneas, or sun flower, turns with its biossom all day to follow the sun ; and at night, retraces the same course to meet him as he emerges, in the morning, from the east. Calandrini found that vine leaves turned to the 58 light when separated from the stem and suspended by a line thread.* This last observation seems to show, that the important agency of light, though constituting a vital phenomenon, is effected upon physical principles. I shall now examine what are the changes effected. Priestley, in 1778, observed that plants, under certain cir- cumstances, emitted oxygen gas.t Ingenhausz afterwards determined, that the leaves performed this function and only at such times as the sun's light shines full upon them. Thus it was found that when the leaves of a plant were made to pass under into a glass receiver, inverted and full of water, that the upper surfaces gave bubbles of oxygen gas, as long as the sun shone on them.j This effect seems to follow chiefly from the agency of light. Subsequent experiments proved, that it was not the water which be- came decomposed ; since no bubbles appear when that fluid has been boiled ; but that they depended upon carbo- nic acid gas, dissolved by the water, and that their number will be in proportion to the quantity of that gas.§ Hence then from these data we learn the agency of sunshine. Water is not decomposed to any extent, whereas oxygen gas is liberated, therefore the carbonic acid must. The plant retains one of the constituents (carbon) for its nourishment; while the other (oxygen) is set at liberty and rises in the bell, hi the dark it is found that plants reverse this operation; that is, they give out carbon and absorb oxygen. But the extent at this time is very trifling. Otherwise the carbon taken in for nourishment during the day would be lost during night, (particularly in those sections of the earth where the night nearly equals the day,) and the plants ul- timately decline. This result would be contrary to obser- vation ; and as it is, we perceive how plants, upon the Smith's Botany, t On air. | On vegetation. § Encyc. Method. Physiol. 59 whole, conduce to the general economy by subtracting carbon from the carbonic acid of the atmosphere, and re- placing it by oxygen gas, which is so essential to the life of all animals. Sunlight has a very considerable deoxi- dizing powers as may be seen by exposing nitrate of sil- ver to it for a short time. The salt will be decomposed, and this results in consequence of the light subtracting oxygen. But carbonic acid is not so easily decomposed by this single power, so that we may consider the above to be effected by two affinities, depending both upon the plant and light. The nature of the agency of light is shown by another experiment. When plants are exposed to hydrogen in the dark, they still remain green ; though without this gas the absence of light would occasion that green to become a faded white colour.* Hydrogen gas has its most powerful affinity for oxygen; and the simila- rity of effects intimates that light also exerts the same kind of agency. From this experiment we might be led to suppose that the green colour depends in some manner upon the supply of carbon. We find that when the sun shines upon a plant carbon is readily obtained from at- mospheric carbonic acid, and the colour becomes fresh and green. The presence of hydrogen is able to produce the same effect,! apparently, because it takes the oxygen of carbonic acid and leaves the carbon to unite to the plant. But in the dark no carbon is furnished, since there is no effectual agent present, and the plant loses its green colour, and fades to a whitish one. With these remarks I shall conclude the subject of light ; since, as has before been observed the range of experiment is by far too limit- ed to give much information upon the peculiarities of its agency. * Smith's Botany. t Thompson's Chem. vol. 4. 60 atmospheric air. [Oxygen.) It is well known that the vital functions cannot long continue without the assistance of this air. It follows, therefore, that the formation of animated matter absolute- ly depends upon it or some other possessed of similar pro- perties. It will not, therefore, be necessary to dwell long on this point ; as the nature of its agency is of most im- portance. The experiments of Ray, Boyle, Muschen- broeck, and Boerhaave, all prove, beyond a doubt, that no plant vegetates in the vacuum of the air pump. It follows, therefore, that no seed will germinate unless atmospheri- cal air, or some air having similar properties, have access to it ; and it is for this reason that seeds will not germi- nate at a certain depth below the surface of the earth.* Guided by similar phenomena, the agriculturist finds that ploughing the soil is the surest way to destroy weeds and grasses ; by which process the sod is turned over on them, and they become hid from the air in consequence of being hid in the furrow. It is now determined that it is the oxygen in atmospheric air which is of such importance ; and that no seed will germinate in any other gas unless mixed with it. An experiment of Mr. Humboldt corrobo- rates this very beautifully. This gentleman found that seeds vegetate more rapidly when steeped in a solution of chlorine; and it is the distinguished property of this sub- stance to liberate oxygen by decomposing water. At Vi- enna, seeds which had been long kept, and which had con- stantly refused to germinate, grew readily when treated with it.t In the commencement of germination, if under favourable circumstances, carbonic acid is given off for a * Ann. de Chim. iii. 57. t Thompson's Chem. vol. 4. €1 time, even when no oxygen gas is present. This, therefore, seems to result from an internal chemical action convert- ing the iarrinaceous matter of the cotyledons into saccha- rine and other nutritive matter. We see a similar phe- nomenon in the malting of grain, It seems, from experi- ment, that the water at such times is not decomposed, since neither oxygen nor hydrogen is liberated. But when the cotyledons have afforded their substance for sup- port, the presence of oxygen becomes absolutely neces- sary ; and as much carbonic acid (in bulk) is found as there is oxygen. This seems nearly all the use of oxygen gas at such times, because as the carnonic acid is just sufficient to require the whole quantity, none can be im- bibed by the see is. They, on the contrary, by such a pro- cess, lose carbon. Saussure determined that wheat and barley consumed oxygen in this manner between ^V o an( ^ ^ of their weight ; whereas beans required as much as 1 ^ T . Hence we see plainly that the quantity varies to a great extent according to the kind of seed. In these in- stances beans seem to require, at least, ten times as much oxygen as wheat and barley. A comparison of the expe- riments here detailed, with those mentioned when treating of light, point out a singular difference between the econo- my of a seed and that of a plant. The former (seed) seems to require the emission of carbonic acid, while the latter decomposes carbonic acid and retains its carbon. It is true they are under very different circumstances, since the plant effects these changes by the agency of light, whereas the seed is deprived of it. It is true, also, that plants themselves, when in the shade, seem to emit carbonic acid.* But under the circumstances most ad- vantageous to each this difference evidently exists. It * Ingenhausz on Vegetation. 62 has been shown that plants cannot thrive without oxygen ; and Saussure, in his researches on vegetation, discovered that in the day time they give it out, (chiefly taken from the carbonic acid which is absorbed by them for the pur- pose of subtracting its carbon,) and in the night they take in a fresh supply. It would be useless to detail all such peculiarities ; those already noticed are sufficient to show the general agency of oxygen gas or atmospheric air ; and almost all the important facts on this subject may be found amply noticed by Dr. Thompson, in his system of chem- istry, vol. 4. The presence of oxygen gas, after respiration has com- menced, is justly considered as indispensable ; but its utility during all the previous changes of animal existence, is as yet very much overlooked. I think there can be no doubt but that one general principle governs both vegetable and animal formation, and that whenever such operations take place, whether in the adult or embryo, the same agents are directly or indirectly employed. Dr. Ewell,* made experiments which show the importance of oxygen gas at this early period of animal existence. He ascertained, that the semen of man owes its fluidity to oxygen ; or rather that it absorbs this gas, and then becomes fluid. He remarks that " after making several experiments, and reflecting on the subject, he is convinced that the presence of pure vital air, or oxygen gas, is necessary to give the first ani- mation to the embryo formed in the uterus. That it is only after this union, with a little oxygen, that the embryo is enabled to receive nutriment from the mother, and that, consequently, coition will always be unfruitful unless it takes place in pure air." Whatever may be the agency of oxygen gas upon the embryo in the womb, it is manifest that * Letters on Generation, Med. Repos. No. 38, 63 its supply, per vaginam, must be very limited. Dr. Ewell, states another of his experiments, which may be considered, however, as relating more to the changes necessary for nourishment, than as proving the nature of incipient anima- tion. " Two frogs engaged in copulation, were taken and held in vessels containing pure distilled water; one vessel of water was impregnated with nitrogen gas, another with carbonic acid gas, a third with atmospheric air, and a fourth with oxygen gas. In each of these, the frogs deposited their filaments which was carefully attended to, for several days. It was found that only the filaments in the vessels contain- ing oxygen and atmospheric air, had the least appearance of tadpoles." Other facts are stated, by Dr. Ewell, apper- taining to propagation. They may be seen in his letter to Dr. Miller.* Bird's eggs are constructed so as to be sup- plied with atmospheric air or its constituent oxygen gas. They have all at the but or large end a pouch called the folliculus eeris, for the purpose of containing the air. The vitellus or yolk, as appears by the hen's egg, is so poised by thin menbranes, that the cicatricula (very near which the func turn saliens, or first point of animation is observed) may always face upwards. This is effected by the orga- nization, which makes that portion of the vitellus, which is opposite the cicatricula and outside the line of suspension, the heaviest ; and it has two prominent advantages. It always keeps the neighbourhood of the functum saliens (in every position of the egg) nearest to the two great chemical agents, caloric and vital air. The first is furnished by the hen bird, and the last by the follicle or air bag. Whatever be the shape or kind of egg, this arrangement will occasion such approximation ; generally the air is collected in- the but, because this end is the highest. During incubation *Med. Repos. No. 38. 64 there is a still closer approach of the vitellus to the folli- culsts' sens. It is not necessary to attribute this phenome- non to a vital power ; since it takes place m consequence of chemical changes rendering the yolk specifically lighter. Indeed, it extends the truth that nature makes a liberal use of her physical laws even in the very foundation of life ; and it is even proved that when the egg is kept up- right on its but, the vitellus will rise to the point, and thus leave the follicule.* By the natural position, however, it is manifest, that though still guided by the same laws they must approach each other. Dr. Paris, in his memoir on the physiology of the egg,f gives the following description. " The external shell and the internal membrane with which it is lined, constitute the varieties of the folliculus seris ; its extent in the recent egg is extremely small, and before its exclusion from the uterus, it does not appear to exist. It would seem to com- mence at the moment the egg is deposited by the bird. A small portion of the watery contents of the egg transpire through the shell, and the air then rushes through the obtuse end, and inflates the follicule," &c. "Its size and subsequent increase are to be explained upon the same principle ; which they establish an important rela- tion between the diminution of the bulk, of the ovular contents and the extent of this preumatic apparatus. Dur- ing the progress of incubation, it is dilated to a very con- siderable magnitude." A few days after incubation, blood vessels are observed to " extend and multiply their rami- fications on the yolk and white, by which, the blood is ex- posed to the action of the air in the follicle, oxygenated and returned to the embryon." This use 3 Dr. Paris re- * Barr's Buffon, vol. 3. page 24, t Ann. Philos. for 1821. 65 marks, is manifested by the position of the blood vessels, as well as by the air itself, which, before incubation, is atmospheric, but which afterwards becomes contaminated with carbonic acid gas. The increase which this air at the but of a hen's egg obtains by incubation, is, accord- ing to Dr. Paris, as nearly ten to one. Whatever ob- structs the inflation of this follicle and the renewal of its air destroys the embryo. The experiments of Reaumur offer abundant proof of this truth. In his attempts to de- velope the egg by the heat of dung, they, for a long time, failed, owing as the subsequently discovered, to the im- purity of the atmosphere. He also varnished eggs, so as to prevent the access of air ; and found that when such were placed under the hen, they invariably perished. Spallanzani instituted many experiments with the same view. " I have often," says he, " placed the eggs of ter- restrial and aquatic insects under the receiver of an air pump ; but none ever hatched in this situation, although in every other respect in a condition to do so." Boer- have also remarks, that " ovula quorum cunque insecto- rum, in vitris accurate clausis, non producunt" It is a fact well known in the farm yard, that turkeys frequently destroy or smother their eggs by a too constant and assi- duous attention. Dr. Paris then proceeds to notice that the air follicule may also have a secondary office to perform, namely, that of producing by its air a part of those necessary chemical changes which the albumen and vitellus are found to undergo. It will not be necessary to extend this inquiry ; we see plainly the importance of oxygen gas, or atmospheric air for all kinds of embryos ; and the animal as well as vegetable one seems to require the supply for the purpose of getting rid of carbon. The adult animal 9 66 still displays the same economy ; but plants seem to give out carbon only in the night or shade, and then in exceed- ingly small quantity.* When treating of respiration as a part of the process of sanguification, I shall take up the consideration of oxygen ; also, subsequently when examin- ing irritability as a property of animated matter. For the present it will be sufficient to remark, that oxygen gas is intimately concerned in every vital function, both animal and vegetable, wherever assimilation or secretion is per- formed. AGENTS IN GENERAL. I have been led to include atmospheric air among che- mical agents ; because its presence, which is almost uni- versal, always promotes changes of composition. But upon an examination it will be perceived that its influence depends merely upon presenting a substance, (oxygen) which has a strong chemical affinity for most other organic substances. It certainly has no power of itself to dispose bodies to union ; which is the strict signification of an agent. On the contrary, it may be considered in the very oppo- site point of view ; for it is evident, that if the atmospheric pressure were taken off from all bodies there would be more aeriform states, and therefore more chemical com- binations. In noticing the vital function, we are often led to consider bodies as agents, when in truth their influence depends upon presenting materials with strong chemical affinities. The gastric juice is most generally called an agent ; but if it is at all so, it must depend upon being a solvent, or upon possessing some of those mentioned pre- * Thompson's Chem. vol. iv. Vegetation. 67 viously to atmospheric air. So also we might regard ex- ercise, appetite, disease or violent injuries, as agents, since they all predispose the body to a new series of chemical changes. Guided by such considerations, it is evident that the number of agents would be unreasonably and in- finitely extended. I shall therefore pass over their con- sideration, and treat of alteratives, which are the most notable of the kind. ALTERATIVES. By this term, I mean all such substances as have the power of producing an alteration in the irritable action of animated matter. There is no name expressive of such a class of bodies, unless it be this one. I shall not, there- fore, dwell on its merits, but proceed with its present ap- plication. Alteratives are either mechanical or chemical; but the nature of my subject leads me to the considera- tion of the latter. I must remark, however, that the for- mer kind act a highly important part in the animated body. All distensions of the heart, womb, bladder, and other vis- cera, appear of this nature. Mechanical alteratives, by their size, figure, or weight, may lead almost directly to chemical decomposition. Chemical alteratives consist of such bodies as affect ir- ritability by their peculiarity of composition. Arsenious acid (white arsenic) will illustrate the distinction. By its weight, size, or irregularity of shape, it is always, in the first instance, a mechanical alterative ; but, by its qualities of composition, which are evidently unconnected with the foregoing properties, it acts as a chemical alterative. Chemical alteratives are divided into sedatives and sti- muli. The former are supposed always to diminish the extent of irritable action, and the latter to augment it. This distinction arises from their ultimate effects ; but the method by which these are brought about, leads to another subdivision of both* They may alter the amount of irri- tability, by acting either on the composition (in the che- mical sense) or on the structure. As agents, it is not ne- cessary that they should always effect chemical changes. Indeed, by doing so they very frequently prove injurious. The influence of such substances as do not sensibly change the composition of animated matter, is extremely obscure. Many have accounted for it, by supposing, that physical properties were displayed by the constituting particles ; hence arose the terms sharp, dull, or rough taste. When we consider, that every body has a peculiar taste, no mat- ter what its composition may be, and that the effect of tasting does not seem to alter such chemical composition, we might be lead to suppose, that such properties depend upon some configuration characterising the smallest sensi- ble particles. But this explanation is, at present, generally abandoned, for several reasons. Either the properties of astringents or antispasmodics must be in opposition to those which we should expect to follow from the above explanation. If it be supposed that atomic figure can contract the irritable fibre, then it will be hardly possible to suppose that the same can produce a relaxation. We know, moreover, that such properties result from the che- mical composition, and that the body possessed of them never loses them by any mechanical change. Dr. Park* observes, that " the various kinds and degrees of sensa- tion which arise from the application of different substances to our organs may be referred to their perculiar modes of * Oft the Laws of Sensation, Journal of Sciences and Arts, No. 2. 69 action ; and, accordingly, they are as various as the nature of the substances." This gentleman considers, that sen- sations are produced by chemical agents, and remarks, that they " are more durable in their impression, as they are dissolved in the fluids on the sentient surface, and re- quire more time for the changes they produce, to be again obliterated ; and, accordingly, until this has been effected, the organ may be considered as having its susceptibility for that particular impression partially suspended. Or, the substances applied, no longer producing the same changes, no longer excites the same sensation. Thus, substances kept long applied to our organs of taste, lose their power of exciting sensible impressions ; as, wine, long held in the mouth, loses the flavour peculiar to it, and if several kinds of wine be tasted in quick succession, it soon becomes difficult or impossible to distinguish them." I confess, when these effects are confined to a short space of time, it is impossible to perceive any thing sufficiently definite to be considered chemical ; but, by extending the review, there seems reason for supporting the opinion. Nerves are so extremely irritable, that the most limited and eva- nescent changes of structure may cause sensation. We know, for instance, that alcohol has the property of coag- ulating albumen in the animal fluids, by uniting to the al- kali which renders it soluble.* This is a perfect decom- position. When flesh, or almost any animal solid, is steeped in alcohol, the albumen coagulates, and forms those flakes which render the fluid turbid, and turns the whole sub* stance, after some time, into a white mass. Now, it can readily be supposed, that such a change which subtracts both the alkali and albumen from the substance of an ir~ * Brande's Paper, Phil, Trans, for 1809 70 ritable nerve, will, at its commencement, be able to excite sensation. All the alteratives need not act precisely by this decomposition ; but, the instance will show, that they may occasion changes capable of altering the extent of ir- ritability. Besides, we should recollect, that such sub- stances, by acting only on a single constituent, may prove very effectual without our being able to perceive the least evidence. Escharotics are known to destroy nearly the whole texture, as well as composition, and, therefore, we feel less hesitation in asserting that the change is chemical. Many of these substances produce similar effects on the dead and living matter ; and, in such cases, we have a di- rect proof of their nature. Astringents and antiseptics are of this kind. The agency of the first is not distinctly understood ; but we know that it does not depend upon vitality, since the same takes place with the dead fibre. Antiseptics, on the other hand, must act chemically, during life, on the putrid portion, in order to change its fetid smell, and therefore we may extend its power over the others which are nearly in the same state ; particularly since we find, that it checks or destroys their tendency. Even light, which is a stimulus to the optic nerve, and which is known to convey with itself, through the dense texture of glass prism, its caloric and electricity, may, when it enters the eye, occasion a tendency to decomposi- tion, or its incipient form. Herschel, in making his obser- vations on the sun, found that the irritation proceeded from the red rays, which are known to produce heat in the great- est degree ; and the experiments of Mr. Brande (before noticed) show, that a very small power of electricity is capable of affecting albumen. We need not suppose that such incipient changes would be inconsistent with the per- manent character of irritability ; the same power which 71 removes the nervous matter after its inevitable and inces- sant waste, without our being conscious of the change, can provide for both cases. When we consider the struc- ture of a nerve, we will be aware of the number of varia- tions to which it is liable. The true medullary filaments are surrounded by a vascular texture which follows closely in contact, through all their irregularity, and is replete with blood vessels analogous to the pia mater, then this is cased within two membranous coats exteriorly, it is evi- dent, that whatever substance causes these membranes to contract, will diminish the circulation of blood through the nerve; for whether the medullary matter is in mass, and incapable of contraction, or as Mr. J. Bell* supposed, in zig-zag filaments, or, as has lately appeared, in globules, still compression or elongation of the whole nerve must shorten its diameter, and they crowd the blood vessels. Now, as Mr. Bell remarks, " pressure by impeding the circulation of the blood in these vessels, soon effects the sensibility of the nerve ; for, however the function of the nerve may directly result from its organization, yet the life and vital energy is received from the blood in the circula- tion through it, and cannot long continue if that blood be interrupted in its course." Such a substance as has the least power to occasion membranous contraction, will,, therefore, have a tendency to lessen sensibility, or in other words, to act as a sedative ; though before such contraction takes place, its presence may stimulate or increase sensa- tion. Such seems the nature of cold applications, and, perhaps, such sedatives as opium, which have been sup- posed in the first instance to stimulate. When we im- merse a hand in very cold water, at first the sensation * Anat. vol.2. 72 amounts to pain, but after a while this feeling completely subsides, or is at least lessened very nearly to that extent ; yet this is not owing to the subtraction of caloric, for if the other hand be immersed in water of the same tempera- ture as the first at the time sensation ceased, we will again be effected with a feeling of coldness. Cold air contracts the skin when it occasions numbness, and therefore may effect the membranous coats of nerves in the same way. But it is useless to be throwing away even conjectures ; the subject is certainly a very unsatisfactory one, and the names by which we indicate the bodies under considera- tion may be the least likely to throw light on their true nature. If relaxation of habit leads to an excess of sen- sibility, then astringents, producing an opposite action, may appear to have some claims for the character of a se- dative. There is reason to suppose that the irritability, or, as it is generally called, sensibility of a nerve is inti- mately connected with the degree of circulation through its substance ; yet the principle upon which its existence, as well as transmission depends, is so completely obscure as to warrant our being satisfied with the knowledge of the mere fact. I shall, therefore, pass over all these substances which, acting as alteratives, either to stimulate or allay the irritable fibre. It is sufficient to remark, that if these effects do not depend upon chemical action, they certainly do upon qualities immediately and exclusively resulting from the chemical composition of bodies. The next subject to be considered is the formation of animated matter. 73 THIRD DIVISION. PRODUCTION OF ANIMATED MATTER. SANGUIFICATION* When we consider the complex structure of the living body, as well as the routine of motions constituting its functions, we cannot be surprised at its continual decay. Admonished by appetite, all animals endowed with the power of locomotion seek nourishment, which by an operation of constitutional changes, obtains the power of vitality, and takes the place of parts no longer fit for vital functions. Necessity does not always however dictate hunger or thirst ; like sleep these seem to follow some laws of muscular motion. Man generally feels his peri- odical return of appetite every three or four hours ; (ex- cluding the time of sleep, where there is little or no active sensation •,) this is the term occupied by the gastric opera- tion, and certainly does not imply any corporeal necessity, since we know that a fresh supply has passed on to minister to its wants. But it shows, beside the force of habit, that incessant support is requisite for our consump- tive fabric ; all its laws are selfish as well as imperious. Whatever may be the form of habit, we find that the effect for which it is intended, always is more perfect when it occurs with regularity. Hence the uniform return of ap- petite always tends to give better sustenance than when more nutricious food is taken at short and irregular peri- ods. In the animal functions there are two principal causes of destruction — motion and chemical affinity. The first is always augmented by health and muscular exercise, 10 74 and gives rise to the necessity of more food at one time than another ; chemical affinity, on the contrary, is gene- rally speaking a permanent cause, since the matter, which always regulates its extent, is similar from one period to another. Plants have no locomotion ; so that they require a less amount of food, as well as a more uniform supply. Assimilation with them is nearly one uninterrupted pro- cess, until circulation ceases in the autumn. In the following remarks I shall confine myself to the assimilating operations of mankind chiefly ; and shall di- vide the subject into the formation of blood and the forma- tion of the animated structure. DIGESTION. As all the corporeal structure proceeds from the blood, we cannot conceive the long continuance of life without this fluid, or something analogous to it. Plants have a sap which is capable of furnishing all the solid parts during summer; and at the opening of spring (during which time it is little else than waterj it meets with nu- triment deposited in the autumn, so as to become enriched early in its ascension. Animals which are called cold blooded, have this fluid with all its qualities except colour. In short, we find its importance manifested in every form and stage of life. The source of blood in the embryo is very little under- stood. But the most probable opinion seems to be that there is no continuity of circulation from the maternal vessels.* We see this fact illustrated in eggs and seeds. The chick must have its system independent of the hen ; consequently, we must suppose that it fabricates its own * Dr. Chapman on Foetal Circulation. 75 blood ; the same, therefore, may take place in the uterine embryo. How this is effected leads to a very obscure but interesting inquiry. In the chick the blood is observed long before the solid structure, and therefore can hardly be supposed to have its origin from any extent of organic functions. We certainly form an overrated opinion of the sanguiferous process when we confine our views of it to that performed by the adult. Even in the foetal state we must cut off digestion and respiration, and in the early stages of existence the agency of vascular connection. How much less reason, then, is there for supposing a vital origin of blood at the time when it is confined to the punctum saliens or irritated speck in the yolk of a hen's egg. If on the other hand we consider the materials as well as the vessels of a limited circulation, as being fur- nished by the mother, then the blood may originate from the external application of chemical agents, as heat, light, &c. ; influenced by these, the male semen may also com- bine in the formation of blood. It is as rational to sup- pose that the embryo should be irritable as any other part of the female body which results from assimilated nutri- ment. But I shall abandon a subject which is so mani- festly conjectural, and proceed to notice the process by which blood is formed in the adult system, and which will be found to give strong evidence of having a chemical origin. The food is masticated in the mouth, mixed with the saliva, and transferred, by swallowing, into the sto- mach ; here it undergoes changes of composition and be- comes chyme. This chyme passes through the stomach into the duodenum, where it meets with the bile and pan- creatic juice, and by their chemical action becomes chyle and excrement. As these substances proceed through the in- testines they pass by a system of absorbents, called lacte- 76 als, which gradually take off the chyle, while the excre- ment, unfit for nutriment from the beginning, or rendered so in consequence of the changes of digestion, continues to proceed through the intestines, and is finally evacuated. The lacteals, by their ramifications, convey the chyle into the common reservoir of all absorbents, called the thoracic duct ; this duct opens (in man) into the angle formed by the union of the left subclavian and jugular veins; and thus the chyle enters the blood. It is then carried by the circulation to the lungs, where it meets with changes which convert it into red, and, apparently, perfect blood. From this outline we perceive three important changes ; namely, from food to chyme, from chyme to chyle and ex- crement, and from chyle to blood. These are certainly the leading ones ; but there are various others which are not so notable. We shall now notice the foregoing more particularly. It has been contended by many physiologists, that digestion begins in the mouth. In some animals, whose appetite seems too great for the capacity of their sto- mach, we find that the portions which they swallow (but which are unable to enter lower than the bottom of the oesophagus) become digested ; it is probable that the saliva then performs the principal operation, since it pos- sesses so strong an affinity for oxygen as to become charged with it before it mixes with the food. But whether this opinion be correct matters very little ; we know it acts as a solvent, and all changes which it could produce previous to entering the stomach must be very limited. The quan- tity of saliva secreted during the ordinary meal of a healthy man has been estimated at six ounces. It has been concluded, from the experiments of Ste- vens, Reaumur, Spallanzani, Scopoli, Brugnatelli, Cari- mini, &c, that the formation of chyme is brought about by 77 the action of a particular liquid secreted by the stomach, and therefore called the gastric juice. It seems that this operation depends upon a fluid ; for when food is shut up close in balls, and swallowed, no important change takes place ; but when these balls have holes, the food becomes chyme. The process terminates in three or four hours. The case of the woman in the clinical ward of La Cbarite, and who had a fistulous opening through her stomach, illustrates the regularity of this period. In common de- scription it has been said, that the gastric juice converts all substances into chyme, and that this chyme is a homo- genous substance. We are to consider that such a defini- tion of the power peculiar to gastric juice, is far too vague and extensive. When the usual food has been suddenly laid aside for other of a different kind, we know that bad digestion often takes place. Dr. Adam's experiments go to prove that the gastric juice is always the same;* and therefore we may consider the deficiency to arise from the properties alone. We know, further, that the husks of grain, woody fibres, and a thousand other substances in food, never be- come chyme, but exist as mixtures. This fact shows, that chyme is not a homogenous mass ; but that it is made up by a compound resulting from the decomposition of sub- stances which undergo changes readily, as well as of such other parts whose texture and composition are too power- fully constituted. Richerand justly remarks, that a sub- stance to be fit for our nourishment should be capable of decomposition and fermentation ; or, in other words, ca- pable of undergoing an inward and spontaneous change, * On Morbid Poisons. 78 so that its elements and relations may be altered.* This necessity entitles us to consider that digestion is of a che- mical nature. Where would be the necessity of this ten- dency to chemical changes, if they were to be opposed by the vital influence ? If the chyme were always to be of a ■similar composition, it would not be in opposition to the opinion. The ultimate constituents of all animal food are always the same, and but three or four in number : carbon, hydrogen, nitrogen and oxygen ; when of a vege- table nature, the only difference will be in the absence of nitrogen. This is not all : the proximate principles of food resemble each other so much that an analysis can, in some instances, scarcely make out the difference ; and those which are entirely without this general resemblance, pass off to constitute the faces. Thus, a dog cannot digest the whole bone ; his gastric power cannot assimilate the phos- phate of lime which differs from the gelatine in its che- mical constituents, and not in texture, since mastication and the muscular motion of his stomach reduce both to an impalpable consistence. This process gives the appear- ance of assimilation to the whole mass : but when the gelatine, which is the truly digested constituent, becomes absorbed by the lacteals, we find the earthy salt unaltered, and constituting the excrement called album grcecum. I shall pass over the gastric juice itself, since all the me- thods hitherto made use of to procure it are not only ob- jectionable themselves, but they have led to unsettled dis- putes about its properties. The resemblance that the chyme bears to a homogenous substance, and the facility with which all variety of food enters into such a constitu- tion, have led physiologysts, in general, to deny that di* * Phvsiolosrv. ■79 gestion is a chemical process ; it shall, therefore, be my present object, to examine the solidity of this opinion. In the first place, where shall we look for limited vital influence, if not in the canals and cavities of the body ? Is it not absurd even to suppose any ? As I have before re- marked, this property depends upon matter, and no reason should induce us to suppose that it may exist where there is none. It follows, unequivocally, that where inanimate substances of a complex nature fill up, or are passing through such spaces, that their tendencies to decomposi- tion will be as strong as any where else in nature under similar chemical advantages. The true vital economy is, therefore, in taking advantage of such tendency, by fur- nishing chemical agents which, by their affinity, shall give rise to the compounds observable throughout the body. Of such a nature seem the gastric and pancreatic juices, the bile, and a number of others. The most inconceivable distinctions have been adopted to make the principles of life as little understood as possi- ble. The gastric juice has been endowed with a vital influence 5* but what can be more absurd, when we re- flect, that this fluid while separated in the stomach and mixed with the food, must also be supposed to have in- telligence of what is good or what is bad for the body at large ? It is ridiculous to think of such an agent ; the gas- tric juice must produce its effect, as all other substances do, by chemical or physical qualities in general. Surely the vital functions are wonderful enough by furnishing this fluid, rather than any other ineffectual one, without making all its agents conjurors. But it is begging the question, when no proof can be offered. Have we not abundant proof, that the vital power is nothing when unconnected * J. Bell Anat. vol. 3. page 214. 80 with the general system ? There is not a single part of the body, even the most highly endowed, which can when un- connected, either communicate the living power to an in- animate body in contact, or withstand by its own strength of vitality the tendency to decomposition. How then can we consistently suppose, that the gastric juice, which is sent from the living texture, can alone possess the power of making the food resist chemical changes, or of ob- taining, without such changes, the vital property ? We might as well maintain that the bile, pancreatic juice, and other agents for decomposition, operated by inherent vitality. The distinction is indeed, since the most im- portant change seems to be effected by these fluids. On general principles, there should be as great an anti- chemical vitality in the intestines and bladder, as in the stomach ; but such an opinion would be contradicted by the most superficial observation. Mr. John Bell, because he was informed that a cow can digest her secundines or membranes, gives up his faith in the chemical agency of the gastric juice : " This throws us back," he remarks, " from the simple idea which we should be apt to entertain of the nature of the change produced by digestion, viz. that it is chemical. For we see that the nature of the solvent thrown out from the stomach, and its chemical properties, may be changed by an alteration in the action of the coats of the stomach." It remains, however, to be proved that the nature of the gastric juice is changed ; Dr. Adam's experiments show the contrary. And even if such were the case, it would only prove, what is already well known, that one body acts with more chemical ener- gy than another. But surely we cannot overlook the fact, that the gastric juice is emitted, like the saliva and other secretions, by an action of the solid texture. There is 81 nothing more strange in the gastric fluid being thrown into the stomach more profusely by the presence of one kind of food than another, than that the saliva should be secre- ted more plentifully by savoury meats than by a chip of wood. Until we are better acquainted with the peculiarity of stimuli, we cannot say that such is not the case, when the usual diet has been changed. But after all, is the di- gestion of meat by a cow or horse stranger than that by man, the dog or cat ? Habit makes the same substance be secreted more profusely at one time than another, and the irritability of the organ itself is always intimately concerned ; since less nutritious food may become suited to the stomach, and its bulk as well as indigestible con- stituents even promote the operation. By this principle gramnivorous animals may be brought to live on animal food ; and after being accustomed to this their stomachs will become incapable of digesting vegetables, and vice versa ; even man whose power seems most general from habit, may by living long on vegetable food be rendered unfit for the digestion of flesh. I am far from maintaining that this process is independent of the vital influence. Whatever may be the nature of such an existence, whether really dependent on physical properties or not, we must still consider its phenomena as vital. The object in view is to show that laws which have belonged to matter since creation are not destroyed by life ; and that the nature of our conformation directs them by agents which they would obey any where else; just as we see a river still flowing through all its natural and artificial embankments. We must be aware, that even in the midst of the most vital substance, decomposition can take place from the presence of a chemical agent ; no one surely can pretend that it is the vitality of that part itself which makes amends for 11 82 those changes. The connexions with hlood vessels, nerves. &c. accomplish this; principally from being themselves irritated by the injury. It is totally unsupported by ana- logy to give this multiplied power to the gastric juice, even though of an irritable nature ; it is totally devested of connecting organs, as nerves, &c. Much less can we diffuse it through cavities ; particularly when matter with the strongest tendency to decomposition, is passing through them ; and some of which, as the intestines, are found not to be able to prevent the usual chemical changes of putrefaction, when there are no substances furnished with the power of causing a new play of affinities. I shall now notice some further chemical parts of the process. The gastric juice is said to be antiseptic, and this has been considered by many as a proof of its vital agency. There is not,, however, a single one of its cha- racters so decidedly chemical as this ; besides, it is no property of life that one isolated substance should protect another and prevent decay. The analogy is probably drawn from an injured limb recovering its strength ; but, again, it must be repeated, that the limb does nothing but receive the changes. Its irritable structure prompts the action which propels the new supply ; but cannot alone protect the limb. So it is with every detached produc- tion of the body, though endowed with the most delicate irritability^ unless possessed also of an independent circu- lating system, its operation of defending itself, or any other body in contact, by that property, is no stronger than that of inanimate matter. The operation in the stomach of rabbits,, as stated by Dr. Wilson Philip,* shows, that digestion takes place on the * On the Vital Functions 83 surface of the food where it lies in contact with the sto- mach, which is the source of the gastric fluid. For this purpose we see the utility of a fact stated by that author, namely, that after a short time, these surfaces of food change, and are carried by muscular motion to the pyloric extremity, until the central portions are brought in contact with the stomach. There is also a property of the sto- mach, particularly that of a calf, whereby milk and the serum of blood are coagulated immediately.* This, very probably, acts an important part of digestion ; but, if so, it must be by its chemical properties alone, since Dr. Young's experiments in particular show that the opera- tion goes on as well out of the body. This gentleman found that seven grains of the inner coat of a calf's sto- mach, infused in water, gave a liquid which coagulated more than a hundred ounces of milk ; that is to say, more than 6,857 times its own weight.! Is it, therefore, so re- markable, that with such an agent as this, the food should be made to enter into other chemical compounds than those of fermentation or putrefaction ? As to its utility, our im- perfect knowledge of coagulation prevents a decided opi- nion ; it evidently separates the albumen of food with great readiness, and, therefore, may be the means em- ployed to furnish that highly important material to the sys- tem without requiring its reformation. It is to be remark- ed, however, that other offices would have to combine ; and there is no experimental foundation for the opinion. It need not now be urged as an objection to the chemical character of digestion, that, unless in disordered health, there is no complete fermentation or putrefaction. The very phenomena of dyspepsia show, that the tendency is * Hunter's Animal Economy. t Thomson's Chem. vol. iv. 84 never extinct ; and facts well established all go to prove, that the nature of the process consists not only in a series of active chemical changes, but in a muscular arrange- ment to discharge the food before its natural tendencies, even out of the body, could be developed. After under- going imposed changes in the stomach, and remaining there only for the short space of three or four hours, it is evacu- ated into the duodenum, there immediately to undergo others. Now, where I would ask is the time or opportu- nity for spontaneous changes ? Nay, beside these now men- tioned, it can be shown, by another arrangement, that na- ture designs that they should occur as little as possible. Dr. Philip* states, that the food which is in the py loric por- tion of the stomach is always most perfectly digested, and is quite dry in comparison to the undigested food at the cardiac extremity, which is mixed with a large proportion of fluid. What more obvious deduction can we draw from this singular fact than that the pyloric portion of food, since it has undergone all the imposed changes which should occur in the stomach, is rendered comparatively dry, in order to diminish its lasting tendency to spontaneous decomposition ; while, on the other hand, that at the car- diac portion is mixed with fluid to promote more rapidly the action of the gastric juice, &c. 1 shall now, in a ge- neral manner, bring to view the circumstances which in- duce chemical action in the stomach ; and by keeping in view the foregoing remarks, we will be enabled to con- clude correctly as to their nature. 1st. The saliva is a fluid wiih a strong affinity for oxy- gen ; the general agency of solution is also augmented by the gastric juice. The importance of this state of consis- * Vital Functions, 85 tency has led to the axiom " corpora non agunt nisi sint soluta," and its truth has scarcely met with a contradic- tion. Our conformation bears testimony of its importance during digestion. Teeth, or something analogous, are al- ways requisite to grind down the food. When these do not perform their office, the ill effects are manifest ; very old persons without teeth, or such persons who eat in haste, or bolt their food, are generally troubled with indi- gestion. 2d. There is an elevation of temperature during diges- tion. This circumstance conduces to chemical action, whether it is furnished for the purpose, or exists as a con- sequent. Cold-blooded animals are known to digest much slower than hot-blooded ones ; and Spa'lanzani has shown, that the gastric juice 5 at a temperature below seven de- grees Reaumur, or about 48 degrees Fahrenheit, is no more effectual in softening or dissolving food, than plain water.* If we consider this elevation of temperature as a conse- quent of digestion, then there will be more reason for supposing that true chemical changes occasion it. 3d. The properties of such food, as have undergone perfect digestion, are completely changed, both as to taste, smeil, and colour. These changes begin so soon that after the food has remained a few minutes in the stomach, they can be easily noticed. This fact, as Speert justly re- marks, shows that chemical action is the first to take place in the stomach, since no other power could have operated in so short a *ime. 4th. The digestion generally takes place best in such food as most readily undergoes chemical decomposition. 5th. The gastric juice acts on the stomach itself after life. Mr. Hunter long ago noticed this fact on the hu- * Richerand's Physiol. t On the Stomach. 86 man stomach. (Phil. Trans, for 1772.) This gentleman supposed it necessary that the animal should be in health, immediate)}' preceding death, in order that the secretion of the gastric juice may be natural, and capable of dis- solving the dead stomach; but Mr. John Bell remarks, that he found the stomach of children, who had died after a long illness, digested by the secretion of the stomach.* Dr. Wilson Philip states that the gastric juice of rabbits can so completely digest its own stomach, after death, as to leave no trace of former structure. (Enquiry into the Vital Functions.) Now, it may be asked why the gastric juice does not produce the same effect during life, pro- vided its agency is chemical ? To this it ma) be answered, that like all other changes in the living body, even if it does take place, we may be so constituted as not to be aware of it. But the best reason seems to be that the living stomach is always covered with its peculiar fluids, which by interposition defend the living structure, and which must be thrown out on its surface by ever} 7 irritating material. In the stomach there exists an abundance of what Mr. Bell calls the " general vascular secretion" mixed with its glandular secretions ;t these must evidently be decomposed even before the organization, furnishing the gastric juice, can be acted upon ; and during life such changes are prevented from extending by a constant ab- sorption and fresh secretion. After life, this vascular se- cretion can only serve as a protection while it remains unaffected ; but after decomposition takes place it even acts injuriously by the absence of absorption. The pro- tecting effect of fluids, which apparently for this purpose cover the smallest fibres, may be noticed among fishes ; where it is remarked that those which can throw out on * Anat. vol. 3. f Anat. vol. 3. 87 their bodies the most of that thick mucous fluid which characterises all of them, more or less, can remain long- est alive when exposed to the action of the air. Now, does it not seem unreasonable to suppose that all these chemical agents should be crowded together in one process, and that the most natural, without that process being chemical ? If only one were observable we might hesitate ; but I cannot see how we can overlook the pre- sence of so many. It has been said that gases should re- sult from chemical changes in the stomach. This un- doubtedly would be the case if the decomposition de- pended upon the internal action of the nutritious parti- cles; provided, also, they remained a sufficient time under such circumstances, which is found not to be the case. It by no means follows that the same result should take place, where the decomposition is effected by one agent, as the gastric juice. But I shall show, that with all this arrange- ment the most unequivocal signs of spontaneous de- composition do actually exist in a limited degree. Dr c Prout, whose authority stands high on this subject, ob- serves, that " a gaseous product is usually evolved" during the action of the gastric, pancreatic, and biliary fluids.* By other authorities it seems, also, that the gases formed through the alimentary canal (including the stomach) have a fixed ratio and relation to each other. " From the ex- periments of Magendie and Chevreul, it appears that the oxygen gas which usually exists in the stomach in a con- siderable proportion when compared with the other gases r gradually diminishes, and at last disappears as we pro- ceed along the course of the alimentary canal; while at the same time the proportion of carbonic acid and hydrogen gas increases."! The following gives a view of their results. * Ann. Philos. for 1819, t Thompson's Chem. book 5, 88 Oxyg. Carb. acid ) Hydrog. | Nitrog. | Carb. hyd. Stomach, Ccecuta, Rectum, 11 00 00 00 00 00 14 00 12 50 42 86 3 55 7 40 00 71 45 67 58 45 96 00 00 12 50 11 18 - 100. In the small and large intestines these gases were also found to exist in variable and considerable quantities, but with less regularity. These gentlemen examined the bo- dies of four criminals executed in Paris, very soon after death. Their results may be seen more particularly in the Ann. de Chim. et Phys. ii. 292. We learn from Dr. Prout's paper on sanguification,* be- fore alluded to, that the chyme itself gives no traces of an albuminous principle ; (in which term Dr. Prout in- cludes the perfect albumen, fibrine and colouring principle of the blood ;) but that its formation takes place in the duodenum, and some distance down in the intestines. The most important change must, therefore, take place after the chyme leaves the stomach, and unites to the bile and pancreatic juice.* This gentleman is of opinion, that the blood begins to be formed from the food, in all its parts, from the first moment of its entrance into the duodenum. As to the action of the bile and pancreatic juice, little is distinctly known except their importance ; though even this point has been questioned. Berzelius has shown that the bile becomes decomposed by its union with the chyme ; and Dr. Prout, in his paper on sanguification, states, that he always found that the acidity of the chyme, which was almost invariable, became neutralized by its addition. Now, these facts show the importance of bile ; notwithstanding the remark, that when the ductus communus choledicus is obstructed, no manifest deficiency of chyle is observable. Probably the truth would not be so favourable were the fact better established. Ann. Philos. for 1819. f Thompson's Chem. book v. 89 I have but a few remarks to offer on the chyle. While in the intestines, or mouths of the lacteals, its true charac- ter is hardly perceptible ; it undergoes coagulation very slowly and imperfectly, and does not assume a reddish co- lour when exposed to the air. Hence, Dr. Prout supposes, that it then contains a very small proportion only of a principle analogous to fibrine, " or at least this principle exists, as yet, in a very imperfect state, and no colouring matter." When the chyle is found in the thoracic duct, (where the absorbents empty their contents from the body at large,) it bears a close resemblance to blood, and seems only to differ in its colour. To a certain degree it also has the last quality ; for its white particles become pink- ish when exposed to the air.* This perfection of chyle, without any manifest progress, may result from a tendency to inward changes, first established in the duodenum and intestines. The absorption by lacteals seems, as Dr. Prout remarks, to be merely a mechanical process. One of the most singular phenomena that occur during the process of vegetable digestion, is the formation of nitrogen. The flesh and other parts of an animal confined altogether to this kind of food, contains nitrogen gas as a constituent, although vegetables are almost all without it. This is very singular, inasmuch as nitrogen has not yet been decom- posed, while no doubt can be entertained but that it oc- curs from digestion. Its compound nature has been sus- pected, however, by several chemists, and Mr. Miers pub- lished a number of ingenious experiments in order to show that it is a compound of oxygen and hydrogent Berze- lius maintained that it is not a simple substance. J When we consider that it must have been produced by the pro- * Prout. t Ann. Philos. iii. and iv. % Ann. Philos. U. 12 m cess of digestion, we will form a better opinion of its na- ture by suspecting the correctness of our knowledge, or at least the deficiency of the means which are possessed to detect its composition. During the respiration of nearly pure oxygen gas, a portion of it disappears, and an equal bulk of nitrogen appears in its place. The substitution is greatest at the commencement, and amounts at an average to near 80 cubic inches. This curious fact was established by Messrs. Allen and Pepys, whose experiments on respi- ration were conducted on a very large scale. Yet, in the ordinary process, no nitrogen seems to be formed. So, also, when a mixture of 79 hydrogen, and 21 oxygen gas, is breathed, nitrogen appears among the products. The experiment seems to confirm Mr. Miers's idea not only of the compound nature of nitrogen, but of its constituents. Indeed, when we consider how instantaneously carbon unites to oxygen during respiration, we will be less sur- prised that hydrogen should also combine with oxygen, and form a compound not to be imitated easily in the la- boratory. RESPIRATION. I shall finish this view of the sanguiferous process by continuing the remarks on respiration. It is re- markable that this process so universally imperious upon all kinds of animals, never has manifested more than two offices ; that of giving colour and fibrine to the chyle, and that of subtracting carbon from the system. I cannot but think, that the extent of its importance is highly undervalued. All the labours of philosophers, for years past, have been concentrated in the few gases effected by respiration ; and all the changes produced both on the 91 chyle and blood, have been limited to the subtraction of carbon. It appears to me, that more important and definite knowledge would arise were the investigation confined to the blood itself, than to the external characters of respira- tion; the true changes must exist in the blood of the pul- monary veins, and more solid information might accrue, by comparing this with the blood of the pulmonary arte- riesj which is replete with the matter about to be changed. It is not so important to know, that carbon is given off as to know in what state such a change has left the circula- ting materials. We have yet to learn why it is, that car- bon seems in such profusion and waste, whereas the oxy- gen, hydrogen, and nitrogen, never make their appear- ance as separate secretions. The supply of all is daily continued from the nutriment ; and carbon is generally found in the compound secretions, as well as the others. This substance must result chiefly from the waste of all the organic texture, (since the chyle is but a trifling in- terference both from quantity and quality ;) what then be- comes of the other constituents ? the absorbents which take up one must take up all, if the decomposition be effectual, and convey them into the circulation ; yet here they have not been found in a separate state ; but if they form soluble combinations, the blood seems best adapted to display them. As it is, respiration consists in the evolu- tion of carbon, and in the negative effect of giving the ve- nous blood a florid colour, (since it is the absence of car- bon which seems to cause this phenomenon.) During this process there is a separation of moisture, which arises principally from the substance of the lungs ; experiments show that little or none of the atmospheric oxygen goes for its formation. Crawford has also determined that venous blood has less specific caloric than arterial blood, in the proportion of 8.9,. to 10.3. and therefore, the la- 92 tent caloric of the former, as it becomes liberated during respiration, enters into union with the arterial blood, as fast as it is formed, and thus leaves the lungs at their original temperature. During circulation, the arterial blood is gradually converted into venous ; consequently, its specific caloric diminishes, and it must give out heat. This is the reason that the temperature of the extremities does not diminish, or that of the lungs increase. Dr. Davy has since proved, that Crawford's estimate is by far too high ; since he found that the specific caloric of arterial blood is but 0.913, when that of other is 0.903. Dr. Crawford also adopted the theory of Dr. Black ; by supposing that a great quantity of caloric is given out by the union of oxy- gen and carbon, which he considered sufficient, not only to carry off the newly formed water in the state of vapour, and to raise considerably the temperature of the air re- spired, but to support the temperature of the body. This has also met with a contradiction from the examination of Delaroche and Berard, who have shown that the specific caloric of oxygen and carbonic acid differ much less than Crawford supposed ; that of the first being but 0.8848, when the last is 0.828. The theory of Dr. Crawford displays unusual elegance, but we must look elesewhere than on respiration to discover the true sources of animal heat. Chemical changes no doubt contribute largely, but they are not those in the lungs. Thus then, though un- willingly, we are obliged to curtail the function of respi- ration to its power of subtracting carbon. Its operation on the chyle is thus described by Dr. Thompson ;* " It appears from the most accurate observations hitherto made, that neither chyle nor lymph contain fibrine, which forms a conspicuous part of the blood. This fibrine is employ- ed to supply the waste of the muscles, the most active * Chem. books. 93 parts of the body, and therefore in all probability requir- ing the most frequent supply. Nor can it be doubted that it is employed for other useful purposes. The quantity of fibrine in the blood, then, must be constantly diminishing, and therefore, new fibrine must be constantly formed. But the only substances out of which it can be formed are. the chyle and lymph, neither of which contain it. There must, therefore, be a continual decomposition of the chyle and lymph going on in the blood vessels, and a continual new formation of fibrine. Other substances also, may be formed; but we are certain this must be formed there, be- cause it does not exist previously. Now, one great end of respiration must undoubtedly be to assist this decomposi- tion of chyle, and complete formation of blood. In what manner the chyle, or a part of it, is converted into fibrine, it is impossible to say ; we are not sufficiently acquainted with the subject to be able to explain the process. But we can see, at least, that carbon must be abstracted from that part of the chyle which is to be converted into fibrine. Hence, as the process of blood making advances, there must be a greater and greater redundance of carbon in the liquid. Unless this redundance were removed, the process could not go on, and probably the whole would run into putrefaction. We may conclude, then, that one great use of respiration is to abstract this carbon, by form- ing with it carbonic acid. How this is performed, indeed, it is impossible at present to explain; but the fact is un- doubted." Messrs. Allen and Pepys have shown, by their experiments, that the body of a healthy full-sized man, gives off daily, by respiration, an average of eleven troy ounces of solid carbon. This must evidently be infinitely more than what proceeds from chyle, since chyle is but an exceedingly small proportion of the food eaten. One 94 year of such respiration would make a man give off from his lungs near 335 pounds troy of solid carbon, a weight which almost equals twice the body itself. Dr. Prout* has shown that the carbon they evolved is different in different periods of the day. At noon it is near its maximum, and at its minimum about midnight ; and at morning twilight it begins to increase. This gentle- man also found, that alcohol and all fermented liquors di- minished the proportion, and likewise that when the con- stitution is affected by mercury the same takes place. Dr. Fyfe remarked the same phenomena, and observed further, that a course of nitric acid and vegetable diet produced the same effect.! Fishes require but little at- mospheric air : it appears that a man consumes fifty thou- sand times as much oxygen gas as a trench. J Yet the presence of this principle is equally necessary for the ex- istence of both and for all other animals. These are the principle facts of respiration ; with which I shall close this subject. There is no function more purely chemical as far as it is at present understood; for a full and impartial detail I cannot refer to a better work than that of Dr. Bos- tock. FOURTH DIVISION. ASSIMILATION. Before entering on this intricate consideration, it will be but justice to remark, that speculation constitutes its great features. We know the materials and the product, but know little positively of the agents proximately con- cerned, or of their connexion during the progress of as- similation. Wherever, however, experiments appear, I * Ann. Philos. 2. and 4. t Ibid 4. i Thompson's Chem. book §. 95 shall give them place, if sufficiently authentic, no matter what opinion they may contradict, or what unpleasant conclusion they may lead to. This is absolutely neces- sary if truth is at all to be regarded upon the subject of our existence; and when they are as fairly impeached as they have been established, and by the same experimental method, it will be the only time to overlook them or throw them aside. COMPOSITION AND FIGURE. I have before remarked, that the blood of animals and the sap of vegetables furnish the materials for assimila- tion. The formation of these fluids should also be in- cluded within this process ; but I have already noticed that operation, and there seems naturally to be a distinc- tion. My first examination will be of the blood itself. When the blood has been drawn from an animal, and al- lowed to stand, it coagulates, and by this process be- comes divided into two parts. The coagulum itself (which has also been called cruor, because it alone retains the red colour peculiar to blood) constitutes one part, and the other consists of a limpid straw-coloured fluid, which is called serum. Diseases, and a variety of different other circumstances have the power of altering the proportion of these constituents ; but that most usual is about one part of cruor to three of serum.* Blood by the same pro- cess gives out vapour with a peculiar smell as well as some carbonic acid gas which was formed and dissolved previous to coagulation. This spontaneous decomposition of the blood is not retarded or promoted by external agents, such * Thomson's Chera. book v. 96 as air or its absence, temperature or dilution with water ; electricity when given in large shocks through the body has been said to prevent the coagulation ; such is also the effect of violent and fatal passions.* The cause seems confined to the blood itself; and the peculiarities of its operation led Mr. Hunter to suppose that the blood has vital properties: Dr. Gordon has rendered it probable that heat is thus evolved. t The serum is found to contain either a free or car- bonated alkali, since it turns the syrup of violets to a green colour. Rouelle and Dr. Marcet determined that the al- kali is soda, whereas Dr, Pearson very plausibly considers the alkali in the animal fluids to be potassa. It is proba- bly of little consequence either way, as both have the power of dissolving albumen, which seems their most ex- tensive use in the animal economy. Serum also contains albumen in a considerable quantity, also a very large pro- portion of water. Lactate of soda, and the muriates of soda and potassa to a very trifling amount, as well as diffe- rent phospates. Berzelius is of opinion that phosphorus sulphur, and the bases of lime and magnesia, exist as con- stituents of albumen, and are only produced as salts, he. by incineration. The cruor, when carefully washed by a gentle stream of cold water, is separated into a white, solid, and elastic sub- stance, having all the properties of Jibrine, and into the colouring matter which the water dissolves. Berzelius and Brande have shown that the cruor also contains albumen ; but, as Dr. Thomson remarks, it is impossible to separate the serum completely from the cruor, and, therefore, the albumen they noticed may belong to the serum. When * Ann. Philos. iv. 139. f Hunter on Blood. 97 the colouring matter of the blood is incinerated, about One third per cent., oxyde of iron may be extracted from its ashes ; and to this oxyde has been attributed 'he colour of the blood. When, however, we consider its very small proportion, and the fact of its being denied to exist in blood by different chemists, there will appear but little reason to suppose we know the true cause. Berzelius found the ashes to amount to only one eightieth of the co- louring matter, and of this there is not more than one half oxyde of iron ; he is also of opinion, that it is the iron itself, and not its oxyde which exists in the blood.* Fourcroy analyzed the blood of a human fcetus, and found mat it differed from the blood of the adult in three things : 1. Its colouring matter is darker, and apparently more abundant; 2. It contains nofibrine, but probably a greater proportion of gelatine than the blood of adults ; 3. It contains no phosphoric acid.t The absence of fibrine may be owing to the rapid formation of muscular matter at this time of life ; the other differences must also depend upon fcetal peculiarities. Thus we have a view of the materials in blood. Like all animal substances, albumen is capable of ex- isting in various states, both when coagulated and ur.coag- ulated, and of forming a number of distinct species ; such as the curds of milk, white of eggs, and that in the blood. Coagulated albumen forms an essential part of bone and muscle ; brain may be considered as a species of it, and so may the lens of the eye. Cartilage, nails, horns, and hair, are almost entirely composed of it. It forms the membra- nous parts of many shells, sponges, &c. and is, in short, * Ann. Philos. ii. 202. t Ann. de Chim. vii. 162. 13 93 one of the most general and important of the animal sub- stances.* Mr. Hachett has shown that albumen may be converted into gelatine, another important animal produc- tion. Nitric acid has this power, and although we are not to suppose that the same operation takes place in the body, we learn that if it can result from chemical affinity, there is nothing to prevent production on similar princi- ples in the body. Their resemblance is more strongly pointed out by analysis. Carbon. Oxygen. Hydrog. Nitrog. Gelatin, Albumen. 47 8 52 8 27 2 7 9 23 87 7 5 16 9 15 7 X = 100 parts- By applying the atomic theory to these results, it ap- pears that albumen differs from gelatine, by having two ad- ditional atoms of carbon, and one atom less of hydrogen. Now, we know that respiration has the power of subtract- ing carbon, and the hydrogen exists in every animal com- pound. The fibrine has also its varieties, and constitutes the basis of all muscles. For this purpose it seems to require no further change from the state in which it exists as a con- stituent of blood, than to become more firm by deposition. We cannot undertake to show how a muscle gets its shape, but the texture of fibrine is not unlike that of the muscle when well washed in water. We may even conceive in a general manner how its structure arises; for, in every in- stance, the smallest faciculus of fibrine is enclosed in a co- vering of cellular matter, which is principally composed of the other constituent of blood ; namely, albumen. When * Thomson's Chem. 99 they are both thrown out by the arteries, the influence of some of the agents (as galvanismj might coagulate the lat- ter around the fibrine, and they multiply the facicule.* In short, when we examine the muscular structure, these two constituents of blood will be found to occupy almost the entire substance including blood vessels and nerves. The last seems to be nearly constituted by albumen, and I shall, subsequently, show, that the blood vessels have their ori- gin from the foregoing ingredients. It would occupy too much time to notice all the animal productions, or their shades of difference ; I shall, therefore, designedly omit doing so, and refer to Dr. Thomson's system of chemistry for a collected account. As to the principle by which such productions are ef- fected, although it is not in our power to offer experimen- tal proof, we know that it must be of a chemical nature. No other agent has the property of altering chemical com- position ; and some of these very animal productions have been imitated by operating chemically on others. But the vegetable kingdom offers the greatest variety of examples ; several of which I shall now mention. 1. Oxalic acid may be found by treating sugar with nitric acid. 2. Camphor ; by treating oil of turpentine with muriatic acid. 3. Tan- nin; imitated by digesting charcoal in nitric acid. 4. Su- gar; by boiling almost any animal or vegetable substance for several hours in a weak solution of sulphuric acid. 5. Gum; may be formed from starch. 6. Citric acid; from the same substance by chlorine. 7. Saclactic acid; and 8. Malic acid; from gum by nitric, i). Bitter principle of quassia may be imitated by digesting alcohol some * Sir E. Home is of opinion that muscular fibre is formed by the serous globules. (See page 107.) 100 months on wheat flour. 10. Bird lime, by fermenting the middle bark of holly, and then boiling the residue to dryness. 11- Resin, by treating bitumen with nitric acid. 12. Extractive, by treating guaiacum with the same acid,* &c. &c. These are considered as vital productions, and their imitations are either identical in external and chemi- cal characters, or so nearly so, that very little doubt can be left of their chemical formation by secretion. It may, however, be said, that this conclusion is not correct, be- cause chemistry has not produced each of these imita- tions from the flood of plants, which seems to be done when they result from secretion, and it may be de- nied that one secretion is at any time formed from another. To that objection it may be answered, that in all human probability it will never be in the power of the objector to prove, that nature is not thus imitated ; and therefore, why should mere doubt on that subject pre- vent our adopting a position which is strengthed by colla- teral proof? My object in this essay is to prove by phe- nomena, facts and analogy, that the same power which is so astonishingly active in searching, as it were, through matter infinitely more compact and penetrable than orga- nised substances, can and does operate in the different changes of life. If life were sufficient to perfect our struc- ture, why should so much of it be hourly cast off? What renders such rejected parts unfit ? No agency of life, most surely ; it is the action of substance on substance, even in the midst of life. It is true, that the vital phenomena do not depend upon the mechanical action of organs alone, but it is equally true, that they are not confined, indepen- dent of all other natural agency, to a vital principle, * Thomson's Chem. vol. iv. passim. 101 There are true chemical phenomena, as Fourcroy re- marks, in the bodies of all animals. Products and changes result from the intimate attraction which governs the dif- ferent particles composing the organic tissue. " Liquids solidify and concrete, while solids become dissolved by the invariable laws of solution ; salts chrystalize and are uni- ted one to the other ; elastic bodies form and expand in the midst of cavities and dilatable reservoirs. In the most tortuous ducts, or tubes mucous fluids thicken or become more fluid ; insipid and colourless bodies acquire both the opposite qualities : oily matter is produced or saponified ; precipitations are formed and prevented ; salts change their bases and become mutually decomposed; others are constituted, while acids are formed and alkaline or metal- lic oxides liberated."* These are facts which no one of the least observation can doubt, and are absolutely demon- strative of chemical changes. But further, we find com- pounds formed in the living body precisely of the same nature as invariably results from chemical union. A fair deduction therefore it would seem must be, that this prin- ciple of composition guided them in the living body ; thus we find iron, mercury and other metallic substances con- verted into the same oxydes, within the sphere of vitality as they are when exposed to chemical action without it ; they will unite to ac'ds just as well in either situation. So also as to gases >alts and acids. The ammonia of the body is the same as that of the laboratory ; and if we analyze the carbonic acid, carburetted and sulphuretted hydrogen, nitrogen, and its compounds, the phosphates, muriates, car- bonates, &c, the uncombined acids so manifestly and fre- quently resulting from the principles of life, we must be * Connaiss. Chim. 102 convinced that they were formed under the operation of the most perfect as well as active chemical laws. There are other substances as madder, indigo, garlic, &tc, which pass into the circulation, and may be found unaltered in the different secretions. A theory has been broached to account for these facts, by one whose ardour in favour of sympathy seems to have carried him beyond fair reasoning or probability in support of his speculations. Dr. Chap- man, in his notes to Richerand's physiology, styles the humoral pathology " an absurd system ;" and in his zeal for alteration hazards the idea " that the process of assimila- tion, whether performed by the chylopoietic viscera or by the absorbent apparatus, completely decomposes all sub- stances subjected to its influence ; and however various in their principles, reduces them to one homogeneous fluid, bland and inoperative in its nature, or in other words, renders them fit for the purposes of nutrition. But in the excretions and secretions, beyond the sphere of vital powers, chemical action takes place ; by which those substances are in part, or entirely regenerated" A few remarks will show how very little is gained by this substitute. In the first place, chemistry is allowed to ex- ercise its power in the secretions, which is really more than could have been expected. In the next place, we are told that these secretions are " removed beyond the sphere of vital functions;" and this situation may, of course, be in the very substance of a gland. It is in these shrines of life, then, that Dr. Chapman supposes chemi- cal action can best succeed. Would it not be fair (though the contrary was meant to be implied) to conclude, there- fore, that chemical union must take place in every other part of the living body? But we are further informed that a regeneration of the same substances, as were re- 103 ceived into the stomach, takes place in the secretions^ which we are in the habit of considering as onl\ parts of the assimilated food. And yet, though at first thoroughly decomposed, the original substances can be regenerated after their constituents have circulated through the body, and, in all human probability, become incorporated in the most remote extremities. This does not seem much short of a miracle. If I did not fear being thought disrespect- ful, I should say it could only be accomplished by a con- vention of all the secreting organs, in which it was agreed that common stock should again be made. But even then a few delinquent organs might be found to spoil the har- mony intended, by permitting the whole of their share of matter or workmanship to slip out of the body. Any one who is devested of prejudice can hardly deny that the humoral pathology has some claims to attention ; and to abuse the whole as an absurdity because somewhat of this may be traced in particular expressions, is doing the greatest injustice to the principle. It is a fact, that where any change of composition takes place it must be proximately effected by the inanimate quali- ties of matter. I do not deny that the vital structure renders it more definite of a final end ; but it is by the difference of its chemical agents that it does so. How much less, then, have we reson to detract from the char- acter of chemical action in tubes and cavities ? All glands are composed of tortuous tubes, and within those the changes take place ; the length and conformation of such vessels show the intention to be, that the substances shall act by their chemical power, aided by those which they meet on their way. The muscular structure, on the other hand, seems thrown out directly from the delicate extremities of arteries, because as the fibrine, albumen, &c, 104 exist already formed in the blood they require little else than a deposition and coagulation ; and certainly are not in need of further changes of composition by being com- pelled to react in tortuous tubes and under a most retarded circulation. Another circumstance we should keep in mind, since it shows the existence of chemical affinities in these situations. Disease, which always implies debility in the vital functions, leads to the greatest variety in the se- cretions, and often changes the character of any one so as not to leave a doubt. Now if such secretions depended upon a vital power alone, its deficiency would be more likely to lessen their amount than change their ordinary qualities ; but chemical compounds always occur in the greatest variety when the substances are more numerous. In disease, not only the composition of the blood becomes altered, but during its disordered circulation materials are crowded together which otherwise would have been lo- cated in various parts of the system. Under such circum- stances the chemical character of the secretions becomes more remote from those which depend upon the regula- lated function. During that disease, known by the name of diabetes, in which the urine is excessive in quantity, the serum of blood often assumes the appearance of whey; and Dr. Wollaston has shown that it contains no percep- tible quantity of sugar, even when the urine is loaded with it.* These remarks must suffice, since little definite in- formation can be offered ; but I apprehend that whatever may be the peculiarity of the vital arrangement, its mate- rial productions must invariably result from true chemical affinity, promoted by some or all of the agents mentioned in the former part of this essay. * Thomson's Chera, book 5. 105 FIGURE. Upon this subject the late experiments of Sir Everard Home will be found more curious and important than any of which I am at present aware ; they must also constitute the entire subject, since I am desirous of confining this essay to as limited a form as possible. It is well known among the numerous original ideas of Mr. Hunter, that he maintains that the blood formed its own vessels independ- ent of any communication with those already existing ; or, in his own words, that " the blood moves in the living solids which it both forms and supports," and that " when new vessels are formed, they are not always elongations from the original ones, but vessels newly formed, which afterwards open a communication with the original." Now, although we may suppose the blood to have irritability, (which is what the author implies, and which in my opi- nion is perfectly reasonable,) without conceding to the ironical language of Mr. John Bell, that, therefore, " it should have the privilege of knowing when to exert itself,'* or " that it should have some kind of intelligence or con- sciousness, by means of which it could understand when it were within and when without the body ; and whether in certain circumstances, it were fit that such vessels should be formed." Intelligence can only exist in complete living systems ; and there are thousands apparently without it which have both irritability and definite functions. This quality is never a character of detached parts, even of the brain, which is its seat. The irritability of a finger just cut off is as great as before the operation, and its organization is infinitely better adapted for the exercise of sensibility, (since it possesses nerves) than the blood ; yet we cannot 14 106 be so forgetful of this property as to suppose that the dis- jointed finger possesses the least extent of it. The fol- lowing experiments will show that the blood does produce its own vessels, and that too by the agency of its chemical and physical properties. In Sir Everard Home's paper upon coagulation (croonian lecture*) we find the following account of blood taken from his own arm. " In about five minutes something was seen to be disengaged in different parts of the coagu- lum, (beginning to show itself where the greatest number of globules were collected ;) and from thence passing in every direction with considerable rapidity through the se- rum, but not at all interfering with the globules themselves, which had all discharged their colouring matter. Where- ever this extricated matter was carried, a net-work imme- diately formed, anastimosing with itself on every side, and through every part of the coagulum. When the parts be- came dry, the appearance of a net work remained unal- tered. In some instances, bubbles were seen to burst through the upper surface of the coagulum ; this, how- ever, did not prevent the ramifications that have been described, from taking place. These changes were observed with strict attention through a microscope. Sir Everard Home has presented engravings of their appear- ance, and it is absolutely impossible to overlook the strong resemblance which they bear to designs of organized sub- stances. This gentleman further remarks, that " if the blood is cold when it is exposed in the microscope, and there is a large quantity of serum on the glass, the net work is only formed in those parts where clusters of glo- bules are collected," and further, that " when clear serum, * Phil. Trans, for 1818. 107 without any globules is put upon the glass, nothing is ex- tricated. In this paper it is also shown that after blood had remained extravasated, and become vascular, a short time was sufficient to make them become regular tubes, having distinct and I separable coats. From these facts :e learn that a gas forms the blood vessels with their ramifica- tions, and that it originates from the serous globules. This shows that these globules undergo chemical changes; not ac- cidentally or in a limited number, since the passage form- ed by some of the gas through the upper surface of the coaguluni, did not put a stop to the tubular formation. This gas was determined to be carbonic acid; which whether it was derived from the serous globules or from different parts of the body during circulation, is always, in organic matter, a proof of chemical changes. Their utility in the production of blood is made manifest by an experiment of Sir E. Home, instituted for the purpose ; he " placed a vessel nearly filled with blood drawn from the arm, under the receiver of an air pump, and by ex- haustion, extracted the gas contained in the blood. This blood deprived of its gas, when coagulated, exhibiting no appearance of net work. In that part which had co- agulated before the exhaustion was completed, the net work was beautifully distinct." This gentleman injected these vessels, and concludes, that " as the injection could only fill the spaces from which the carbonic acid gas was extracted, it cannot be doubted that the channels were formed by the gas." Sir Everard Home also mentions the previous experiments of Mr. Bauer, which confirm the foregoing rationale by showing a similar process for vege- table formation. " In his close attention to the changes that took place, he was very much struck with the rapid increase of the tubular hair of the root of a young plant 108 of wheat, in its earliest stage of vegetation ; and fixing his whole attention upon that part of the plant, he observed small pustules of a slimy substance arising under the epi- dermis, on the surface of the young root. In a few seconds, a small bubble of gas burst from the root into the slimy matter, which it extended, in a moment, to the length the hair was to acquire ; and the slimy matter, sur- rounding the gas, immediately coagulated, and formed a canal. He repeated his observations on another plant, whose pubescence consisted of a jointed hair, and obser- ved the same effect to take place ; a bubble issued from the young stalk, and extended the slimy mucus to a short distance, forming the first joint, which immediately coagu- lated and became transparent : at its extremity, a new pustule, of the slimy mucus, accumulated, into which, in a short time, the gas/rom the first joint rushed, and then in a moment a second joint was formed. In the same manner he observed the formation of ten or twelve joints to take place." It now only remains to show that the ana- logy is as manifest in pus which is known to be secreted for the object of granulation. For which purpose I ^hall continue Sir Everard Home's experiments as he describes them.* '• As the globules of pus are similar to those of the blood, I made experiments upon the fluid in which they are suspended, and found inspissation to produce the same effect on if as coagulation does on the other ; that a similar net-work is formed, and apparently by the same means (since, if pus is deprived of its carbonic acid gas, of which it contains a large quantity, by exhaustion in the air pump, no such net-work takes place.) This is a fact of considerable importance in practical surgery ; for as * Phil. Trans, for 1819. 109 we know that inspissated pus can become vascular, simi- lar to coagulated blood, we have arrived at the principle on which granulations depend, and from whence they de- rive the power of contraction which is found to be inhe- rent in them. We also can account for the great advan- tage of compression on the surface of soies; since, by that means, all the superfluous pus is removed, leaving only enough for inspissation, in which state the carbonic acid gas is extricated, forming channels so as to admit of its becoming afterwards vascular, and then taking on the form of healthy granulations. Sir Everard Home con- cludes that the pus is turned into new flesh, and offers the following facts. A healthy sore, when examined with a microscope, had the eminences on its surface (these were apparently composed of small clusters of tortuous blood- vessels ;) the hoilows were rilled with pus. After five or ten minutes' exposure, a very thin transparent pellicle co- vered the whole surface, while bubbles of gas were seen to make their appearance in different places. In a few mi- nutes, more blood entered and diffused itself through the net-work of vessels, (formed by the gas,) which at this time were so weak, that putting the foot with the sore, to the ground, ruptured them. These canals, however, though so weak on the first day, were found on the second to have become permanent tubes, covered over by cuticle. The degree of coagulation determines the extent of vascularity ; this fact was proved by the addition of muriate of ammo- nia as well as cold water, which have the property of pro- ducing coagulation much more speedily than atmospheric air. Sir Everard Hom^ supposes that the blood (having a strong affinity) absorbs the carbonic acid gas as it enters these newly tormed vessels. This gentleman shows the 110 following reasons for supposing that the muscular fibre is made from the globules of the blood.* 1. The fibre can be separated until it appears, by mi- croscopic measurement, not larger in diameter than those globules of blood. 2. Muscular fibre, when thus dissect- ed, appears, through the microscope, as compocud of globules so as to form a line. 3. The globules of bl> od, when deprived of their colouring matter, (which envelops them, and is three times as great,) while floating in the se- rum, are seen to have an attraction toward ope another, and to unite; but " that while the globules are enveloped in their colouring matter, they are not seen to run together and coalesce with one another in the field of the micro- scope. It is, therefore, probable, that the attraction by which this effect is produced only takes place between globules deprived of their colour." Thus have we seen that the agents, the matter, and the productions of life, are chiefly referible to the phenomena of chemistry. This ascendancy is not confined to the be- ginning or end ; we must notice its progress through every stage, even from the first dawn of animated existence. Regulated by the most inconceivable wisdom, life is sus- tained by the universal laws of nature; and if our pride fondly gazes at the mystery of generation let us also learn to be instructed by the extinction of life; and instead of overrating our own conformation, let us reverence the w r isdom which can cause life to arise, and be guided by the universal laws of matter ! I shall now enter upon an inquiry into life itself; and in doing so the truth shall alone be sought after, without reference to opinion or prejudice. * Phil. Trans, for 1818. Ill ANIMATION. In collecting together the phenomena of assimilation^ numerous obstacles must ever oppose themselves. The firs', combinations of matter are so extremely minute that, in all human probability, the commencement of organiza- tion wiil never be perceptible. All that the eye can do is to observe its growth ; and, at the earliest period of this advantage, life is found already to exist. It is for this rea- son chiefly, that the origin of vitality lies so deeply ob- scured. Our conclusions, at present, must be governed by analogy and general views ; and although the evidence which thus results is not of the highest degree, it is cer- tainly entitled to be next, By such means, though with more certainty, the existence of a Supreme Director is demonstrated when the works of nature are surveyed. The inquiry whether animation can result from any possible modification in the composition of inanimate mat- ter, has frequently entered into metaphysical discussions. I must confess it has often astonished me how very easily satisfied some inquirers have been. A view limited to three or four properties of matter, such as dimension, figure, or weight, have been twisted into every form, and when these failed to give life, the subject has been con- sidered as examined But who has ever investigated the chemical laws to their full extent, or brought to view the incalculable variety of its products ? These surely can never be overlooked when we are surveying the property of matter ; and ages will roll by before any mortal can experimentally deny their power. But it appears to me that the solution can never result from a consideration of the properties of matter alone ; other circumstances full 112 as imperious must be thoroughly understood, and these are so numerous as to render general reasoning unfounded. We are in the habit of saying one body has the power of uniting to another, but we speak incorrectly, or rather pre- suppose other agents. A familiar example will illustrate my meaning* Sulphuret of iron is weli known to be a material product, or, in other words, proximately formed by the laws of matter ; yet with all this certainty we can- not suppose that it invariably results from these laws alone. Although the constituents possess a perfect affini- ty for each other, they have no inherent power sufficiently strong to bring them together when outside of the least perceptible distance. The same circumstance takes place in all chemical compounds. Let the power for union be ever so strong, their presence is also requisite, and this never proceeds from their material properties ; they also depend on agents, such as temperature, solution, tritura- tion, and a thousand others emanating from the laws of the universe. Hence then though animation should proceed from the proximate influence of material properties, we cannot limit it to these alone. If conclusions are to be drawn, they should be founded upon the phenomena of vitality, which are daily passing before our eyes, and speak true knowledge to the understanding. We ought ever to be guided by what we know, and that range is too limited to attempt to draw general conclusions from the properties of matter. It is impossible, at present, to demonstrate unde- niably the correctness of either opinion; the object of this essay is to bring forward facts which have a tendency to show the connexion of chemistry with animated matter. The remarks of Buffon " that the reproduction of an animal or vegetable cannot be explained in a satisfactory manner, if a clear idea of the operation of nutrition is not 113 obtained,'* seem to me, to be forcibly true. Nothing can be more analogous to the production of life than its subse- quent support; I shall accordingly commence with this view. BufFon,* founded his theory of nutrition upon the idea, " that there exists an infinity of living organic par- ticles in nature ; that their production is of little expense to nature, since their existence is constant and invariable ; and that the causes of death on'y separate without de- stroying them. Therefore the matter which an animal or vegetable assimilates, is an organic matter of the same nature as the animal or vegetable itself," This observa- tion is undoubtedly true with one exception. It is impos- sible to admit the " constant and invariable" existence of any living particle; the supposition is directly contradict- ed by the most superficial view of matter. But on the other hand we must admit that the particles of assimilated nutriment are endowed with as much vitality as any which constitute the body itself. Hence this naturalist drew a correct conclusion when he remarked that " the matter which an animal or vegetable assimilates, is an organic matter of the same nature, as the animal or vegetable it- self." This however is very far from the view which he wished to inculcate. But what can be more inconsistent with observation than to suppose that the generation of an animal or vegetable depends upon the union of living par- ticles, which existed with this characteristic since creation began, and that death only separates (hem without destroy- ing their vitality ? Such a theory, though endowing matter so profusely, c uld not reserve for itself one living parti- cle to sustain its own existence, and has not been able to survive the author whose brain was the most congenial *?afarai History. 1.5 114 hot bed that it ever had. We may presume therefore that an absolute extincton of life does take place; let us now apply this fact. The nutriment which supports the body by adding living matter, was previous to its changes during assimilation perfectly inanimate. How can we consistently account for the acquisition of this vital property, without attribut- ing it to the changes of composition occurring during that process ? These we have already shown to be of a chemical nature ; and we are not justified in doubting, until at least as strong evidence of contrary nature shall point an ex- planation of the phenomena. But let us examine the sub- ject closer. There is not the slightest proof that nutri- ment can be thus endowed by mere contact with living matter, independent of such changes of composition ; and, if we rely upon general reasoning, we must be convinced that it does not. In the first place, the existence of the phenomena decidedly points out the necessity of such changes; and in the next, it is perfectly in contradic- tion to our knowledge, to maintain that life can be trans- ferred from substance to substance, by simple juxtapo- sition. Irritability, which is all the life we can suppose, when characterising a substance, may impart motion to a fo- reign body in conjunction, while that situation remains ; but to endow this last with its own properties is far different. It is absurd to suppose that this property which depends upon, and is limited to, the matter possessing it, can act beyond that matter, But let us entertain a proper idea of irritability, or even its more complicated forms constitu- ting the living system. Has it any existence without the application of a stimulus ? Not the slightest. When we take a muscle and excite its contractions, we are correctly satisfied that it is then alive. Without an exciter we never 115 could suppose it, and when that exciter is removed we have no right to do so, for it is unequivocally dead. Hence, then, we learn, that life is an effect depending upon at least two inanimate substances having a peculiar chemical and physical composition. Hence, also, we learn, that irrita- bility has no influence beyond these limits, and that when it can be manifested in adjoining matter, it must originate upon the same principles, independent of any connexion. We are, therefore, I think, entitled to consider that irrita- bility does arise in the assimilated nutriment, by mere contact with the living solids. But there is a degree of evidence that this property is acquired before any such union takes place. The substance of the blood is un- doubtedly derived from the nutriment ; therefore, all Mr. Hunter-s arguments for its vitality, (and which an eminent writer considers as " the best established doctrine of mo- dern physiology," must confirm the origin of this property. The iibrine has also been found irritable by the experiments of Circaud and Delametherie j* which seems to prove that this property is acquired during circulation. After this shall it be denied that assimilation is of a chemical nature ? This would indeed be contending for argument sake. There is not only direct evidence that the blood undergoes true chemical changes ; (see respiration ;) but the total difference in composition, between chyle and the food, leaves scarcely a doubt. (See digestion.) If the property of irritability does not proceed from chemical changes in our food, why should the rejection of any be necessary ? Why should this excess of matter so mani- festly useless, be at any time the result of a vital process ? The most rational answer seems to be, that vitality is de- * See page 13. ante. 116 pendent upon a peculiarity of chemical composition, and that such substances as are formed by too powerful an affi- nity to admit of decomposition in the body, can never, by any vital process, residing in that body, be rendered sus- ceptible of animation. The foetal blood is allowed not to be coeval with the first organization which is the rudiment of the original vital foundation ; hence this blood, as well as its irritability, must be generated. by chemical changes effected in the matter constituting nourishment at this early period of imperfect existence. Lastly ; Sir Eve- rard Home's paper shows, that granulation and the forma- tion of blood vessels, which cannot be excluded from vitality, depend upon a combination of the physical and chemical properties of the blood, or pus in animals, and the sap in plants.* Irritability, like a chemical property, depends upon composition more than dimension or figure ; if the substance capable of exhibiting it be divided into pieces, the property is not extinguished ; but when treated with a chemical agent it is destroyed in proportion to the extent and perfection of its power. Thus we have exhi- bited an instance where vital matter originates independ- ent of the generative process ; and have shown reason for supposing that it depends upon chemical composition. Let us point out a few more important considerations. John Hunter supposes that the blood forms its own ves- sels ;f all practical observation must lead us to the same conclusion. When a piece is cut out from a nerve, we know that it becomes filled up so as to render that nerve complete or nearly so, "by means of the blood forming a union of coagulum :; and that the coagulum becomes more and more of the texture 5" but what assimilating or se- creting vessels are [here in this coagulum to effect such a * See nase 103. ante, t On the Blood, 117 change, unless those formed of itself ? Those that belong to the sound portions may even send proper matter; but if these are supposed to have no power of extension, as Mr. Hunter remarks, we must suppose that all vascular apparatus which afterwards gives this coagulum the pro- perty of a nerve, is formed by the coagulum. But this I shall not consider important to establish, since the polypus and other animals, the umbilical chord as well as all the vegetable kingdom show that animation may exist without nerves* Sir Everard Home's experiments on blood and pus prove that blood vessels are formed by the blood, inde- pendent of nerves or any necessary connexion with the body His experiments also led him to suppose that flesh is formed by pus. If these facts be extended what do they lead to ? Why, that all the other parts contained therein have a similar origin, and that granulation is in the end but a process of union by the first intention, since new vessels are united to the old ones by contact. We have seen that pus forms the blood vessels and flesh for such a breach ; what more vital or important parts can any structure have than these ? Surely we can have but little doubt concern- ing the origin of the minor apparatus such as absorbents. One other consideration strongly confirms the foregoing. If any system of vessels is always necessary to form another, how is the first set supported ? if by another, how is this last supported ? we must introduce another and another set, until they are brought to atomic magnitude, and even then nothing will be gained since the very last must have its system of supporting vessels. We shall inevitably come to the conclusion that one whole set origi- ninates from the blood without any vascular apparatus. This may seem too extensive for admission ; but the reason is that we confine our view to the most complex stage. 118 All that we now gaze at with wonder, was once simple and limited ; where mutual assistance was either feeble or extinct. Can we then hesitate in believing that when such a limited vascular system originates independently of any other, it can become complex and extensive by a continuation of arrangement ? Hence then we learn that the blood or something similar is qualified to form all the parts of a complex system ; how much more qualified, then, must it be to form the simplest circulating apparatus, without nerves, and conducing to the support of the most limited animation ? Let us now examine of what nature blood must be for this purpose. We have seen that changes of composition in inanimate matter (during digestion, respiration, he.) give rise to the formation of blood ; therefore wherever these exist, under such circumstances (which are undoubtedly dependent up- on chemical affinity) life may result. We are too much in the habit of confining our attention to the origin of blood in adults ; let us, therefore, turn to the human embryo or the chick in ovo. The embryo has been supposed to have an in- dependent circulation;* and this opinion is supported by di- rect analogy from the egg or seed. How then does it even accumulate its blood, since it performs neither digestion nor respiration ? Certainly not by the process of an adult. But if the human embryo be supposed to receive its nourishment, assimilated, from the mother, we will abandon the instance and bring forward the chick in ovo, where no connexion whatever exists. In this no material assimilation, no di- gestion or respiration seem to take place when the blood appears at the punctum saliens ; its origin, or at least ac- cumulation, must be from beginning to end, from the egg Dr. Chapman on foetal nourishment, 119 substance, and that too without any vital apparatus, (in appearance) sufficiently vigorous to have an agency. To this instance I will add the seal in which we must suppose the power of life infinitely more simple. From such con- siderations we should be inclined to believe, that blood may originate without the aid (in the commencement) of a vital structure. It is not necessary that this should be blood of our bodies, or even the same as first becomes visible in the chick. The fluid which originates in the seed or plant is totally dissimilar and yet it produces ves- sels and all the vital structure ; neither is pus or serum exactly the same though possessed of such a power. Hence we learn that a vital structure may be formed by other than the complete blood, and life exist or be sup- ported. To recapitulate : All the foregoing observations intimate that a fluid (analogous to blood) of variable nature, maybe formed, (to appearance, without a vital agency, and principally from combinations of inanimate matter,) which shall have the power of forming a vital apparatus, provided, always, that circumstances which are not pecu- liar to life shall be favourable. It will now be my object to bring forward instances which have been considered favourable to such opinion ; and it is to be remarked that, throughout, nothing but the very simplest organization will be found to exist. When parts of plants or animals (which undergo ready decomposition) are infused in water and well corked up in a phial, animalculse invariably ap- pear after a few days.* This experiment is easy of suc- cess, and the following facts have been found to follow : That it makes little or no difference whether the organic matter be infused in its natural state ; or whether, boiled, * Needham on Tnfusions. J 20 roasted, or otherwise exposed to an elevation of tempera- ture sufficient to destroy all the forms of life, with which we are acquainted : The animalculae still appear during corruption. That this generation takes place, particularly in jelly, (even after having been roasted or boiled,) though trans- fered as rapidly and guardedly as possible. That it only takes place in such matter as can undergo what is considered spontaneous decomposition. That the animalculae are always multiplied in proportion to the extent of that decomposition. That they are generated throughout the matter ; even in parts which have not been exposed to the air ; as when a mass of jelly is thrown into boiling water, to make the infusion. That chemical agents are always necessary, &c. &c. In opposition to the apparent deduction of these facts, it has been supposed that eggs, conveyed through the me- dium of the air or water, are always deposited on the or- ganized matter previous to corruption ; and that chemical combinations, though absolutely essential, do not give rise to animation, (which, however, seems to consist of lit- tle more than irritable motion.) This supposition, it is to be remarked, has no solid foundation ; no eye has ever seen such eggs either in the air, water, or the corrupted matter, which is considered as a mere nidus. Neither can it be presumed that such eggs are of greater magni- tude than the animalculae; many of which are only visible during motion. Even Leuwenhock's statement is more rational, when he contended that he could distinguish the sexes of the animalculae, for he actually saw something* But allowing (for the sake of investigating truth) that there are eggs thus deposited, can we indulge the belief 121 that they will be able to survive roasting or boiling ? They certainly cannot have more vitality than the animalculae themselves, which are found to perish by the slightest change or exposure. And admitting, further, that such eggs might be deposited while the organic matter was transferring to the phial, why do they generate in such swarms throughout the matter ? Or how is their vitality preserved after that matter has been thrown into a vessel of boiling water and immediately corked up ? These cir- cumstances should be well refuted ; for they bear heavy against the egg system. Leuwenhock, when he observed animalculae in the sordes, which accumulates about teeth, resorted to the opinion that they themselves are transfer- red through the air, water, &c. There is the same objec- tion in this case as in the foregoing ; and this naturalist was not guided by experimental conviction at the time he advanced the opinion. The fact turns out, when we ex- amine the subject, that his head was turned about, proving that the animalculae, in male semen, were the true offspring in miniature ; and therefore he could not leave it to be thought by the world that his favourite theory qualified the mouth for foetal generation. He accordingly maintained, that in the last case, animalculae were conveyed by eating or drinking rain water, he. But it is well known that persons who do not eat cheese have them also, (or the re- verse) and that nothing similar to them is found to exist in rain water.* It has also been noticed, as a proof that regular generation takes place among animalculae, that the paste-eel, (a species,) when cut in the abdomen, frequently gives birth to numerous young eels. This fact, however, does not in the least account for their first appearance in paste under the circumstances before noticed. All that * Barr's Buffon p. 189. vol. 3. 16 122 seems proved, is, that such animalculee have also the power of regular generation ; and that, heing thus more perfect, there is a greater opening for the equivocal origin of vi- tality. Buffon observes that when blighted corn is examined numerous animalculse are observed to inhabit its sub- stance ; and seem to be confined altogether in their pro- duction to the rotten farina. These he states "may be made to live and die alternately, and as often as we please." And further, that " there are still others, even in great quantities, which are at first kinds of vegetables, afterwards become species of animals, then return again to vegeta- bles, and so alternately. w This naturalist also remarks that '* there are, perhaps, as many beings, either living or vegetating, which are produced by the fortuitous assem- blage of organic molecules, as by a constant and suc- cessive generation."* Yet Buffon supposed that he thus proved generation never to be equivocal ; because he considered what others call animalculae or small ani- mals, to be nothing more than moving machines, or his own living organic particles which death never destroyed. But his experiments may be viewed in a very different light, even though marshalled to support a very improba- ble theory ; for whether he supposes these animalculae to be mere moving machines or not, they have every appear- ance of animation. Besides, the proof given by assimila- tion, that inanimate mat;er becomes vital, (apparently in consequence of chemical changes, and certainly without the regular process of generation,) we may add that from the presence of worms in the stomach and intestines. It k&s been supposed that those are conveyed in without *Idejj)jVol.3.p.222, 123 food ; but is not this as badly supported as any ? Inde- pendent of the implied admission by medical practitioners when they give directions not to consider such worms as the cause, but altogether as symptomatic (which is literally nothing else than the effect) of disordered digestion, their origin seems proved to be in the stomach and intestines, by the fact that no such worms are known to exist out of the body, and instantly perish when exposed. They are always distinct from the body, and only appear at such times and places as indicate the greatest latitude to che- mical combinations. Why do they not oftener manifest themselves when the same food is eaten daily ? Particu- larly as digestion is found not to destroy their vitality. In the pustules of psora (itch) there are animalculae as well as in other eruptions ; in the secretions (as semen) and in almost all animal or vegetable fluids, after remaining some time at rest in the living structure. To leave animals, and descend : we meet with a very common occurrence which passe* unnoticed from its familiar appearance ; I mean the formation of mould in a dirty tea pot ; or on the margin of vessels holding infusions. We can hardly sup- pose that this is a species of tea, or that it came from China ; yet it is an animated production, in appearance similar to that examined by Sir Joseph Banks. But it is needless to examine the subject further. There are che- mical changes always antecedent to the appearance of these animated productions ; so there are in assimilation, The materials are the same, as well as most of the agents . regular generation seems throughout to be but a process of assimilation ; first, in the ovaria, to form the embryo, (as other living and definite structure of the female is formed.) then in the uterus, aided stili by the female ; or independently of all connexion, as in eggs and seeds. Thf 124 great obstacle to fortuitous generation must, therefore, be the process of assimilation ; for when this succeeds, a fluid will be produced capable of forming a vital circulating structure, (as blood vessels,) particularly as there appears no necessity for a complex system to support animation, Plants, seeds, embryos, and the imperfect classes of ani- mals show, that the process is not always the same ; and that it is equally effectual when curtailed of the principle features which characterize it in adults. The generating fluid (similar to blood) is manifestly proved by these ex- amples to be of different natures ; so that it is impossible to foresay what its origin must always be in a living body* As to the objection of final ends, we are as much at a loss in one case as the other. The animalculae and worms seem equally useless in the living fluids, whether brought to life by regular or fortuitous generation ; and the fact is well known, that as we descend and examine the power and process of generation in the lower classes of animals, we find the most astonishing deviations from the common form. Sexes do not appear necessary for the procreation of a polypus, which gives birth to new ones by simple division | or to those animated creatures who generate by shed- ding a limb. In these cases living systems are formed, (inde- pendently of any connexion) in parts, which previously seemed dependent members ; and they prove that the simplest structure is sufficient to support such system. Further, we should reflect that animation is founded upon irritabillity, which seems nothing more than a property of matter depending upon the action or influence of stimuli, on an indefinite structure and composition. Before the application of a stimulus we have not the slighest evidence of irritability, (and indeed it seems impossible by any other means to prove it ;) hence it is the matter which 125 qualifies the existence of animation more than the process of generation. Other circumstances in the regular pro- cess do undoubtedly exist, for which it would be presump- tion (at the present imperfect state of knowledge) to give such a rationale ; but the object is merely to examine the outline or rather the nature of one of its principles. In the pursuit of truth we should rely upon facts more than opinion ; for the last never can unfold the woiks of God, or manifest His wisdom, whereas the first are always illustrative. The ancients admitted the fact of fortuitous generation, and quietly established the maxim, " corruptio unius, generatio alterius ;" but after the discovery of ani- malculse in serum, by Leuwenhock, philosophers became warm with contention. This naturalist, after several times retracting his opinions, maintained them to be embryos in miniature, Buffon on the other hand opposed Leuwen- hock, by contending that they were nothing less than his immutable but fanciful, " living organic particles ;" while Needham had the boldness to suppose their origin to be equivocal, or resulting from material laws, independent of regular generation. These opinions had a fashionable ex- istence, and then subsided, leaving but little taste for fur- ther inquiry. But notwithstanding such opposite views, the facts noticed by these philosophers became the more confirmed, and must still continue to exist, unless nature forgets herself so far as to overturn her present regula- tions. I shall close this essay without drawing a single conclusion, persuaded that the facts must answer for themselves. FIKIS. COL This boc COLUMBIA UNIVERSITY LIBRARIES This book is due on the date indicated below, or at the expiration of a definite period after the date of borrowing, as provided by the library rules or by special arrangement with the Librarian in charge. DATE BORROWED DATE DUE DATE BORROWED DATE DUE C28 (167) 50M :ollection I-QH3U5 Em6 1822 try mm>& >V pajr. ih ;" r\tf •"^' sfe