length, in the first volume of this work. Fifthly. Bichat admitted a fifth vital property, under the name animal contractility, which comprised voluntary muscular contraction;—treated of elsewhere as one of the functions of the body. It differs from organic contractility, in its exciting cause not being seated in the organ in which it is developed, that is, in the muscle, but in the brain; and, moreover, whilst the other varieties of contractility. are irresistibly connected with, and proportioned to, the kind of sensibility correspondent to them, this is not the case with animal sensibility, and its play is never continuous.

From the distinction we have endeavoured to draw, between the fundamental vital properties and the functions, it will be obvious, that the ingenious division of Bichat is susceptible of farther curtailment by analysis.

A vital property must be one possessed by all living bodies; it is fundamental in the tissues, and differs according to the precise structure of the tissue. It is found in the vegetable, as well as in the animal. Neither of the two last properties of Bichat, however, corresponds with this definition. They do not exist in the vegetable. They require not only a nervous system, but a brain that can conceive and will. They are both, indeed, complicated functions, and as such have been considered at great length, elsewhere. By ultimate analysis, therefore, the five vital properties of Bichat may be reduced to the two we have previously mentioned:—sensibility, and motility. Perhaps we ought to rest satisfied with the admission, that every primary tissue is capable of being acted upon by appropriate stimuli, or is sensible; and that it possesses the additional property of moving, in consequence of such impression. Physiologists have, however, attempted to simplify the subject still farther, and to reduce the vital properties to one only. Such is the view of Broussais, who considers contractility to be the fundamental vital property of all the tissues. We have elsewhere shown, however, that even in the muscular fibre it is by no means clear, that positive contraction of the fibres occurs, and that the two extremities of a muscle are conceived, by some late physiologists, to be brought into approximation by their fibres assuming a zigzag arrangement. In the primary nervous, and cellular tissues, the existence of such contractility is yet more doubtful.

Adelon, again, considers that sensibility is the only living property that must be admitted. "Hitherto," he remarks, "physiologists have separated the susceptibility of receiving the impression that excites the movement, from the faculty of producing it, and have admitted two vital properties under the names sensibility and motility. Supposing an instant, however short, between the moment of impression, and that of the motion which follows it, they have looked upon the act of receiving the impression as distinct from that of moving in consequence of it. But these acts VOL. II.

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are really but one. It is the movement executed by a part, in consequence of an impression, which proves that the part has been sensible to such impression. To feel, as Chaussier and Bichat have remarked, is merely to vary the mode of existence in consequence of an impression. It is merely moving in a manner which is neither physical nor chymical. This is evident where the movements are occult: without the results induced by these movements, sensibility would not have been manifested." For these and other reasons he concludes, that "the two properties, sensibility and motility, are reducible to one only, which may be called sensibility, if desired, but which must carry with it the idea of motion, and is the active, motive faculty of living matter." The term sensibility is, however, unfortunate, in consequence of its conveying the notion of mental perception, and of such acceptation having been received into physiology, as designating a function. It has, consequently, been proposed to substitute the term excitability, incitability, or irritability, but with the same signification. Rudolphi prefers incitability, (Erregbarkeit,) as not liable to the objection that may be urged against the others, of having been employed in other significations. This incitability differs in the different organs and tissues; in the muscles it is termed irritability, (Muskelkraft, Reizbarkeit;) in the nerves, sensibility, (Nervenkraft, Empfindlichkeit;) and by some physiologists, in the membranous parts it is called contractility, (Spannkraft, Zusammenziehungskraft.)

Such are the phenomena which indicate the existence of the vital principle, and such the laws by which it seems to be governed. By certain physiologists, it is considered to influence solids only; by others, it has been considered to reside in the fluids also, and especially in the blood. The notion of the vitality of this fluid was espoused by the celebrated John Hunter, and to him we are indebted for many of the facts and arguments, adduced in its favour, and which have impelled the generality of modern physiologists to admit its existence. The analogy of the egg had demonstrated that life is not restricted to substances which are solid and visibly organized. The fresh egg, like other living bodies, possesses the ordinary counteracting powers communicated by vitality, and resists those agents which act upon the dead egg as on other animal substances deprived of the living influence. The fresh egg may be exposed for weeks, with impunity, to a degree of heat, which would inevitably occasion the putrefaction of the dead. During the time of incubation, the egg of the hen is kept at a heat of 105° for three weeks; yet, when the chick is hatched, the remaining yolk is perfectly sweet.

The power of resisting cold is equally great. Hunter performed several experiments, which show the power of the vital principle in resisting cold, and the influence of cold in diminishing the energy of the vital principle. He exposed an egg to

the temperature of 17° and of 15° of Fahrenheit, and found that it took about half an hour to freeze it. When thawed, and again exposed to a cold atmosphere, it was frozen in one-half the time, when exposed to a temperature of 25°. He then put a fresh egg, and one that had previously been frozen and again thawed, into a cold mixture at 15°; the dead egg was frozen twenty-five minutes sooner than the fresh. These experiments led to the legitimate inference, that the egg possessed the principle of life, and although fluid, must have enjoyed the properties, which we have described as characteristic of vitality;—of being acted upon by an appropriate irritant, and of moving responsive to such irritation.

Similar results to those obtained with the egg followed analogous experiments with the blood. On ascertaining the degree of cold, and the length of time necessary to freeze blood taken immediately from the vessel, he found that, as in the egg, a much shorter period, and a much less degree of cold, were requisite to freeze blood that had been previously frozen and thawed, than blood recently taken from the vessel. The inference, deduced from this, was, that the vitality of recent blood being comparatively unimpaired, it was enabled to resist the cold longer than blood, whose vital energy had already been partly exhausted by previous exposure.

The fluidity of the blood, whilst circulating in the vessels, has been regarded as an additional evidence of its vitality. It is obvious that such fluidity is indispensable, seeing that it has to circulate through the minute vessels of the capillary system, and that the slightest coagulum, forming in them, would lead to morbid derangements. Yet the blood is peculiarly liable to become solid by its constitution, and whenever it is removed from its vessels, coagulates. This is not owing simply to the cessation of its circulation, for if it be kept at the same temperature as in the living body, and be made to circulate with equal rapidity through a dead tube, it equally becomes solid. The cause, consequently, that maintains its fluidity, is presumed to be the vital agency.

Another argument in favour of the vitality of the blood is drawn from the facts connected with its coagulation,—facts, which show, that the process is but little influenced by physical agents, and which have induced Magendie to infer,—with many other physiologists, who are but little disposed to invoke the vital agency,— that the coagulation of the blood cannot be ascribed to any physical influence, but that it must be esteemed essentially vital, and as affording a demonstrative proof that the blood is endowed with life." It has, indeed, been attempted to show, that there are certain phenomena which demonstrate that the vitality of this fluid increases or diminishes with the vitality of other parts of the body. When blood is drawn from a vessel it does not instantly coagulate or die; and, by observing the length of time consumed in the process, it has been thought, that we might be, in

some measure, able to estimate the degree of vital energy it possesses. In diseases, where the vital action is exalted, as in inflammation, the blood is found to coagulate much more slowly than in a state of health, and the coagulation itself is more perfect, whilst in diseases that are dependent upon a diminution of the vital energy, the opposite is the fact; because, in the first case, it is presumed, the blood possesses the vital principle in a higher degree than natural, and consequently resists, for a longer period, the influence of the physical agents to which it is exposed; whilst, in the second case, it possesses the vital principle to a less degree than natural, and therefore yields sooner to the influence of those agents, the coagulation, however, in all instances being analogous to the rigidity of the muscles which takes place after dissolution, and indicates the final cessation of vitality.

The buffy coat or inflammatory crust of the blood, called, also, corium phlogisticum, and crusta pleuretica, is a circumstance connected with the blood's life, which has been invoked by the supporters of this view of the subject. The terms are applied to an appearance of the crassamentum, which is owing to its upper portion containing no red particles, but exhibiting a layer of a buffcoloured coriaceous substance lying at the top, owing to the red particles, during coagulation, sinking to the lower portion of the clot, before coagulation is completed; hence the colourless state of the upper surface. At the same time, the whole of the coagulated portion is much firmer than usual. The red particles, in such case, have time to subside before the coagulation is complete, which takes place more slowly than in health; and this is conceived to be owing to the blood's possessing a higher degree of vitality, a view which is confirmed by some experiments of Mr. Thackrah. These consisted in receiving blood, taken from the vessels of a living animal, in a full and uninterrupted stream, into different cups, and noting the time at which coagulation commenced in each. Blood, for example, was taken from a horse at four periods, about a minute and a half being allowed to intervene between the filling of each cup. In the first cup, coagulation began in eleven minutes and ten seconds; in the second cup, in ten minutes and four seconds; in the third cup, in nine minutes and thirty-five seconds; and in the fourth cup, in three minutes and twenty seconds. In another experiment, blood was drawn into three separate cups, from the veins of a slaughtered ox, the first of which was filled in the first flow; the second about three minutes afterwards; and the third a short time before the death of the animal. Coagulation commenced in the first cup in two minutes and thirty seconds; in the second, in one minute and thirty-five seconds; and in the third, in one minute and ten seconds. In a similar experiment, coagulation commenced, in the first cup, in two minutes and ten seconds; in the second, in one minute and forty-five seconds; and in the third, in thirty-five seconds.

Similar phenomena are found to occur in the human subject. Blood, to the amount of about a pint and a half, was taken from the arm of a female labouring under fever. A portion of this, received into a cup on its first effusion, remained fluid seven minutes; a similar quantity, taken immediately before tying up the arm, was coagulated in three minutes and thirty seconds. Of blood, taken as in the last experiment, from the arm of a man, the first portion began to coagulate in seven minutes; the last in four. The vitality of the system, and with it the vitality of the blood, being diminished by each successive abstraction of that fluid, it coagulated or died sooner and sooner in proportion as it was previously more and more enfeebled.

It is obvious, however, that if these and other arguments lead to a belief in the vitality of the blood, they are equally favourable,— many of them at least,—to the life of the chyle; which, we have seen, accurately resembles the blood in every property, except in that of coloration; and if we admit the blood to be possessed of life, a question arises, respecting the part at which the nutritive substances, taken into the system, become converted into the nature of the being they are destined to nourish, and receive the principle of life. This must be either through the admixture of the fluids poured out from the supra-diaphragmatic portions of the alimentary canal, from those of the stomach or small intestine, or owing to the mysterious and inappreciable action exerted by the chyliferous radicles themselves, which separate the same fluid, chyle, from every substance that may be submitted to their action.

These are the only fluids that have been suspected to be endowed with vitality. None of the others exhibit analogous phenomena, when exposed to similar agencies.

On the whole, we are led to the conclusion, that, the vital principle animates both solids and fluids, but all that we seem to know regarding it is in the language of Dr. Barclay, "that all the organisms of animals and plants are formed out of fluids, and that in a certain species of fluid, secreted from the parent, and afterwards inclosed in a very thin and transparent vesicle, there is a living organizing principle, which also acts upon the fluid in a way which we know not, forming out of it a regularly organized system of solids, and forming not only the rudiments of that system, but causing it afterwards to be nourished, and to grow through the medium of fluids, which are moved and distributed under the influence of this organizing animating principle."

Our knowledge being limited to this category, we are compelled to study life in its results or manifestations. These, as we have seen, constitute the science of biology or physiology.