Page images
PDF
EPUB

EXTERNAL CONDITIONS OF LIFE.

83

any law relating to such a harmony, which has never, in fact, been connected with any other essential biological character. This great gap exists as much with regard to the successive states of the same organism as to the scale of organisms. The necessary revision might be best applied first to the lowest states; as the egg and the lowest organisms appear able to sustain wider differences of temperature than those of a higher order: and several philosophical biologists have even believed that life may have been always possible on our planet, notwithstanding the different systems of temperature through which its surface has successively passed. On the whole, the sum of our analyses may seem to disclose, amidst many anomalies, a general law that the vital state is so subordinated to a determinate thermometrical interval, as that this interval perpetually diminishes as life becomes more marked,-in the case both of the individual and of the series. If even this general law is not yet scientifically established, it may be supposed how ignorant we are of the modifications. produced in the organism by variations of external temperature, within the limits compatible with life. There has even been much confusion between the results of abrupt and gradual changes of temperature, though experiment has shown that graduation vastly expands the limits within which the human organism can exist; and again, between the influence of external, and the organic production of vital heat. This last great error shows that even the laying down the question remains to be done. The same thing may be said of the other exterior conditions, such as light and electricity, of which all that we know in this connection is that they exert a permanent influence needful for the production and support of life. Besides the confusion and uncertainty of our observations, we have to contend with the inferiority of our knowledge of those branches of physics, and with the mischief of the baseless hypotheses which we before saw to infest the study of them. While physicists talk of fluids and ethers, avowing that they do so in an artificial sense, for purposes of convenience, physiologists speak of them as the real principles of two orders of exterior actions indispensable to the vital state. Till

Light, Electricity, etc.

reform becomes substantial and complete in the study of light and electricity, these will remain the exterior conditions of vitality of which our knowledge is the most imperfect.

Molecular conditions.

Passing on from the physical to the chemical conditions of the medium, we find our amount of knowledge scarcely more satisfactory. In strict generality, this study relates to the physiological influence of air and water, the mingling of Air and Water. which, in various degrees, constitutes the common medium necessary to vitality. As M. de Blainville remarked, they must not be considered separately, as in a physical or chemical inquiry, but in that mixture which varies only in the proportions of its elements. This might be anticipated from our knowledge of the chemical constitution of living bodies, the essential elements of which are found only in the combination of air and water: but we have physiological evidence also, which shows that air deprived of moisture, and water not aerated, are fatal to vital existence. In this view there is no difference between atmospheric and aquatic beings, animal and vegetable, but the unequal proportion of the two fluids; the air, in the one case, serving as a vehicle for vaporized water; and the water, in the other case, conveying liquefied air. In both cases, water furnishes the indispensable basis of all the organic liquids: and the air the essential elements of nutrition. We know that the higher mammifera, including Man, perish when the air reaches a certain degree of dryness, as fishes do in water which has been. sufficiently deprived of air by distillation. Between these extreme terms there exists a multitude of intermediaries in which moister conditions of air and more aerated states of water correspond with determinate organisms; and the observation of Man in the different hygrometrical states of atmospheres shows how, in the individual case, physiological phenomena are modified within the limits compatible with the vital state. If we may say that the question has been laid down in this inquiry, it is only in a vague and obscure way. Besides our ignorance of the varying proportions, we have none but the most confused notions about the way in which each fluid participates in the support of life. Oxygen is the only element of the air about

[blocks in formation]

which we have made any intelligent inquiry, while physiologists entertain the most contradictory notions about azote: and the uncertainty and obscurity are still greater with regard to water. In this state of infancy, it can be no wonder that the science offers as yet no law as to the influence of the medium on the organism- -even in regard to the question whether a certain condition of existence becomes more or less inevitable as the organism rises in the scale.

Study of specifics.

The study of the influence of specifics does not enter here, on account, of course, of the absence of generality; but it should be just pointed out that, reduced as is the number of substances called specifics, there are still enough,—as aliments, medicines, and poisons,-to afford a hint of what might be learned by an exploration of them, in regard to the harmony between the organic world and the inorganic. The very quality of their operation, that it is special and discontinuous, and therefore not indispensable, indicates the experimental method in this case, as being certain, well circumscribed, and very various. This study may then be regarded as a needful appendix, completing the preliminary biological doctrine which I have called that of organic media, and offering resources which are proper to it, and cannot be otherwise obtained. Unhappily, this complement is in even a more backward state than the more essential portions, notwithstanding the multitude of observations, unconnected and unfinished, already assembled in this path of research.

The

History of
Physiology.

If such is the state of preliminary knowledge, it is clear how little has yet been learned of the laws of life themselves. inquiry has gone through revolutions, as other questions have, before reaching the threshold of positivity, in our day. From the impulse given by Descartes, the illustrious school of Boerhaave arose in physiology, which exaggerated the subordination of biology to the simpler parts of natural philosophy so far as to assign to the study of life the place of appendix to the general system of inorganic physics. From the consequent reaction against this absurdity arose the theory of Stahl, which may be considered the most scientific formula of the metaphysical state of physiology.

The struggle has since lain between these two schools,―the strength of the metaphysical one residing in its recognition of physiology as a distinct science, and that of the physicochemical, in its principle of the dependence of the organic on the inorganic laws, as daily disclosed more fully by the progress of science. The effect of this improved knowledge has been to modify the conceptions of metaphysical physiology: the formula of Barthez, for instance, representing a further departure from the theological state than that of Stahl; as Stahl's already did than that of Van Helmont, though the same metaphysical entity might be in view when Van Helmont called it the archeus, and Stahl the soul, and Barthez the vital principle. Stahl instituted a reaction against the physico-chemical exaggerations of Boerhaave; but Barthez established, in his preliminary discourse, the characteristics of sound philosophizing, and exposed the necessary futility of all inquisition into causes and modes of production of phenomena, reducing all real science to the discovery of their laws. For want of the requisite practice in the positive method, the scheme of Barthez proved abortive; and, after having proposed his conception of a vital principle as a mere term to denote the unknown cause of vital phenomena, he was drawn away by the prevalent spirit of his time to regard the assumed principle as a real and complex existence, though profoundly unintelligible. Ineffectual as his enterprise proved, its design with regard to the advancement of positive science cannot be mistaken. The progressive spirit is still more marked in the physiological theory of Bichat, though we find entities there too. These entities however show a great advance, as a determinate and visible seat is assigned to them. The vital forces of Bichat however still intervene in phenomena, like the old specific entities introduced into physics and chemistry, in their metaphysical period, under the name of faculties or occult virtues, which Descartes so vigorously hunted down, and Molière so happily ridiculed. Such is the character of the supposed organic sensibility, by which, though a mere term, Bichat endeavoured to explain physiological phenomena, which he thus merely reproduced under another name: as when, for instance, he thought he had accounted for the successive flow of different

HISTORY OF PHYSIOLOGY.

87

liquids in one canal by saying that the organic sensibility of the canal was successively in harmony with each fluid, and in antipathy to the rest. But for his untimely death however, there can be no doubt that he would have issued into an entire positivity. His treatise on General Anatomy, though appearing a very few years after his treatise on Life and Death, is a great advance upon it; and even in the construction of his metaphysical theory of vital forces he certainly first introduced, under the title properties of tissue, a conception of the highest value, destined to absorb all ontological conceptions, and to prepare for the entire positivity of the elementary notions of physiology. The thing required is to substitute properties for forces; and Bichat's treatment of tissue fulfilled this condition with regard to a very extensive class of effects: and thus his theory, while it amended the metaphysical doctrine of Stahl and Barthez, opened the way to its entire reformation by presenting at once the germ and the example of purely positive conceptions. This is now the state of physiological philosophy in the minds of the majority of students; and the conflict between the schools of Stahl and Boerhaave,-between the metaphysical and the physico-chemical tendency,-remains at the point to which it was brought up by the impulse communicated by Bichat. It would be hopeless to look to the oscillations of this antagonism for an advance in science. If the one doctrine prevailed, science would be in a state of retrogression; if the other, in a state of dissolution; as in our social condition, in the conflict of the two political tendencies, the retrograde and the revolutionary. The progress of physiology depends on the growth of positive. elementary conceptions, such as will remand to the domain of history the controversy from which nothing more is to be expected. Abundant promise of such an issue now appears the two schools have annulled each other; and the natural development of the science has furnished means for its complete institution to be begun. This I look upon as the proper task of the existing generation of scientific men, who need only a better training to make them adequate to it. If, from its complexity, physiology has been later than other sciences in its rational formation, it may reach its maturity more rapidly from the ground

« PreviousContinue »