PHYSIOLOGY is the science which treats of the powers that actuate the compo nent parts of living animal bodies, and of the functions which those bodies execute. It presupposes, therefore, a knowledge of the structure of the body, which is the object of anatomy ; the latter may be called the science of organization, while physiology is the science of life. The two subjects are so closely connected, that they would be most advantageously considered in connection with each other. Hence the reader will find many physio logical considerations under the articles ANATOMY and COMPARATIVE k to:mut, which indeed he should peruse as an in troduction to the present article.
Genet'al View of the Functions exercised by the animal Body.
The term life denotes one of those ge neral and obscure notions produced in our minds by certain-series of phenome na, which we have observed to succeed each other in a constant order, and to be connected together by mutual relations. Being ignorant of the bond of union which connects these, although we are convinced of its existence, we have de signated the assemblage of phenomena by a name which is often regarded as the sign of a peculiar principle ; although it should indicate nothing more than the collection of appearances, which have given rise to its formation. Thus, as our own bodies, and several others, which resemble them more or less strongly in form and structure, appear to resist for a certain time the laws which govern in animate matter, and even to act on sur• rounding objects in a manner quite con trary to these laws, we employ the ex pressions of life and vital power, to de signate these at least apparent exceptions to general rules. Our only method of fixing the meaning of these words is, to determine exactly in what these excep tions consist. With this object, let us consider the bodies alluded to in their active and passive relations to the rest of nature. Let us contemplate, for instance, the body of a female in the vigour of youth and beauty; those rounded and voluptuous forms; those graceful and easy motions; those cheeks glowing with the roses of pleasure; those eyes spark hug with the inspirations of genius, or fired by the warmth of love; that physi ognomy enlivened by the sallies of wit, or animated by the fire of the passions ; all unite to form a truly enchanting ob ject. A single moment is sufficient to
destroy this pleasing illusion : sensation and motion often cease on a sudden, with out any apparent pre-existing cause ; the muscles, losing their plumpness, shrink, and expose the angular projections of the bones; the lustre of the eyes is gone, the cheeks and lips grow livid. These are only the prelude to still more unpleasant changes: the flesh turns successively to blue, green, and black; it imbibes the moisture of the atmosphere, and, while one part is evaporated in pestilential ema nations, the other melts into a putrid sanies, which also is speedily dissipated. In short, after a few days, nothing re mains but a few earthy, or saline princi ples; the other elements having been dispersed in the air, or waters, to form new combinations.
This separation is the natural effect of the action of air, moisture, and heat, that is, of all-the surrounding external agents, on the dead body ; and it arises from the elective attractions which these agents possess for the materials of the body. Yet it was equally surrounded by them during life : their affinities for its com ponent parts were the same ; and the latter would have yielded in the same manner, if they had not been held to. gether by a superior power, the influence of which continues to operate until the moment of death.
This resistance then, of the laws which act on dead matter, is one of the particu lar ideas entering into the general notion of life, which seems, in a more especial manner, to constitute its essence ; for without it life cannot be conceived to exist, and it continues uninterruptedly until the moment of death.