I. GENERAL VIEWS.—We shall define LIFE to be the state of action peculiar to an or ganised body or organism. This state com mences with the first production of the germ; it is manifested in the phenomena of growth and reproduction ; and it terminates in the death of the organised structure, when its component parts are disintegrated, more or less completely, by the operation of the com mon laws of matter. This definition differs but little from that given in many physiological works—" Life is the sum of the actions of an organised being;" and we apprehend that we are more in accordance with the common usage of the term, in employing it to designate rather the state or condition of the being exhibiting those actions, than the actions themselves. In this sense alone it is properly contrary to Death, the condition of an organised body in which not only have its peculiar actions ceased, but its distinguishing properties been abolished (see DEATH); and it is then also contradistin guished from dormant vitality, a state fre quently observed, in which living actions are suspended, but the vital properties of the or ganism retained, so as to be capable of again exhibiting them when the requisite conditions are supplied.
Life or vital activity, then, manifests itself to us in a great variety of ways,—in all those phe nomena, in short, which it is the province of the physiologist to consider. The changes ex hibited by any one living being, in its normal condition at least, have one manifest tendency, the preservation of its existence as a perfect structure ; by these it is enabled to counteract the ever-operating influence of chemical and physical laws, and to resist, to a greater or less extent, the injurious effects of external agen cies. The first inquiry, then, which we have to make, in the inductive study of physiology, is into the conditions of these phenomena; and as in this process we follow precisely the same track as that over which the physical philo sopher has already passed, we may advantage-. ously avail ourselves of his guidance in it.
In seeking to establish the laws by which the universe is governed, or, in other words, to obtain general expressions of the conditions under which its changes take place, the en quirer first collects, by observation or expe riment,* a sufficient number of instances having an obvious relatioNo one another, with the view of determining the circumstances com mon to all. The facility with which this pro cess is performed will obviously depend upon the simplicity of the phenomena, and the rea diness with which they admit of comparison. Where their antecedents are uniformly the same, they only need to be associated a suf ficient number of times, for the mind to be satisfied of the constancy of the relation; and the general law of the effects is easily deduced. Thus, the law of gravitation is ascertained by the comparison of a number of corresponding but not identical phenomena; and the nume rical ratio is established which governs the attracting force. To extend the application of this law, however, to phenomena that seemed beyond its pale, required the almost super human genius of Newton; but the idea, once conceived, was easily carried out when the re quisite data were attained. But what is the nature of the law of which we have just spo ken as regulating the attractive force ? It is simply an expression of the property with which the Creator has endowed all forms of matter, that its masses shall attract or tend to approach each other in a degree which varies in a certain ratio to their mass and distance. This property, it must be recollected, is only assumed to exist, as the common cause of the actions constantly occurring under our notice. If none of these actions were witnessed by man,—if, for example, but one mass of matter existed in the universe,—it might be endowed with this and every other property which we are accustomed to regard as essential to matter; and yet, from gravitation never being called into action, the mind would remain ignorant of the attribute.