There was a time when certain proximate principles, as the chemists called those substances, found m organized bodies, and which enter into the composition of vegetable and animal tissue, and occupy an intermediate position between the bodies recognized as elements, and fully organized living tissues ; there was a time, we repeat, when these complex substances were supposed to owe their origin to something more than ordinary chemical affinity. As usual in the history of science, when something has been obscure, an occult force was supposed to account for the mystery attending the composition of these substances. The force thus called in was styled “ Vital Force,” merely a name for an unknown cause or causes. Chemistry has also been divided into two distinct departments, simply because of the supposed differences between the deportment and composition of organized bodies and inorganic bodies. We say supposed differences. There are striking differences between a living organism and a dead mass of matter ; but we are not now speaking of that mystery of mysteries, life ; we are not even speaking of living things; only of the substances which enter into and make up the separate parts of living things ; parts which, by themselves, do not live, cannot live, but which, together, make up that “unity in multeity,” which we call a living thing. If we cut out a brain or a heart from a living animal, these organs (although manifesting, perhaps, in a more striking degree than any others, the subtile principle of life,'So long as they remain attached to the rest of the living organism,) cease to live; become as dead as a 8od,or a bough lopped from a tree, nay, die even quicker than the bough ; for it is a most singular law of life, that the lower in the scale of animated being an organism exists, the greater is the power of living vested in individual organs. The heart and the brain, thus isolated, die. Seizing the time before decomposition (which also implies, in every case, recomposition “ into something new and strange,") sets in, we may subject the substances contained in either, to the most rigid examination without detecting the slightest difference between it and other dead matter, of the same kind, found in minerals or gases. We are,therefore, forced to the conclusion that no difference exists, in the essential nature of these substances. Just here ,.we encounter a difficulty. The heart or the brain may be fed to other animals,digested and assimilated into new organisms, may even become a part of other hearts and brains in the living animals which devour them. But if we take the substances of which the heart and brain are composed and resolve them into their elements, and feed them to other animals, we find they are not all assimilated. The phosphorus in the brain may even act as a violent poison, and produce death in the animals to which it is fed. But were we to stop here, and make, prematurely, the absurd generalization, that no inorganic matters can he assimilated, we should have committed a grave error. What is meant by assimilation ? It is the conversion of substances taken as food into the substances contained in the body.' In other words, decomposition and recomposition. This decomposition and recomposition is strictly a chemical process; demonstrated to be so by the artificial production of many organic constituents outside of either plants or animals in the laboratory of the chemist. As a chemical process, it is subject to the same laws as other chemical processes. One of these laws is, that the occurrence of chemical reae-