not to be directly excreted, is further employed in the organism, and exerts an influence on the chemical processes taking place, and may therefore produce disturbances in them. An example will explain this: In a large number of mammals the glycocol formed in the organism is not separated by the kidneys under ordinary circumstances; but a quantity of benzoic acid taken with the food is sufficient to fix the glycocol with the formation of hippuric acid, and to separate it in this form. These and similar facts, which can be mentioned in large numbers, have a very important signification, for they give the strongest support to the assertion that the chemical process in the animal body may be considerably changed by apparently slight circumstances. If we accept this, and consider the occurrence of substances still unknown, and present, perhaps, only in very small quantity in the animal organism, we will obtain a hint as to the explanation of effects which many foreign substances produce, though in very small quantities, on the organism. Who does not know the action of strychnia, curarine, prussic acid, and similar poisons?
As our knowledge of these poisons has increased, we have found that they never act on the whole organism, but always on particular organs or groups of organs; these may be the nerves, the muscles, the glands, or only a portion of them. While the curarine paralyzes all voluntary muscles, the heart perceives nothing of its effects; on the other hand, the poison of the fly-agaric—muscarine—paralyzes the heart, but not the voluntary muscles. Strychnia acts only on certain portions of the spinal marrow, opium only on parts of the cerebrum; phenomena which remain completely unintelligible until we attempt to explain them from a chemical point of view, and assume that, at the points accessible to the action of these poisons, there occur, in very small quantities, substances which are of the highest importance to the vital action of the organism, and which are decomposed by them. Of course, chemistry has not yet shown us any essential difference between striped and unstriped muscles, between brain and the spinal marrow, or between the different parts of these organs; but, as the observation of certain lines in the spectrum has led to the discovery of new elements, so may the action of these poisons, at some future time, serve as a guide in searching for these suspected substances.
The chemistry of the animal body is not simply confined to the formation and decomposition of definite chemical compounds; the organism also makes use of certain physical phenomena which are inseparably connected with the chemical, namely, the electric and the thermic. The former take part in the excitation of the nerves, perhaps also in some of the chemical processes; the latter are to be considered as the source of heat in warm-blooded animals as well as of the mechanical force developed by the different muscles. These important facts throw light on the total character of the chemical