When Buchner a few years ago, by simple pressure, forced from the yeast cell a little limpid fluid and with this was able to induce the same chemical reactions that the living yeast plant produces when brought in contact with a sugar solution, it became clear that the typical formation of alcohol and carbon dioxide is not the result of the life of the yeast plant as formerly supposed, but is instead to be attributed to something—a chemical substance—easily separable from the yeast cell, and quite capable of causing the fermentation of sugar. This reaction, which had for so long been looked upon as a typical illustration of the power of life in inducing chemical change, is merely a simple process of enzymolysis. The yeast plant, it is true, produces the enzyme; but the isolated ferment, once formed, is just as capable of decomposing the sugar as the yeast plant itself. Indeed, the latter is able to accomplish this chemical reaction, solely because of the presence of the enzyme or ferment, now called zymase. In all forms of animal and vegetable tissue, intra- and extra-cellular enzymes abound; enzymes of varied nature, endowed with the power of inducing chemical reactions of diversified character. Those previously referred to in the breaking down of protein material, both in digestion and in autolysis, are typical of what may be found in many of the fluids and in most of the tissues of living organisms. Enzymes which induce hydrolytic cleavage are especially abundant; sugars, proteins and fats all falling as prey to their power of breaking down the respective molecules into smaller and simpler ones better fitted for distribution or utilization. Further, enzymes of the amidase type, which have the power of removing nitrogen from nitrogenous compounds, are equally conspicuous in many phases of intermediary metabolism, especially where changes of nuclein material are involved. In this reaction the elements of water are apparently alone involved, but in some mysterious fashion the enzyme causes a retention of oxygen while the hydrogen passes off with one atom of nitrogen in the form of ammonia, thus leading to the formation of a new substance with one more atom of oxygen than the body from which it was formed and with one less atom of nitrogen and of hydrogen. In this way, gradual oxidation results without free oxygen being involved, while at the same time the content of nitrogen is reduced. Again, there are enzymes separable from the tissues of the body which bring about the destruction of uric acid, not, however, by a process of annihilation, as might be implied by the above statement, but by a method of cleavage in which new bodies less complex are formed. Equally manifest is the action of enzymes which bring about glycolysis, i. e., the destruction of sugar as in the blood; while the separation of the amido group from amino-acids, the oxidation of aromatic aldehydes, the splitting apart of a substance like arginine into urea and ornithine, and a host of kindred reactions, all
