which the heat and energy originate, and upon which life is so alarmingly dependent—going on, not chiefly in the lungs or blood, but in every cell of the body, is responsible to an enzyme, or catalase, known as an oxidase. The result of these elements, which is the bringing about of the union of oxygen with the tissue, is perfectly well known, but the chemical nature and the physical characteristics of the oxidases, are problems for speculation.
The enzymes in plant cells are similar at least in action to the corresponding ones of animals; but, in addition to those possessed by animals, plants have ferments which enable them, in the sunlight, to use carbonic acid gas in building up some of its cell constituents.
The method used in the laboratory for demonstrating the presence of an enzyme is very simple. The tissue to be examined is finely minced and ground up in a mortar. In order to facilitate the division of the cells, sand may be used in the grinding. The pulverized mass is then mixed with water or a dilute salt solution, which dissolves the enzyme. To find out what the nature of the enzyme may be, a small amount of the solution just prepared above, free of residue, is added to a solution of a substance, as starch, fat, or proteid, which an enzyme may decompose. After the course of a few hours the mixture is "tested for the splitting products of the respective substance added. If such be found and none were in either solution when kept separate, it may be safely concluded that an enzyme has been discovered in the tissues examined. Very likely it can be demonstrated that the tissue contains more than one ferment, by showing that the tissue extract will split more than one class of substances.
It has been but recently discovered that enzymes or, better, proenzymes have an interaction. The pure secretion from the pancreas does not digest proteids. The unadulterated juices from the intestinal wall do not split up proteids. But a mixture of the two secretions possesses marked proteolytic powers. This phenomenon has also been observed with other ferments.
It has been known for years that certain finely divided metals, like silver, platinum, gold and others, possess the property of accelerating some of the reactions of, or chemical changes in, inorganic chemistry. As an example—if any one of the above metals be added to a solution of hydrogen dioxide, the compound is decomposed into its constituents, water and oxygen. It remained, however, till recent years for a young man working in the physiological laboratory of one of our great universities to show that these finely divided metals, elements of the inorganic world, could perform the function of a body ferment. Finely powdered platinum prepared by precipitation—known as platinum black—when added to a simple fat, decomposes it, in the same manner as a body enzyme would do. The metal has practically all the char-