to transform amino-acids into amides, and still others capable of splitting up amides. Equally important, and even more suggestive, are the data which have been collected recently regarding oxidative processes in the tissues of the body. Specific ferments, known as oxidases, are found widely distributed in many organs and tissues, and it is difficult to escape the conclusion that as intracellular enzymes they have an important part to play in some, at least, of the transformations characteristic of tissue katabolism.[20] As a single example, mention may be made of aldehydase, which accomplishes the oxidation of substances having the structure of aldehydes into corresponding acids. Ferments or enzymes of this class are found in the liver, spleen, salivary glands, lungs, brain, kidneys, etc., and they may well be considered as important agents in the chemical transformations going on in the tissues of the body. It would take us too far afield to enter into a detailed consideration of these intracellular enzymes; it must suffice to emphasize the general fact that in all the tissues and organs of the body there are present a large number of enzymes of different types, endowed with different lines of activity, and consequently capable of accomplishing a great variety of results in metabolism. Oxidation may still be a dominant feature in nutrition, oxidative changes may characterize more or less every tissue and organ in the body, but the processes are subtle and are not to be defined in harmony with simple chemical or physical laws. The living cell, with its intracellular enzymes, is the guiding and controlling power by which the processes of katabolism are regulated in harmony with the needs of the body. Complex organic matter is broken down step by step in the various tissues, with gradual liberation of the contained energy; processes of hydrolytic cleavage alternate with processes of oxidation, the molecules acted upon growing smaller with each downward step, until at last the final end-products are reached, viz., carbon dioxide, water, and urea, which the body eliminates through various channels as true physiological waste-products. [20] See M. Jacoby: Ueber die Bedeutung der intracellulären Fermente für die Physiologie und Pathologie. Ergebnisse der Physiologie, Erster Jahrgang, 1. Abtheilung, p. 230.