PHYSIOLOGICAL OXIDATIONS. 869 



which in some way activate the oxygen. Enzymes of this char- 

 acter have been found ; they are designated in general as oxidases or 

 as oxidases and peroxidases, the former term referring to those 

 enzymes that effect oxidations in the presence of oxygen, while 

 the latter is applied to certain enzymes supposed to act only in the 

 presence of peroxids. The most conspicuous of the oxidases found 

 in the animal body is the one capable of oxidizing aldehydes (sal- 

 icylic or benzoic aldehyde) v into the corresponding acids, and hence 

 designated specifically as aldehydase. This enzyme has been 

 extracted especially from the liver, lung, and spleen. An oxidase 

 known as tijrosinase, first found in plant juice, has also been isolated 

 from animal tissues. It oxidizes tyrosin with the formation of 

 homogentisinic acid. So also oxidases are described capable of 

 oxidizing xanthin to hypoxanthin or to uric acid.* The process 

 of destructive metabolism of sugar in the body, glycolysis, may 

 be effected, it will be remembered, by the tissue juices squeezed 

 from the organs, or even by extracts of the tissues of muscle, liver, 

 etc. It may well be believed, therefore, that the oxidation of 

 this most important food material is accomplished by the action 

 of one or more enzymes. Such facts as these lend great probability 

 to the belief that eventually it will be shown that the oxidations in 

 the body are effected by the influence of oxidases or peroxidases 

 acting singly, or in combination, or in sequence with the hydrolytic 

 enzymes. 



While it is perfectly obvious that more facts are needed before 

 positive statements are warranted regarding the chemistry of the 

 oxidations in the body, the view entertained regarding the general 

 process in the body is that the material protein, fat, or carbohy- 

 drate is first split into simpler products by the action of a hy- 

 drolytic enzyme, or a series of hydrolytic enzymes, formed in the 

 cells. These reactions are not attended by any marked formation 

 of heat. The split products thus produced are then acted upon by 

 oxidases with the formation of certain intermediate products and 

 eventually of carbon dioxid, water, etc., and the liberation of heat. 

 A specific instance of this serial action has been given in reference 

 to the oxidation of sugar (p. 824) : According to Stoklasa, the sugar 

 is first split into lactic acid, and this into carbon dioxid and alcohol ; 

 the alcohol then by the action of a series of oxidases is oxidized to 

 acetic acid, formic acid, carbon dioxid, and water. From our 

 present standpoint, the production of heat in the body, it is impor- 

 tant also to bear in mind the general view advocated by Speck and 

 others namely, that the chemical changes or metabolism of the 

 body may be divided into two general classes: first, the heat-produc- 



* For further details see Oppenheimer, "Die Fermente und ihre Wir- 

 kungen," second edition, 1903. 



