962 NUTRITION AND HEAT REGULATION. 



doubt, therefore, of the existence of intracellular enzymes, and that 

 these substances play a conspicuous part in the metabolism of food 

 material. The lipase, the diastase, and the autolytic enzymes 

 (proteases) just referred to all belong to the group that cause 

 hydrolytic cleavages that is, they induce splitting or decompo- 

 sition of the material by a reaction with water. The supposition 

 has naturally been made that probably the oxidations of the body 

 are effected also by enzymes which in some way activate the 

 oxygen. Enzymes of this character 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. Bach 

 and Chodat* have simplified this conception by the hypothesis 

 that all the oxidizing enzymes of the tissues are peroxidases, that is 

 to say, substances which have the power of liberating active oxygen 

 from hydrogen peroxide or similarly constituted organic peroxides. 

 They assume that there are present in the tissues certain organic 

 substances produced by the cells, of an enzyme nature, and 

 designated as oxygenases, which have the property of com- 

 bining with the oxygen furnished by the blood to form organic 

 peroxides, and that these peroxides, under the influence of per- 

 oxidase, give up their oxygen in atomic or active form, which then 

 effects the characteristic physiological oxidations. This view 

 can be presented schematically by the following equations, in which 

 A represents the oxygenase, P the peroxidase, and B the tissue 

 material which undergoes oxidation: 



A + 2 = A0 2 (organic peroxide) 



A0 2 + P + B = BO + AO + P. 



According to this view the oxidations in the body are primarily 

 due to the formation of the organic peroxides, and the mode of 

 action of these peroxides would be represented outside the body by 

 the reactions of hydrogen peroxide (H 2 O 2 ). As a matter of fact 

 it has been found that many of the characteristic oxidations that 

 occur in the body, such as the oxidation of the fatty acids at the 

 /9-carbon atom in the chain, the oxidation of glucose to glycuronic 

 acid, etc., may be imitated outside the body by oxidation with 

 hydrogen peroxide, but not by other oxidizing agents, f This 

 collateral evidence gives important support to the theory. On 

 the other hand, oxidases or peroxidases have been discovered in 

 the blood, milk, and in various of the tissues of the body, such as 

 the lymphocytes, sperm cells, etc.J They can be tested for by a 



* Bach, "Handbuch d. Biochemie, Erganzungsband," 1913. 

 t Consult Dakin, "Oxidations and Reductions in the Animal Body," 1912. 

 I For discussion and literature consult Kastle, "The Oxidases," Bulletin 

 No. 59, 1910, Hygienic Laboratory, Washington, D. C.; also Bach, loc. cit. 



