970 NUTRITION AND HEAT REGULATION. 



strated by the fact of autolysis,— that is, if living tissue is taken 

 from the body, with precautions against contamination by bac- 

 teria, and while under perfect aseptic conditions is kept warm 

 and moist, it will digest itself. The protein is split up into the same 

 simple hydrolytic products as are obtained by boiling it with 

 acids. It has been shown that this digestion is due to enzymes^ — 

 autolytic enzymes — formed within the living tissue. There is no 

 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 Hberating 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, which take up oxygen to form 

 compounds of the nature of peroxides, and which they designate 

 as oxygenases. These oxygenases or organic peroxides when acted 

 upon by the peroxidase give up oxygen in active form, which then 

 effects the oxidations. If potato peelings, for example, are extracted 

 with water, the extract itself is not able to cause oxidation of easily 

 oxidizable substances such as pyrogallol. But if this extract is 

 mixed with the residue, or with a solution of hydrogen peroxide, 

 active oxidations can be produced. Using the above terminology 

 the aqueous extract of the potato peelings contains the enzyme, 

 peroxidase. This enzyme in the presence of hydrogen peroxide, 

 or a similarly constituted organic peroxide, such as the oxygenase 

 assumed to exist in the residue in the above experiment, sets free 

 atomic oxygen and thus brings about physiological oxidations. 

 This view can be represented schematicall}^ by the following 

 equations, in which P represents the peroxidase; B. the material 

 which undergoes oxidation, and A, the material in the tissues 

 which takes up oxygen to form a peroxide: 



A + O2 = AO2 (organic peroxide or oxygenase) 



AOo + P + B = BO + AO + P 



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



