1238 PHYSIOLOGY 



time in the body, though there is some reason to assume its formation 

 in the process of carbon assimilation in the green leaf. If we adopt 

 the views of Bach and Chodat we must assume that every animal cell 

 contains organic peroxides as well as peroxidases, or else that it can 

 under physiological conditions form these substances. Since there is 

 also evidence of the presence of reducing substances in the cells, we 

 may conveniently assume, with Ehrlich, that distinct side-chains of the 

 protoplasmic molecule have specific affinities for oxygen. When all 

 these affinities are saturated, these side-chains will act as peroxides, 

 parting with their oxygen with extreme ease, whereas when the greater 

 number are unsaturated, the resultant effect will be that of a reducing 

 agent. The same protoplasmic molecule may therefore, according 

 to its state of saturation with oxygen, act either as an oxidising or 

 reducing agent, and can effect, probably through the intermediation of 

 specifically adapted oxidases, the oxidation of the various food-stuffs 

 stored up as the paraplasm of the cell. Since the oxidative processes 

 are determined, not by the presence of oxygen, but by the functional 

 activities of the tissue, we must assume that the peroxidases are not 

 preformed in the cell, but exist as precursors, zymogens, from which 

 they can be set free in accordance with the necessities of the 

 cell. 



It is probable that many of the food-stuffs or other proximate 

 constituents are not directly accessible to oxidation, and that the 

 first step in their utilisation is a process of cleavage or hydrolysis, which 

 itself involves the presence of specific ferments. Thus, so far as we 

 can tell, the amino-acids undergo deamination before oxidation. They 

 can thus be stored up in the cell either free or in the form of protein 

 and present no point of attack to oxygen until the process of hydrolysis 

 and deamination has taken place. This course of events is certainly 

 true for some of the members of the purine group. Under the action of 

 animal tissues, guanine, as has been shown by Schittenhelm and 

 Jones, is converted to uric acid. This conversion involves (1) the 

 deamination of guanine and its oxidation to xanthine, and (2) the 

 oxidation of xanthine to uric acid. In the same way adenine is 

 converted into hypoxanthine, and this, by a series of oxidations, 

 through xanthine into uric acid. The changes involved in the con- 

 version of guanine are shown us follows : 



HN CO HN CO 



NH..C C NH + H.HO = = NH, 4- CO C NH 



J^CH \CH 



N c N' HN C--N' 



