136 PRINCIPLES OF PHYSIOLOGY 



and wear, is shown by the appearance of 

 these bodies. 



We have only recently had a glimpse into 

 the transformations by which members of 

 this series, ending in uric acid, are formed. 

 This is done by the activity of various enzymes 

 found in the tissues. These have been 

 extracted and their chemical activities studied, 

 .and there can be little doubt that each of these 

 nucleo-zymases takes its share in the work. 

 Some may bring oxygen into play (oxidases), 

 while others effect specific chemical changes. 

 It would seem that in the liver there also 

 may be an enzyme which breaks up uric acid 

 itself. The ultimate result of these remark- 

 able changes is that substances arising from 

 the breaking up of nuclei are gradually trans- 

 formed into uric acid, which (as urates) is 

 -eliminated in a soluble form. Finally, a 

 substance known as hippuric acid is elim- 

 inated in small amounts in the urine. It 

 abounds in the urine of herbivora, arising from 

 substances in the food of such animals, and be- 

 longing to the benzoic acid series. If benzoic 

 acid is given to a man, it unites with glycine 



