SECT. 9] PROTEIN METABOLISM 1085 



correspondence is striking, but of course the greater part of the uric 

 acid formed in normal life originates from ammonium lactate 

 rather than from xanthine. Morgan's results agree with those of 

 Przylecki & Rogalski, and were obtained by a different method 

 (methylene blue). At the 7th day the yolk-sac and blastoderm gave 

 a positive result, but yolk and white were negative. Xanthine oxidase 

 was present in the kidney on the 15th day and rose extraordinarily 

 sharply in the liver at the time of hatching. 



Table 139. Przylecki & Rogalski's figures. 



Przylecki & Rogalski not only found that before the time at which 

 uric acid appears in the excreta the embryo has no power of forming 

 uric acid, but also that it destroys it if provided. The right-hand part 

 of Table 139 makes this clear, for in the early stages of development a 

 heated emulsion of embryonic tissues with added uric acid always 

 contains more of this substance at the end of the experiment than a 

 parallel flask which has not been heated. Between the 7th and loth 

 days, however, a change takes place, and, after that time, the presence 

 of uricase can no longer be demonstrated. It is plain that the facts 

 revealed by the Polish workers fit in well with those described above. 

 But the fact that the uricase does not disappear until the i oth day may 

 mean that before that time uric acid is formed from substances such 

 as ammonium lactate and equally rapidly broken down to allantoin. 



