[082 



PROTEIN METABOLISM 



[PT. Ill 



urea and uric acid, expressed as milligrams per cent, of dry weight 

 of embryo, have all been placed on the same graph. Here the com- 

 parison becomes very interesting, for, just as urea was previously 

 found to rise to its maximum 

 2 days before uric acid, so now 

 ammonia is at its maximum (or, 

 more correctly, higher than at 

 any other time so far deter- 

 mined) 5 days before urea. 

 These time-relations between 

 ammonia, urea and uric acid, 

 during ontogenesis, are sum- 

 marised in Table 138. The 

 nitrogenous excretory product 

 which has the smallest mole- 

 cular weight and the highest 

 nitrogen percentage reaches its maximum earliest in ontogenesis ; that 

 which has the largest molecular weight and the smallest nitrogen 

 percentage reaches its maximum latest. The simplest product of 

 deamination is the first to appear 1, the most complicated is the last. 

 Yet the latter accounts for 91-5 per cent, of the total nitrogen excreted 

 by an embryo throughout its development, and the former for only 

 I per cent., while the intermediate compound, urea, accounts for 

 7*6 per cent. 



Table 138. 



Time of Absolute % of 



peak of maxi- milligrams the total 

 mum pro- nitrogen ex- nitrogen ex- 



Days 



Fig- 323- 



Total 



11-124 



A very interesting way of expressing the relationships here involved 

 is shown in Fig. 324, where the milligrams of ammonia, urea, and 

 uric acid nitrogen excreted per embryo per day are plotted against 

 the time of development on semilog, paper. These curves correspond 



^ The ammonia may of course be derived from some substance other than protein, 

 such as adenylic acid. 



