1078 PROTEIN METABOLISM [pt. iii 



The only amino-acids which failed to give an increase were cystein 

 and serine: ammonium carbamate was effective but ammonium 

 carbonate was not. Per mg. of injected substance the increase in urea 

 was from o-og to 0-40 mgm. 



In Fig, 314 the urea content is seen related to dry weight of embryo. 

 Here we have a peak at the gth day instead of an inflection; the urea 

 excretion fails to keep pace with the increase in dry matter, and drops 

 to a possibly constant level of 30 mgm. per cent. As before, it is 

 the gth day which is prominent. 



Would the excretion of uric acid follow a similar course to a peak 

 about half-way through development? Uric acid had been first 

 reognised in the allantoic Hquid of the chick embryo in 18 ig when 

 L. L. Jacobson of Copenhagen ^ 

 described it as at first clear and ool-l 

 pale yellow, containing uric acid 

 in solution, but later depositing 

 urates in masses, which, he 

 thought, also contained protein. 

 "Diese Fliissigkeit", said Jacob- 

 son," die in der ersten Tagen der 

 Ausbriitung hell ist, wird nach- 

 her mehr zahe und schleimig, 

 weisse Anhaufungen schwim- p- 



men in derselben ; diese vermeh- 



ren sich, worauf die wasserigten Telle verschwinden, so dass man in 

 den letzten Tagen der Ausbriitung eine bedeutende Menge diese 

 Anhaufungen in einem dicken und zahen Schleim gehallt, in der 

 Allantois findet." Jacobson identified the uric acid by the murexide 

 test. Jacobson's discovery was confirmed by Prevost & Le Royer in 

 1825, by Sacc in 1847 and by Stas in 1850. 



Two methods were used in estimating the uric acid in order 

 to allow for the fact that, owing to the growth of the embryo, the 

 whole scale of uric acid production is outside the best range of 

 one method. As a micromethod for the early stages the colorimetric 

 technique of Benedict & Franke was used, and for the later period the 

 ammonium chloride precipitation method of Hopkins. The gradual 

 increase in milligrams per embryo of uric acid made a very regular 

 curve. In Fig. 315 is shown the milligrams per cent, wet weight, and 

 here the significant plateau appears. In the first 7 days of develop- 



