SECT. 9] 



PROTEIN METABOLISM 



embryo, as is the case in the allantoic liquid, but it remains constant 

 throughout. No communication between cloaca and amniotic fluid 

 exists till later — after the 17th day, according to Gasser. Kamei's 

 figures for total non-protein nitrogen basic and non-basic by phospho- 

 tungstic acid remain difficult to interpret, partly owing to their 

 small number, but it is interesting that he found a definite increase 

 in the ammonia and urea con- 

 centration of the amniotic fluid. 

 Such easily soluble and diffusible 

 molecules would be expected to 

 penetrate the walls of the allan- 

 tois, and to turn up elsewhere. 



Targonski has calculated the 

 ratios Nitrogen in embryo/Nitro- 

 gen in amniotic liquid and Nitro- 

 gen in amniotic liquid/Nitrogen 

 in allantoic liquid. Both these are 

 plotted in Fig. 334. 



The first ratio is high and rising, 

 for the denominator is remaining 

 constant and the numerator is 

 steadily increasing, but a maxi- 

 mum occurs on the 12th day, 

 owing to the sudden inrush of 

 protein from the albumen-sac into the amnios through the sero- 

 amniotic connection, and afterwards a fall takes place. The same 

 relations hold inversely for the amniotic and allantoic liquids, for 

 the nitrogen of the latter is at first abundant compared to that of the 

 former, but, after the events of the 12th day, this is no longer the case. 

 Targonski 's curves illustrate the effects of the opening of the sero- 

 amniotic junction. 



9-7. The Origin of Protective Syntheses 



The only other matter which must be considered under the heading 

 of the protein metabolism of the bird's egg is the synthesis of orni- 

 thuric acid by the embryo. It is obviously a matter of great interest 

 to determine the time in ontogenesis at which the embryo becomes 

 able to carry out those chemical protective syntheses which are so 

 interesting a feature of the metabolism of the adult, Takahashi, who 



Days 5 



Fig. 334- 



