SECT, 9] 



PROTEIN METABOLISM 



[063 



were few in number, and the values were extremely small, dis- 

 agreeing with the results of all other workers. They have not there- 

 fore been included in these graphs. Fig. 299 illustrates, of course, 

 the increasing dryness of the embryo. On the same graph are plotted 

 the more recent results of Cahn, who has estimated the arginine 

 contained in the embryo during incubation. These are seen to agree 

 to some extent with those of the Japanese worker, the difference 

 being probably due to the fact that Cahn only gives his dry weights 

 of embryos after removal of fat. These curves, however, do not 

 bring out any important rela- 

 tion. The value of Cahn's work 

 Hes rather in the fact that, just 

 as Plimmer & Lowndes ex- 

 amined the structure of the pro- 

 tein molecule of the whole egg 

 throughout incubation, so Cahn 

 examined that of the embryo. 

 As Table 133 demonstrates, the 

 percentage of nitrogen remains 

 perfectly constant in the dry fat- 

 free and ash-free protein of the 

 embryonic body. A few figures 

 were also given by Cahn show- 

 ing a constant nitrogen-content 

 of the proteins of the yolk and 

 white. This would suggest that, 

 although the proteins of the egg 

 as a whole undergo a rearrange- 

 ment in being converted from egg into embryo proteins, the latter do 

 not themselves change through embryonic hfe, but remain of the same 

 constitution when once they are formed. Such a conclusion is strongly 

 supported by Cahn's figures for the arginine-content of the protein 

 of the embryonic body, for, as Table 133 shows, this also is constant. 

 The very slight variations in the nitrogen-content of the protein 

 molecule were regarded by Cahn either as technical errors due to 

 incomplete removal of fat and ash, or perhaps as being due to the 

 presence in different organs of different proteins varying slightly 

 in this respect, and appearing now in one predominance, now in 

 another, according to the differential growth of the various parts of 



N E II 68 



Days 



Fig. 299. 



