io64 PROTEIN METABOLISM [pt. iii 



the body. The arginine referred to in Fig. 299 and Table 133 was 

 exclusively that resulting from the hydrolysis of the proteins, and was 

 estimated by decomposition with arginase and estimation of the urea 

 so formed by the xanthydrol reagent. Cahn also investigated the 

 amount of total arginine in the whole egg during incubation and 

 found no change whatever. This was contrary to Sendju's findings, but 

 agreed more or less with those of Plimmer & Lowndes. Cahn stated 

 that the arginine-content of the proteins of the non-embryonic parts 

 of the egg remained approximately constant (7 per cent.) throughout 

 incubation. These observations certainly make it appear as if neither 

 the egg proteins nor the embryo proteins change intrinsically during 

 development, apart from the breakdown which has to go on in order 

 that the one may be transformed into the other. 



Table 133. 



Arginine % of 

 water-, fat- and 



ash-free em- 

 bryonic proteins 



•16 



Ik 



7-2 



7-1 



7-IO 



Another amino-acid which has been closely studied is cystine. 

 Sendju's experiments, in which all the cystine, both free and com- 

 bined in proteins, was estimated by the Okuda iodimetric method, 

 did not give very illuminating results, though the passage of this 

 amino-acid from the yolk and the white into the embryo is easily 

 seen in Fig. 300. The diminution in total cystine stands in contra- 

 diction with the findings of Plimmer & Lowndes. Expressed in 

 milligrams per cent, wet weight, the cystine as measured by Sendju 

 can be observed in Fig. 299. The analogous curve constructed from 

 Cahn's data is shown on the same graph, but his more important 

 finding was that the amount of cystine in the protein molecule was not 

 constant. The figures in Table 134 illustrate this. For the middle part 



