1096 



PROTEIN METABOLISM 



[PT. Ill 



150 



13 140 



vertical lines-fiske 8c 



Boyden'a limits 

 - O Targonski's points for 

 uric acid nitrogen 

 • Targonski total nitrogen 

 A Kamel total nitrogen 



of creatine and amino-acid nitrogen, which latter in the early stages 

 accounts for as much as 40 per cent, of the total nitrogen ^ 



Although the absolute amounts of the excreted nitrogenous waste 

 products are the values which it is most important to know, the 

 concentration of them in the allantoic Hquid is of some interest. 

 Here the most complete series of estimations is that of Fiske & Boyden, 

 plotted in Fig. 332. The vertical lines show the range of variation 

 in their figures, and the white and black circles refer to Targonski's 

 points. At the beginning the 

 composition of the allantoic 

 fluid, as regards its nitrogenous 

 crystalloids, quite closely re- 

 sembles the concentrations 



found in the plasma of adults. 



. y 120 



Fiske & Boyden regard it as a o 



mere filtrate till the end of the | 

 5th day. After that time the con- ^ 

 centration of uric acid steadily ^ 

 rises, at least until the end of the ^ 

 13th day. The concentration of c 

 the residual nitrogen, on the '^ 

 contrary, falls markedly until | 

 the gth or loth day, as would § 

 be the case if the formation of o 

 any quantity of urea and am- 

 monia was suspended when the 

 formation of uric acid began, 

 and afterwards rises again, as 

 would be the case if other substances, such as amino-acids or 

 creatinine, began to enter into it. About the end of the 2nd week 

 of incubation the allantoic fluid acquires more urates than it can 

 dissolve— thus it is sometimes milky as early as the 7th day, and 

 sometimes clear as late as the 13th. Besides this turbidity, the 

 urates are deposited as slimy stringy masses, which, though at first 

 soft, eventually become hard and almost brittle. Fiske & Boyden 

 observed that as much as 87 per cent, of the total uric acid present 

 may be contained in these deposits. Boyden has drawn attention 

 to the blister-shaped vesicles which often, if not always, occur within 

 the inner wall of the chick's allantois in the region of the amnio- 



1 See the foot-note on p. 977 and Table 163. 



Days 



Fig. 332- 



