SECT. 9] PROTEIN METABOLISM 1123 



the embryo, the total volume of liquid, or some other detail 

 essential for making any calculation or comparison. A tabular 

 presentment of their figures is given by Prochovnik; the values 

 vary from 27 to 420 mgm. per cent. Nevertheless, in certain 

 instances, it is possible to calculate the amount of urea present 

 per 100 gm. of formed embryo, thus: 



Table 156. 



Sheep 



Cow 



Cat 



It is evident that in all cases the amount of urea produced by 100 gm. 

 of foetus and excreted into the allantoic liquid declines as development 

 proceeds. 



It is interesting that Schondorff in 1899 concluded that the con- 

 centration of urea in the amniotic liquid in man was of much the 

 same order as that in the blood and milk — another hint, perhaps, that 

 such a diffusible molecule cannot be concentrated in a limited 

 space, and so of interest in view of the discussion on p. 1 133. It is 

 evident, of course, that the urea in the amniotic liquid might come 

 from the maternal circulation, but, on the other hand, it is certain 

 that the foetus contributes largely to it, for as early as 1843 Prout 

 found urea and uric acid in the fluid from the ureters of a human 

 8-month embryo and later Virchow; Schwarz; Dohrn, and Panzer 

 all found urea and uric acid in the embryonic bladder. Then Wohler 

 found in 1846 a small uric acid calculus in a stillborn foetus, and 

 uric acid infarcts in the kidneys of human embryos were reported by 

 Hoogeweg; Virchow, and Salomonsen. 



Gusserov in 1872 began a new line of investigation. His experi- 

 ments proved that not only excretion of urine into the amniotic 



