II30 PROTEIN METABOLISM [pt. iii 



be done on the basis of a calculation giving the maximum amount of 

 protein which the maternal apparatus could supply to the embryo 

 in the time. 



The data of Table 158, mentioned above, are in some ways rather 

 difficult to interpret. The urea concentration in the amniotic liquid of 

 the cow and sheep does not change much during pregnancy, nor does 

 its percentage in terms of total nitrogen, though here there is a slight 

 decrease. In the allantoic liquid the absolute quantity of urea is 

 very much greater. The decrease in the proportion of urea nitrogen 

 is more marked in the allantoic liquid of the cow than of the sheep. 

 The amount of allantoin present in both liquids is considerable, 

 and increases with length of pregnancy in the cow, but not in 

 the sheep. The amino-acids, including hippuric acid, were abundant, 

 especially towards the middle of pregnancy, in the allantoic liquids 

 of sheep and cow, and they increased more rapidly the younger 

 the foetus. In the cow the amino-acids make up the same proportion 

 of the total nitrogen in the allantoic fluid, but rise in the amniotic, 

 while in the sheep exactly the reverse process takes place. In the 

 allantoic fluid of the sheep there was a considerable increase of 

 hippuric acid as pregnancy advanced, both absolute and propor- 

 tionate, but in the amniotic fluid the tendency was the other way. 



"The picture of foetal metabolism", said Lindsay, "thus shown 

 by the chemical composition of the early allantoic liquid is one of 

 low deaminising power as indicated by the low urea output, the 

 absence of ammonia, and the high proportion of amino-acids." A 

 final remark which might be made before leaving these questions is 

 that the very high allantoin content of the early allantoic urine 

 might be taken to indicate an intense nucleoprotein metabolism (for 

 here only purines would be concerned, unlike the bird), in which 

 case the findings of LeBreton & Schaeffer (p. 11 53) on the chemical 

 nucleoplasmatic ratio would be seen in a new light. 



Traces of proteins are found in the amniotic and allantoic liquids 

 of mammals, but for this see Section 22. 



9-14. Protein Utilisation of Explanted Embryonic Cells 



The metabolism of mammalian embryonic cells in tissue culture 

 has been studied by Holmes & Watchorn, in experiments which 

 bear the same relation to the subject of this section as those of 

 Cohn & Murray to the section on growth. They used kidney and 



