io88 PROTEIN METABOLISM [pt. iii 



combustion for the production of energy. According to Sendju, the 

 tryptophane per egg descends from 134 mgm, to 60, a loss of 74 mgm. ; 

 and the tyrosine, beginning at 420 mgm., falls to 260, this being a loss 

 of 160 mgm. 



Nitrogen 

 (mgm.) 

 74 mgm. tryptophane contain ... 9-868 



160 mgm. tyrosine contain ... ... 12-374 



Total ... ... 22-242 



Supposing, then, that these two amino-acids are the only ones, or 

 even the principal ones combusted during development, it would 

 follow that about 50 per cent, was burnt and 50 per cent, was available 

 for the work of haemoglobin formation or other uses. It is certainly 

 strange that tyrosine and tryptophane should be precursors of a 

 purine, but it must be remembered that in the bird uric acid corre- 

 sponds to the urea of mammals, and is produced from the ammonia 

 due to deamination of combusted proteins. 



It is interesting to compare the estimates of protein catabolism 

 obtained by assessing the coagulable protein disappearing with those 

 obtained by assessing the total nitrogen excreted. Sakuragi found 

 that the coagulable protein diminished during development from 

 1846 mgm. of nitrogen per cent, to 1698 (see Table 135). 148 mgm. 

 are therefore lost per cent, of the contents of an average egg, which 

 amounts to 67 mgm. per individual egg. Yet none of the investigators 

 who have estimated the excreted nitrogen have recovered a corre- 

 sponding amount: 



Milligrams 

 nitrogen 

 per embryo 

 Coagulable nitrogen disappearing ... Sakuragi 67 



Waste products appearing (in nitrogen) Fiske & Boyden 36 



Fridericia 23 



Needham 1 2 



Targonski 8 



Kamei i 



There is thus some reason for believing, whichever of these sets of 

 data turns out to be nearest the truth, that the protein combusted 

 is probably not more than a third of the coagulable protein dis- 

 appearing. The fate of the rest still remains doubtful. Whether the 

 ovomucoid takes part in combustion is a question at present unanswer- 

 able; all that can be said is that there is no preferential absorption of 

 ovomucoid as against ovoalbumen from the white. 



