SECT. 6] 



OF THE EMBRYO 



923 



% 



days, comes just in the trough of protein absorption. The two pro- 

 cesses seem to be entirely distinct, as is clearly shown by the broken 

 line representing protein combustion in Fig. 250. The 15th day peak 

 corresponds remarkably well with the fact that about that time the 

 vascular bag or "avian placenta" of Duval is formed by the fusing 

 ends of the allantois. The accelerated absorption of protein from the 

 egg-white shows itself as clearly in Fig. 250 as does the accelerated 

 diminution of bulk of egg-white in Fig. 199. It is also interesting to 

 note the effect of relating absorption to dry and to wet weight. The 

 increasing dryness of the em- 

 bryo has the result of minimis- 

 ing both the trough at the 7th 

 day and the peak at the 15th. 



The process by which a 

 knowledge of the absorption 

 curve for fat was derived dif- 

 fered in no way from what has 

 already been seen in the case 

 of protein, except that it was 

 less complex, fewer correc- 

 tions to the basic values being 

 necessary. Unfortunately, the weight 

 resulting curves cannot claim 

 the same degree of accuracy as may be accorded to those for protein, 

 for an at present unresolved discrepancy exists in the literature between 

 the measurements of egg-fat. As will be seen in Section 8-4, from 

 the 7th to the 14th day the fat lost, as determined by the averaged 

 chemical analyses, is considerably in excess of that lost as determined 

 from the carbon dioxide output, even assuming that all the carbon 

 dioxide was derived from fat, which is not true. But it is probable 

 that this error, which is certainly real and of some theoretical im- 

 portance, does not upset the general shape of absorption curves 

 calculated disregarding it. When its nature is cleared up, the fat 

 absorption curve may have to be revised. 



In Table 112, the various stages of the calculation are set out. 

 Columns i to 4 need no comment. In Cols. 5, 6 and 7 are shown, first, 

 the fat in milhgrams per whole egg, calculated for the interdiurnal 

 periods from the experimental data of Eaves; Idzumi; Murray; and 

 Sakuragi ; secondly, the fat in the embryo calculated for the same 



Dry Web 



5 10 15 



Absorption curves 



Fig. 250. 



