SECT. 6] 



GENERAL METABOLISM 



925 



lapses of time, and, finally, the difference between the two, in other 

 words, the milligrams of fat present in the non-embryonic part of 

 the egg in the intermediate periods. In Col. 8 is found the miUigrams 

 absorbed each day expressed in percentage of what at that day 

 remains to be absorbed. This is the column representing the amount 

 of fat handed over to the embryo out of 100 mgm. of external fat 

 between each two days. Cols. 9 and 10 express the same value only 

 related to 100 gm. of embryo, wet and dry. When Cols. 9 and 10 

 are plotted upon a graph, very 

 interesting curves are seen. 

 Fig. 251 shows that the ab- 

 sorption curve for fat rises and 

 falls in much the same way as 

 that for protein. It possesses a 

 peak about the loth day, and 

 another rapid rise about the 

 i8th^. What is at once notice- 

 able is that these periods 

 do not synchronise with the 

 period of pre-eminent fat com- 

 bustion. The 15th day is the 

 centre of the period at which 

 the respiratory quotient is 0-73 (Bohr & Hasselbalch), yet at that very 

 day there is a distinct trough in the curve of fat absorption. We see, 

 then, that, as with protein, so with fat, there is no chronological 

 relation between combustion and absorption. 



Secondly, it may be pointed out that the observation of Gage & 

 Gage, that Sudan III eggs do n'ot give coloured embryos till the 

 middle of development, fits in well with the absorption curve now 

 found. Up to the 8th day absorption of fat goes on very slowly. 



The third point of interest is this. Although the curve for fat rises 

 and falls in much the same way as that for protein, it does it at quite 

 different times ; it does not resonate with it ; protein peaks correspond 

 to fat troughs and vice versa. This is well seen in Fig. 252, which shows 

 the averages between wet and dry weights in each case. It should 



^ The only other absorption-curve which has been studied is that for lead (Bishop). 

 It shows a marked trough at the 15th day, corresponding with Fig. 251. This is 

 interesting because Bishop concluded on quite other grounds that lead is present in yolk 

 almost wholly in combination with lecithin (e.g. 99 % of it is ether-soluble) . Lead 

 lecithin and lead oleate can, indeed, be isolated from yolk. 



