i2o8 METABOLISM OF LIPOIDS, STEROLS, [pt. iii 



to be very variable. Riddle is certainly right in saying that after 

 the 1 2th day the phosphatides are utiHsed more rapidly than the 

 neutral fats, and the neutral fats more rapidly than the proteins. 

 Riddle also found that yolk being absorbed from the foHicle which 

 secreted it in the ovary shows a more rapid utilisation of the phos- 

 phatides than of the neutral fats, but this may hardly be more than 

 a coincidence. Iljin in his turn estimated the lecithin and residual 

 protein phosphorus in the yolk only, before and after development, 

 obtaining the following figures : 



Phosphorus in milU- 

 grams per egg 



Protein Lecithin 

 phosphorus phosphorus 



Yolk at beginning ... ... 150 65 



" Spare yolk " at end 32 17 



Absorbed by embryo... ... 118 38 



Iljin's protein phosphorus figures do not correspond very well with 

 those of Masai & Fukutomi, or of Plimmer & Scott, but his ether- 

 soluble phosphorus ones do. Something must certainly have gone 

 wrong with Iljin's vitellin analyses. 



It was left for Cahn to make a proper series of lipoid phosphorus 

 determinations on the embryo during its development. The results 

 of his work were very interesting. Whether his absolute quantities 

 were in good agreement with the figures of Plimmer & Scott cannot 

 be stated, as the latter workers unfortunately omitted to give any 

 absolute figures, confining their statements to percentages of the total 

 phosphorus. Cahn found, as might be expected, that the total 

 amount of lecithin phosphorus in the embryo rose with the growth 

 of the body, but regularly, that is to say, not remaining very low 

 till the 15th day and then suddenly rising rapidly, like the neutral 

 fat. This difference in shape of the curves can be seen from Fig. 

 379, which is taken from his paper. When the lipoid phosphorus 

 was related to wet and dry weight, however, more interesting curves 

 appeared, as shown in Fig. 380. In per cent, of the moist tissue one 

 finds a regular augmentation until the 15th day, after which a 

 plateau supervenes up to hatching, though afterwards the curve 

 again rises, and a chick 2 days after hatching contains as much as 

 660 mgm. per cent, wet weight. Then, as might be anticipated from 

 a plateau on a wet weight curve, the dry weight curve rises to a 

 peak, and thereafter falls away. This peak occurs, in the case of the 



