I2i6 METABOLISM OF LIPOIDS, STEROLS, [pt. iii 



in total choline, and made a few estimations by means of his own 

 method to see whether this was so. Choline, by reacting with urea, 

 might be the precursor of guanidine, and the formulae of the three 

 substances lent a certain colour to the suggestion : 



CH,.CH.(OH) 



I + 



OH-N-(CH3)3 



CO-NH, 



i 



CH^.CHaCOH) 



N-CH3 

 I 

 C=NH 



I 

 NH2 



NH2 



1 

 C=NH 



NH2 



Sharpe's results are seen in Fig. 386, from which it is clear that the 

 total choline content of the hen's egg diminishes from 400 mgm. per 

 cent, on the ist day of development to 220 mgm. per cent, at the 2 ist. 

 This decrease, argued Sharpe, 

 meant a loss of total choline of ''°°'' 

 130 mgm.; and Burns found a 

 rise in the amount of total 

 guanidine per egg of from 80 

 to 260 mgm., i.e. an increase of 

 180 mgm. Although, on the 

 basis of the transformation 

 pictured above, igm. of chohne 

 should yield 2 gm. of guani- 

 dine, yet the correspondence 

 was sufficient to justify Sharpe's 

 remark that in all probability 

 choline was here the precursor 

 of guanidine. 



The shape of Sharpe's de- 

 scending total choline curve 

 cannot be emphasised, as it is 

 constructed from so few points, 



Choline 



• Total choline (Sharpe) 

 O Free '> (Sharpe) 

 O Free (OKada) 



Days-*-5 



Fig. 386. 



but it may be remarked that it begins to fall much earlier than the 

 lipoid phosphorus, either in the experiments of Plimmer & Scott or in 

 those of Masai & Fukutomi. Is there here a possibility that the choline 

 portion of the lecithin molecule may be detached before the phos- 

 phoric acid, so that the latter would remain ether-soluble? 



The subject of choline in the egg was carried a stage further by 

 Okada, who estimated the free choline only during development. 



