1220 METABOLISM OF LIPOIDS, STEROLS, [pt. m 



doubly refracting property, and upon cooling they again become 

 anisotropic. Cholesterol esters are remarkably resistant to autolytic 

 change, and this was found by Hanes to be a property of the 

 droplets in the liver also. They retained their anisotropism for 

 10 days when autolysed at 37°, and at last changed to long needle- 

 like crystals, which showed the reversible anisotropism on heating. 

 Hanes concluded that during development esters of cholesterol 

 appeared in the chick's liver and the lipoids disappeared. He cor- 

 related these changes with ossification and the arrival of calcium for 

 deposition in the bones as calcium phosphate, drawing attention to 

 the fact that if, as Plimmer & Scott had demonstrated, the lecithin of 

 the yolk was broken down to provide the inorganic phosphorus, 

 something must happen to the fatty acids of the lipoid molecule. 

 The lecithin, said Hanes, must be absorbed gradually by the vitel- 

 line vessels, and carried to the liver, together with neutral fat, 

 cholesterol, vitelHn, etc. The lecithins then breaking down to yield 

 glycerophosphoric acid, the latter or some closely related substrate 

 for Robison's bone enzyme travels to the bones, and the phosphorus 

 being liberated, is deposited as calcium phosphate. Meanwhile, the 

 two fatty acid molecules left by the decomposition of the lecithin 

 would esterify some or all of the cholesterol which had also been 

 absorbed by the vitelline vessels. The only weak point about this 

 scheme was that, if cholesterol was going to be esterified in the liver, 

 why should it ever have been free, in view of the great amounts of 

 fatty acids everywhere in the egg? However, no doubt Hanes had in 

 mind some special activation of the cholesterol molecule which could 

 take place only in the liver. He found that the cholesterol ester 

 droplets disappeared from the liver after hatching, though a fortnight 

 later they were still abundant, and they were not present in the liver 

 of the adult hen. 



Hanes also examined the fat droplets of the yolk-sac. Here he 

 found a good many with the property of double refraction, but 

 they had other characteristics which sharply distinguished them 

 from the anisotropic droplets of the liver. Thus they did not lose the 

 property when heated to 90°, they stained with neutral red, and 

 exhibited myelin forms upon the addition of water. Nile blue sul- 

 phate stained them blue. They behaved in every way, in fact, like 

 kephalin or sphingomyelin. However, at the time of hatching, the 

 yolk-sac, now within the body of the chick, showed fatty droplets 



