CONSTITUENTS OF THE YOLK. 359 



tablets of this substance form, for the most part, not rhombs, 

 but compressed parallelepipeds, whose angles are different from 

 those of cholesterin ; while the cholesterin-tablets generally present 

 re-entrant angles, in these elongated tablets the acute angles are 

 obliquely truncated. These crystals separate on gradual evapo- 

 ration from the ethereo-alcoholic solution in feathery groups. 

 They fuse more readily than those of cholesterin. The circum- 

 stance of their appearing to dissolve readily in cold alcohol, 

 when they are still mixed with yolk-fat, would afford no proof of 

 their non- identity with cholesterin, since it is a well-known pro- 

 perty of the latter to dissolve freely in cold alcohol, in the presence 

 of oily fats and soaps. 



I am still doubtful whether margaric and oleic acids are con- 

 tained in fresh yolk-fat ; they may be unquestionably detected in 

 it after exposure for some time to the air. Gobley considers that 

 both these acids, together with glycero-phosphoric acid, are formed 

 by the decomposition of an indifferent matter to which he has 

 recently applied the term lecithin. 



This lecithin has not yet been obtained by Gobley in an isolated 

 and perfectly pure condition : it separates from the ethereal extract 

 of the dry yolk, on the evaporation of the ether, in the form of a 

 matiere visqueuse, to whose investigation Gobley attaches a very 

 great value, although most other fats, when similarly treated, 

 yield a physically similar, although chemically very different 

 matiere visqueuse. I have been unable to discover any peculiarity 

 in it ; for all oleaginous fats yield, under favourable conditions, a 

 similar mass, which consists essentially of margarin with a little 

 olein. It is, however, true that the substance which contains the 

 phosphoric acid occurs in that portion of the fat which first 

 separates from the ethfereal solution during evaporation. This 

 substance, mixed with olein and margarin, and likewise with 

 another matter, to which Gobley has applied the term cerebrin, 

 is, according to his later researches, a perfectly neutral body, 

 which, when treated with mineral acids or alkalies, both in its 

 aqueous and alcoholic solutions, and even when the access of 

 atmospheric oxygen is excluded, yields glycero-phosphoric acid, 

 together with oleic and margaric acids. If in this process an 

 organic be substituted for a mineral acid, the same action takes 

 place, but less readily. Gobley found 8-426g- of lecithin in the 

 yolk of egg. 



Cerebrin is obtained by treating the matiere visqueuse with 

 alcohol and an acid, and allowing it to stand undisturbed : it then 



