356 THE FLUIDS OF THE EGG. 



of ammonia and similar substances would extract a fat containing 

 phosphorus. (Even the milk-globules are not entirely impermeable, 

 and are distorted by ether, although less fat is abstracted from 

 them than from the yolk-globules when acted upon under similar 

 relations.) 



The pigments of the yolk form, together with the non- 

 phosphorised and phosphorised fat, a principal part of the contents 

 of these cell-formations, in which I have been unable to trace a 

 nucleus or anything analogous to such a structure ; at all events, 

 when the yolk-cells have been treated with hydrochlorate of 

 ammonia, they are invariably found to acquire a more intensely 

 yellow colour than the fat-globules which have no investing mem- 

 branes. They certainly are generally much larger than the latter, 

 and must, on this account, also appear more highly coloured : 

 some of the fat-globules are, iiowever, wholly devoid of colour. 

 According to these observations, the yolk-globules must occupy 

 an intermediate place between the milk-globules and the blood- 

 corpuscles; approximating most nearly to the former in their 

 abundance of fat, and to the latter, in the quantity of phosphoric 

 acid which they contain, and in their ferruginous pigment. 



Since we are as yet unable distinctly to define the differences 

 existing between the chemical constituents of the yolk-globules and 

 those of the intercellular fluid, we will merely take a general view 

 of the respective elements of the yolk. 



We have already spoken (in vol. i., p. 364) of vitellin, the 

 most important albuminous constituent of the yolk. We did not 

 then venture to depart from the ordinary view which regards the 

 vitellin as a special kind of protein-body ; but yet, however averse 

 we are from making any assertion in reference to the supposed 

 identity of similar bodies, we cannot withhold our opinion that the 

 so-called vitellin is nothing but a mixture of albumen and casein. 

 The amorphous, dark granules of the yolk consist of pure casein 

 free from alkali, but which is as rich in phosphate of lime as 

 ordinary casein. The true intercellular fluid of the yolk contains 

 no casein, and simply dissolved albumen which is poor in alkali. 

 It must be observed in the first place that it would be incorrect to 

 maintain that the vitellin is coagulated by ether ; for on repeating 

 the experiment (as we have often done) of shaking the fresh yolk 

 with ether and water, we find that under the fatty and yellow- 

 coloured stratum of ether, there is formed a white and somewhat 

 viscid mass, which has erroneously been regarded as coagulated 

 vitellin. When these flakes are collected on . the filter, after 



