366 THE FLUIDS OF THE EGG. 



The white flakes that are insoluble in the solution of hydro- 

 chlorate of ammonia, and consist for the most part of the mem- 

 branous investments of the yolk-globules, must be washed with 

 distilled water to remove the hydrochlorate, and must then be 

 dried and weighed. 



The sugar must be determined from the alcohol-extract (after 

 it has been freed from fat), either by fermentation, or by Fehling 

 and Trommels method. 



Lactic acid, even when it is actually present, occurs in such 

 small quantity, that we can scarcely hope to be able to determine 

 its amount. 



To determine the quantity of the fat and of the phosphorised 

 matters, we must evaporate the yolk-fluid and dry it at 110, 

 before we extract it with ether. An accurate separation of the 

 different substances soluble in ether is at present impossible ; we 

 shall, however, refer somewhat fully to the methods of separating 

 and quantitatively determining the phosphorised substances of the 

 fats, of the salts of the fatty acids, and of certain lipoids, when we 

 treat of the cerebral and nervous tissues, since the phosphorised 

 matters there fall especially under our notice. We have already 

 (in vol. i., p. 247) indicated the general method of distinguishing 

 the neutral fats from the fatty acids, and of separating them from 

 each other. 



We refrain from offering any remarks on the physiological im- 

 portance of the individual constituents of the yolk, since this subject 

 will be fully noticed in the history of development. It is certainly 

 no rash conclusion to believe that in the egg the animal substrata 

 are deposited in a condition ready for the formation of cells and 

 tissues, and to base our view of the metamorphosis of food into 

 organised matters on the constitution of the egg and the develop- 

 ment of the embryo in it. We should hence be guilty of useless 

 repetition if we were, in this chapter, to discuss the importance of 

 each individual constituent of the egg in relation to the history of 

 development. 



