THE CHOLESTERINS. 79 



remarkable difference, as compared with the fats, in their behavior 

 toward water. Of this they apparently take up one-quarter of their 

 own weight, and on stirring give rise to a pasty, frothy mass. 



From their ethereal compounds cholesterin can readily be separated 

 by treating with diacetic-ethyl ether, which dissolves the cholesterin 

 and leaves the ethers behind. 



Of the functions of the cholesterins nothing is as yet known. It 

 is interesting to note that they inhibit the activating properties of 

 lecithin upon hsemolytic substances. If washed red corpuscles are 

 thus treated with cobra poison no haemolysis occurs, while this 

 takes place if a trace of lecithin is added. Should, however, a small 

 amount of a methyl-alcoholic solution of cholesterin be simul- 

 taneously added no haBmolysis occurs. 



The isolation of the cholesterins will be described in a future 

 chapter. 



After having thus studied the three great classes of food-stuffs 

 which plants are capable of elaborating from water, carbon dioxide, 

 and certain mineral salts, and which are also represented in the 

 animal body, we shall now proceed to a survey of the natural 

 decomposition-products of these substances which are formed during 

 their passage through the animal body, and which are of more or less 

 interest as indicating the manner in which these decompositions 

 are effected. Like the substances that have already been con- 

 sidered, these products will be taken up only in a general way at 

 first ; while their special study, as well as their methods of isolation 

 and quantitative estimation, will be considered in succeeding chapters, 

 in connection with the chemical study of those tissues in which they 

 are principally encountered. At this place general facts only are to 

 be impressed upon the mind of the student, so that he w r ill be pre- 

 pared to understand the composite chemical structure of the various 

 tissues and organs of the body, as will be described later. 



