156 Canadian Record of Science. 



•under 4 per cent. The milk of the ass only contains a little 

 over 1 per cent, of fat. That of the porpoise contains 45 ■ 8 

 per cent. fat. 



The casein and albumen belong to the class of organic 

 bodies called albuminoids. They differ from the other 

 constituents of the milk in containing nitrogen, and are 

 of great nutritive value. 



In. composition they very closely resemble one another, 

 but they differ in some of their properties. The casein is 

 coagulated by the addition of acetic acid. The albumen is 

 not. The casein may also be separated from the albumen 

 by filtration through porous earthenware. If a porous 

 earthenware cell, such as is used in many forms of galvanic 

 batteries, be closed by an indiarubber cork, perforated to 

 admit of a glass tube which is connected with an apparatus 

 for exhausting the air, and then plunged into a vessel of 

 milk, the water, the sugar and the albumen will pass into 

 the cell, while the casein and the fat will remain outside. 

 A portion of the salts will pass into the cylinder; another 

 and larger portion will remain in combination with the 

 casein. 



The casein can be freed from the fat by treatment with 

 ether, which dissolves the fat and leaves the case in 

 behind. 



Magnesium sulphate also precipitates casein from cow's 

 milk. T The albumen can be precipitated from the filtrate 

 by the addition of acetic acid and boiling. 



Our knowledge of the albuminoids of milk is not veiy 

 exact. Some authors think that the different forms are 

 only modifications of casein ; others believe that there are 

 several albuminous substances, and that casein itself is not 

 a simple body. For our purposes it will be sufficient to 

 class them under the common name of albuminoids, includ- 

 ing in this term both casein and albumen. 



The quantity of albuminoids contained in the average 



1 Not from human milk. Biedert & Schroter, Jahresber f. 

 Thier-Chem, 1888, p. 103. 



