Chemical Constituents of the Animal Body. 191 



alcoholic solution of cadmium chloride. The cadmium 

 salt is then decomposed in alcohol with ammonium car- 

 bonate. After filtration of the precipitated cadmium, the 

 lecithin is deposited from the alcoholic solution on concen- 

 tration, and is purified by dissolving in chloroform and 

 adding acetone to this solution, which causes the precipi- 

 tation of the lecithin. Similar products containing nitrogen 

 and phosphorus have been obtained from various tissues, 

 but it is doubtful whether any have yet been obtained in 

 a pure condition. Some of the brain lipoids yield on 

 hydrolysis the carbohydrate galactose, and have been there- 

 fore designated galactolipins. 



Part II. The Carbohydrates. 



Several classes of substances are included under the 

 designation of carbohydrates, some of which have the 

 composition represented by the formula C 6 H 12 6 . This 

 might be written 6C + 6H 2 O, and owing to this fact the 

 name of " carbohydrate " has been given to these sub- 

 stances. Such a formula for a pure substance is, however, 

 in the present stage of the development of chemistry, quite 

 meaningless. The name carbohydrate has, nevertheless, 

 been maintained, and the substances included under the 

 designation form a well-defined class. 



Carbohydrates form an important part of the total 

 bulk of the tissues of plants ; in animal tissues the amount 

 is relatively much smaller. From the fact, however, that 

 they form an important constituent of the ordinary mixed 

 animal diet, they are substances of considerable importance 

 in the domain of animal physiology. 



The classes included under the designation carbo- 

 hydrate are the following : (a) the sugars, (6) the starches, 

 (c) the celluloses. 



