SUGAKS. 49 



being formed exclusively in animal or vegetable bodies. They 

 are of definite chemical composition, and crystallizable. The 

 most important groups of this class, i. e. the sugars and fats, are 

 composed of carbon, hydrogen, and oxygen, whence they are 

 sometimes called Hydro-Carbons. They are distinguished 

 from another class of organic substances by the fact that 

 they do not contain nitrogen ; which has given them the 

 name of Non-nitrogenized Principles. They are in part 

 introduced into the body as food, and in part formed in the 

 economy by special organs. In the former instance, they 

 undergo an elaborate preparation by digestion before they 

 become part of the organism, differing in this respect from 

 the inorganic principles, which are absorbed unchanged 

 With the exception of butter and the sugar of milk, they are 

 never discharged from the body in health, but disappear in 

 the processes of nutrition. In this respect, also, they differ 

 from the inorganic principles, all of which are discharged 

 from the body, most of them in the condition in which they 

 entered. 



The most important principles of this class may be divided 

 into two great groups, the Sugars and the Fats ; in addition 

 to which we have, lactic acid and the lactates, pneumic acid, 

 pneumate of soda^ the fatty acids and their combinations, 

 and certain organic salts which are found in the bile. 



Sugars. 



The varieties of sugar with which we are most familiar, 

 of which cane sugar may be taken as the type, are not 

 found in the animal body, but belong to the vegetable 

 kingdom. These, which form an important element of 

 food, must be modified by digestion before they become 

 proximate principles. For a long time it was supposed 

 that sugar was an exclusively vegetable production and 

 consumed by animals ; but late experiments, especially those 

 of Bernard, have shown that sugar is constantly produced by 

 animals, presenting, in this instance, marked differences from 

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