380 NUTRITION. 



classes of animals. Sugar is never discharged from the body 

 in health, 1 nor is it deposited in any part of the organism, even 

 as a temporary condition. It generally disappears in the pas- 

 sage of the blood through the lungs. How is sugar destroyed, 

 and what relation does it bear to nutrition ? In studying the 

 changes which it is capable of passing through, it has been 

 found that it may be converted into lactic acid, or be changed 

 into carbonic acid and water ; but precisely to what extent the 

 sugars undergo these changes, or how they are acted upon by 

 the inspired oxygen, it has been impossible thus far to deter- 

 mine. "We must be content to say that the exact changes 

 which the sugars undergo in nutrition are unknown. They 

 seem very important in development, being abundant in the 

 food and formed largely in the system in early life. 2 They 

 certainly do not enter into the composition of the tissues ; 

 and it would seem that they must be important in the two 

 remaining phenomena of nutrition, namely, the formation 

 of fat and the development of animal heat. The relations 

 of sugar to these two processes will be taken up under their 

 appropriate heads. 



The fats taken as food are either consumed in the organ- 

 ism, or are deposited in the form of adipose tissue. That 

 the fats are consumed, there can be no doubt ; for, in 

 the normal alimentation of man, fat is a constant article, 

 and it is never discharged from the body. We are forced 

 to admit, however, that the changes which fat undergoes in 

 its process of destruction are not thoroughly understood. 

 All that we positively know is, that the fatty principles 

 of the food are formed into a fine emulsion in the small in- 

 testine, and are taken up, chiefly by the lacteals, and dis- 

 charged into the venous system. For a time, during ab- 



1 We have already noted the exceptional discharge of sugar, fat, and nitro- 

 genized matter in the milk. 



2 We have already noted these facts, as well as the production of glyco- 

 genic matter and sugar in animals deprived entirely of starch and sugar in their 

 food, when it seems that the formation must take place from the albuminoid 

 principles. 



