CONSTITUENTS OF FOOD. 95 



is converted into fat. When animals are fattened 

 on food destitute of nitrogen, only certain parts of 

 their structure increase in size. Thus, in a goose, 

 fattened in the method above alluded to, the liver 

 becomes three or four times larger than in the same 

 animal, when well fed with free motion, while we 

 cannot say that the organised structure of the liver 

 is thereby increased. The liver of a goose fed in the 

 ordinary way is firm and elastic ; that of the im- 

 prisoned animal is soft and spongy. The difference 

 consists in a greater or less expansion of its cells, 

 which are filled with fat. 



In some diseases, the starch, sugar, &c., of the 

 food obviously do not undergo the changes which 

 enable them to assist in respiration, and consequently 

 to be converted into fat. Thus, in diabetes mellitus, 

 the starch is only converted into grape sugar, which 

 is expelled from the body without further change. 



In other diseases, as for example in inflammation 

 of the liver, we find the blood loaded with fat and 

 oil ; and in the composition of the bile there is 

 nothing at all inconsistent with the supposition that 

 some of its constituents may be transformed into fat. 



XIX. According to what has been laid down in 

 the preceding pages, the substances of which the 

 food of man is composed may be divided into two 

 classes ; into nitrogenised and iion-nitrogenised. The 

 former are capable of conversion into blood ; the 

 latter incapable of this transformation. 



