FORMATION OF FAT. 91 



stances which thereby pass into fat, must disengage as 

 much heat- as would raise the temperature of 200 Ibs. 

 of water by 70, that is, from 32 to 102. 



Thus, in the formation of fat, the vital force pos- 

 sesses a means of counteracting a deficiency in the sup- 

 ply of oxygen, and consequently in that of the heat 

 indispensable for the vital process. 



Experience teaches us that in poultry, the maximum 

 of fat is obtained by tying the feet, and by a medium 

 temperature. These animals, in such circumstances, 

 may be compared to a plant possessing in the highest 

 degree the power of converting all food into parts of its 

 own structure. The excess of the constituents of blood 

 forms flesh and other organized tissues, while that of 

 starch, sugar, &c., is converted into fat. When ani- 

 mals 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 organized structure of the liver is 

 thereby increased. The liver of a goose fed in the 

 ordinary way is firm and elastic ; that of the imprisoned 

 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 



