ANIMAL CHEMISTEY. 401 



accumulation of fat does not corne from oily food alone, for 

 starch and sugar can be converted into fat by the chem- 

 istry of life. It is on account of this conversion that pota- 

 toes increase the butter or fatty part of the milk in the 

 cow. For the same reason the butter in milk is greater in 

 amount in the morning milk than in that of the evening, 

 when in cold weather the cow is kept in a warm stall 

 through the night, there being more starchy and sugary 

 matters converted into fat when there is less necessity for 

 their consumption in the production of heat. For the 

 same reason, also, in the fattening of animals in cold weath- 

 er, the more comfortably they are housed the less food will 

 it take to fatten them. 



569. Heat in Carnivorous and Herbivorous Animals. It is 



obvious that carnivorous animals do not eat as much heat-making food as 

 herbivorous animals do, while they eat more of building-food; and yet 

 they have as much heat as the herbivorous animals, and do not have any 

 greater development of structure. This seems to be in contradiction to 

 the views presented of the purposes of food ; but the apparent discrepancy, 

 for it is only apparent, can be easily explained. There are two sources of 

 the fuel used in maintaining animal heat, viz., the food and the waste of 

 the tissues of the body. Now the heat in carnivorous animals is derived 

 almost wholly from the latter source, for they are so active in their habits 

 that there is much greater wear and tear of the tissues than in herbivorous 

 animals. You can realize this difference in activity if you observe the 

 constant restlessness which lions, tigers, hyenas, etc., manifest in their 

 cages in a menagerie. Herbivorous animals are so inactive that when 

 they are left to their natural habits they can live on food which contains 

 but very little nitrogenous substance, as common grass, potatoes, etc. But 

 when they are worked by man, if they are not fed in part on some of the 

 grains, they will lose flesh for want of building-food. But there is another 

 difference between carnivorous and herbivorous animals, which accounts 

 for the absence of that overheating that we might reasonably expect from 

 such an amount of heat-food as is commonly eaten by herbivorous animals. 

 They perspire freely, much more so than carnivorous animals, and a large 

 part of the heat made by their food passes off therefore as latent heat in 

 the vaporization of the perspired matter. 



