48 PHYSIOLOGY AT THE FARM. 



aliments supplied by the mare's milk to the foal while sucking 

 are very different from those contained in the grasses and the 

 like, on which the young horse is afterwards reared. It is 

 now ascertained, however, that the proximate principles of the 

 animal kingdom, which serve for the nutrition of animals, are 

 chemically very much the same as those subservient to nutri- 

 tion afforded by the vegetable kingdom. The mother's milk in 

 every species of mammal is for the present the best standard 

 available to enable us to determine the due constitution of the 

 diet of that species. As a general rule, the proximate principles 

 adapted to animal nutrition are arranged under the three heads, 

 albuminous, oleaginous, and saccharine. Substances coming 

 under each of these descriptions are found in the milk of the 

 mare, while corresponding substances are discoverable in the 

 herbaceous food of the young horse after weaning. The 

 albuminous constituent of milk is caseine, the saccharine con- 

 stituent sugar of milk, and the oleaginous constituent oil or 

 butter. In the earlier days of animal chemistry, caseine was 

 confounded with albumen. From that principle, however, it 

 differs in several essential respects, particularly in not being 

 coagalable by heat. Caseine is still, however, ranked as an 

 albuminoid principle. There is no albumen in normal milk, 

 though it appears to be present in the colostrum, or the milk 

 first drawn after parturition. Neither is there fibrine in 

 healthy milk. Thus caseine is the only plastic or nitro- 

 genous nutritive principle in milk. It is not present in a 

 very high proportion in mare's milk, notwithstanding that 

 the amount of solid substance in mare's milk is rather above 

 the general average. The proportion of fat, and also that of 

 sugar, is high. The salts usually discoverable in milk are the; 

 chlorides of sodium and those of potassium, phosphates of the 

 alkalies, phosphates of lime and magnesia, a small proportion 

 of oxide of iron, together with potash and soda, united with 



