188 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



II. ANIMAL FOODS. 



The most important of the foods of animal origin are milk and 

 animal flesh, or meat. 



1. Milk will be considered more at length under the Secretions, 

 details being given as to the composition and characteristics of the milk 

 of different animals. It is at present only necessary to refer in outline 

 to its composition to indicate in a general way its nutritive value. Milk 

 contains an average, in 100 parts, of 85.7 parts water, 5.4 parts of 

 albuminous bodies, 4.3 parts of fats, 4 parts of sugar, and 0.6 parts of 

 inorganic salts. Of the inorganic salts, potassium phosphate, calcium 

 phosphate, and potassium chloride are in greatest abundance, while 

 sodium chloride is in smaller amount ; iron has also been found to 

 be present. Milk, therefore, contains examples of all the different 

 nutritive principles, proteids, carbo-hydrates, fats, and salts, and these 

 arranged in the proportion which is best suited for nutritive purposes. 

 All mammals, in the earliest period of their extra-uterine life, are 

 nourished solely on milk, and their rapid growth and development in 

 this period is without doubt largely dependent upon the manner in 

 which the different food-principles are combined in milk. Milk, there- 

 fore, may be regarded as a typical food. Buttermilk is the name 

 which is given to the fluid which remains after the fats have been 

 removed by churning. It is less nutritious than milk to the extent to 

 which the fats have been removed, but, all the other principles remain- 

 ing, it may serve useful nutritive purposes. It has an acid reaction, 

 from the fermentation of the milk-sugar into lactic acid. Cheese 

 consists of the casein and fats, the casein being coagulated, either 

 through the spontaneous development of acidity, when it is termed 

 a curd, or by the addition of the milk-curdling ferment from the stomach 

 of the calf. It therefore consists principal^ of albuminous bodies and 

 fats, the whey, in which the salts and sugar remain dissolved, being 

 largely forced out by pressure. It is hence well suited to form an 

 addition to foods which are poor in albuminoids and fats, as in certain 

 vegetables, such as potatoes and rice. The whey of milk contains the 

 sugar and lactic acid, which is developed from the fermentation of the 

 sugar, salts, and a certain amount of milk-albumen. It also has con- 

 siderable nutritive value, and seems especially to stimulate intestinal 

 peristalsis, and therefore to be, to a certain extent, laxative. 



2. Meat. — Next in value to milk as food comes the flesh of animals. 

 The nutritive principles of meat are contained within the muscle-fibre ; 

 the juice obtained by subjecting muscle to pressure contains myosin and 

 ordinary albumen, inosite or muscle-sugar, and glycogen, as representa- 

 tives of the carbo-hydrate group, while within the connective tissue 



