324 PRACTICAL PHYSIOLOGY 



CHAPTER VII. 

 MILK. 



MILK contains proteins, fats, carbohydrate, salts and water. The fat 

 is suspended in the form of a fine emulsion. The proportion of these 

 bodies varies in the milks of different animals. Naturally that pro- 

 vided by the animal is the best for its own species. The more quickly 

 a young animal grows the greater is the percentage of protein and 

 salt, in the mother's milk. Thus, a puppy doubles its weight in eight 

 days; its mother's milk contains 7'1 per cent, of protein and 1-3 per 

 cent, of ash. On the other hand, a child takes half a year to double 

 its weight; human milk contains only 1-5 per cent, protein and 0'2 

 per cent. ash. The mother's milk forms a perfect food for the young 

 growing animal but it is deficient in iron. It has been shown that 

 the young animal has sufficient iron stored within itself until it can 

 begin to get its own further supply of iron. Thus the young rabbit 

 contains within itself a sufficient supply until it is able to eat green 

 food. This is important from the medical point of view, and shows 

 the necessity of weaning a child at the proper time in order that a 

 proper supply of iron may be obtained in the food. 



In everyday life the two kinds of milk of the greatest importance 

 are cow's milk and human milk. As hinted above, the two milks vary 

 in composition. 



Water. Protein. Fat. Carbohydrate. Salts. 



Cow's milk, - 87'4 3'4 37 4-8 '7. 



Human milk, - 90*2 1-5 3'1 5'0 '2 



Other milks used for human consumption are : 



Water. Protein. Fat. Sugar. Salts. 



Goat's, - - 87-3 3 "5 3 '9 4-4 -8 



Ass's, - - 92-5 1-7 '4 5-0 '4 



It will be seen that, as regards cow's and human milk, the amount 

 of fat and of carbohydrate is nearly the same in both, the amount 

 of protein and salts is more in cow's than in human milk. To make 

 cow's milk, therefore, of approximately the same percentage composition 

 as human milk, it is usual to dilute it with an equal bulk of water 

 and to add fat and carbohydrate in proportion. This fat is usually in 

 the form of cream, but, in the case of the very poor, cotton-seed oil 

 will serve a similar purpose. Similarly with the carbohydrate that 

 of milk is milk-sugar or lactose and is expensive but the addition 

 of cane sugar serves well and if anything renders the milk more 

 palatable. In passing, it may also be noted that a good non-skimmed 



