144 THE CHEMISTRY OP THE FARM. 



palmitic and oleic acid. The glycerides of stearic, 

 myristic, lauric, capric, capryllic, caproic, and butyric 

 acid are also present in small quantity. The last four of 

 these acids are, when in the free state, more or less 

 soluble in water. The glycerides of oleic acid, and of 

 the soluble fatty acids, are fluid fats at ordinary tem- 

 peratures ; the remaining fats are solid. The proportion 

 of fluid and solid fats varies somewhat with the diet and 

 condition of the animal ; in summer-time the proportion 

 of fluid fats is greater than in winter. 



The sugar contained in milk is known by chemists as 

 lactose or lacton. 



The composition of cow's milk is affected by various 

 circumstances; under extreme conditions it may con- 

 tain from 10 to over 16 percent, of dry matter. The 

 milk is poorer when the quantity produced is large, 

 or the diet insufficient, and richer when these con- 

 ditions are reversed. A cow is generally in full milk 

 from the second to the seventh week after calving; 

 after this period the milk gradually diminishes in 

 quantity, but increases in richness. A separation of 

 cream takes place in the udder; the milk first drawn is 

 poor in fat, and the richness increases as milking pro- 

 ceeds, the last-drawn milk containing two or three 

 times as much fat as the first- drawn. The evening's 

 milk is usually somewhat richer than that of the morning, 

 the assimilation of food taking place to a larger extent 

 between the morning and evening than between the 

 evening and morning milkings. The milk of old cows 

 is said to be poorer than the milk of young cows. The 

 richness of milk depends also much on the " race " of 

 the cow, the fat being the constituent most affected. 



