GENERAL CHEMISTRY OF MILK 127 



and up; for the summer calving cows it is down and up; and for fall 

 calving cows gradually up and down." They state further that 

 "season and stage of lactation operate together in fall and winter 

 and in opposite direction in the summer." 



Lythgoe states that in Massachusetts the legal limit of 13 per 

 cent, solids was reduced to 12 per cent, for May and June in 1886 

 on account of the lower solids in warm weather. In 1896 the fat 

 standard of 3.7 per cent, was reduced to 3 per cent, for April, May, 

 June, July, and August, and in 1899 September was added to these 

 months. In 1908 a uniform standard of 12.15 per cent, solids and 

 3.35 per cent, fat was established for the entire year. 



According to Trunz the ash content is smaller in spring and 

 summer than in winter. 



The fat increases slightly when the temperature is falling and 

 declines when it is rising. The stable should be comfortable. 

 If it is either too warm or too cold the fat decreases. Shelter from 

 cold and inclement weather preserves the normal composition of 

 milk, while exposure injures it. Warm drinking-water increases 

 the flow of milk, probably because cows drink more of the warm 

 water than of the cold. 



Good or bad weather and storms seem to have no noticeable 

 effect on the milk-supply. 



7. Exercise and Nervous Influences. Moderate exercise re- 

 duces the milk flow, but the milk is then richer in fat. A great 

 deal of exercise, such as climbing hills, unfavorably influences 

 the amount and kind of milk produced. 



Any adverse nervous influence impairs the milk-supply. Ill- 

 treatment, sudden fright, shock, or rage materially reduce the 

 quantity and quality of the milk. 



8. Influence Due to the Skill of the Milker. It is a usually 

 accepted fact that a skilful milker can obtain a richer milk 

 from a cow than an inexperienced milker. This is explained 

 by the fact that a good milker empties the udder and adds 

 the rich milk from the upper parts of the udder to the bulk. 

 Furthermore, it is frequently claimed that a cow must become ac- 

 customed to the same milker in order to readily yield her whole 

 supply. Carlyle doubts the accuracy of this statement. After 

 a series of experiments he came to the conclusion that in so far as 

 the amount of milk and total production of butter-fat is concerned 

 the changing of milkers at every milking resulted in a direct gain 

 with but two exceptions. The increase, however, was so slight 

 that very little importance can be attached to it. The author 

 concluded from his experiments that changing milkers has no ap- 

 preciable effect upon the milk and butter produced when all the 

 cows in a herd are kindly treated. 



