VAEIATIONS IN COW'S MILK 39 



decrease in the quantity of milk, wMle, on the other 

 hand, a lessening of the percentage of fat is often accom- 

 panied by an increase in the volume of the milk. 



Although recent experiments have thrown much 

 light upon the influence of food on the milk secretion, yet 

 there is need for further information on many points. 

 For instance, it is not known with certainty if it is pos- 

 sible by long continued, particularly unfavorable, one- 

 sided composition of food, to produce lasting changes 

 in the fat content of milk and in the solids not fat. 



Lactose occurs in milk in but one form and the char- 

 acter of proteids is not affected by the nature of the 

 foods. On the other hand, the milk fats vary, sometimes 

 there is more and sometimes less olein, which affects the 

 consistency of the butterf at, and the percentages of vola- 

 tile fatty acids may vary considerably. It has often been 

 said that the fats taken with the food do not pass un- 

 changed into the milk. Only when a great quantity of 

 food, rich in a kind of fat that can be distinguished 

 chemically, is fed, is it possible to find small quantities 

 of that fat in the butterf at of the milk. 



But little is known positively concerning the causes 

 of the variations in the composition of the butter- 

 fat and especially concerning the influence of the food 

 upon it. The milk fat may originate in the fatty tissue 

 of the animal, from the fat stuffs taken with the food 

 and, apparently, also, directly from the carbohydrates 

 consumed. There are a number of other conditions, 

 as the composition of the ration, excessive feeding 

 with fatty foods, starvation, etc., that have some in- 

 fluence in this direction but, as they are of no sanitary 

 importance, it is unnecessary to discuss them here in 

 detail. 



It is generally believed that odors and tastes pass 

 from the food that is consumed into the milk. The 



