6 MILK AND THE PUBLIC HEALTH chap. 



the public health standpoint the broad variations in the 

 chemical content of milk are of much greater importance. 



The solids left after milk is evaporated are conveniently 

 divided into the fat and the solids not fat. The percentages 

 of these constituents present in milk have been made the basis 

 of legal enactments (see page 315). Briefly stated, these are 

 to the effect that (a) if milk contains less than 3 per cent of 

 milk fat, the presumption is that the milk is not genuine, and 

 that fat has been abstracted or water added ; (b) if it contains 

 less than 8-5 per cent of milk solids, the presumption is that 

 the milk is not genuine and is adulterated with water. 



It is of importance to consider to what extent the fat and 

 solids not fat are affected in milk obtained from cows under 

 different conditions. The following are the most important 

 known or alleged causes of variation. 



1. The Breed of the Cow. — It is well known that some 

 breeds of cows produce milk of much higher quality, especially 

 as regards its fat content, than others. This is illustrated in 

 the followino; table from Yieth : 



Milh Solids in Milk of Cows of Different Breeds (percentages). 



Dutch cows, which are fairly numerous in some parts of 

 Essex, give abundant milk, but of low fat content. It may be 

 said that whatever the breed of cow average mixed milk con- 

 tains milk solids well above the legal standard. 



2. Seasonal Variations. — Richmond,^ from his extensive 



Dairy Chemistry, 1899, ji. 127. 



