COMPOSITION AND PROPERTIES OF MILK 293 



this cause may be judged from the following figures, quoted by 

 Van Slyke : 



FAT IN FOUR SUCCESSIVE PORTIONS OF MILK OBTAINED AT A SINGLE 

 MILKING FROM EACH OF THREE DIFFERENT Cows. 



It will be seen from the following more complete analyses l 

 that the percentages of the other constituents are not appreci- 

 ably affected : 



It was formerly believed that this phenomenon was due to 

 the natural separation of cream from the milk while standing 

 in the udder. In view of the structure of the milk gland, and 

 the processes by which milk is formed, this hypothesis appears 

 to be untenable. It is more probable that it is due to gradual 

 reduction of pressure as the milk is withdrawn from the udder. 

 This, it has been said, diminishes the resistance and facilitates 

 the escape of the fat globules. 



Physical Properties. The appearance, taste, and odour 

 of milk are familiar. It is commonly described as an opaque, 



1 Snyder. 



