32 MILK IN THE UDDER 



eaten by the dairy cow is changed in the cow's 

 digestion into soft liquid material. This is ab- 

 sorbed by the circulation which carries it to the 

 udder. The cow's udder is a large sponge filled 

 with cavities, in the walls of which the blood 

 tubes form a fine network. The surface of the 

 cavities is like fine velvet made up of tiny par- 

 ticles of animal matter called cells. This velvet 

 lining draws liquid nourishment from the cir- 

 culation beneath, and transforms it into milk. 

 Many of the tiny particles composing the velvet 

 become so filled with milk material that they 

 burst, and others are squeezed loose and fall 

 off with the milk into the channels. The blood 

 itself contains floating particles of solid material 

 called white blood cells. They are round and 

 soft like tiny drops of white jelly. These also 

 work their way through the walls of the chan- 

 nels and fall into the milk. As a result, the 

 milk which flows from the small channels of the 

 udder into the large channels and finally reaches 

 the teats carries with it considerable material 

 which is shed from the lining of the udder, and 

 which can easily be seen in milk under a mag- 

 nifying glass. 



The gray oval spaces in the picture are the 



