THE FEEDING OF MILCH CATTLE 307 



richness of the ash in potash and its poorness in 

 soda, for the ash of blood, on the contrary, contains 

 much soda and only a little potash. 



In the cow the mammary gland, which is covered 

 with fatty tissue and folds of skin, consists of two 

 portions which are separated from one another by 

 a wall of muscular tissue which runs parallel to the 

 long axis of the body. Each of these halves 

 possesses a grape-like shape and is composed of a 

 great number of smaller or larger flaps, which are 

 traversed by small branching ducts. These snfatf 

 ducts unite to form wider ones, which finally open 

 into a broad passage which empties into the milk 

 cistern — a large hollow space lying above the teats. 

 If the small ducts above mentioned are followed 

 into their finest capillaries they are found to end 

 in tiny sacs or alveoli, which compose the small 

 flaps. The alveoli are furnished with a delicate 

 homogeneous membrane on which a single layer of 

 so-called epithelial cells lies. A dense network of 

 the finest blood and lymph vessels surrounds the 

 outer walls and supplies the epithelial cells, from 

 or in which the milk arises, with the necessary 

 material. Numerous nerve fibres imbedded along- 

 side the blood capillaries regulate the activity of 

 the alveoli. The alveoli, therefore, are that portion 

 of the mammary gland in which the materials form- 

 ing the milk undergo conversion. Whether the 

 alveoli are partly or entirely destroyed and then 



