26 BUTTER-MAKING. 



secretion have been studied considerably, many things in this 

 connection are not well understood. Previous to the year 

 1840 it was thought that the only function of the milk-gland 

 was to filter the milk as it transuded from the blood. It was 

 supposed that the quality and quantity of milk depended 

 entirely upon the food. The theory has also been advanced 

 that the major portion of the milk constituents was a decom- 

 position of the product of the lymph bodies of the blood. It 

 was believed that the lymph bodies were a source of nourish- 

 ment to the foetus, and that the calf received its nourishment 

 from the same source after it was born as it did previous to 

 birth. It was supposed that after the birth of the calf the 

 opening on the uterus through which the food was supplied 

 was closed, and that a new opening was formed in the milk- 

 gland. These two theories have now been practically over- 

 thrown. It has been demonstrated that the major portion of 

 the milk is formed within the milk-gland. The fat, casein, 

 milk-sugar, and part of the albumen are supposed to be formed 

 in the udder. This conclusion is substantiated by the fact 

 that these substances do not appear in the blood, at least not 

 to such an extent as to warrant the assumption that they are 

 not manufactured in the cow's udder. The total amount of 

 fat in the blood of the cow would not equal the fat in the milk 

 from one milking. 



By some it is maintained that the substances in milk which 

 are found in solution may be transuded directly from the 

 blood. Here again milk-sugar is found to be in perfect solu- 

 tion in the milk, but this substance can be found nowhere in 

 nature besides in milk. It is not present in the blood of the 

 animal, consequently it must be manufactured within the 

 gland itself. The water of milk, and the ash constituents which 

 are in solution, are probably transuded directly from the blood. 

 No attempts have been made to determine definitely ho\v 

 casein and albumen are formed within the gland. 



The theory advanced for the formation of fat is, that the 

 epithelial cells break down and form f^t. When the breaking- 



