28 BUTTER-MAKING. 



The chief incentive to milk secretion is maternity. As soon 

 as the young mammalia is born the blood which went to the 

 uterus to supply the calf is turned towards the udder instead. 

 As soon as this current of blood begins to flow, all of the blood- 

 vessels and capillaries in the cow's udder swell. This causes 

 the minute blood-vessels or capillaries which form a network 

 in the walls of the alveoli to swell. This swelling stimulates 

 the epithelial cells to activity. 



Conditions Affecting Secretion of Milk. — There are a 

 great many conditions which affect the milking capacity of a 

 cow. These conditions may be conveniently grouped into two 

 classes according to their causes : (1) conditions which are con- 

 trolled largely by man, and (2) conditions which are inherent 

 to the cow. 



1. Some of the chief conditions which reduce the secretion 

 of milk and are largely controlled by man are: improper care 

 and treatment of the cow, lack of proper food, incomplete and 

 improper milking, irregularity, and long periods between 

 milkings. Pregnancy, nervousness, or excitement of any kind 

 affect the proper working of the milk-glands considerably. 

 These latter causes, however, are not always controlled by man. 



2. Without denying the influence of those conditions men- 

 tioned above, the conditions which chiefly affect the milk- 

 secreting capacity are inherent. It does not matter how much 

 good care and food a cow receives, if she does not possess 

 these inherent necessary qualities. As was mentioned before, 

 the milk-secreting capacity depends upon the number of gland- 

 lobules, upon the amount oj blood which is supplied to these secre- 

 tory parts, and upon the capacity of the cow to digest and assmnYcte 

 food. 



The number of gland-lobules is beheved to increase until 

 the cow is about seven years old. The milk-secreting glands 

 are present only in a rudimentary form, until the cow has had 

 her first calf, or is well advanced in the first stage of pregnancy. 

 The giand-lobules then increase in number up to the age of 

 about seven. The relative number of lobules in the cow's 



