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- 
troiled 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 of blood which is supplied to these secre- 
tory parts, and upon the capacity of the cow to digest and assimilate 
jood. 
‘The number of gland-lobules is believed 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 gland-lobules then increase in number up to the age of 
about seven. The relative number of lobules in the cow’s 
