CONDITIONS AFFECTING SECRETION OF MILK 29 



according to their causes: (i) conditions which are controlled 

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

 and improper milking, irregularity, and long periods between 

 milkings. Pregnancy, nervousness, or excitement of any kind 

 affects 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, the amount of blood which is supplied to these secretory 

 parts, and the capacity of the cow to digest and assimilate food, 

 and possibly upon a stimulating body fluid not yet well under- 

 stood. 



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 udder can 

 only be approximately ascertained. The size of the udder in 

 some measure indicates this. A cow with a large flexible udder'is 

 usually a good milker, due to the fact that a large udder usually 

 contains a large number of gland-lobules. 



The amount of blood which is turned through the cow's udder 

 to supply the milk-secreting cells may be approximately ascer- 

 tained by the size of the blood vessels. The blood from the heart 

 enters the udder near the region of the hips. It then passes down 

 through the udder, along the abdomen just beneath the skin, 

 until it reaches a point about midway between the flank and the 

 girth. At this place it penetrates the abdominal wall and enters 

 the thorax. The place at which the blood penetrates the abdom- 



