48 



MILK 



The ultimate follicles contain the secretory organs, the alveoli. 

 Three to five ultimate follicles are grouped together, and have 

 a common outlet into a milk-duct. They are about TO to iV cm. 

 in diameter, while the alveoli are of microscopic size (Fig. 14). 

 The follicles develop during pregnancy and reach their maximum 

 development during lactation. They shrink after milk secretion 

 ceases, but develop again during succeeding periods of pregnancy. 

 The follicles are lined with epithelial cells, which play as we 

 have seen a most important role in milk secretion. They are 

 supplied with blood by capillaries. Some follicles may degener- 



Fig. 14. Gland during secretion of milk, magnified 800 (Ernst). 



ate after a lactation period, and new ones are then formed during 

 later periods, so that productiveness may increase with each new 

 period of lactation. This, however, rarely happens after the fifth 

 or sixth year. 



It may be inferred from our studies of the mechanism govern- 

 ing milk secretion and from the anatomic ^structure of the udder 

 that milking is an art that requires practice, a suitable tempera- 

 ment on the part of the operator, and skill. It is not merely a 

 manipulation of the teats. The milker must be able to influence 

 the maternal instinct of the cow and thereby induce her to will- 



