PRINCIPLES AND PRACTICE 
OF MILK HYGIENE 
CHAPTER I 
PHYSIOLOGY OF MILK SECRETION 
Certain facts concerning the physiology of milk 
secretion are of importance in milk hygiene. These will, 
therefore, be briefly presented. 
Udder Structure and Cell Activity—The udder or 
mammary gland of the cow consists of a large number 
of alveoli or acini arranged in lobules or groups and 
held together by connective tissue. The alveoli of each 
lobule communicate with a common duct which, after 
emerging’ from the lobule, continues its course in the 
interlobular connective tissue toward the milk cistern. 
The ducts from the several lobules unite to form the 
larger milk canals. The latter increase in size as they 
approach the milk cistern, in which they terminate. 
From the bottom of the milk cistern, a short, narrow 
canal, called the teat canal, extends through the lower 
end of the teat to the exterior. The udder of the cow 
contains four of these glandular systems, one for each 
teat. Each glandular system is spoken of as a “ quarter.” 
The alveoli are lined with glandular epithelial cells 
which, in the actively secreting udder, are separated from 
the capillaries by only a thin basement membrane. These 
cells select from the blood circulating in the capillaries 
certain materials which they convert into those substances 
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