CHAPTER II. 
SECRETION AND CONTAMINATION OF MILK. 
20. Structure of the Udder. 
The udder of the cow where the milk is secreted, consists 
of two glands connected with each other along the median line, 
and with the posterior part of the abdomen, by fibrous tissue. 
Each quarter has one opening or teat. The teat is hollow, hav- 
ing an opening at the lower end closed by a sphincter muscle. 
The chamber of the teat opens into another chamber in the 
lower part of the udder just above the teat. From this cham- 
ber ducts diverge, dividing and growing smaller and smaller. 
The two. halves separated by the fibrous band along the median 
line are entirely separate. The ducts end in little chambers 
about a thirtieth of an inch in diameter. These chambers or 
ultimate follicles are lined with cells. Arteries, blood vessels 
and nerves surround them and the blood brought by the arte- 
ries is changed by the cells into milk. 
21. Secretion of the Milk. 
While some parts of the blood may be taken into the milk 
without change, and white blood corpuscles are actually found 
in milk, the blood is for the most part changed by the cells. 
The fat globules are produced in the cells and discharged into 
the ducts. 
If samples of the fore milk and strippings be analyzed, the 
per cent solids not fat will be found to be about the same in 
both. The strippings will, however, be much the richer in fat. 
This may be because there is a natural creaming in the udder 
on account of the fat globules being lighter or, because the fat 
globules being in an emulsion they are retarded more by fric- 
tion in their passage through the ducts than the soluble com- 
ponents of the milk. 
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