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TYPES AND MARKET CLASSES OF LIVE STOCK 



known as the ultimate follicles, acini, or alveoli. The teat-canal, 

 milk-cistern, and ducts are lined with columnar epithelium. 



The alveolus (plural, alveoli) is the sacculated distention 

 found in groups of three to five on the end of the minute milk- 

 ducts. It is the essential part of the gland. It is lined by a 

 single layer of epithelial cells which are especially concerned 

 in milk production. The alveolus is only 1-30 of an inch in 

 diameter, and its cavity is from 1-250 to 1-100 of an inch in 

 length and from 1-1300 to 1-800 of an inch in diameter. New 

 ducts and alveoli may be formed up to about the fifth or sixth 

 year, thereby increasing the producing capacity of the cow. 



Fig. 48. Where Milk is Made. 



Group of alveoli, a, Duct; b, capillary network; c, alveoli; d, epithelial 

 cells; e, fibrous tissue. (After Hough & Sedgwick.) 



The entire gland may be compared to a large bunch of 

 grapes; the main duct of the gland branches very much as the 

 stem of the bunch of grapes branches; and just as the branches 

 and sub-branches of the stem lead to the grapes, so the branches 

 of the duct lead to the alveoli of the gland. If we pack the 

 bunch of grapes in a small basket of sawdust, so that the saw- 

 dust fills up loosely the spaces between the individual grapes 

 and the branches of the stem, we may develop our comparison 

 further; the sawdust stands for the connective tissue in which 

 the ducts and alveoli are embedded, and the basket stands for 

 the capsule. 



