JUDGING THE DAIRY TYPE OF CATTLE 299 



sists of a fleshy framework, filled with secreting' tissue. 

 Dissecting an udder we find that it is somewhat spongy of 

 texture, pinkish-white in color, and full of many Holes or 

 canals, much like a sponge. When cut more or less, milk 

 escapes from the incision. Above each teat is a cavity 

 known as the milk cistern or milk reservoir, from which 

 the milk is drawn through the teats. At the lower end of 

 each teat, a small muscle (the sphincter) encircles the out- 

 let with enough force, ordinarily, to prevent the escape of 

 milk unless the milking operation is on. 



The process of milk secretion may be briefly described 

 as follows: Bach gland of the udder is composed of a 

 quantity of structures known as lobes, lobules and alveoli. 

 These may be compared to a bunch of grapes, the lobe rep- 

 resenting the bunch, the lobule one grape and the alveoli 

 smaller glands or ducts within the one fruit. The alveoli 

 are exceedingly small and can be seen only under a micro- 

 scope of high magnifying power. Two processes, says 

 Smith,^^ from whom the author freely quotes, contribute 

 to the formation of milk. In one, the cells lining the al- 

 veoli of the gland are shed bodily, and from the fat of the 

 milk, while in the other water, protein, salts, etc., are formed 

 from the lymph in the gland by the ordinary process of 

 secretion. The gland of an animal - that has never ' been 

 pregnant contains much smaller and less numerous alveoli 

 than a secreting gland. The alveoli of the non-pregnant 

 animal are found to be packed with small, rounded cells of 

 very slow growth. When the animal becomes pregnant the 

 gland enlarges, the alveoli increase in number, but remain 

 packed with the cells until parturition approaches or occurs. 

 The solid masses of cells are now cast ofi^, and leave behind 

 them alveoli lined with a single layer of secretory epithe- 

 lium, the function of which is to produce the milk. The 

 shedding of the mass of cells which originally occupied the 

 alveoli, supplies the colostrum or first milk. The cells in 

 the active gland are loaded with material, much of it being 



^A Manual of Veterinary Physiology, 4th ed., London, 1912, p. 726. 



