CHAP IV. 



THE MAMMARY GLAND. 

 COMPOSITION OF TRE ASH OF COWS MILK. 



279 



Chloride of sodium 



Chloride of potassium 



Potash . 



Lime 



Magnesia 



Oxide of iron . 



Phosphoric acid 



Sulphuric acid 



Silica 



16-23 

 9-49 



2377 



17-31 

 1-90 

 0-33 



29-13 

 1-15 

 0-09 



99-40 



In what way do the tissues of the mammary gland prepare milk from 

 the blood which comes from the heart ? Milk, like bile, gastric juice, 

 pancreatic juice, saliva, and urine, is a secretion, and it is formed 

 through the activity of certain living cells which constitute the internal 



Fig. 67. Magnified Sectional Views of the Mammary Gland 

 during the Period of Lactation. 



A, Section of a small lobule of the gland, magnified GO diameters ; 1, ground- work of 

 connective tissue supporting the glandular tissue ; 2, terminal branchlet 01 one of the 

 excretory tubes ; 3, alveoli. 



B, Four alveoli, magnified 200 diameters, showing the lining epithelial cells and some 

 milk globules. 



lining of the ultimate branches or sacs of the mammary gland. Each 

 terminal branch, in fact, is formed by the confluence of several blind, 

 saccular or flask-shaped, wavy tubes, called alveoli 1 (fig. 67). 



The cow's udder, or milk-bag, is provided with four delivery tubes 

 or teats, each of which (fig. 68), with its gland, is termed a " quarter." 

 When a cow is said to have " lost a quarter," it means that one of the 

 teats has ceased to yield milk. Besides the external covering which 

 binds together the whole of the udder, each gland has its own special 

 fibrous envelope, and is distinct from, and independent of, the other 

 glands ; hence, though the function of one gland, or " quarter " may 

 be impaired, the others may continue to act in the usual way. The 

 orifice at the free end of the teat is a narrow tube, which is ordinarily 

 closed. In the body of the teat this tube is much wider, but becomes 

 constricted again at the region where the teat merges into the udder. 

 Above the constriction is a large space, " the milk cistern/' or 



1 Lat. alveolus, a little hollow. 



