THE MAMMARY GLANDS. 2031 



composition of human milk includes over 86 per cent, of water, about 3 of albuminous 

 substances, 5.3 of fat, 5 of sugar, and less than i per cent, of salts. The chief mor- 

 phological constituents of milk are the milk-globules (fat droplets liberated from the 

 alveolar cells), that vary in size from the most minute spherules to those having a 

 diameter of from .003 .005 mm. and, exceptionally, even twice as much. Their 

 average number per cubic millimetre is something over one million (Bouchut). 

 Whether the milk-globules are enclosed within extremely thin envelopes of casein is 

 still uncertain. Whether the fat is actually produced within the cells, or is to be 

 regarded as only in transit, and, likewise, whether the milk leaves the cells already 

 emulsified, are also questions undecided. 



During the last weeks of pregnancy and for two or three days after its termina- 

 tion, the breasts contain a clear watery secretion, known as colostrum, that differs 

 from milk in containing relatively little fat and numerous conspicuous bodies the 

 colostrum corpuscles of uncertain form and size. These bodies are usually spherical, 

 but may be irregular in outline, and measure from .oi2-.oi8 mm., although they 

 may attain a diameter of more than .040 mm. Their protoplasm is markedly granu- 

 lar and often of a yellowish or reddish-yellow tint. The colostrum corpuscles are 

 modified alveolar epithelial cells that have been cast off during the initial changes and 



FIG. 1714. FIG. 1715. 



cX 

 \ 



"O 



6 



\ 



Human milk. X 500. Colostrum, showing corpuscles 



and oil-drops. X 500. 



expansion of the alveoli preparatory to the establishment of lactation. They again 

 appear after this function has ended, and may continue to be expressed from the gland 

 for months or, in exceptional cases, for even years. 



Vessels. The arteries supplying the mamma are principally the second, third, 

 and fourth anterior perforating branches of the internal mammary. These vessels, in 

 addition to their distribution to the skin and more superficial parts of the breast, send 

 deeper twigs to the glandular tissue, which eventually break up into capillary net-works 

 enclosing the alveoli. The lower and lateral portion of the organ receives an addi- 

 tional supply from the external mammary branches from the long thoracic artery from 

 the axillary. During lactation these vessels are markedly increased in size. The 

 veins follow chiefly the arteries, emptying into the internal mammary and the long 

 thoracic. The cutaneous veins, which during lactation are enlarged and show through 

 the delicate skin as a net-work of blue lines, in part join those accompanying the arteries 

 and in part form vessels that take an independent course over the clavicle to 

 become tributary to the external jugular vein. Within the areola the cutaneous 

 veins form a plexus that more or less completely encircles the nipple and receives 

 its blood. 



The lymphatics of the mamma are exceptionally numerous and important. The 

 deeper ones surround the groups of alveoli as channels that lie within the interlobular 

 connective tissue and pass towards the surface, where they join the rich subareolar 

 plexus. The latter also receives the collecting stems from the close cutaneous net- 

 works that drain the integument covering the nipple and areola. With the exception 



