264 NORMAL HISTOLOGY. 



Over both areola and nipple the skin is provided with large sebaceous 

 glands, the secretion of which is increased during lactation and serves as 

 protection during nursing. Sweat-glands are wanting over the nipple but 

 large and modified in the periphery of the areola. The surface of the latter 

 is modelled, especially towards the close of pregnancy, by low rounded 

 elevations that mark the position of the subcutaneous areolar glands of 

 Montgomery. The latter are rudimentary accessory masses of glandular 

 tissue, from 1-4 mm. in diameter, and correspond in general structure with 

 the mammary glands. Their ducts open by minute orifices on the surface 

 of the areola. 



Milk. The fully established secretion of the mammary gland is an 

 emulsion, the fat-globules being suspended in a clear colorless watery plasma. 

 The composition of human milk includes over 88 per cent, of water about 

 3 of proteid substances, 4 of fat, 5 of lactose, and less than i per cent, 

 of salts. The chief morphological constituents of milk are the milk-globules, 

 as oil droplets liberated from the alveolar cells are called; these vary in size 

 from the most minute spherules to those having a diameter of 3-5 /* or more. 



Q 



O 



FIG. 312. Human milk ; A, ordinary secretion ; , showing colostrum corpuscles and oil-drops. X 400 



Their average number per cubic millimeter is something over one million 

 (Bouchut). Whether the milk-globules are enclosed within extremely thin 

 envelopes of casein is uncertain. It is probable that the fat-particles are not 

 produced within the gland-cells, but are taken up and temporarily stored by 

 their cytoplasm. A variable number of migratory leucocytes, more or less 

 filled with fat-particles, are usually present in milk. 



During the last weeks of gestation and for two or three days after its 

 termination, the breasts contain a clear watery secretion, known as colostrum, 

 that differs from milk in possessing relatively little fat and numerous conspicu- 

 ous bodies, the colostrum corpuscles. The latter are spherical, but may 

 be irregular in outline, and measure from 1218 /-*, although they may attain 

 a diameter of more than 40 fi. The corpuscles are composite bodies and 

 consist of a complex of leucocytes greatly distended with fat-particles and of 

 modified alveolar epithelial cells. Their cytoplasm is markedly granular and 

 often of a yellowish or reddish-yellow tint. They appear after lactation has 

 ended and may be expressed from the regressing gland for months or, in 

 exceptional cases, for even years. Quite commonly the mammary glands in 

 both sexes, during the first few days after birth, yield a secretion resembling 

 colostrum, popularly known as "witch-milk." 



At birth the gland is represented by the lactiferous ducts with their 

 ampullae, the smaller collecting ducts and the rudimentary alveoli. The 

 mammae remain small and immature during childhood until the approach of 



