626 LACTATION. [CHAP. XLIV. 



dilated as they approach the nipple, and the dilatations are called 

 reservoirs. In the human subject, these are very small; but in 

 the cow, they are large enough to hold a quart. 



The nipple is surrounded by a dark-coloured circle, termed the 

 areola, smooth in the child, but slightly tuberculated at the period 

 of puberty. In the child, it is about half an inch in diameter ; 

 but in the adult, about an inch ; while during lactation, it increases 

 to two inches. After impregnation, it changes from its reddish 

 colour to a dark brown. 



A secretion is poured out from the mucous follicles, which lubri- 

 cates the skin about the nipple. 



The terminal follicles of the gland were injected by Mascagni ; 

 but for almost all that we know of the minute anatomy of the 

 breast, we are indebted to the beautiful researches of Sir Astley 

 Cooper, published in 1840. 



The surface of the breasts, in the unimpregnated state, is smooth 

 and compact ; but as pregnancy advances, they become uneven, in 

 consequence of the distension of the follicles with secretion. 



The nipple, before puberty, forms an almost smooth conical 

 eminence ; but in lactation it becomes flattened, so that its extre- 

 mity becomes the broader part, and thus it is more readily held 

 by the child's mouth. Its characters have been minutely described 

 by Sir Astley Cooper: "At sixteen years it is slightly wrinkled; 

 at seventeen, it has small papillae upon its surface ; from twenty 

 to forty years, the papillae are large ; from forty to fifty, the nipple 

 becomes wrinkled; from fifty to sixty, the nipple is elongated; 

 and in old age, it usually has a warty appearance." 



The cutis of the nipple contains a great number of papillae. It 

 is sensitive and highly vascular. " The direction of these papillae 

 is from the base towards the apex of the nipple ; so that they are 

 pushed back as the mammilla enters the mouth of the child, and 

 thus greater excitement is produced." Connected with the cutis 

 of the nipple are numerous non-striated muscular fibres, to the 

 presence of which the erection of the nipple is due. 



In their minute structure, the lacteal glands are closely allied to 

 the pancreas and salivary fluids. 



The gland structure is arranged so as to form lobules, which are 

 connected together with a considerable quantity of firm areolar 

 tissue (vol.i. p. 78). 



The terminal follicles are about the 2^-oth of an inch in dia- 

 meter. They are lined with a layer of delicate epithelial cells, 

 which become much altered at the time of lactation. At this time 



