During the lying-in period and during lactation, the mammary glands often attain considerable proportions, feeling very firm and extending to the axillary space. Before empjying into the nipple, the excretory ducts widen very considerably into the sinus lactei (Fig. 4). This dilatation occurs really first during milk-secretion, but afterwards un dergoes only a slight retrogression. The milk itself is an emulsion of serum and fat, the latter originating in the epithelial cells I of the glands. The appearance of the fat globules in these cells is best observed at the beginning of the secretion of milk, and in the colostrum, the thin fluid which is poured out from the nipple during the first stage of glandular activity. The quality and quan tity of the milk secretion are of the greatest interest to the obstetrician and physician, less so to the surgeon. On the cessation of lactation, the acini collapse, though they do not disappear, but persist without secreting, only to be again, during the next pregnancy, first filled with cells and later again with milk. The connective tissue of the gland remains relaxed, and is soon transformed into fatty tissue, but it does not again take on the firm hyaline condition seen in the virgin state of the gland.
With the complete cessation of ation about the fiftieth year, at the time of the so-called involution, atrophy of the gland-tissue begins—that is to say, a withering of the glandular lium and collapse of the acini. Only the excretory ducts remain, though
their epithelium withers. At the lobular ends of the excretory ducts of old women, we may often Snd the traces of the collapsed canals. (Fig. 8).
The breast of an old woman consists, then, of nothing more than con nective tissue with fat and these gland-canals. Whatever portion of the gland-substance disappears is at times so completely compensated for by the addition of adipose tissue, that the breasts of well-nourished old women often have a round form and do not appear at all atrophied, although there may be no glandular tissue remaining. In thin old women many thick elastic fibres are found scattered through the connective tissue. The capillaries are partly obliterated, but, what is more noteworthy, a great number of the lymph capillaries have disappeared (Langhaus). Cystic dilatation of the milk-ducts, with the formation of a brownish or greenish thin or viscid secretion is very frequent in old women. Although these changes are not infrequently absent, I still regard them as regular and physiological.