284 THE MAMMARY GLANDS, BY C. LANGER. 



The changes that take place in pregnancy, preparatory to the 

 active performance of the function of the gland, consist, in the 

 first place, in an increase of the secreting surface. The acini, 

 with the ducts, become wider, the hyaline layer of the walls 

 thinner ; fat vesicles appear in their interior, at first few in 

 number, and only in the centre of the cell masses, but sub- 

 sequently in such quantities that they entirely fill the dilated 

 and bulbous terminations of the ducts that have in the mean- 

 while undergone great augmentation in size, and compress 

 their epithelial lining closely against the wall. The inter- 

 lobular connective tissue becomes constantly looser, and 

 contains more and more fat, and the dense part of the stroma 

 diminishes in quantity, though it never altogether disappears, 

 since even in nursing women it forms a solid nucleus in the 

 centre of the gland. As these changes do not occur quite 

 simultaneously in all parts of the gland, an opportunity is 

 afforded in puerperal women dying shortly after delivery, to 

 observe many transitional forms of the acini. 



It cannot be doubted that the fat vesicles, which constitute 

 the morphological elements of the milk, proceed from the epithe- 

 lial cells of the acini ; for, in the first place, the first visible oil 

 drops appear in the very centre of the epithelial masses, whilst 

 again, in the milk first secreted (colostrum) spheroidal nucleated 

 cells occur, distended with fat vesicles, and, lastly, in the acini 

 of the gland in nurses, not only isolated, but serially arranged 

 groups of cells may be found filled with oil drops. I have met 

 with cells containing several small fat molecules, and with others 

 containing a nucleus around which a crescent of larger mole- 

 cules had been deposited. In serially arranged cells containing 

 oil drops these occupy that portion of the cell which is directed 

 towards the cavity, whilst the nucleus is situated nearer to the 

 wall of the acinus. This explains why the walls of empty 

 acini not unfrequently appear to be still beset with fat vesicles. 

 Clearly these represent epithelial cells that have been distended 

 and have burst, allowing the fat drops to escape. It is still 

 questionable whether such epithelial cells die and are imme- 

 diately replaced by others, or are capable of producing a 

 succession of fat molecules. The latter is perhaps the correct 

 view, and is, at all events, in accordance with the observations 





