THE LACTEAL GLANDS. 277 



corpuscles, with the brilliant aspect of fat-drops, suspended in 



it. These corpuscles — the milk-globules — vary in size, from 



immeasurable minuteness up to O'OOl — 0002"' and more, and 



most probably do not consist of the fatty part of the milk 



alone, but have also a delicate invest- Fi 274. 



nient of casein, and it is to them that _. 3 



a 

 the whiteness of the milk is owing. ° . p # o 



With respect to the formation of the a . ®.°o° ° o ' 

 milk, it is to be remarked that, except °/^° #° 

 at the periods of lactation and preg- 

 nancy, the glands contain nothing but a small quantity of a 

 yellowish viscid mucus, with a certain number of epithelial cells, 

 and are lined up to their extremities by an epithelium, which 

 in that situation is tesselated, but externally is more cylin- 

 drical. With conception, this state of things is altered. The 

 cells of the gland-vesicles begin to develop, at first a little, and 

 subsequently more and more fatty matter within them, and to 

 enlarge, so as entirely to fill the terminal vesicles. To this is 

 added, before the end of pregnancy, a new formation of fat- 

 containing cells in them, by which the older cells are forced 

 into the lactiferous ducts, which they gradually fill. Thus it 

 happens, that although a true secretion is not at that time set 

 up, still in the latter half of pregnancy a few drops of fluid 

 may be expressed from the gland, which, as is shown by its 

 yellow colour, is not milk, but nevertheless contains a certain 

 number of fat- globules from the more or less disintegrated 

 fatty cells, exactly resembling the subsequent milk-globules, 

 and also contains such cells either with or without a tunic — 

 the so-termed colostrum corpuscles. On the commencement of 

 lactation after parturition, the cell-formation in the gland- 

 vesicles proceeds with excessive energy, in consequence of 

 which the secretion collected in the lactiferous ducts and 

 gland-vesicles is evacuated, as the colostrum or immature milk, 

 the true milk taking its place. 



The latter, in the extremities of the gland, consists only of 

 some fluid and cells entirely filled with fat -globules, which 

 sometimes occupy the gland-vesicles alone, sometimes associated 

 with pale epithelial cells, which, however, always contain more 



Fig. 274. Elementary forms in milk, x 350 diam.: a, milk-globules ; b, colostrum 

 corpuscles ; cd, cells with fat-globules from the colostrum, one (d) with a nucleus. 



