CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 615 



is enlarged preparatory to lactation, the alveoli are at first solid 

 masses of cells with little or no lumen, and a lumen is established 

 subsequently by the discharge of the central cells. It is usu- 

 ally supposed that the cells so discharged, some undergoing 

 much, others comparatively little change, supply the colostrum 

 corpuscles just spoken of, and at the same time furnish the 

 globulin and excess of albumin also characteristic of colostrum. 

 But this is not certain. The alveoli at this time contain pecul- 

 iar cells resembling colostrum corpuscles except that they are 

 free from fat ; and it is suggested that these being discharged 

 and taking up fat in amoeboid fashion become colostrum cor- 

 puscles. Some regard the colostrum corpuscles as simply leu- 

 cocytes which have similarly taken up fat. 



409. The mammary gland is present both in the female 

 and the male child at birth ; and in both sexes at and for a few 

 days after birth is thrown, in common with all the other secret- 

 ing glands, into secretory activity, and a small quantity of milk, 

 the " witches' milk " so called by the Germans, is discharged 

 from the nipple. This milk resembles in all essential features 

 the milk of lactation. In both sexes this initial activity soon 

 passes off, the gland in the female further developing at puberty, 

 but in the male remaining, save in exceptional cases, in its infan- 

 tile condition or somewhat retrograding. 



410. The secretion of milk. From what has been already 

 said it is obvious that the secretion of milk, while resembling 

 the secretion of the other secreting glands which we have studied 

 in being essentially an activity of the epithelium cells lining the 

 alveoli, nevertheless presents certain interesting features special 

 to itself. If the account given in 404 be a true one, morpho- 

 logical changes in the cells are more prominent than in the case 

 of other glands ; and we may interpret the appearances there 

 related somewhat as follows. When the discharged gland with 

 its low epithelium begins the work of loading, the cells distinctly 

 *grow.' Their cell-substance increases in bulk, and elongating 

 projects into the lumen of the alveolus. At the same time the 

 nucleus divides as if the cell were about to give birth to new 

 cells ; but at first at all events no division of the cell-substance 

 takes place, and the new nuclei lie imbedded in a common cell 

 body. The cell-substance meanwhile puts on secretory activ- 

 ity ; it deposits in itself material to form milk. The deposit 

 of fat is conspicuous and easily recognized, but we may fairly 

 infer that the other less easily distinguished proteid and carbo- 

 hydrate materials are deposited in the cell-substance in a similar 

 fashion. Then follows the ejection of the prepared material ; 

 and this may take place in one of two ways. The oil globules 

 of fat may be protruded from the cell-substance much in the 

 same way that an amoeba extrudes its excrement, and possibly 

 other constituents of milk may be ejected by a similar method. 



