SECT. 210.] FORMATION OF THE MILK. 475 



added, before the cud of pregnancy, a new formation of cells con- 

 taining fat, in the gland-vesicles, so. that the older cells become 

 forced into the lacteal ducts, and gradually fill them. Thus it 

 happens that, although no proper secretion yet takes place, that 

 some drops of a fluid can, as a rule, be pressed out of the gland 

 in the latter half of the pregnancy. This fluid is not, indeed, real 

 milk, as its yellowish colour will show; but still it contains a certain 

 numher of fat-globules, quite similar to the subsequent milk-glo- 

 bules ; and these are derived from the fatty cells, more or less 

 disintegrated, and with them entire cells of the same kind are 

 also seen, with or without an envelope; and these are the so-called 

 colostrum bodies. When lactation commences after parturition, 

 the formation of cells in the gland-vesicles attains an unusual 

 energy, so that the fluids collected in the lacteal canals and acini 

 arc discharged in the first three to four days as colostrum, or im- 

 mature milk, which then gives way to the secretion of the true 

 lacteal fluid. 



In the extremities of the gland, the milk consists of only a little 

 fluid, and cells completely filled with fat-globules ; these cells 

 sometimes fill the acini to the exclusion of all others, but some- 

 times arc accompanied by paler epithelial cells, likewise containing 

 more or less fat. These two kinds of cells have a common origin, 

 cither by a process of free cell-formation, or by the continual mul- 

 tiplication of the epithelial cells, in a manner analogous to the 

 formation of the sebaceous matter of the skin (vide § 74). These 

 cells, which I will call milk-cells, break down into their elements, 

 the milk-globules, even before they leave the lacteal ducts ; their 

 envelopes, and generally, also, their nuclei, disappearing entirely, so 

 that the excreted milk presents, as a rule, no trace of its mode of 

 origin. At the most, there are found in it heaps of milk-globules, 

 of various sizes and much isolated, which may also be called colos- 

 trum corpuscles, from their resemblance to those occurring in the 

 colostrum.— The secretion of the milk, therefore, is essentially 

 dependent upon a formation of fluid and fatty cells in the 

 gland -vesicles, and, accordingly, belongs to the category of 

 secretions in which morphological elements play a part. The 

 affinities of this fluid are especially with those secretions which 

 contain fat, as the sebaceous matter of skin, in which cells are 

 found exactly similar to those in the acini of the mamma? and in 

 the colostrum. 



In newly-born infants, the mammae very frequently contain a 

 small quantity of a fluid resembling milk in its appearance and 



