380 



EXTERNAL INTEGUMENT. 



Fig. 99. Lobule of the mam- 

 mary gland.* 



separate orifices. The structure of this apparatus is similar 

 to that of glands in general : the glandular culs-de-sac are 

 filled with cells resembling those of 

 the sebaceous glands ; the epithelial 

 covering of the lactiferous canals 

 or tubes has, however, a tendency 

 to become columnar. In passing 

 through the nipple, these tubes trav- 

 erse a sub-cutaneous connective 

 tissue abounding in smooth muscu- 

 lar elements, either transverse or 

 circular; the contraction of these 

 muscular fibres, which are only 

 an exaggeration of the smooth 

 muscles normally attached to the 

 dermis, causes the elongation and 

 stiffness, or, in short, the erection 

 of the nipple (see p. 364). 



The secretion of milk is effected in the same manner as 

 that of the sebaceous glands : by a moulting of the globules ; 

 at the beginning of the secretion, this mode of production 

 may be readily observed, globules being still found which, 

 after undergoing fatty degeneration, are not entirely dis- 

 solved, and appear as cells containing numerous drops of fat : 

 these are the globules of the colostrum (Fig. 100). The 

 colostrum is thus the result of a secretion not yet firmly 

 established, or rather interrupted by some intercurrent cause, 

 such as the return of the catamenia or pregnancy in a nurs- 

 ing mother. 1 



1 This opinion as to the formation of milk by the moulting of 

 the cells is not held by all physiologists. Cl. Bernard's theory is 

 as follows: " There takes place a sort of budding (bourgeonnement) 

 of the superposed cells, in which the materials of the milk, casein, 

 butter, etc., are prepared; the coat of the lacteal cell is then dis- 

 solved in an alkaline fluid, and milk is produced." Ch. Robin, on 

 the contrary, maintains that the cul-de-sac of the breast, which 

 are lined with epithelium during pregnancy, and while little or no 

 secretion is taking place, lose this epithelium as soon as the secre- 

 tion is established. If this be so, the special phenomena of secre- 

 tion must take place in the wall proper of the culs-de-sac. Ch. 

 Robin also explains the origin of the globules of the colostrum by 

 looking upon them as white globules, degenerated or transformed 

 leucocytes. Whenever the leucocytes (white globules) remain 



v, v, v, Glandular vesicles, forming by their union a lobule. 



