220 NORMAL HISTOLOGY. 



process results in an enlargement of the leucocyte, and, in extreme 

 cases, to an obscuring of the nucleus and cytoplasm by fat-globules, 

 so that the whole appears as though composed of an agglutination 

 of numerous drops of fat (Fig. 195). 



As the functional activity of the gland matures the epithelial 



FIG. 194. FIG. 195. 



Fig. 191. Dividing epithelial cells from the mammary gland of the guinea-pig. (Michaelis.) 

 The figure represents the proliferation of the cells by the indirect mode before lactation 

 has been established i. e., during the maturation of the gland. 



Fig. 195. Colostrum-corpuscles and leucocytes from the colostrum of a guinea-pig. 

 (Michaelis.) 



cells lining its acini produce drops of fat in the cytoplasm bor- 

 dering on the lumen, and these are subsequently discharged into 

 the lurnen, forming the fat or cream of the milk. The casein of 

 the milk appears to be produced in the following manner : it has 

 been observed that during lactation the nuclei of some of the cells 

 present changes in form that lead to the inference that they undergo 

 division by the direct mode i. e. 9 without passing through the 

 phases of karyokinesis. It thus happens that some of the epi- 

 thelial cells contain two nuclei. These cells, after a while, project 

 into the lumen of the acinus, the two nuclei lying in a line perpen- 

 dicular to its wall. It is supposed that the nuclei nearest the lumen 

 become detached, together with some of the cytoplasm, and that the 

 chemical constituents of the nucleus and cytoplasm enter into the 

 formation of the casein. Such free nuclei have been observed in 

 the lumina of the acini, and it is known that the chromatin which 

 they contain disintegrates and eventually disappears (chromolysis), 

 so that it is not found in the secreted milk. It is probable that the 

 other constituents of the nucleus likewise undergo chemical changes 

 (karyolysis) (Fig. 196). 



