172 JOHN SUNDWALL 



later on after ramification. The epithelial wall, which avei-ages 

 from 12 to 18m in thickness, is composed of from one to two 

 layers of cells similar in arrangement to those described for the 

 primary ducts. The larger interlobular ducts generally possess 

 two complete layers while in the smaller ones there is a notice- 

 able reduction of the cells which form the outer layer. Conse- 

 quently in these smaller ducts many of the epithelial cells 

 extend down to the basement membrane. 



The single layer cells are cylindrical in form. The cytoplasm 

 stains deeply and evenlj^ in the various cytoplasmic stains. 

 Study of these cells by means of the oil immersion shows the 

 cytoplasm to be very finely granular. No basal filaments or 

 secretory granules can be seen in the general stains. I did not 

 see in my preparations the central bodies described by Zimmer- 

 mann. Tissues fixed in acetic osmic bichromate and stained 

 in acid fuchsin-methyl green show numerous mitochondria. 

 These are described under 'Mitochondria.' The cell boundaries 

 are indefinite and only in the thinnest sections can they be made 

 out clearly. As in the other ducts where a second layer of cells 

 is present the inner layer sends basal processes between them 

 which reach the basal membrane. The nuclei, which average 

 from 6 to 8^, are round or oval and show the same staining char- 

 acteristics as those of the primary ducts. 



The cells in the outer layer, which, as already stated, are fewer 

 in number, are more or less elongated — this elongation being 

 parallel to the circumference of the duct. Here also the cell 

 boundaries are indefinite. The cytoplasm stains similarly to 

 that of the cells of the inner layer. In very thin sections both 

 stain with the same degree of intensity. In thick sections, how- 

 ever, the inner layer appears more densely stained. This obser- 

 vation was made by Fleischer, who states, as a consequence, 

 that the cytoplasm of the cells of the inner layer stains more 

 intensely than does that of the outer layer. In my opinion this 

 apparently deeper stain is due to the fact that these inner cells 

 are more numerous and more compact, while those of the outer 

 layer are fewer in number and more loosely surrounded by other 

 cells. The nuclei of these cells are either oval or elongated, the 



