Structure of the Tissue. 



11 



should be considered, according to the investigations of Benda and 

 Bertkau, as involuntary muscle cells because of their appearance 

 and their staining qualities. They probably play a part in the 

 emptying of the glandular ducts and the milk secretion. 



Blood capillaries, lymph vessels and nerves run in the inter-and intra-lobular con- 

 nective tissue, which is strengthened by elastic fibres, and contains involuntary muscle 

 cells. Therefore, the same tissue elements are represented as in the teats, with the ex- 

 ception of the many-layered pavement epithelium. 



Fig. 6. 



Structure of the mammary gland in secretion, Hematoxylin. 1 X 800. 

 (a) Secreting glandular alveoli, (b) Alveoli with dormant cells. 



At the end of pregnancy the picture again changes consid- 

 erably. The protoplasm of the previously clear epithelial cells of 

 the secretory system becomes cloudy, the nuclei larger, their chro- 

 matin collects in flakes on the periphery of the nuclei, the borders 

 of the cell become indistinct, the cells become swollen, the nucleus 

 lies in the center, and the indications of the division by indirect 

 fission of the nucleus appear relatively in groups. Some epithe- 

 lial cells show two nuclei at this stage; towards the alveoli fat 

 globules appear. Leucocytes with which a few eosinophiles are 

 mixed, collect beneath the epithelial cells and penetrating the 



