GLANDS 



255 



the several chapters in which they are described in detail. This type 

 includes the testis, the prostate, the cerumiuous glands, many of the 

 ductless glands, and also some authors describe the ovary and the lungs 

 as comforniing- to the glandular type of structure. 



The mixed glands include some tubules which are characteristically 

 mucous, while others are typical serous secreting. Occasionally both 

 types of secreting cells are contained within the same tubule. 



Mucus-secreting cells possess the general .characteristics which 

 have been previously recited 

 under the head of goblet cells 

 (Chapter II). When void of 

 secretion the cytoplasm of 

 mucous cells is granular, 

 their nucleus centrally situ- 

 ated, and their shape more or 

 less columnar. The pre-secre- 

 tion ^accumulates in the cen- 

 tral portion of the cell and 

 occupies an area, adjacent to 

 the glandular lumen, which 

 steadily increases in size until 

 the greater part of the cyto- 

 plasm has been replaced; the 

 nucleus is pushed to the proxi- 

 mal or attached end of the cell ; 

 and the whole cell often be- 

 comes swollen and distended to more than double its original size. Finally 

 the cell membrane ruptures and the mucus pours out upon the free sur- 

 face of the membrane. 



At the base of the mucus-secreting cells, and between them and 

 their basement membrane, are groups of epithelial cells having a finely 

 granular cytoplasm, which form crescentic cell masses, the demilunes 

 of Heidenhain (crescents of Gianuzzi). In the tubules of some glands 

 these demilunes are extremely minute, in others they occupy a con- 

 siderable portion of the epithelial coat and encroach upon the glandular 

 lumen. Their significance is not definitely understood. They have 

 been considered as representing either secreting cells which are in a 

 state of rest following the discharge of their secretion, or as primordial 

 cells which by reproduction give origin to tnie mucus-secreting cells. 

 It is quite possible that both of these functions are assumed by the several 



FIG. 256. TRANSECTION OF THREE SECRETING 

 TUBULES OF THE SUBMAXILLARY GLAND OF 

 MAN. 

 A, a serous tubule; B, a mucous tubule; C, 



a mucous tubule with a demilune, d. Hematein 



and cosin. X 665. 



