GLANDS 



55 



FIG. 45. EPITHELIAL CELLS SECRETING Mucus. 

 From a section of the mucous membrane of the human stomach 

 Xs6o. p, Protoplasm; s, secretion; a, three cells, two empty, 

 the third showing the beginning of mucoid metamorphosis; e, the 

 cell on the right is discharging its contents; the granular proto- 

 plasm has increased and the nucleus has become round again. 



where they become changed into clear droplets of mucus. A discoid 

 mass of secretion is thus produced which is quite sharply marked off from 

 the underlying cytoplasm 

 (Fig. 45, a and b). As 

 the cytoplasm becomes 

 increasingly transformed 

 into secretion, the elon- 

 gated nucleus becomes at 

 first round, and then flat- 

 tened. It is forced to 

 the base of the cell where 

 it is lodged in a small amount of unchanged cytoplasm (Fig. 45, b-d). 

 The secretion is then gradually discharged through the distended top- 

 plate, which is often ruptured in sections, and the nucleus again becomes 



round and moves toward the cen- 

 ter of the cell. Most gland cells 

 are not destroyed by the act of 

 secretion, but may repeat the 

 process several times. An ex- 

 ception occurs in the case of the 

 sebaceous glands, in which the 

 cells disintegrate and are cast off 

 with their products. In the 

 mucous cells of the intestine, 

 secretion is formed below and 

 discharged from the free surface 

 at the same time. The cells, as 

 seen in Fig. 46, arise near the 

 bottom of tubular depressions 

 lined with simple columnar epi- 

 thelium. By the formation of 

 new cells below them they are 

 pushed toward the outlet of the 

 tube. Thus the youngest cells 

 are at the bottom of the pit and 

 the oldest are at the top. For a 

 time the secretion develops faster 

 than it is discharged, and the 

 cells enlarge as seen in the middle 

 part of the gland; later, as elimi- 

 nation exceeds production, they 

 become narrow, and their final 

 stages, as compressed cells with 



Gland lumen. 





FIG. 46. INTESTINAL GLAND FROM A SECTION OF THE 



HUMAN LARGE INTESTINE. X 165. 

 The secretion formed in the goblet-cells is here col- 

 ored blue; usually it is pale as in Fig. 45. In zone I 

 the goblet-cells show the beginning of secretion; that 

 expulsion has begun is evident from the presence of 

 drops of secretion in the lumen of the gland. 2, 

 Goblet-cells with much secretion. _ 3, Goblet-cells 

 containing less secretion. 4, Dying goblet-cells, 

 some of which still contain remnants of secretion. 



