SECRETION. 



33 



FIG. 35. EPITHELIAL CELLS SECRETING Mucus. 



From a section of the mucous membrane of the stomach of man. 

 X 560. p, Protoplasm; s, secretion; a, two empty cells; the 

 cell between them shows beginning mucoid metamorphosis; e, 

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

 protoplasm has increased and the nucleus has become round 

 again. 



The fluid secretion and sometimes the granules are discharged from the 

 free surface. 



Such cells are 

 striking examples of 

 the polarity of cells, by 

 which is meant a dif- 

 ferentiation of proto- 

 plasm along the axis 

 of the cell. The basal 

 portion receives the 

 nutriment to be made into secretion. It often exhibits striations, rods, or 

 filaments known as ergastoplasm (Fig. 34, A). The distal portion which 



contains the elaborated product 



9 is obviously of a different nature. 



Very many kinds of cells give evi- 

 dence of polarity. The nuclear 

 constituents also may be arranged 

 in relation to this same axis or 

 to another, but nuclear polarity 

 which is manifest during mitosis; 

 may be disguised or lost at other 

 times. 



In mucous cells as in serous, 

 secretion begins with granule 

 formation. The granules soon 

 change into clear masses of mu- 

 cus, which accumulate toward 

 the free surface and are more or 

 less sharply separated from the 

 unchanged protoplasm beneath. 

 The mucus is, however, pene- 

 trated by strands of protoplasm 

 which contain the centrosome. 

 As elaboration of mucus continues 

 the nucleus is crowded to the base 

 of the cell, and may become round 

 or flattened (Fig. 35). Then the 

 secretion is gradually discharged, 

 apparently with the rupture of the 

 top plate. If the cell is not de- 

 stroyed the nucleus returns to its 



Secretion. 



Protoplasm 

 and nucleus. 



Gland lumen. 



I ' .- 



FIG. 36. INTESTINAL GLAND FROM A SECTION OF 

 THE LARGE INTESTINE OF MAN. X 165. 



The secretion formed in the goblet-cells is colored 

 blue. In zone i the goblet-cells show the begin- 

 ning 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 secre- 

 tion. 4, Dying goblet-cells, some of which still 

 contain remnants of secretion. 



