DIGESTION. 



93 



membrane is tall, narrow and cylindric in shape, and consists of mucus- 

 secreting goblet ceUs. The outer half of the cell contains a substance, mu- 

 cinogen, which produces mucin. The gastric glands in both situations are sur- 

 rounded by a fine connective tissue, which supports blood-vessels, nerves, 

 and lymphatics. 



Changes in the Cells During Secretion. During the periods of rest and 

 secretory activity the cells of the glands undergo changes in structure which 



FIG. 13. 



Diagram showing the relation of the ultimate twigs of the blood-vessels, V. and 

 A, and of the absorbent radicles to the glands of the stomach and the different kinds 

 of epithelium viz., above cylindric cells; small, pale cells in the lumen, outside 

 which are the dark ovoid cells. (Yeo's " Text-book of Physiology.") 



are supposed to be connected with the production of the pepsin and hydro- 

 chloric acid. During rest, the protoplasm of the central cells becomes filled 

 with granular matter; during the time of secretion this disappears, presumably 

 passing into the lumen of the tubule, and as a result the protoplasm becomes 

 clear and hyalin in appearance. The granular material is probably the 

 mother substance, pepsinogen, which, inactive in itself, yields the active fer- 

 ment, pepsin. The parietal cells during digestion increase in size, but do not 

 become granular. It is at this period that they secrete the hydrochloric acid. 



