CHAP. L] 



DIGESTION. 



273 



by changes really comparable to those of the pancreas are obscured. 

 For we find that in the newt the cells, when examined in a living 

 condition, are granular throughout when at rest but during activity 

 develope a clear outer zone, the granules becoming restricted to 

 the inner zone. And in many mammals similar changes may be 

 demonstrated by the use of osmic acid (Fig. 52). In some mammals 



FIG. 52. GASTRIC GLAND OF MAMMAL (Mole) DURING ACTIVITY (Langley). 



c, the mouth of the gland with its cylindrical cells. 



n, the neck, containing conspicuous ovoid cells, with their coarse protoplasmic 

 network. 



/, the body of the gland. The granules are seen in the central cells to be limited 

 to the inner portions of each cell, the round nucleus of which is conspicuous. 



no very obvious difference between rest and activity can be made 

 out; and it is possible that in these a regeneration of granules 

 takes place during activity as well as during rest and that in pro- 

 portion as granules are being used up, so that the amount of 

 granules remains fairly constant. 



Moreover we have evidence of the existence in the gastric 

 membrane of a zymogen, a mother of pepsin, a pepsinogen; 

 though owing to the facility with which apparently the conversion 

 of pepsinogen into pepsin takes place, the matter is not so clear as 

 in the analogous case of trypsinogen ; and it would appear that the 

 amount of pepsinogen and the abundance of visible granules in fresh 

 living cells run parallel to each other with considerable regularity. 



F. 18 



