76 PHYSIOLOGY. 



tion. This "mixed" gastric juice is a secretion compound of a very 

 small percentage of free hydrochloric acid together with the proteo- 

 lytic ferment, pepsin, in a rather saline solution. We know that the 

 pepsin, for instance, of the gastric juice, is not found as such in the 

 blood, requiring only to be filtered from the same for use, but 

 that it is the result of the activity of the cells and yielded by them. 



A characteristic microscopical feature of the cells of secretory 

 glands in general is that the protoplasmic portions are crowded with 

 fine granular bodies before secretion, but that during and particularly 

 after secretion their numbers are very perceptibly diminished. From 

 this it was inferred that, while the granules might not in themselves 

 represent the important ingredients of the various secretions, yet they 

 were responsible and directly concerned in their manufacture. 



The cardiac glands are composed of two distinctive types of cells : 

 columnar epithelium lining the lumen and the large spherical or 

 oval cells located on the periphery. The former are termed chief, or 

 central, the latter parietal, cells. 



The pyloric glands are constructed of but the one kind, epithelial 

 in nature, similar to those found in the cardiac cells and termed 

 chief, or central. 



The central cells of both the cardiac and pyloric glands are found 

 to be heavily charged with minute granules before digestion; in fact, 

 such numbers are present as to interfere with the staining of the cells 

 with aniline dyes, because of the protoplasm being obscured. During 

 secretion some of the granules are discharged into the lumen, pre- 

 sumably through the protoplasmic movements of the cells as agents 

 or media. After digestion, therefore, the cells show a difference, 

 principally in that there is a decrease in the number of granules 

 present, manifested by either a clear path along the periphery or by a 

 shrunken appearance of the cells with fewer granules. The material 

 for the formation of these granules is taken by the cells from the 

 lymph which constantly bathes them, and through the influence of the 

 protoplasm is manufactured into granules. 



The central are the cells which are directly concerned in yielding 

 the very important and proteolytic element of the gastric juice, the 

 pepsin. Without its presence in an acidulated medium, the normal 

 processes of proteolysis are unable to be accomplished in the stomach. 

 These granules are not pure pepsin to be passed along the lumen and 

 so enter the composition of the gastric juice, but are, rather, a zymo- 

 gen substance acting as a precursor, which is readily converted into 



