120 



PHYSIOLOGY 



CHAP. 



These phenomena noted on the dog were confirmed for man, as 

 shown in Figs. 39 and 40. 



Langley repeated these observations on fresh preparations of 

 the gastric mucous membrane, and noted changes which, although 

 different, lead to the same interpretation as that of Heidenhain. 

 In abstinence the chief cells are strongly and uniformly granular ; 

 during digestion they become clearer, and are differentiated into 

 two zones, the outer of which (f or \ the cytoplasm) does not 

 exhibit granules, which only appear in the inner zone. Since, as 

 we shall see, the extracts of gastric mucosa contain more pepsin 



Fio. 40. Cross-section of cardiac glands during digestion. (Bohm and v. Davidoff.) sos. 

 References as in Fig. 39. 



and chymosin, according as the number of granules in the chief 

 cells of the fundus and pyloric glands is greater, this confirms the 

 theory which attributes the formation of the enzymes of the 

 gastric juice to these cells. 



The granules seen in the cells of the gastric gland in the 

 fresh state do not, however, represent the enzymes of the gastric 

 juice, but contain the zymogens, i.e. the proteins from which pepsin 

 and chymosin are formed during the process of secretion. 



Schiff first recognised that active pepsin comes from the 

 transformation of an inactive substance found in the gland cells, 

 which he called propepsin. The experiments of Ebstein and 

 Griitzner confirmed this theory. They gave the name of peptic 

 zymogen or pepsinogen to the inert substance which is converted 

 into pepsin. They found that in a watery, non-acidulated, or 

 glycerol extract of gastric mucosa, a certain amount of pepsinogen 



