ZOOLOGY, ENTOMOLOGY, AND MEDICINE 249 



pepsin immediately in contact with the wall of the stomach is 

 rendered inert by the oxidative processes of the cells. This 

 theory assumes that normally a balance exists between the oxi- 

 dative processes of the cells of the mucosa and the digestive 

 action of the pepsin in the stomach. If this balance is de- 

 stroyed, as for example by depriving a limited area of oxygen 

 by cutting off the blood supply, thereby decreasing the oxi- 

 dative processes of the area, this area should be digested by 

 the pepsin with the production of ulcer. 



That the mucosa is digested with resulting ulcer under such 

 a condition, has been verified by many observers. 



REPORT OF EXPERIMENTS 



The following experiments were devised to imitate the pro- 

 tective mechanism as set forth in the foregoing hypothesis : 



In Figure 1, (a) is a rubber cuff holding vessels (b) and 

 (c) in position as indicated; (d), a piece of platinum mesh 

 tied over the end of cylinder (b), and (e) a piece of gastric 

 mucosa of the dog tied over the platinum mesh. Before the 

 platinum mesh was tied over the end of the cylinder, platinum 

 black was deposited on it by means of the direct electric cur- 

 rent. To 15 c.c. of gastric juice of the dog, 15 c.c. of hydrogen 

 peroxide were added, and the resulting solution was made 

 acid with hydrochloric acid to the same extent as the original 

 gastric juice. This solution was poured into cylinder (b), 

 and the whole preparation placed in a water bath at 38 C. 

 Immediately after the solution was poured into the cylinder 

 an evolution of oxygen gas was observed in the region of the 

 platinum mesh. This, of course, was due to the decomposition 

 of the hydrogen peroxide by the platinum black. Thus the 

 mucosa was exposed to the action of the gastric juice in the 

 presence of atomic oxygen. After six hours, the piece of 

 mucosa was removed from the tube and photographed (Fig. 

 2A). It may be seen that the central circular area exposed to 

 the action of the gastric juice in the presence of atomic oxy- 

 gen had not been digested. 



Another preparation, similar to the one described, except 

 that no platinum black was deposited on the platinum mesh, 

 was made and placed in the water bath at 38 C. On addition 

 of the gastric juice diluted with hydrogen peroxide no oxygen 



