524 LECTURE XXII. 



gastric juice has the same effect as a pure acid solution of the corresponding 

 concentrations. The following experiment is important: If soda or lime- 

 water be introduced into the stomach of an animal in the midst of the 

 process of digestion, there is a rapid diminution in the amount of secretion 

 from the pancreas. 



We have here a new link in the chain representing the mutual dependence 

 of one organ upon another. The pancreas regulates its activity according 

 to that of the stomach, and is governed chiefly by the acid produced in the 

 latter. The next question that arises is how the hydrochloric acid of the 

 stomach effects the stimulation of the pancreatic gland. There are two 

 possibilities. It may be that the acid stimulates the peripheral end- 

 apparatus of the centripetal nerves in the mucous membrane, or that it 

 acts upon the nerve center of the secretory cells of the pancreas, or upon 

 the cells themselves, after it has been taken up by the blood. The latter 

 method of action is improbable for a number of reasons. Pawlow showed 

 that the acid taken up by the blood could only have an indirect action; 

 namely, by diminishing the alkalinity of the blood. Now, normally, the 

 alkalinity of the blood is increased by the production of hydrochloric 

 acid, and even in case of an absorption of hydrochloric acid, it remains 

 higher than usual during the period of digestion. Direct experiment con- 

 firms this view, for, on the one hand, it is not possible to stimulate the 

 secretion of the pancreatic gland by means of introducing hydrochloric acid 

 into the rectum, while, on the other hand, the action of the hydrochloric 

 acid is still felt even when its passage out of the stomach is prevented. 1 



Now how shall we explain the action of the hydrochloric acid? Pawlow 

 brings out the following points: Trypsin reacts best in an alkaline 

 solution, but is still active in a neutral or even barely acid solution. As 

 soon as the amount of acid becomes in any way considerable, the action 

 of the trypsin is prevented. Now the pancreatic juice always contains an 

 abundance of alkali by means of which the acid in the chyme is neutral- 

 ized. The more acid the stomach produces, the more acid reaches the 

 intestine with the chyme, and the more alkali is required to combat the 

 injurious effect of the acid. The fact that the secretion of the pan- 

 creas is governed by that of the stomach tends to equalize the conditions. 

 If the amount of pancreatic juice secreted were independent of the hydro- 

 chloric acid in the chyme, then it would often happen that the trypsin 

 would be made inactive, and the activity of the pepsin, which under normal 

 conditions is prevented by the neutralization of the acid it requires, would 

 continue in the intestine. The whole arrangement may be traced in the 

 cycle of common salt, somewhat as follows : The cells of the stomach 

 prepare hydrochloric acid from the sodium chloride in the blood. The 



1 L. Popielski: Inaug. Diss. St. Petersburg (1896); Zentr. Physiol. 10, 405 (1896); 

 Pfliiger's Arch. 86, 215 (1901), and Zentr. Physiol. 16, 43 (1903). 



