118 THE WORK OF THE DIGESTIVE GLANDS. 



In addition we have had a dog (Dr. PopielsM) whose stomach was 

 divided into two parts near the pyloric region, into each of which a 

 fistula-tube was brought. If now acid were introduced into the larger 

 segment the pancreas remained at rest. On the other hand, when acid 

 was poured into the pyloric portion, a secretion of pancreatic juice 

 appeared, but only when the acid passed on into the duodenum. This 

 is in harmony with the fact that the flow of pancreatic juice rises and 

 falls in undulatory fashion, obviously from its connection with the entry 

 of the acid food mixture into the intestine. One must be very partial 

 to forced conclusions, who interprets the action of acids upon the 

 pancreas as anything else but reflex. We may mention here once more, 

 that in the case of the pancreas, the necessity is completely removed of 

 discussing a direct penetration of food materials into the lumen of the 



gland . 



The interesting question remains of how we are to account for the fact 

 that the acid has an effect. The substance, as we have already said, forms 

 a connecting link between gastric and intestinal digestion. This fact is 

 undisputed, but why does the acid and not something else serve as the 

 connecting link ? Naturally, we cannot as yet claim to have solved this 

 question scientifically, we can only bring forward some hypotheses. As 

 is known, the pancreatic ferments act best in an alkaline medium. 

 When weakly acid their effect is less, and with any pronounced degree 

 of acidity it soon becomes nil. Hence it may be conceived that the 

 pancreatic juice comes in to neutralise the acid which causes it to flow, 

 and thus to provide a suitable medium for the activity of its ferments. 

 At the same time the pancreatic juice protects itself against the destruc- 

 tive action of the pepsin, for which a neutral or alkaline medium is very 

 unsuitable. Thus the fruitful idea of Biiicke that the bile arrests 

 the action of pepsin in the duodenum and provides favourable conditions 

 for intestinal digestion may also be extended to the pancreatic juice. 

 At the same time another important significance of this relationship 

 lies near. For a peculiar and as yet not quite obvious reason, the gastric 

 juice is secreted with the most concentrated strength of hydrochloi'ic 

 acid possible. This hydrochloric acid, according to the present teaching 

 of physiology, is prepared from the sodium chloride of the blood. An 

 excess of alkali thus arises in the blood, and this must, in order to 

 preserve the mean chemical composition of the fluid, be removed from 

 it. The hydrochloric acid, however, after fulfilling its function in the 

 alimentary canal, would again be absorbed, and thereby in turn lead to 

 a marked diminution of the alkalinity of the blood. Consequently the 

 reaction of this fluid would suffer great variations in both directions 

 during digestion ; but as we know, this is a factor the constancy of which 

 is of great importance to the chemical processes which transpire in the 



