164 THE WORK OF THE DIGESTIVE GLANDS. 



numerous the forms of stimuli employed ? And yet this great mass of 

 work could not in the smallest degree answer our question. It offered 

 to us the analytical consideration of a long series of facts without any 

 inner connection. But as to why the one kind of food is held back 

 while the other is moved forwards, or why the one is moved quickly 

 and the other slowly, there was no reply ; and yet is not the com- 

 plex food mixture somehow separated into its components during 

 the onward movement? All these processes must, as a matter of 

 fact, take place, because upon the food, which is a mixture of 

 different substances, the various juices are poured out in different 

 parts of the alimentary canal, and in varying combinations, both 

 quantitatively and qualitatively. Why, therefore, and from what 

 combination of separate elementary conditions is this propagation of 

 the food effected, and with the purposiveness of a delicate and ingenious 

 mechanism ? The synthesis of the actual progress, and the mechanism 

 of the movements, have been till recently as little brought under 

 investigation as had the synthesis of the secretory work of the digestive 

 apparatus. The credit of having begun this synthesis belongs to two 

 German investigators (Hirsch and v. Mering), who simultaneously 

 discovered that the passage of food from the stomach into the intestine 

 is quantitatively regulated from the upper segment of the latter, in 

 such a way that the expelling movements of the stomach are tempo- 

 rarily inhibited by a reflex from the duodenum, which closes the pylorus 

 each time after a portion of the stomach contents has passed into the 

 intestine. Our investigations have been carried on along the same lines, 

 and have already yielded interesting results. In the first place, it was 

 discovered (experiments of Dr. A. 8. Serdjukow} that the duodenal 

 mucous membrane, apart altogether from the fulness of the tube, 

 regulates the passage of food from the stomach into the intestine by its 

 behaviour towards the acid reaction of the gastric contents. When one 

 continuously injects, through a duodenal fistula, either small quantities 

 of acid solutions, or of pure gastric juice, a solution of soda which had 

 previously been introduced into the stomach may be kept there for an 

 unlimited time. If, however, no acid be injected into the duodenum, 

 the solution of soda generally leaves the stomach very quickly. This 

 cannot be accounted for by a reflex mechanically called into play, for if 

 all the other conditions remain unaltered, and a solution of soda be 

 poured into the duodenum, the escape of the solution from the stomach 

 is not prevented. On the other hand, we have observed that the 

 passage of acid solutions out of the stomach is remarkably slower in 

 the case of dogs with a pancreatic fistula than in those without one. 

 Each time that the intestine receives a portion of the acid contents of 

 the stomach, a reflex act is set up which temporarily occludes the 



