PHYSIOLOGY OF THE DIGESTIVE GLANDS 433 



the main function of the stomach is to crush or triturate the food or to 

 act on it chemically. The great French scientist Reaumur and a little 

 later the Italian Abbe Spallanzani (1729-1799) attacked this problem by 

 methods that anticipate those of Rehfuss and Einhorn. Spallanzani ulti- 

 mately devised the method of swallowing small perforated wooden tubes 

 containing foodstuffs and covered by small linen bags. After the bags 

 were passed per rectum, he found that considerable erosion or digestion 

 of the food had occurred, but that the wooden tubes, however thin- 

 walled they might be, were not crushed. In order to secure samples of 

 the gastric juice free from food, the only method available to the older 

 investigators consisted in swallowing sponges attached to threads, which 

 after being for some time in the stomach were withdrawn and squeezed 

 dry of juice. 



The next great contribution came from this country, where, in 1833, 

 Dr. Beaumont, while a surgeon in the service of the American troops 

 located at Mackinaw, made observations on a Canadian voyageur by the 

 name of Alexis St. Martin, who by the premature discharge of his gun 

 had wounded himself in the stomach, the wound never healing but leav- 

 ing a permanent gastric fistula. Beaumont arranged to keep Alexis St. 

 Martin in his service for several years, during which time he made 

 numerous observations on the process of digestion in the stomach 

 observations many of which are of great value even at the' present day. 



By none of these methods, however, could a sample of pure gastric 

 juice be secured while the digestive process was actually in progress. 

 To make the collection of such a sample possible, Heidenhain devised a 

 method of isolating portions of the stomach wall as pouches opening 

 through fistulas on the abdominal wall. The results of Heidenhain 's 

 experiments are, how r ever open to the objection that the secretion in 

 the isolated pouches may not really correspond to that occurring in the 

 main stomach, since the connections of the pouches with the central 

 nervous system must have been severed. In order that these connec- 

 tions might remain as nearly intact as possible, the Russian physiologist, 

 Pavlov, 1 devised an ingenious operation -in which the pouch, or " minia- 

 ture stomach, ' ' remains connected with the main stomach through a con- 

 siderable width of mucous and submucous tissue and in which the nervous 

 connections are not severed. The essential nature of this operation 

 will be evident from the accompanying diagram. (Fig. 148). 



The most recent investigations have been made by Cannon 3 and by 

 Carlson. 4 The former fed animals food impregnated with bismuth sub- 

 nitrate, and then exposed the animal to the x-rays. A shadow is 

 produced by the food mass in the stomach, and from the changes in the 

 outline of this shadow facts have been collected, not only concerning the 



