PHYSIOLOGY OF THE DIGESTIVE GLANDS 469 



The most recent investigations have been made by Cannons and by Carlson.* The 

 former fed animals food impregnated with bismuth subnitrate, 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 movements of the viscus, but also concerning the rate of discharge of 

 food into the intestine and therefore the duration of the gastric digestive process. 

 Carlson's contribution has been rendered possible by his good fortune in having in 

 his service a second Alexis St. Martin, a man with complete closure of the esophagus 

 and a gastric fistula large enough to permit of direct inspection of the interior of 

 the stomach. Seizing the opportunity thus presented, Carlson during the last four 

 or five years has devoted his attention exclusively to a thorough investigation, not 

 only of the movements of the stomach, but also of the rate of secretion of the gastric 

 juice under different conditions. He has also, with praiseworthy enthusiasm and keen 

 scientific spirit, extended his observations both on laboratory animals and on himself 

 and his coworkers, so as not to incur the error, which is all too frequently made of 

 confining the observations to one species of animal. 



The Nervous Element in Gastric Secretion 



The first stimulus to the secretion of gastric juice is nervousjn origin, 

 and is dependent on the gratification of the appetite and the pleasure of 

 taking food. This fact, after having been suggested by observations 

 made in the clinic, was first thoroughly investigated by Pavlov, who for 

 this purpose observed the gastric secretion flowing either from a fistula 

 of the stomach itself, or from a "miniature stomach," in dogs in which 

 also an esophageal fistula had been established. When food was given 

 by mouth to these animals, it was chewed and swallowed in the usual 

 manner, but before reaching the stomach, it escaped through the esopha- 

 geal fistula. This experiment is known as that of "sham feeding." 

 Within a few minutes after giving food the gastric juice was found to 

 be secreted actively, and if the feeding process was kept up, which could 

 be done almost indefinitely since the animal never became satisfied, the 

 secretion continued to flow. Thus, in one instance Pavlov succeeded in 

 collecting about 700 c.c. of gastric juice after sham feeding an animal 

 for five or six hours in the manner above described. 



After the stomach has emptied itself of the food taken with the pre- 

 vious meal, it is said by Pavlov to contain only a little alkaline mucus. 

 The more recent work of Carlson, however, shows that this is not strictly 

 the case, there being more or less of a continuous secretion of gastric juice 

 An the entire absence of food. The amount varies from a few c.c. up to 

 / 60 c.c. per hour, more secretion being produced when it is collected every 

 | five or ten minutes than if it is collected every thirty or sixty, thus 

 indicating that, ordinarily, some escapes through the pylorus into the 

 duodenum. The secretion contains both pepsin and hydrochloric acid. 

 As to the cause of this continuous secretion, little is known. It may be 

 an example of the periodic activities of the digestive glands described by 



