146 MANUAL OF PHYSIOLOGY. 



2. Pepsin, the specific substance which gives the gastric juice 



its digestive qualities, is a nitrogenous ferment which, 

 with the foregoing acid, acts on proteids. About .3 

 per cent, is present in the secretion of the human 

 stomach. It is probably associated with other less 

 known ferments, one of which curdles milk without the 

 presence of any acid. . 



3. A variable quantity of mucus is found in the secretion of 



the stomach. 



4. It contains .2 per cent, of inorganic salts, chiefly chlorides 



of sodium, potassium and calcium. 



Method of Obtaining Gastric Secretion. Formerly 

 attempts were made to obtain gastric juice by obliging a dog 

 while fasting, to swallow a sponge, and withdrawing it when 

 saturated with the gastric secretion ; or a fasting dog, allowed to 

 swallow insoluble materials, was killed, and the secretion pro- 

 duced was collected from the stomach. It is best obtained di- 

 rectly from a fistulous opening in the abdominal wall communi- 

 cating with the stomach. 



A gastric fistula was first made by accident. It was a case in 

 which the surgical treatment of a gunshot wound of the stomach 

 of a man left a permanent fistula, by means of which the gastric 

 secretion was carefully investigated. Thus a man proved a valu- 

 able subject for experimental research. 



It is not a difficult matter to reach the stomach by making an 

 artificial opening through the wall of the abdomen, and, having 

 brought the serous surface of the gastric wall into firm connec- 

 tion with the serous lining of the abdominal wall, to open the 

 stomach. The juxtaposition of the parts as well as the patency 

 of the fistula can be secured by a suitable flanged canula closed 

 with a well-fitting cork. By removing the cork the gastric juice 

 may be obtained in small quantities, and various kinds of food 

 may be introduced through the canula, and the changes occur- 

 ring in them studied. 



For experimental purposes an artificial gastric juice may be 

 used. This can be made from the gastric mucous membrane of 



