CH. VIII.] GASTRIC JUICE. IQ5 



standard test meals is more important than that of the 

 juice as actually secreted. The hydrochloric acid, secreted 

 mainly by the oxyntic cells of the fundus, neutralises the 

 alkaline salts of the saliva to form sodium chloride. It 

 also combines with the proteins of the saliva and of the 

 food to form acid-protein compounds. These function as 

 weak acids. In this way the percentage amount of free, 

 uncombined hydrochloric acid in the gastric contents may 

 be very considerably less than in the naturally secreted 

 juice. Further alterations are brought about by the 

 fermentation of the carbohydrates to lactic acid. This is 

 mainly caused by certain organisms called sarcinae, which 

 are very commonly present in the stomach. If the starchy 

 foods are thoroughly masticated and mixed with the 

 saliva, the polysaccharides are rapidly broken down by 

 the ptyalin to maltose. This is passed through the pylorus 

 and leaves little for the sarcinae to ferment. The presence 

 of much lactic acid generally indicates a diminished secre- 

 tion of hydrochloric acid, which inhibits the action of the 

 lower organisms. 



Ewald test meal. The patient under investigation is 

 starved for at least 12 hours. The meal consists of 400 cc. 

 of weak tea, without milk or sugar, and 50 grams, of dry 

 toast, which should be well masticated. After i hour the 

 gastric contents are removed by syphonage through a soft 

 rubber stomach tube. 



The fluid obtained is measured and filtered. The 

 normal physiological volume is between 40 and 70 cc. A 

 marked increase in volume probably indicates motor 

 insufficiency of the stomach, or hypersecretion, the latter 

 generally being associated with an increased amount of 

 hydrochloric acid (hyperchloridia). 



Chemical examination. The reaction of the filtered 

 juice is nearly always acid to litmus paper. The percent- 

 age amount of the following substances must be deter- 

 mined : 



