GASTRIC DIGESTION. 73 



By further fermentation the lactic acid undergoes this 

 change: 



2C 3 H 6 3 = C 3 H 7 C0 2 H + 2C0 2 + 2H 2 . 



butyric acid 



The glucose may be fermented to alcohol: 

 C 6 H 12 6 = 2C 2 H 5 OH + 2C0 2 



alcohol 



and this be converted to acetic acid: 



C 2 H 5 OH + 2 = CH 3 C0 2 H + H 2 0. 



acetic acid 



The so-called "heart-burn," which is one of the accompanying 

 symptoms of gastric fermentation is caused by the eructations of 

 gas carrying the acids up into the throat, where they cause irrita- 

 tion of the mucous membrane. The methods of treatment based 

 upon administration of hydrochloric acid, creasote, or other anti- 

 septic substances is not for the purpose of removing the acids, but 

 to stop the fermentation. Treatment with alkaline substances like 

 magnesia or sodium bicarbonate neutralizes the acids, but does not 

 prevent fermentation. 



The acid phosphates may be present in the normal 

 gastric juice. When present they increase the acidity of the 

 juice or cause an acid reaction in the absence of free acids. 

 An example is the potassium compound, KH 2 P0 4 , which 

 is found in the stomach after meat has been eaten. 



The pepsin can be obtained from the gastric juice or 

 mucous membrane of the stomach in a number of ways. 

 Like most of the animal ferments, it can be extracted from 

 the membrane by glycerin, and this glycerin solution can 

 be preserved for any length of time. If it is to be used 

 immediately, water containing about 0.2-per-cent. hydro- 

 chloric acid can be employed for extraction. If the dry 

 substance is desired, it may be thrown down with finely- 



