ACTION OF THE GASTRIC JUICE IN DIGESTION 195 



degree of acidity is variable, and that the normal acid may be replaced, 

 without loss of the digestive properties of the secretion, by lactic, oxalic, 

 acetic, formic, succinic, tartaric, citric, phosphoric, nitric or sulphuric 

 acid. 



Saline Constituents of the Gastric Juice. It has been shown that 

 artificial mixtures containing the organic matter of the gastric juice and 

 the proper proportion of free acid are endowed with the digestive prop- 

 erties of the normal secretion from the stomach, and that these proper- 

 ties are rather impaired when an excess of its normal saline constituents 

 is added or when the relation of the salts to the water is disturbed by 

 concentration ; but physiologists attach little importance to .the saline 

 constituents, except sodium chloride, which is thought to be concerned 

 in the production of hydrochloric acid. 



Action of the Gastric Juice in Digestion. Certain of the substances 

 most readily attacked by the gastric juice are acted on by weak acid 

 solutions containing no organic matter ; but it is now well established 

 that the presence of a peculiar organic matter is a condition indis- 

 pensable to actual digestion. It has also been shown that liquids con- 

 taining the organic constituent of the gastric juice have no digestive 

 properties unless they also possess the proper degree of acidity ; and 

 it is as well settled that liquids containing acids alone have no action on 

 albumins similar to that which takes place in digestion, and that when 

 these substances are dissolved, it is simply accidental. 



The presence of any one particular acid does not seem essential 

 to the digestive properties of the gastric juice, so long as the proper 

 degree of acidity is preserved ; and it is important that the normal acid 

 can be replaced by other acids, for in case any salt were introduced 

 into the stomach which would be decomposed by the acid of the gastric 

 juice, digestion would be interfered with, unless the liberated acid could 

 take its place. 



In studying the physiological action of the gastric juice, it must 

 be borne in mind that the general process of digestion is accomplished 

 by the combined as well as the successive action of the different diges- 

 tive secretions. The act should be viewed in its ensemble, rather than 

 as a process consisting of several successive and distinct operations, in 

 which different classes of alimentary matters are dissolved by distinct 

 liquids. The food meets with the gastric juice, after having absorbed 

 a large quantity of saliva ; and it passes from the stomach to be acted 

 on by the intestinal secretions, having imbibed both saliva and gastric 

 juice. 



When the acts which take place in the mouth are properly per- 

 formed, the following alimentary substances, comminuted by the action 



