226 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



ever it is necessary to have the normal juice for examination. A silver canula 

 is placed in the fistula, and at any time the plug closing the canula may be 

 removed and gastric juice be obtained. In some cases the oesophagus has 

 been occluded or excised so as to prevent the mixture of saliva with the gastric 

 juice. Gastric juice may be obtained from human beings also in cases of vom- 

 iting or by means of the stomach-pump, but in such cases it is necessarily 

 more or less diluted or mixed with food and cannot be used for exact analyses, 

 although specimens of gastric juice obtained by these methods are valuable in 

 the diagnosis and treatment of gastric troubles. 



Properties and Composition of Gastric Juice. The normal gastric secre- 

 tion is a thin, colorless or nearly colorless liquid with a strong acid reaction 

 and a characteristic odor. Its specific gravity varies, but it is never great, 

 the average being about 1002 to 1003. Upon analysis the gastric juice is 

 found to contain a trace of proteid, probably a peptone, some mucin, and 

 inorganic salts, but the essential constituents are an acid (HC1) and two 

 enzymes, pepsin and rennin. A satisfactory analysis of the human juice has 

 not been reported, owing to the difficulty of getting proper specimens. 

 According to Schmidt, 1 the gastric juice of dogs, free from saliva, has the 

 following composition, given in 1000 parts: 



Water 973.0 



Solids 27.0 



Organic substances 17.1 



FreeHCl 3.1 



NaCl 2.5 



CaCl 2 0.6 



KC1 1.1 



NH 4 C1 0.5 



Ca 3 (P0 4 ) 2 1.7 



Mg 3 (P0 4 ) 2 0.2 



FePO 4 0.1 



Gastric juice does not give a coagulum upon boiling, but the digestive enzymes 

 are thereby destroyed. One of 'the interesting facts about this secretion is the 

 way in which it withstands putrefaction. It may be kept for a long time, for 

 months even, without becoming putrid and with very little change, if any, in 

 its digestive action or in its total acidity. This fact shows that the juice 

 possesses antiseptic properties, and it is usually supposed that the presence of 

 the free acid accounts for this quality. 



The Acid of Gastric Juice. The nature of the free acid in gastric juice 

 was formerly the subject of dispute, some claiming that the acidity is due to 

 HC1, since this acid can be distilled oif from the gastric juice, others contend- 

 ing that an organic acid, lactic acid, is present in the secretion. All recent 

 experiments tend to prove that the acidity is due to HC1. This fact was first 

 demonstrated satisfactorily by the analyses of Schmidt, who showed that if, 

 in a given specimen of gastric juice, the chlorides were all precipitated by 

 silver nitrate and the total amount of chlorine was determined, more was 

 1 Hammarsten : Text-book of Physiological Chemist'ry (translation by Mandel), 1893, p. 177. 



