194 GASTRIC DIGESTION 



in the case of St. Martin, according to the observations of Beaumont 

 and Silliman, was 1005 ; but later, F. G. Smith found it in one instance, 

 1008, and in another, 1009. There is every reason to suppose that the 

 secretion, in the case of St. Martin, was normal, and 1005 to 1009 may 

 be taken as the range of specific gravity in the human subject. 



The gastric juice, if kept in a well-stoppered bottle, will retain its 

 chemical and physiological properties for an indefinite period. The 

 only change that it undergoes is the formation of a pellicle, consisting 

 of a vegetable confervoid growth, some of which breaks up and falls 

 to the bottom of the vessel, forming a whitish flocculent sediment. In 

 addition to this remarkable property of resisting putrefaction, putre- 

 factive changes are arrested in decomposing animal matters, both when 

 taken into the stomach and when exposed to the action of the gastric 

 juice out of the body. 



The following analysis by Bidder and Schmidt gives the mean of 

 nine observations on dogs : 



COMPOSITION OF THE GASTRIC JUICE OF THE DOG 



Water . . . .'.- ."; ' ' , . . . . . W j>;- ;. . 

 Ferment (pepsin) . ?~~ . ".'. . . V V. ' . 



Free hydrochloric acid . . 



Potassium chloride . . . . . . . . "'* 



Sodium chloride . . . . . . . , . . 



Calcium chloride . . . . . . . ... 



Ammonium chloride .......... 



Calcium phosphate . . . . . . . . . . 



Magnesium phosphate . . . . . . . . 



Ferric phosphate . . ,..-.-.. . . . . . 



1000.000 



In another series of three observations, in which the saliva was 

 allowed to pass into the stomach, the proportion of free acid was 2.337, 

 and the proportion of organic matter was slightly increased. 



Organic Constituent of the Gastric Juice. Pepsin is a ferment, or 

 enzyme, peculiar to the gastric juice and essential to its digestive prop- 

 erties. When the gastric secretion was first obtained, even by the 

 imperfect methods employed anterior to the observations of Beaumont 

 and of Blondlot, an organic matter was spoken of as one of its con- 

 stituents. The gastric juice also contains a milk-curdling enzyme. 



Free Acid of the Gastric Juice. The character of the free acid was 

 long a question of uncertainty and dispute ; but physiologists now adopt 

 the view that the gastric juice contains free hydrochloric acid, with pos- 

 sibly a small quantity of lactic acid. It is admitted, however, that the 



