248 DIGESTION. 



would undoubtedly "be the case if it contained a free acid. 

 The simple reply to this is that there is sufficient evidence 

 to show that it is not the fact. Melsens, using a specimen of 

 fluid obtained by Blondlot from the dog and given to Du- 

 mas, found that seventy-three grammes of juice dissolved, in 

 twenty-four hours, 0*108 of a gramme of calcareous spar 

 (crystallized carbonate of lime). He confirmed this observa- 

 tion by several experiments, so that there can be no doubt 

 as to its accuracy. 1 



It is plain, therefore, that while the acid phosphate of 

 lime has been shown to be a constant constituent of the pure 

 gastric juice, contributing, in a certain degree, to its acidity, 

 it is not by any means to be regarded as the sole acid prin- 

 ciple ; the phosphate probably existing in this form by virtue 

 of the presence in this fluid of a free acid. 



On what does the Acidity of the Gastric Juice depend ? 



This is the simple question to which the foregoing discus- 

 sion naturally leads ; and it is one which can be answered 

 almost with positiveness, though it is not settled to the sat- 

 isfaction of all physiologists, and there are some conflicting 

 observations which can be harmonized only by new re- 

 searches. 



Aside from the conditions under which acids, such as 

 the butyric, acetic, or the lactic, are developed from articles 

 of food taken into the stomach, the evidence is strongly in 

 favor of free lactic acid as the principle on which the gastric 

 juice mainly and constantly depends for its acidity. There 

 also exists a certain proportion of the biphosphate of lime ; 

 and this is the only condition in which a phosphate of lime 

 can exist in the presence of free lactic acid. 



The observations of Bidder and Schmidt indicate, appar- 

 ently, a quantity of chlorine in the gastric juice not to be 



1 MELSENS, Recherches sur VAcidite du Sue Gastrique, Comptes JRendus, Paris, 

 1844, tome six., p. 1289 et seq. 



