CHEMICAL PHENOMENA OP DIGESTION. 139 
2d. A peculiar organic matter destructible by heat. We 
merely give attention here to the cause of the acid re-action 
of the gastric juice. Two opinions in science prevail at the 
present dayjregarding the cause of this acidity : the one ad- 
mits this property to be owing to the presence of biphos- 
phate of lime ; the other attributes it to an acid in a free 
state, existing in gastric juice. The principal fact relied 
upon for denying the existence of a free acid in gastric juice, 
and admitting alone the presence of biphosphate of lime, 
consists in the circumstance that gastric juice acted upon by 
an excess of carbonate of lime does not disengage carbonic 
acid. Experience has shown to us that this is occasioned 
by the excessive dilution of the acid in the gastric juice, 
which allows the carbonic acid produced to be dissolved as 
fast as it is formed. It was simply necessary for us to con- 
centrate the gastric juice in order to obtain with chalk an 
evident effervescence. Moreover, we have observed that 
gastric juice dissolves neutral phosphate of lime, and, we 
are assured that this salt is completely insoluble in the bi- 
phosphate of the same base. From these experiments we 
have concluded that the acidity of gastric juice is due, not 
to biphosphate of lime, but to the presence of a free acid. 
The authors who have asserted the presence of an isolat- 
ed acid in gastric juice differ in opinion upon its nature ; 
while some admit it to be acetic, the majority consider it 
hydrochloric acid, others again phosphoric acid, and some 
lactic acid. 
We have in succession sought to prove these different 
acids to exist in gastric juice. Before indicating the steps 
we pursued in these experiments, we will observe that they 
were made with very pure gastric juice taken from different 
healthy dogs. 
Acetic acid being volatile, we submitted the gastric juice 
to distillation at a mild heat, with the necessary precaution 
to avoid the rude jumping and mechanical passing over of 
the liquid ; the first products collected and tried with litmus 
