142 CHEMICAL PHENOMENA OF DIGESTION. 
discovered in this operation a striking analogy with the 
phenomena produced by the distillation of the gastric juice, 
namely — that in the first parts of the distillation, only pure 
water passes, but that towards the end an acid liquor, and 
that there remains a liquid residue strongly acid and effer- 
vescing with the carbonates. In distilling water acidulated 
with lactic acid, to which was added a small quantity of 
chloride of sodium, we obtained a still greater analogy, that 
is to say, we saw three distinct periods exhibited in the 
distillation, absolutely like that of the gastric juice : in the 
first, only pure water distilled over afterwards, an acid not 
precipitating salts of silver ; and the last drops carried with 
them hydrochloric acid. This experiment nicely explains 
the presence of hydrochloric acid in the ulterior products of 
the distillation of gastric juice; this acid, in fact, proceeds 
from the decomposition of the chlorides by the lactic acid 
in the concentrated liquors. If this fact is not sufficient to 
prove that gastric juice contains no free hydrochloric acid, 
the following experiment will clear up all doubts in this 
respect — 
If starch be boiled with hydrochloric acid, it soon loses its 
property of turning blue with iodine, whilst with lactic acid 
it undergoes no alteration even after prolonged boiling. On 
another side, if you boil starch with hydrochloric acid to 
which has been added a lactate soluble in excess, it will be 
observed that the fecula remains unchanged, as though lac- 
tic acid alone was the subject of the operation. This ex- 
periment plainly proves that hydrochloric acid cannot exist 
in presence of a lactic in excess. By similar evidence it 
may be proved that the existence of hydrochloric acid is 
inadmissible in the presence of a phosphate or an acetate in 
excess. 
Taking up again these experiments, we see that lactic 
acid, and the acid of gastric juice, offer properties in common 
with each other: they are fixed by heat, carried along with 
the vapour of water in distillation, and disengage hydro- 
