FUNCTIONS OF DIFFERENT FORMS OF CELLS. 533 
in the pyloric region do not contribute to the formation of acid. 
In tin' frog the Bource of the ferment is an alkaline juice fur- 
nished by the oesophageal glands, whilst the cells in the Btomach bear 
resemblance to the border cells of the mammal, and here alone the 
acid of the juice is secreted. The deeper parts of the cardiac glands, 
where there are fewer border cells, do not give an acid reaction, the 
acid reaction being evident only at the mouths and upper parrs of the 
glands. 
Claude Bernard 1 attempted to mark out the place where the free 
hydrochloric acid first appeared, by injecting intravenously a solution of 
ferric lactate followed by a solution of potassium ferrocyanide (these two 
compounds react with the production of Prussian blue only in the 
presence of a mineral acid). After the lapse of three quarters of an 
hour the animal was killed and the tissues examined. A blue pre- 
cipitate was only observed on the surface of the mucous membrane 
of the stomach, especially in the neighbourhood of the lesser cur- 
vature, but no trace of blue in the glands. This experiment might, 
at first sight, lie taken as indicating that the hydrochloric acid is first 
set free on the stomach itself, and is not formed in the cells of the 
gastric glands. Such a conclusion would be unwarranted. What the 
experiment dues teach is that there is no accumulation of "rid in the 
cells, but that the acid as rapidly as it is formed is thrown out of the 
cells as a secretion. 
Briicke 2 tried to solve the same problem by exposing the stomach of 
an animal in which digestion was actively going on, and carefully 
removing all but the mucous coat; both in the pigeon and in the rabbit 
the reaction of the exposed mucous layer to litmus paper was found to 
lie faintly alkaline or very faintly acid, practically neutral, but on 
testing the inner surface of the mucous membrane it was, as usual, 
intensely acid. This again is an experiment which, had it given a 
positive result, would have shown conclusively that the acid was 
secreted by the gland-cells : but, giving as it did a doubtful or negative 
result, it teaches little, and by no means proves the statement that 
the acid is not formed in the glands but in the stomach. In cutting 
into the stomach wall in this manner, sources of alkali are tapped 
in the small blood vessels and lymph spaces which are capable of 
supplying more than sufficient alkali to neutralise any acid in the 
gland lumina. 
Briicke himself was not satisfied with this experiment, and attacked 
the problem by another method, which gave him results from which he 
concluded that the acid is really formed in the glands, and not in the 
stomach cavity. In birds, the gastric glands are compound glands 
forming flask-shaped bodies large enough to be easily seen without 
magnification. These compound glands possess also a flask-shaped 
cavity communicating with the stomach cavity by a comparatively 
narrow duct. Into this central cavity of the gland the secretion passes. 
Briicke took the secreting stomach of a fowl which had been killed 
during digestion, washed it out with magnesia suspended in water to 
neutralise the free acid on the surface of the mucous membrane, and 
sought out one of the above-described glands filled with secretion. 
1 " Lceous sur les proprietes physiol.," Paris, 1859, vol. ii. 
2 Sitzungsb. d. Jr. Akad. d, Wissensch., Wien, 1859, Bd. xxxvii. : ■' Vorlesnngen," 
Aufl. 4, Bd. i. S. 306. 
