FUNCTIONS OF DIFFERENT FORMS OF CELLS. 533 



in the pyloric region do not contribute to the formation of acid. 

 In the frog the source of the ferment is an alkaline juice fur- 

 nished by the oesophageal glands, whilst the cells in the stomach 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 parts 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, be 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 does teach is that there is no accumulation of acid 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 

 be 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 "Lecons snr les proprieties physiol.," Paris, 1859, vol. ii. 



" Sitzungsb. d. Jc. Akad. d. JVissensch., "VVien, 1859, Bd. xxxvii. ; " Vorlesungen," 

 Aufl. 4, Bd. i. S. 306. 



