90 Miss M, P. FitzGerald. The Origin of the [June 4 
neutral red. Previous to immersion in the staining fluid, the sections were 
carefully washed in distilled water to remove the alcohol used for fixation, to 
prevent the yellow coloration which would otherwise have resulted on the 
application of the dye. With the excepfion of the nuclei staining a pink 
colour of moderate intensity, the parietal cells remain uneoloured by this 
method; they are, therefore, well differentiated from the chief cells, which 
are stained crimson. In a vertical section of that part of the gastric mucosa 
in which the parietal cells are most numerous, the neck region of the gland 
tubules appears as a clear band, as the surface epithelium and the cells of 
the crypts are also stained crimson. 
From the results obtained in the gastric mucosa of the rabbit previously 
injected with a solution containing equal parts of an aqueous solution of 
2°25-per-cent. ammonium ferric citrate and of 1°5-per-cent. potassium ferro- 
cyanide, it may be said in conclusion that the occurrence of Prussian blue, 
not only in the lumina of the gland tubules, but also in the canaliculi in the 
parietal cells, makes it certain that the hydrochloric acid is, at least, already 
formed and free in the secretion as it appears in the canaliculi. Whether 
the acid, or, more correctly speaking, whether its hydrogen ions occur in the 
cytoplasm of the cells still remains an open question, although the very faint 
blue occasionally observed in a parietal cell seems to postulate an affirmative. 
It is, moreover, to be noted that if the acid is formed and set free in the 
canalicuh, then the cytoplasm lining the latter must constitute a membrane 
permeable to the H and Cl ions, but not to 1, K, PO,, or CO3. If that 
were entirely the case, no free acid should occur in the lymphatics besides. 
the tubules. The acid here can only be derived from the cytoplasm of the 
parietal cells, and if the latter have absorbed it from their canaliculi, then it 
would be difficult to explain why the cytoplasm does not neutralise the acid, 
for the removal of the hydrogen ions from the parietal cells must make their 
cytoplasm distinctly alkaline. If, to overcome this difficulty, we suppose that 
the cytoplasm is so constituted as to maintain the ionisation of the hydrogen 
and the chlorine in the presence of alkalies, we attribute a property to it 
that could be also responsible for the formation of the acid in the first place 
in the cytoplasm. 
The occurrence of free acid in the canaliculi, and also, in certain cases, in 
the lymphatic vessels between the gastric tubules, is, therefore, best explained 
by supposing that the cytoplasm of the parietal cells forms in itself the free 
acid, and, under ordinary conditions, that the free acid so formed diffuses into 
the canaliculi, but, under certain conditions, the character of which is 
unknown, the cell loses the sense of direction, so to speak, and, aS a 
