88 Miss M. P. FitzGerald. The Origin of the [June 4, 
solution which contains the acid, careful teasing is necessary, whether nitric 
acid is present in the solution or not. After allowing the respective 
solutions to act upon the tissues for a certain length of time, the vessels 
containing them were then exposed to sunlight, or to as bright a light 
as was available, for several days; and when the maximum reaction had 
been obtained, the tissues were mounted in 50-per-cent. glycerine ; or, after 
being exposed to light for some time, portions of the tissues were mounted in 
50-per-cent. glycerine, to which a few drops of the reagent were added, and 
again exposed to sunlight in this medium. 
The characteristic reaction was obtained in the tissues acted upon by each 
of the solutions, and drawings were made of specimens mounted in 50-per-cent. 
glycerine. Fig. 18 shows the appearance of a tubule treated with the silver 
nitrate solution without acid, and figs. 19 to 22 the appearance of tubules after 
treatment with silver nitrate solution containing free nitric acid. 
It will be seen that in both cases the parietal cells are differentiated from 
the chief cells, but since the “reduced ” phosphate and carbonate compounds 
of silver are brown in colour, and as the sub-chloride, although violet, reddish 
violet, or bluish violet when in mass, may also be reddish brown, as shown 
by Macallum,* when it occurs in thin layers or deposits, the shade apparently 
depending on the existence of the compound ina finely divided state or other- 
wise, it is clear that it would be impossible to make a definite statement as 
to the presence of an excess of chlorides in the parietal cells in the tubule 
depicted in fig. 18, because the brown colour could also be attributed to the 
precipitation of the “ reduced ” phosphate or carbonate. Such a statement can, 
however, safely be made with regard to the reaction shown in figs. 19 to 22, 
for in these cases, owing to the differentiating action of the free nitric acid 
present in the silver nitrate solution, the reaction can only be due to the 
precipitation of the sub-chloride of silver. 
The intensity of the reaction obtained in the parietal cells of both the 
rabbit and the guinea-pig, and the marked manner in which the parietal cells 
stand out im sitw in the tubules of the rabbit shown in figs. 19, 20, due to the 
chlorides being more abundantly present in these cells than in the chief cells, 
are results which fully corroborate those obtained by Macallum,f when using 
the same method and the same animals, and furnish evidence of the source 
of the hydrochloric acid in the parietal cells, and also give support to the 
view that this is elaborated in the cytoplasm of these cells. 
With the hope of establishing the presence of the acid in the cells by more 
than one method, some experiments were also made with Tropzolin OO 
* A. B. Macallum, ‘ Roy. Soc. Proc.,’ 1905, B, vol. 76, p. 217. 
+ A. B. Macailum, ‘Ergebn. d. Physiol.,’ 1908, vol. 7, p. 628. . 
