446 Drs. 8. M. Copeman and H. W. Hake. [June 19, 
(6) The inorganic chlorides are similarly estimated in another aliquot part 
after evaporation to dryness on a water-bath and charring the residue at a 
gentle heat. 
(c) The total acidity is determined in another aliquot part by titration with 
standard sodium hydrate, using phenolphthaléin as an indicator. 
From these three determinations may be deduced :— 
1. Physiologically active hydrochloric acid = (a—8). 
2. Organic acids = (c—(a—D)). 
All of these various constituents are, for convenience, expressed in terms of 
hydrochloric acid.* 
The term physiologically active hydrochloric acid is intended to include both 
the free acid and that combined with proteids and nitrogenous organic bases, 
since, as originally pointed out by Liittke in 1891,f and more recently 
emphasised by Willcox, much misconception has arisen in the use of the 
terms “free” and “combined” as applied to hydrochloric acid in the gastric 
contents, and it has been erroneously held that the presence of the free acid 
is of more importance than the organically combined acid. But inasmuch as 
the latter may have been free a short time before its estimation, the exclusive 
determination of “free” hydrochloric acid cannot but lead to fallacious 
conclusions. 7 
With this introductory explanation, we may now consider the summary of 
the results which we have obtained. 
(1) Eaperiments on Mice made without Reference to Time of Digestion (Series 1 
to 5, Mice over 12 months old). 
The first five series of experiments (December 19, 1905, to May 7, 1906) 
were made without reference to time of digestion, not because we had not 
* In the estimations of total and inorganic chlorides in mice stomachs, 20 ¢.c. to 50 ce. 
of aqueous extract were taken, according as the extract had been made up to 100 ce. 
or 250 c.c. It might appear probable that a source of error would arise in the charring 
of the residue, due to partial volatilisation of inorganic chlorides ; we tested this point: 
rigidly by repeating the estimations in a very large number of instances, but our 
experience was that there was practically no error, the difference in the titration numbers. 
being no greater than that usually found in closely agreeing estimations. The presence: 
of the charred matter does not interfere in the end-reaction when the quantity of 
chlorides present is comparatively large, but is liable to cloak the reaction when the 
amount is small. To overcome this difficulty we found it was only necessary to add a. 
somewhat larger excess of standard silver nitrate solution, so that when titrating back 
with ammonium thiocyanate the obscuring effect of the charred matter was annulled by 
the extra amount of white silver thiocyanate in suspension. By adopting these: 
modifications and by using N/50 or even N/100 instead of N/10 standard solutions, 
we were able to determine the chlorides in a single stomach with accuracy and 
comparative ease. 
+ Loe. cit. 
