Increase of free hydrochloric acid above 50 degrees (hyperchlorhydria) generally indicates a neurosis, but also occurs in most cases of gastric ulcer and beginning chronic gastritis.
Decrease of free hydrochloric acid below 25 degrees (hypochlorhydria) occurs in some neuroses, chronic gastritis, early carcinoma, and most conditions associated with general systemic depression. Marked variation in the amount at successive examinations strongly suggests a neurosis. Too low values are often obtained at the first examination, the patient's dread of the introduction of the tube probably inhibiting secretion.
Absence of free hydrochloric acid (achlorhydria) occurs in most cases of gastric cancer and far-advanced chronic gastritis, in many cases of pernicious anemia, and, sometimes, in hysteria.
The presence of free hydrochloric acid presupposes a normal amount of combined hydrochloric acid, hence the combined need not be estimated when the free acid has been found. When, however, free hydrochloric acid is absent, it is important to know whether any acid is secreted, and an estimation of the combined acid then becomes of great value. The normal average after an Ewald breakfast is about 10 to 15 degrees.
Töpfer's Method for Free Hydrochloric Acid.—In a beaker take 10 c.c. filtered stomach fluid and add four drops of the indicator, a 0.5 per cent. alcoholic solution of dimethylamido-azobenzol. A red color instantly appears if free hydrochloric acid be present. Add decinormal sodium hydroxid solution, drop by drop from a buret, until the last trace of red just disappears, and a canary-yellow color takes its place ([Plate X, C, C']). Read off the number of cubic centimeters of decinormal solution added, and calculate the degrees, or percentage of free hydrochloric acid, as in Töpfer's method for total acidity.
When it is impossible to obtain sufficient fluid for all the tests, it will be found convenient to estimate the free hydrochloric acid and total acidity in the same portion. After finding the free hydrochloric acid as just described, add four drops phenolphthalein solution, and continue the titration. The amount of decinormal solution used in both titrations indicates the total acidity.
Töpfer's Method for Combined Hydrochloric Acid.—In a beaker take 10 c.c. filtered gastric juice and add four drops of the indicator, a 1 per cent. aqueous solution of sodium alizarin sulphonate. Titrate with decinormal sodium hydroxid until the appearance of a bluish-violet color which does not become deeper upon addition of another drop ([Plate X, B, B']). It is difficult, without practice, to determine when the right color has been reached. A reddish-violet appears first. The shade which denotes the end reaction can be produced by adding two or three drops of the indicator to 5 c.c. of 1 per cent. sodium carbonate solution.
Calculate the number of cubic centimeters of decinormal solution which would be required for 100 c.c. of stomach fluid. This gives, in degrees, all the acidity except the combined hydrochloric acid. The combined hydrochloric acid is then found by deducting this amount from the total acidity, which has been previously determined.
Example.—Suppose that 5 c.c. of decinormal solution were required to produce the purple color in 10 c.c. gastric juice; then 5 X 10 = 50 = all the acidity except combined hydrochloric acid. Suppose, now, that the total acidity has already been found to be 70 degrees; then 70 - 50 = 20 degrees of combined hydrochloric acid; and 20 X 0.00365 = 0.073 per cent.
(3) Organic Acids.—There is no simple direct quantitative method. After the total acidity has been determined, organic acids may be removed from another portion of the gastric filtrate by shaking thoroughly with an equal volume of neutral ether, allowing the fluids to separate, and repeating this process until the gastric fluid has been extracted with eight or ten times its volume of ether. The total acidity is then determined, and the difference between the two determinations indicates the amount of organic acids.