_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 {226} 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.