In reference to the diagnosis of malignant disease of the stomach the relative abundance or absence of free HCl has been pointed out by Ewald as being of importance. In order to determine its existence the patient should take a test breakfast consisting of a cup of weak tea and a little dry toast. An hour later the stomach tube should be passed, and the contents of the stomach drawn off. These are to be tested by Gunsberg's test for free HCl. The reagent consists of 2 parts of phloroglucin and 1 part of vanillin in 30 parts by weight of absolute alcohol. When a few drops of the filtered contents of the stomach are evaporated to dryness in a porcelain dish with an equal quantity of the reagent, if free HCl be present, red crystals will form; should there be much peptone present, no crystals, but a red paste will result.
The absence or deficiency of free HCl occurs in several morbid states, but its presence is a strong point against a diagnosis of malignant disease of the stomach. Hyperacidity, on the other hand, is as characteristic of ulcer as diminished acidity is of cancer.
The mere presence of an acid reaction should not be held as proving the presence of free HCl since this may be caused by acid salts or by free organic acids. Of these latter the most important is lactic acid, and it the practitioner should be able to recognise, since its presence in appreciable quantity in the later stages of digestion is of considerable import, implying as it does that excessive fermentation is going on in the stomach. It can be readily recognised by the use of Uffelmann's reagent, which can be made by adding 1 drop of liq. ferri perchlor. to 1 ounce of a 1 per cent, solution of carbolic acid. This will give an amethyst blue solution, the colour of which is changed to yellow on the addition of the merest trace of lactic acid. Since inorganic acids decolourise Uffelmann's reagent, while sugar, alcohol and phosphates give the same reaction with it as lactic acid, it is necessary to extract the lactic acid by shaking the filtrate left after filtering a small quantity of gastric contents with ether, to allow the ether to separate from the watery solution, and after decanting it to evaporate the ethereal solution until only a few drops remain. If any free lactic acid be present, on adding some of this to Uffelmann's reagent the alteration in colour noted above will take place. The fatty acids, especially butyric acid, give a somewhat similar reaction, but only when present in larger proportions than they are found to occur in the stomach. The presence of lactic acid and the absence of free HCl are strongly suggestive of cancer.
Osier (3) states that in 84 cases of cancer of the stomach out of 94 examined free HCl was absent.