test-tube, and adding a piece of magnesium ribbon. The presence of phosphoric acid is made evident by the characteristic smell of phosphin. If a fragment of the calculus be dissolved in strong nitric acid and ammonium molybdate solution be added, a bright-yellow precipitate of ammonium phosphomolybdate forms in the presence of phosphoric acid.

Triple Phosphates.-In this class of calculi the ammonia may be detected by moistening the calculus with potassium hydroxid, and heating gently. The ammonia evolved may be detected by the smell, and the reaction may be further confirmed by the alkaline reaction of the gas on a piece of moistened red litmus-paper.

Oxalates.-Oxalates leave a grayish-white residue by heating on platinum foils which effervesces with dilute hydrochloric acid. The fragment which has not been ignited does not effervesce.

Cystin. The calculi of this substance are rare, but are readily recognized by dissolving in ammonia. The solution on evaporation deposits crystalline plates which are exceedingly characteristic. The substance is completely volatile on ignition.

EXAMINATION OF THE GASTRIC CONTENTS.

In examination of the gastric contents it is important to start under definite conditions. For this reason it is inadvisable to use the vomit or the gastric contents withdrawn by the stomach-tube except after a test-breakfast. The character of the contents varies widely during the day. Digestion is furthest advanced an hour after a meal, although the secretion of the gastric fluid commences immediately on the reception of the food by the stomach, or perhaps somewhat earlier, from reflex nervous stimulation. The amount secreted in the twentyfour hours is about 13 liters.

The test-breakfast consists of 35 grams of dry unbuttered bread, and 300 c.c. of warm water or weak unsweetened tea, without milk. One hour after the ingestion of the food the contents of the stomach are withdrawn by the stomach-siphon. This apparatus consists of a long red-rubber tube, 7 mm. in diameter, having near the closed end two or three small openings about 5 mm. in diameter. The tube is warmed gently, and introduced into the back of the pharynx, and held there till the patient makes an effort to swallow. It is then gently guided down till the end is well within the stomach. It is often useful to have a mark on the tube to indicate the length necessary to enter the stomach. If too much of the tubing

be within the gastric cavity, the curling of the tube interferes with the proper siphonage. If now gentle pressure be made on the abdominal wall, or the patient be induced to cough, the contents of the stomach will be expelled. The tube should be sufficiently long to have the free end below that within the stomach. Otherwise the tube will not act as a siphon. The contents should be received in a graduated glass.

If the test-breakfast be given in the proper quantity, the amount of fluid which will be obtained will be about 40 c. c. Any sediment which settles out should be examined with the microscope. The fluid should now be filtered and tested for hydrochloric acid and pepsin.

As a rule, the fluid filters easily. As removed from the stomach with the tube the normal quantity of hydrochloric acid is about 0.3 per cent. This appears to be the exact quantity necessary to check fermentative change. If less than this quantity be present, the juice rapidly undergoes fermentation.

The composition of normal gastric juice mixed with saliva was found by Schmidt to be:

From a diagnostic point of view, the important constituents of the fluid are free hydrochloric acid and the digestive ferments. Free hydrochloric acid always exists in the contents of the stomach in health, but may be entirely absent in certain nervous affections and in organic disease of the stomach, particularly in malignant growths attending the cardiac end.

Hydrochloric Acid.—The qualitative detection of hydrochloric acid may be accomplished with one of the anilin dyes or with Günzburg's reagent. Günzburg's test, which has been described in the section on the Gastric Juice, page 61, is best performed by dissolving up a small quantity of phloroglucin and of vanillin in I c. c. of alcohol, and adding to the mixture an equal quantity of the gastric filtrate. The mixture is placed in a porcelain basin, and evaporated over a water-bath. It is not advisable to heat with a free flame. In the presence of 0.05 per cent. of hydrochloric acid, a bright-red stain will be left, and with a larger quantity microscopic crystals will be seen. If the acid be absent, the residue will have a light-brown color.

Of the anilin dyes which have been proposed, Congo-red, benzopurpurin 6B, tropeolin oo, and dimethylamido-azobenzene, are the most used.

These dyes may be used in the form of solution, or more conveniently for clinical work in the form of test-papers. These may easily be made by soaking small strips of filter-paper or perfectly neutral unglazed paper in a strong solution of the indicator, and allowing them to dry in the air. Care must

naturally be taken to have the papers dry in an atmosphere where acid fumes are absent. The test-papers are not so delicate for indicating minute traces of the acids, but in this are perhaps to be preferred for bedside work, as the organic acids themselves will give indications of an acid reaction with solutions of indicators where the papers fail. Of the solutions, according to the author's experiments, the most sensitive is that of Congo-red. With it one is able to detect 4 parts in a million.

Tropeolin oo is also a delicate indicator of free acid. In the presence of acids the solution turns red.

Somewhat more sensitive than tropeolin oo is benzopurpurin 6B. The indicator sold under this name is not always the one which gives a sensitive reaction with acids, and therefore it may be necessary to obtain several samples before the right one is found.

In performing the tests for free acid in the stomach contents, it is only necessary to make up a dilute solution of the indicator, of about 0.2 gram in 50 c. c. of alcohol or water, and use 2 drops of this solution diluted with 10 c. c. of water. The stomach contents are then added drop by drop and the change of color observed.

Lactic Acid.-Lactic acid is produced in the gastric contents from the fermentation arising from the Bacillus lacticus. It may be detected by using Uffelmann's reagent. This is made by dissolving a small crystal of phenol in 10 c. c. of water, and adding a drop of a very dilute solution of ferric