This test, as devised by Penzoldt and Faber, is very simple. Into an empty stomach are taken three grains of potassium iodide in a clean gelatine capsule, with a wineglassful of water.

The saliva is collected at two- or three-minute intervals in separate saucers, and with normal absorption from a healthy stomach iodine may be detected in the secretion in from six and a half to fifteen minutes, but in gastric catarrh it may not appear for several hours. The test is made by dipping a filter paper, previously soaked in starch paste, into the saliva, and adding fuming nitric acid. A blue colour appears if iodine is present. This test is not very reliable, for if the stomach is full of food the reaction is always much retarded, as it also is by fever and in most diseases of the stomach, notably ulcer, carcinoma, and dilatation.