(4) Filter. A suction filter is desirable, and may be necessary when much mucus is present. (5) During filtration, examine microscopically and make qualitative tests for--(_a_) free acids; (_b_) free hydrochloric acid; (_c_) lactic acid. (6) When sufficient filtrate is obtained, make quantitative estimations of--(_a_) total acidity; (_b_) free hydrochloric acid; (_c_) combined hydrochloric acid (if necessary). (7) Make whatever additional tests seem desirable, as for blood, pepsin, or rennin. A. OBTAINING THE CONTENTS Gastric juice is secreted continuously, but quantities sufficiently large for examination are not usually obtainable from the fasting stomach. In clinical work, therefore, it is desirable to stimulate secretion with food--which is the natural and most efficient stimulus--before attempting to collect the gastric fluid. Different foods stimulate secretion to different degrees; hence for the sake of uniform results certain standard "test-meals" have been {215} adopted. Those mentioned here give practically the same results. 1. Test-meals.--It is customary to give the test-meal in the morning, since the stomach is most apt to be empty at that time. If it be suspected that the stomach will not be empty, it should be washed out with water the evening before. (1) Ewald's test-breakfast consists of a roll (or two slices of bread) without butter and two small cups (300 to 400 c.c.) of water or weak tea without cream or sugar. It should be well masticated. The contents of the stomach are to be removed one hour afterward. This test-meal is used for most routine examinations. Its disadvantage is that it introduces, with the bread, a variable amount of lactic acid and numerous yeast-cells. This source of error may be eliminated by substituting a shredded whole-wheat biscuit for the roll. (2) Boas' test-breakfast consists of a tablespoonful of rolled oats in a quart of water, boiled to one pint, with a pinch of salt added. It should be withdrawn in forty-five minutes to one hour. This meal does not contain lactic acid, and is usually given when detection of lactic acid is important, as in suspected gastric cancer. The stomach should always be washed with water the evening previous. 2. Withdrawal of the Contents.--The Boas stomach-tube, with bulb, is probably the most satisfactory form. It should be of rather large caliber, and have an opening in the tip and one or two in the side near the tip. When not in use, it should be kept in a vessel of borax solution, and should be well washed in hot water both before and after using. It is important confidently to assure the patient that introduction of the tube cannot possibly harm him; and {216} that, if he can control the spasm of his throat, he will experience very little choking sensation. When patients are very nervous, it is well to spray the throat with cocain solution.