92 THE GASTRIC JUICE. 



fifth. Place a little upon a paper dipped in starch-paste and dried, 

 or add it to a few drops of starch solution. Then add a few drops 

 of a solution of calcium hypochlorite (chlorinated lime) to set free 

 the iodin, which colors the starch blue. It should appear in the 

 saliva in from eight to fifteen minutes. If the urine is tested in 

 the same manner there should normally be a positive reaction in 

 15 to 30 minutes. 



The clinical tests for hydrochloric acid given above are open 

 to some objections. Many are interfered with by large amounts 

 of albumin and peptones. If they fail in the tests of a gastric 

 juice the biuret test should be tried, and if any of these substances 

 are present they should be precipitated by a 10-per-eent. solution 

 of tannic acid and, after filtering, the liquid should be again tested 

 for hydrochloric acid. There is also a limit to the delicacy of the 

 tests, so that very minute amounts of free acid may not be de- 

 tected. These are so small when they cannot be thus detected that 

 the condition may be considered pathological. 



Methyl-violet is turned blue by about 1 / 3 of a milligramme 

 of acid. Tropseolin 00 is of about the same delicacy. Congo red 

 is somewhat affected by the organic acids if they are not very 

 dilute. The test-paper made from this has the advantage of easy 

 portability and that it can be preserved and also that something 

 can be judged from the imparted color of the amount of acid 

 present. With a large percentage it becomes a blue black, and 

 with a small amount a lighter blue. Phloroglucin and vanillin 

 make a sensitive reagent, it being possible to detect with it one 

 milligramme of free acid in 10 cubic centimeters of juice. 



The lactic acid test with phenol and ferric chlorid is also 

 in some cases uncertain. When it fails, however, the acid is not 

 present. Some common substances, like sugar and alcohol, give 

 the same results as the acid. WTien it is suspected that this is 

 the case, the liquid should be shaken with ether to dissolve the 

 acid, and the ether, after separation from the water, be evaporated 

 to dryness. Dissolve the residue in a little water and test it for 

 lactic acid. Arnold's test is more reliable. 



The results obtained from chemical testing of gastric 

 juice or vomited material are often of great aid in diagnosis. 

 The presence of the organic acids lactic, butyric, or acetic 



