134 THE DIGESTIVE FLUIDS. 



KELLING'S TEST (as modified by the writer). A solution of 

 sesquichloride of iron is prepared, so dilute that a trace of yellow 

 can barely be discerned. Two test-tubes are partly filled with this 

 reagent and a small amount of the filtered gastric contents added to 

 the one. In the presence of lactic acid a distinct yellow develops 

 at once, which becomes especially marked when the tube is compared 

 with the 'control. 



Bo AS 7 TEST. This test is more accurate than the two just de- 

 scribed, but more time-consuming and complicated. It is based 

 upon the decomposition of lactic acid into formic acid and acetic 

 aldehyde, and the demonstration of the presence of the latter. To 

 this end, from 10 to 20 c.c. of the filtered stomach-contents are 

 treated with a slight excess of barium carbonate, and evaporated on 

 a water-bath. The resulting syrup is acidified with a few drops 

 of phosphoric acid, and freed from carbon dioxide by momentary 

 ebullition. On cooling, it is extracted with 100 c.c. of ether by 

 shaking for about thirty minutes. The ethereal extract is decanted, 

 the ether distilled off, and the residue taken up with 45 c.c. of 

 water. After filtering, the solution is treated with 5 c.c. of con- 

 centrated sulphuric acid and a pinch of manganese dioxide, and 

 carefully heated to boiling. Should lactic acid be present, this is 

 now decomposed, and acetic aldehyde liberated, which can be demon- 

 strated by passing the vapor into a test-tube containing Nessler's 

 reagent or an alkaline solution of iodopotassic iodide. In the first 

 instance, yellowish-red aldehyde of mercury is formed, while iodo- 

 form results in the latter, and can be readily recognized from its 

 odor, which becomes marked when the solution is heated. 



Tests for Acetic Acid and Butyric Acid. These acids can 

 usually be recognized by their odor. Chemically they can be 

 demonstrated as follows : 



Test for Acetic Acid. Ten c.c. of the filtered stomach-contents 

 are extracted with ether as above. The ether is distilled off, the 

 residue taken up with a few drops of water and accurately neutral- 

 ized with sodium hydrate. To this solution a drop or two of a very 

 dilute solution of ferric chloride is added, when in the presence of 

 acetic acid a dark-red color develops. With nitrate of silver, on the 

 other hand, a precipitate is obtained which is soluble in hot water. 



Test for Butyric Acid. The ethereal extract of 10 c.c. of the 

 stomach-contents is freed from ether by distillation, the residue is 

 dissolved in a few cubic centimeters of water, and treated with a trace 

 of calcium chloride in substance. In the presence of butyric acid 

 small oil droplets separate out, the nature of which is readily recog- 

 nized from the pungent odor. If, in the place of calcium chloride, 

 a slight excess of baryta-water is used, highly refractive rhombic 

 platelets or granular, wart-like masses are obtained on evaporation, 

 Avhich consist of barium butyrate. 



Butyric acid can also be recognized by the peculiar odor of pine- 

 apple which develops when the dry residue of the ethereal solution 



