TESTS FOB BILE. 187 



by the presence of either or both of the biliary substances proper ; 

 and is not at all dependent on the coloring matter of the bile. For 

 if the two biliary substances, crystalline and resinous, be extracted 

 by the process above described, and, after being dissolved in water, 

 decolorized with animal charcoal, the watery solution will still give 

 Pettenkofer's reaction perfectly, though no coloring matter be pre- 

 sent, and though no green tinge can be produced by the addition 

 of nitric acid or tincture of iodine. If the two biliary substances 

 be then separated from each other, and tested in distinct solutions, 

 each solution will give the same reaction promptly and completely. 



Various objections have been urged against this test. It has 

 been stated to be uncertain and variable in its action. Eobin and 

 Verdeil 1 say that its reactions " do not belong exclusively to the 

 bile, and may therefore give rise to mistakes." Some fatty sub- 

 stances and volatile oils (oleine, oleic acid, oil of turpentine, oil of 

 caraway) have been stated to produce similar red and violet colors, 

 when treated with sugar and sulphuric acid. These objections, 

 however, have not much, if any, practical weight. The test no 

 doubt requires some care and practice in its application, as we have 

 already pointed out ; but this is the case also, to a greater or less 

 extent, with nearly all chemical tests, and particularly with those 

 for substances of organic origin. No other substance is, in point 

 of fact, liable to be met with in the intestinal fluids or the blood, 

 which would simulate the reactions of the biliary matters. We 

 have found that the fatty matters of the chyle, taken from the tho- 

 racic duct, do not give any coloration which would be mistaken for 

 that of the bile. When the volatile oils (caraway and turpentine) 

 are acted on by sulphuric acid, a red color is produced which after- 

 ward becomes brown and blackish, and a peculiar, tarry, empyreu- 

 matic odor is developed at the same time ; but we do not get the 

 lake and purple colors spoken of above. Finally, if the precaution 

 be observed first of extracting the suspected matters with absolute 

 alcohol, then precipitating with ether and dissolving the precipitate 

 in water, no ambiguity could result from the presence of any of the 

 above substances. 



Pettenkofer's test, then, if used with care, is extremely useful, 

 and may lead to many valuable results. Indeed, no other test than 

 this can be at all relied on to determine the presence or absence of 

 the biliary substances proper. 



1 Op. cit., vol. ii. p. 468. 



