TESTS FOR BILE. 185 



cases of jaundice. But it is very insufficient for anything like 

 accurate investigation, since the appearances are produced simply 

 by the action of an oxidizing agent on the coloring matter of the 

 bile. A green color produced by nitric acid does not, therefore, 

 indicate the presence of the biliary substances proper, but only of 

 the biliverdine. On the other hand, if the coloring matter be ab- 

 sent, the biliary substances themselves cannot be detected by it. 

 For if the biliary substances of dog's bile be precipitated by ether 

 from an alcoholic solution, dissolved in water and decolorized by 

 animal charcoal, the colorless watery solution will then give no 

 green color on the addition of nitric acid or tincture of iodine, 

 though it may precipitate abundantly by subacetate of lead, and 

 give the other reactions of the crystalline and resinous biliary 

 matters in a perfectly distinct manner. 



Pettenkofer's Test. This is undoubtedly the best test yet pro- 

 posed for the detection of the biliary substances. It consists in 

 mixing with a watery solution of the bile, or of the biliary sub- 

 stances, a little cane sugar, and then adding sulphuric acid to the 

 mixture until a red, lake, or purple color is produced. /A solution 

 may be made of cane sugar, in the proportion of one part of sugar to 

 four parts of water, and kept for use. y One drop of this solution is 

 mixed with the suspected fluid, and the sulphuric acid then imme- 

 diately added. On first dropping in the sulphuric acid, a whitish 

 precipitate falls, which is abundant in the case of ox-bile, less so in 

 that of the dog. This precipitate reclissolves in a slight excess of 

 sulphuric acid, which should then continue to be added until the 

 mixture assumes a somewhat syrupy consistency and an opalescent 

 look, owing to the development of minute bubbles of air. A red 

 color then begins to show itself at the bottom of the test-tube, and 

 afterward spreads through the mixture, until the whole fluid is of 

 a clear, bright, cherryjred. This color gradually changes to a lake, 

 and finally to a deep, rich, opaque purple. If three or four vol- 

 umes of water be then added to the mixture, a copious precipitate 

 falls down, and the color is destroyed. 



Various circumstances modify, to some extent, the rapidity and 

 distinctness with which the above changes are produced. If the 

 biliary substances be present in large quantity, and nearly pure, 

 the red color shows itself at once after adding an equal volume of 

 sulphuric acid, and almost immediately passes into a strong purple. 

 If they be scanty, on the other hand, the red color may not show 

 itself for seven or eight minutes, nor the purple under twenty 



