214 



THE BILE. 



band being darker than the edges. Beyond the absorption band, the 

 light of the spectrum is dim, fading gradually and terminating some- 

 where about the line G. 



When the purple color produced by Pettenkofer's test with the biliary 

 salts is very pronounced, it is usually found that the fluid is altogether 

 too opaque for spectroscopic examination, even in a layer of only one 

 centimetre. But if it be diluted with water, it becomes turbid, owing 

 to a re-precipitation of cholic acid, and the purple color disappears. 

 This difficulty, however, may be obviated by using a solution of the 

 biliary salts which is sufficiently dilute in the first instance. If sodium 

 glycocholate be dissolved in water, in the proportion of 1 part to 500, and 

 the solution treated with Pettenkofer's test, it gives in a few moments 

 a clear violet-pink color, which afterward becomes a rich purple. This 

 fluid is so opaque that, when placed before the slit of the spectroscope 

 in a layer of one centimetre, it extinguishes completely everything but 

 the red ; and yet it may be diluted with water without showing any tur- 

 bidity or losing its color. A watery solution of this strength is amply 

 sufficient to exhibit the reaction of Pettenkofer's test and the spectro- 

 scopic appearances belonging to it. If any solution, therefore, of the 

 biliary salts should prove, on trial, too opaque for spectroscopic exam- 

 ination when treated by Pettenkofer's test, another portion of it may be 

 diluted, before applying the test, until it is reduced to about the 

 strength of 1 part to 500. Even when a strongly colored purple fluid 

 has been rendered turbid and decolorized by the addition of water, its 

 transparency and color may be again restored by the addition of sul- 

 phuric acid ; but this method is less convenient than the former. 



Fig. 72. 



SPECTKUM OF PETTENKOFEK'S TEST, with the Biliary Salts in alcoholic solution. 



If Pettenkofer's test be applied to the biliary salts in alcoholic solu- 

 tion, its spectrum is modified. There are now two absorption bands 

 instead of one. The first is situated at E, and is identical with that 

 obtained in a watery solution of the same salts. The second is at F, 

 and usually rather narrower and fainter than the first, although some- 

 times the two bands are of equal intensity. 



The pink or purplish -red fluid, produced by Pettenkofer's test with 



