TESTS FOR BILE. 449 



been made into the ultimate composition and the modifications of this and the other col- 

 oring matters. Recent researches have shown that, in all probability, the coloring matter 

 called biliverdine is a mixture of several distinct coloring principles, and that these rapidly 

 change in contact with the oxygen of the air ; so that there is considerable uncertainty 

 with regard to the ultimate composition of these and other substances of the same class. 



Tests for Bile. It is frequently desired, particularly in pathological investigations, 

 to ascertain, by some easy test, the fact of the presence or absence of bile in various 

 of the fluids and solids of the body. It is, indeed, a most interesting physiological ques- 

 tion to determine the course and destination of the biliary salts after the bile has passed 

 into the intestinal canal ; and this can be done only by the application of appropriate 

 tests to the contents of the alimentary tract and the blood of the portal system. The 

 ingredients of the bile which it is important to detect are biliverdine, the biliary salts, 

 and cholesterine. The last-named substance can be detected most readily by applying 

 the method which we have just described for its extraction ; but several tests have been 

 proposed for the detection, on the one hand, of the coloring matter of the bile, and, on 

 the other, of the peculiar biliary salts. 



Test for Biliverdine. There is one test so simple and easy of application, that it alone 

 will suffice for the prompt detection of biliverdine. This is peculiarly applicable to the 

 urine, where the presence or absence of bile frequently becomes an important question. 



We are led generally to suspect the presence of bile in the fluids of the body by their 

 peculiar color. If we spread out the suspected fluid in a thin stratum upon a white sur- 

 face, as a porcelain plate, and add a single drop of nitric acid, or, what is better, nitroso- 

 nitric acid, if the coloring matter of bile be present, a peculiar play of colors will be ob- 

 served at the circumference of the drop of acid as it diffuses itself. The color will rapidly 

 change from blue to red, orange, purple, and finally to yellow. This is due to the action 

 of the acid upon the biliverdine ; and this test does not indicate the presence of either cho- 

 lesterine or the biliary salts. It is used, therefore, only when we wish to determine the 

 presence of the coloring matter of the bile. 



Test for the Biliary Salts. The best, and, indeed, the only reliable test for the biliary 

 salts, was proposed many years ago by Pettenkofer, and this is now generally known as 

 Pettenkofer's test. This requires some care and practice.in its application, but it is entirely 

 reliable; and, although it has been objected that there are other substances, beside the 

 biliary salts, which produce similar reactions, they are not met with in the animal fluids 

 and consequently are not liable to produce confusion. If a considerable quantity of bile 

 be present in any fluid, and if there be not a large admixture of animal matters, the test 

 may be employed without any previous preparation ; but, in delicate examinations, it is 

 best to evaporate the suspected liquid, extract the residue with absolute alcohol, precipi- 

 tate with ether, and dissolve the ether-precipitate in distilled water. By this means a 

 clear solution is obtained, which will react distinctly, even when the biliary salts exist 

 in very small quantity. Pettenkofer's test is applicable to any of the biliary salts, what- 

 ever be their form, and the reaction is dependent upon the presence of cholic acid, which 

 enters into the composition of all the varieties of the biliary acids. 



The following is one of the most common methods of employing Pettenkofer's test : 

 To the suspected solution we add a few drops of a strong solution of cane-sugar in 

 water. Sulphuric acid is then slowly added, to the extent of about two-thirds of the 

 bulk of the liquid. It is recommended to add the acid 'slowly, so that the temperature 

 shall be but little raised. If a large quantity of the biliary salts be present, a red color 

 shows itself almost immediately at the bottom of the test-tube, and this soon extends 

 through the entire liquid, rapidly deepening until it becomes of a dark-lake or purple. 

 If the biliary matters exist in very small proportion, it may be several minutes before any 

 red color makes its appearance, and the change to a purple is correspondingly slow, the 

 whole process occupying from fifteen to twenty minutes. Many organic matters may be 

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