31 



137- To a portion of the filtrate add a little hydrochloric 

 acid and potassium ferrocyauide. A blue color indicates the 

 presence of iron. The experiment may be modified by 

 plachig some thin sections of liver in a solution of potassium 

 ferrocyanide for a few minutes and then in dilute hydro- 

 chloric acid. The sections turn bluish from the formation 

 of Prussian blue. With the microscope blue granules may 

 be seen in some of the hepatic cells. 



138. Pettenkofer's Test for Bile Acids. Take 2 cc. of 

 clear diluted bile in a test tube and add 4 drops of a 10% 

 .solution of cane sugar. Add strong sulphuric acid, drop 

 by drop, cooling the tube in a dish of cold water immedi- 

 ately after adding the acid. Not more than 2 cc. of the 

 acid should be used. Too much heat causes carbonization 

 of the sugar and the test is ruined. If bile acids are 

 present, the fluid at first becomes opaque, then clear, and 

 successively brown, red and purple. It may require an 

 hour or more to accomplish this test. This reaction de- 

 pends upon the production of furfurol (C^HjOCHO) by the 

 destruction of the sugar when the sulphuric acid is added. 

 Furfurol in turn combines with cholalic acid, formed by the 

 action of the sulphuric acid on the bile acids, giving the 

 color. Some other substances, as morphine, albumin, etc., 

 give a very similar color, and the test must, therefore, be 

 used with caution. In very dilute solutions of bile the re- 

 action does not appear and cannot be used satisfactorily in 

 testing urine for the presence of bile. 



Pettenkofer's test may also be quite satisfactorily per- 

 formed more quickly by putting a little of the bile in a por- 

 celain capsule, adding a drop or two of a solution of cane 

 sugar and then a few drops of strong sulphuric acid. 



139. Gmelin's Test for Bile Pigments. Ox gall does not 

 yield this test as readily as that from the omnivora or car- 

 nivora. To a small quantity of bile, in a test-tube, add, 

 drop by drop, nitric acid, yellow with nitrous acid, (if the 



