88 PRACTICAL PHYSIOLOGY. [XL 



3. Pettenkofer's Test for Bile- Acids (Salts) and Cholic Acid. 



(a.) To bile in a test-tube, add a drop or two of syrup of cane- 

 sugar. Pour in concentrated sulphuric acid, at the hue of junction 

 of the two fluids a purple colour is obtained. Furfuraldehyde is 

 formed from the action of sugar and sulphuric acid, and the purple 

 compound is due to the aldehyde compound with cholalic acid. The 

 white deposit seen above the Hne of junction is precipitated bile- 

 acids. They are insoluble in water. 



(/;.) A better way of doing the test is as follows : — After mixing 

 the bile and syrup, shake the mixture until the upper part of the 

 tube is filled with froth. Pour sulphuric acid down the side, and 

 a purple-red colour is struck in the froth. 



(c.) Make a film of bile on a porcelain capsule, add a drop of syrup 

 of cane-sugar, and then a drop of sulphuric acid = purple colour. 



(d.) Or, after mixing the syrup with the bile, add the strong sulphuric acid 

 drop by drop, mixing it thoroughly. Heat gently, and the fluid becomes a 

 deep purple colour. Take care not to add too much syrup, and not to over- 

 heat the tube. If the requisite amount of sulphuric acid be added, the tem- 

 perature becomes sufficiently high (70° C.) without requiring to heat the tube. 



(e.) Strassburger's Modification (e.g., for bile in urine). — To the urine add 

 a little syrup and mix. Dip filter-paper into the fluid and dry the paper. 

 On placing a drop of sulphuric acid on the latter, after some time a purple 

 spot which has eaten into the paper is observed. 



( f. ) Repeat any or all of the above processes with a watery solution of the 

 bile-salts and with acid albumin. 



(g.) In place of sugar furfurol (Mylius) may be used. Add i drop of fur- 

 furol solution (i per 1000) and i cc. of concentrated H0SO4. 



4. Similar purple colour reactions are obtained with many other sub- 

 stances — e.g., albumin and a-naphthol, but the spectra differ somewhat. 



Albumin and Sulphuric Acid, — To a solution of acid-albumin and syrup 

 add strong sulphuric acid, a similar tint is obtained. The spectra, however, 

 are diff"erent, the red-purple fluid from bile gives two absorption-bands, one 

 between E and F, and another between D and E. In the albuminous solu- 

 tions only one absorption-band exists between E and F. 



5. Action of Bile or Bile-Salts in Precipitating Sulphur. 



(a.) In one beaker (A) place diluted bile and in the other (B) water. Pour 

 flowers of sulphur on both. The sulphur falls in a shower through the fluid 

 of A, while none passes through B. 



(b.) Test to what extent bile may be diluted before it loses this property, 

 which is due to the diminution of the surface tension by the bile-salts {M. Hay). 



(c.) Repeat with a solution of the bile-salts. 



Bile-Pigments.— The chief are bilirubin (red), biliverdin (green), 

 and urobilin. 



6. Gmelin's Test for Bile-Pigments. 



{a.) Place a few drops of bile on a white porcelain slab. With 

 a glass rod place a drop or two of strong nitric acid containinr/ 

 nitrous acid near the drop of bile, bring the acid and bile into 

 contact. Notice the play or succession of colours, beginning with 

 gi'een and passing into blue, red, and dirty yellow. 



