148 THE DIGESTIVE FLUIDS. 



alcohol a green fluorescence is observed. In the presence of an 

 excess the red pigment disappears, but reappears upon the further 

 addition of sulphuric acid. On standing, the color gradually turns 

 to a bluish violet. 



As Pettenkofer's reaction can also be obtained with other sub- 

 stances, such as the phenols, the higher alcohols, certain bases of 

 the aromatic series, the higher hydrocarbons, and acids of the fatty 

 series and the benzol series, it is always necessary to isolate previ- 

 ously the biliary acids as Platner's bile, before drawing conclusions 

 from the reaction. Albumins, if present, must in every case first 

 be removed. For, as has been stated, many of these contain carbo- 

 hydrate groups, which on contact with concentrated sulphuric acid 

 give rise to the formation of furfurol. This in turn combines with 

 the aromatic oxy-acids and phenols that result from decomposition 

 of the amido-acids to form colored compounds, which are either 

 identical with or very similar to those obtained in the case of the 

 biliary acids (^ee the reaction of Adamkiewicz and the hydrochloric 

 acid test for albumins). 



Pettenkofer's reaction is, in the case of the biliary acids, referable 

 to the non-nitrogenous acid constituents of these acids, viz., to 

 cholalic acid or one of its congeners. 



Physiological Test. Aside from their reaction with furfurol, the 

 bile-acids, or their salts, may also be identified as such from their 

 effect upon the action of the heart. To this end, the heart of a cura- 

 rized frog is exposed and moistened with a small drop of a 1 per 

 cent, solution of atropin, so as to eliminate the action of the vagus. 

 A few drops of an aqueous solution of the bile-acids are then 

 placed upon the heart, when their retarding action can readily be 

 demonstrated. 



Glycocholic Acid. As has been stated, glycocholic acid is the 

 principal biliary acid that is found in the bile of man. It is formed 

 through the union of glycocoll and cholalic acid, as represented by 

 the equation : 



C 2 H 5 NO, + C^H^Os = C^H^NOe + H 2 O 

 Glycocoll. Cholalic Glycocholic 

 acid. acid. 



It is accordingly decomposed into these constitutents when treated 

 with dilute acids or alkalies under the application of heat. 



In the pure state glycocholic acid occurs in the form of fine, silk- 

 like needles, which are readily soluble in alcohol, less readily so in 

 water, and insoluble in ether. From its aqueous solutions it is 

 readily precipitated on adding a small amount of a mineral acid. 

 The crystals melt at 133 C. It is a monobasic acid, and forms 

 salts which, with the exception of the lead and silver compounds, 

 are all soluble in water and alcohol. The free acid and its salts 

 give Pettenkofer's reaction, and turn the plane of polarization to the 

 right. 



On heating glycocholic acid with concentrated sulphuric acid the 



