162 THE DIGESTIVE FLUIDS. 



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

 the aromatic oxy-acids and phenols that result from decomposition 

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

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

 biliary acids (see 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 from their effect 

 upon the action of the heart. To this end, the heart of a curarized 

 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 2 .H 40 5 = CwHttNO, + H 2 O 



Glycocoll. Cholalic Glycocholic 

 acid. acid. 



It is accordingly decomposed into these constituents 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 

 anhydride of glycocholic acid is precipitated in the form of oily 

 droplets, which subsequently tend to coalesce. This anhydride is 

 termed cholonic acid, and has the composition C^H^NO^ 



According to Michailoff, glycocholic acid when treated with con- 

 centrated sulphuric acid in the presence of acetic acid is said to give 

 an orange color with a green fluorescence. On salting with ammo- 

 nium sulphate a precipitate is formed which in its reactions is 

 identical with biliverdin. Urobilin is said to remain in solution. 

 This observation is of special interest, as showing the possible rela- 

 tionship which may exist between the biliary acids and the bile- 

 pigments. We find, as a matter of fact, that an increase in the 

 production of bile-pigments on the part of the liver is associated 

 with a diminished formation of biliary acids. 



