CHEMICAL BASIS OF THE ANIMAL BODY. 1281 



creatic digestion of proteids, preferably of liver or fibrin. 

 Indole passes over into the distillate, from which it is extracted 

 by shaking up with ether, and is left behind as an impure oily 

 liquid when the ether is driven off by heat. It may also be 

 prepared by heating moist proteids slowly to a red-heat with 

 excess of caustic potash, the indole as before passing over into 

 the distillate. Indole is a crystalline body which when pure 

 melts at 53°. It is soluble in boiling water, alcohol and ether. 

 Reactions. A strip of pine-wood moistened with hydro- 

 chloric acid is coloured bright crimson when dipped into an 

 alcoholic solution of indole. 1 Its alcoholic solution turns red 

 when treated with nitrous (fuming nitric) acid and its aqueous 

 solution gives a copious red precipitate with the same reagent. 

 This reaction is more delicate if carried on by the addition of 

 strong nitric acid first and of a 2 p.c. solution of potassium 

 nitrite subsequently. When indole in dilute solution is mixed 

 with a little sodium nitroprusside and then with a few drops of 

 caustic soda it turns at once violet-blue, and pure blue on sub- 

 sequent acidulation with acetic acid. Skatole yields neither of 

 the above reactions. Indole also forms a well-marked crys- 

 talline compound picric acid (trinitro-phenol) when added to a 

 solution of the acid in benzene, so also does skatole. 



2. Indoxylsulphuric acid. C 8 H 6 N . O . S0 2 OH. The indi- 

 can of urine. 



Indole as previously stated is a characteristic product of the 

 putrefaction of proteids. When administered to animals, it 

 leads to a correspondingly increased output of urinary indican, 

 an increase which is similarly observed as the result of either a 

 normally, pathologically or experimentally increased activity 

 of putrefactive processes in the alimentary canal. Hence indi- 

 can is under normal conditions more plentiful in the urine of 

 herbivora than of carnivora. It is also increased in carnivorous 

 urine under a meat diet, is not increased by the administration 

 of gelatin and is least during starvation, although in the latter 

 case it may not entirely disappear. These facts correspond 

 again to the experimental observations that gelatin does not 

 yield indole during its putrefactive decomposition whereas 

 mucin does, and the latter substance constitutes a part at least 

 of the contents of the alimentary canal during starvation. 

 These statements show clearly the origin and mode of forma- 

 tion of urinary indican, the first-formed indole undergoing 

 oxidation into indoxyl, which is subsequently united to the 

 elements of sulphuric acid and excreted as an ethereal com- 

 pound. 



1 This reaction depends on the presence of coniferin in the pine-wood. 

 Phenol under similar conditions yields a blue coloration. 



81 



