CHEMICAL BASIS OF THE ANIMAL BODY. 1283 



The conditions of its production are in general the same as 

 those for the formation of indole, so that the two substances occur 

 mixed in variable proportions among the products of the putre- 

 factive decomposition of proteids or brain-substance and of the 

 action of caustic potash at high temperatures on proteids. In 

 the former case it appears to be produced at a later stage than 

 is indole, so that on the whole it is most preponderant the 

 longer the putrefactive change is allowed to proceed. Its pres- 

 ence in the faeces is thus due to causes similar to those which 

 account for the presence of indole, and the resemblance is 

 further shewn by the fact that a portion of the first-formed 

 skatole is absorbed, oxidized, and appears externally in the 

 urine as skatoxyl-sulphuric acid (see below). 



Skatole is a crystalline substance which melts when heated 

 to 93, and has a powerfully unpleasant odour, somewhat like 

 that of indole. 



Reactions. Many of the reactions of skatole resemble so 

 closely those of indole that they provide no means for distin- 

 guishing between the two substances. Skatole is, however, 

 characterized by yielding only a milky opacity instead of a red 

 coloration on the addition of fuming nitric acid to its aqueous 

 solutions (see sub indole), in not giving the reaction with a 

 strip of pine-wood dipped in hydrochloric acid which indole 

 does, 1 by its lesser solubility in water and greater resistance to 

 the action of caustic soda. 



5. Skatoxyl-sulphuric acid. C 9 H 8 N . O . SO 2 OH. 



The close relationship between indole and skatole is further 

 shewn by the fact that the latter, like the former, after absorp- 

 tion from the alimentary canal, is oxidized, the product being 

 skatoxyl, C 9 H 8 N . OH, which unites, as does indoxyl, with the 

 elements of sulphuric acid and leaves the body in the urine as 

 a potassium salt of the above acid. 



Our knowledge of the quantitative formation of skatole in 

 the alimentary canal and of its relationship to the simultaneous 

 production of indole is far less complete than is that respect- 

 ing the latter substance. Notwithstanding the close chemical 

 relationship of the two it appears that their physiological 

 behaviour is markedly different. In the first place it seems 

 that the absorption of skatole is less complete than that of 

 indole, since it preponderates in the normal faeces : in accord- 

 ance with this, but little of its ethereal sulphate is found 

 normally in urine. Further, whereas by the ingestion of 

 indole nearly the whole of the sulphates of the urine may be 



1 When however a strip of pine-wood is dipped into an alcoholic solution 

 of skatole and subsequently into strong hydrochloric acid, it is coloured first 

 crimson, which turns to bluish- violet. 



