CHEMICAL BASIS OF THE ANIMAL BODY. 1279 



a small proportion is passed out in the faeces, the larger part 

 however is excreted in the urine as an ethereal salt of sulphuric 

 acid, viz. phenylsulphate of potassium. The latter is typical 

 of an extensive series of similar ethereal sulphates which make 

 their appearance in urine after the ingestion of aromatic sub- 

 stances. 



Phenyl-sulphuric acid. 1 C 6 H 5 . O . S0 2 OH. Apart from its 

 abundant presence in urine as an alkaline salt after the admin- 

 istration of phenol this compound occurs normally in small 

 quantities in most urines, more particularly in those of herbiv- 

 ora, since in these animals the conditions for its formation are 

 especially provided by the preponderance of aromatic compounds 

 in their food and the more marked activity of putrefactive 

 changes in their alimentary canal. The total sulphates in urine 

 consist therefore partly of this ethereal sulphate (together with 

 the similar compounds of cresol, indole and skatole, see below} 

 and of ordinary sulphates. 



7. Cresol. C 6 H 4 . OH . CH 3 . Methylphenol. 



This homologue of phenol exists in three isomeric forms, 

 ortho-, para- and metacresol. It is now known that the phenols 

 which may be obtained by the distillation of urine with acids 

 consist preponderatingly of paracresol, accompanied in some 

 cases by orthocresol and possibly (?) by metacresol in minute 

 amounts. Like phenol it is not found free in urine but as 

 cresylsulphuric acid, C 7 H 7 . S0 2 OH. The general conditions 

 of its presence in urine are practically identical with those for 

 the occurrence of phenylsulphuric acid. When introduced into 

 the animal body the three isomeric cresols undergo distinctly 

 different oxidational changes. 



8. Pyrocatechin. C 6 H 4 (OH) 2 . Ortho-dihydroxybenzene. 



This substance occurs in small amounts in human urine, 

 united with sulphuric acid as a mono-ethereal compound, 

 OH . C 6 H 4 . O . S0 2 OH. It is more plentifully present in the 

 urine of the herbivora, especially of the horse, and is largely 

 increased in amount by the administration of benzene or phenol. 

 It is also stated to occur in cerebrospinal fluid. When present 

 in urine it (together with hydroquinone) confers on this excre- 

 tion, especially if alkaline, the property of turning successively 

 greenish, brown and finally dark-brown or almost black on 

 exposure to the air, and of readily reducing solutions of me- 

 tallic salts, a fact to be taken into account when dealing with 

 the presence or absence of sugar in the urine. Solutions of 

 pyrocatechin turn emerald green on the addition of a few drops 



1 Not to be confounded with phenolsulphonic acid, CeH^OH) . SO2OH. 



