CASTOREUM AND PHENYLIC COMPOUNDS. 123 



the form of glyco-benzoic or hippuric acid C 9 H 9 NO 3 ; and, no 

 doubt, some, at any rate, of the hippuric acid excreted both by 

 vegetable and mixed feeders is derived from the ingestion of cer- 

 tain benzo-genetic articles of food. Similarly, the administration 

 of salicin and salicic aldehyd or acid is followed by the appear- 

 ance in the urine of glyco-salicic or salisuric acid C 9 H 9 NO 4 , 

 readily decomposible into glycocine and salicic acid, just as hip- 

 puric acid is decomposible into glycocine and benzoic acid. 

 Hence the salisuric and salicic acids may be regarded as normal 

 constituents of the urine of the beaver, with which willow bark 

 is well known to be a favourite food. The occurrence of 

 salicic compounds in castoreum also is doubtless due in a similar 

 manner to the food of the beaver. Castoreum, moreover, contains 

 phenol, or coal-tar kreosote, which, according to Staedeler and 

 others, is an ordinary constituent of human urine, and an impor- 

 tant contributor to its characteristic odour. Now, the relation of 

 phenol to salicic acid is very simple. Under suitable conditions 

 salicic acid breaks up into phenol and carb -anhydride, which, 

 under other conditions, re-unite to form salicic acid, thus : 



Phenol Carb-anhyd. Salicic acid 



C 6 H 6 + CO, = C 7 H 6 3 



Remembering that urine of a dark brown colour, or becoming 

 of a brown colour by oxidation, contains a pigment which is in 

 some way or other related to indigo, and also that an apparently 

 similar brown urine is occasionally passed after the internal or 

 external administration of phenol, kreasote, tar-oil, &c., this rela- 

 tionship of salicic and phenyl compounds presents a considerable 

 pathological interest. Phenol may indeed be considered as the 

 nucleus not only of salicic acid, but likewise of tyrosine and indigo ; 

 from both of which it is also readily obtainable. Moreover, by 

 treatment with chlorine, all four bodies yield the same 6-carbon 

 ultimate product, namely, chloranil C6C1 4 O 2 , or perchloroquinone. 



(132.) It now only remains for us to consider the ultimate 

 constitution of tyrosine, and its analogy to hippuric acid. Starting 



