CHEMICAL BASIS OF THE ANIMAL BODY. 1311 



7. Skatoxyl-pigments. 



The skatole formed in the alimentary canal gives rise, like 

 indole, to compounds of skatoxyl with either sulphuric acid 

 or glycuronic acid (see p. 1220). These compounds when de- 

 composed by hydrochloric acid or oxidizing agents give rise 

 to a colouring matter which is more or less red and may exhibit 

 a distinct and strong purple tint. The pigment i.s insoluble in 

 water, but soluble in either alcohol or chloroform, also when 

 freshly prepared in ether but less so if it has been kept some 

 time. Alcoholic solutions are of a reddish-violet colour; 

 ethereal solutions may shew a green fluorescence, which on 

 exposure to the air takes on a reddish tinge. It is also soluble 

 in hydrochloric and sulphuric acids, giving bright red or pink 

 solutions, and in alkalis yielding yellow solutions. No absorp- 

 tion bands for this substance have as yet been described and 

 the whole subject requires further investigation. 



The urinary pigments so far dealt with may be regarded as either 

 normal or pathological, or as resulting from the spontaneous or arti- 

 ficial decomposition of urinary constituents which are at the outset 

 colourless. In addition to these, other colouring substances are not 

 infrequently observed, or colour-reactions obtained, in urines passed 

 after the administration of certain drugs or the consumption of cer- 

 tain vegetable tissues. They are in many cases not unimportant as 

 leading at first sight to possibly erroneous conclusions as to the pres- 

 ence in urine of pathologically important pigments, e.g. of bile or 

 blood. After the administration of rhubarb or senna the urine may 

 be yellow or greenish-yellow, due to the presence of chrysophanic 

 acid [Ci 4 H s (CH 3 )(OH) 2 O 2 ]> an( i similarly after the use of santonin 

 (C^H^Os). In such cases if the urine is strongly alkaline it may be 

 of a red colour ; this is changed to yellow on the addition of hydro- 

 chloric acid, and if it is initially acid, it turns red on the addition of 

 an excess of alkali. After the internal administration of copaiba, 

 the urine turns pink or rose-coloured on the addition of hydrochloric 

 acid and shews three absorption bands, one (narrow) in the orange 

 to the red side of D, one broad band in the green between D and E, 

 similar to that of fuchsine, and one in the blue. Tannin leads to the 

 appearance in urine of gallic acid [C 6 H 2 . (OH) 3 . COOH], which is 

 hence sometimes found normally in the urine of herbivora (horse). 

 In such cases the urine, if made alkaline with caustic potash, turns 

 brown, and bluish-black on the addition of ferric chloride. It also 

 yields a pink coloration with Millon's reagent, similar to that given 

 by proteids or tyrosine. After doses of antipyrin [C 9 H fl N s O(CH s ),] 

 the urine may be dark-coloured and gives a brownish-red colour on the 

 addition of ferric chloride. Fuchsine (liydrochloride of rosaniline, 

 C2oH 19 N 3 . HC1) reappears partly unchanged in the urine, to whu-h it 

 imparts a reddish tinge. It is detected by making the urine alkaline 

 with ammonia and shaking with an equal volume of ether: the latter 

 extracts the colouring matter and into the solution thus obtained ;i 

 thread of white wool is dipped and allowed to dry spontaneously. 



