216 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



spectrum 3) ; by treatment with dilute mineral acids this changes immedi- 

 ately to the spectrum of acid haematoporphyrin. 



5. Chromogens in Urine. In addition to the chromogens of urobilin and 

 haematoporphyrin alluded to in the foregoing paragraphs there are others, of 

 which the following may be mentioned : (a) Indoxyl. The origin of this 

 substance from indole is mentioned on p. 154. It is easily oxidised to 

 indigo-blue or indigo-red. 



20 A < HN H > CH f * = W < NH > C : C < NH > C H ^ + 2H *- 



[indoxyl] [indigo-blue] 



Indigo-red is isomeric with indigo-blue, its structural formula being 



PO C OTT 



C 6 H 4 < ^ > C : C < c H > Nt It is very rare for the urine to be actuall y 

 pigmented with indigo, for the urinary indoxyl is excreted as a conjugated 

 sulphate which resists oxidation. When the urine is mixed with an equal 

 volume of hydrochloric acid, indoxyl is liberated from the sulphate. A 

 solution of a hypochlorite is then added drop by drop, when indigo-blue is 

 formed, and on shaking the mixture with chloroform the indigo-blue passes 

 into the chloroform. (Jaffe.) This test, however, is not a very good one, for 

 the hypochlorite solution has always to be freshly prepared, and even then a 

 small excess will cause the colour to disappear owing to* oxidation of the 

 indigo, and it is difficult to hit off the exact amount to give the reaction. A 

 better test for indoxyl-sulphuric acid (indican) consists in adding 10 c.c. of 

 a 20-per-cent. solution of lead acetate to 50 c.c. of urine, and filtering the 

 mixture. The filtrate is shaken with an equal volume of hydrochloric acid 

 (containing 0*2 to 0*4 per cent, of ferric chloride) and a few c.c. of chloroform. 

 The indigo-blue passes into the chloroform (Obermayer.) (b) STtatoxyl. 

 "When skatoxyl is given by the mouth it passes into the urine, and yields 

 skatoxyl-red on oxidation, (c) Urorosein is distinct from indigo -red. It is 

 produced from its chromogen by the action of mineral acids. It frequently 

 appears when urine is treated with strong hydrochloric acid and allowed to 

 stand, but it appears more readily when an oxidising agent is added as well. 

 It is readily soluble in amylic alcohol, but not in ether. The chromogen is 

 precipitated by saturation with ammonium sulphate. The colour is de- 

 stroyed by alkalis. It shows an absorption band between the D and E lines 

 (fig. 63, spectrum 8). 



6. Pathological Pigments. The most frequently appearing of abnormal 

 pigments are those of blood and bile. The urine may contain accidental 

 pigments due to the use of drugs (rhubarb, senna, logwood, santonin) ; in 

 carbolic acid poisoning pyrocatechin and hydrochinon are chiefly responsible 

 for the greenish-brown colour of the urine, which increases on exposure to 

 the air. The black or dark-brown pigment called melanin may pass into 

 the urine in cases of melanotic sarcoma. For alcaptonuria see p. 169. 



