180 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



those of alkaline haematoporphyrin (fig. 63, spectrum 2). On adding sulphuric 

 acid the spectrum of acid haematoporphyrin is seen (fig. 63, spectrum 1). 

 Occasionally urate sediments are pigmented with a form of the pigment which 

 shows a two-banded spectrum, very like that of oxyhsemoglobin (fig. 63. 

 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. 116. It is easily oxidised to 

 indigo-blue or indigo-red. 



2CeH,<gOH^CH + 0, = C,H,<g^>C:C<g^>C,H, -f 2H,0. 



[indoxyl] [indigo blue] 



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



C,jH4<^--j^^ C "Cn -a />N. I* is very rare for the urine to be actually 



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.) (6) Skatoxyl. — 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 satura- 

 tion with ammonium sulphate. The colour is destroyed 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 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 oases of melanotic sarcoma. For alcaptonuria see p. 132. 



