CHEMICAL BASIS OF THE ANIMAL BODY. 1309 



its spectra to those of hsematoporphyrin. It is obtained from 

 urine by the method employed for the separation of urobilin, 

 or artificially by the action of reducing agents on hsematin, this 

 being the supposed source of its origin in the body. It is 

 soluble in either alcohol, ether, benzene or chloroform. In acid 

 alcoholic solution it shews three absorption bands, one narrow 

 adjoining D on the red side of this line, one half-way between 

 D and E and one between b and F closely resembling the band 

 of urobilin. There is also occasionally a fourth very faint 

 band between the first two bands described above. In alcoholic 

 solution made alkaline by ammonia it yields a spectrum closely 

 resembling that of hsematoporphyrin. But unlike the latter 

 substance its solutions shew a very faint green fluorescence on 

 the addition of zinc chloride and ammonia. The occurrence 

 of hsematoporphyrin in urine has been frequently recorded, 

 and from the spectroscopic appearances described above, some 

 observers are inclined to the view that urohsematoporphyrin is 

 not a single substance but a mixture of hsematoporphyrin with 

 some pigment closely resembling urobilin. 



4. Humus pigments. 



When carbohydrates are treated with acids or alkalis, among 

 the numerous products which arise are certain pigmentary 

 bodies of a more or less dark brown colour. A similar colora- 

 tion is well known as occurring in fruits when bruised or 

 exposed to the air, and generally in decaying vegetable tissues. 

 These substances are known under the name of 'humus. ' When 

 urine is treated with acids in presence of oxygen it acquires 

 a markedly darker colour, and since carbohydrates in small 

 amount are probably present in all urines, there is at once a 

 possibility that some at least of the observed coloration is due 

 to the production of humus-pigmented substances by the action 

 of the acids on the carbohydrates. In accordance with this 

 view certain so-called humus pigments have been prepared from 

 urine, but our knowledge of them is as yet very incomplete. 

 They are stated to be practically insoluble in any solvents other 

 than amyl-alcohol, strong ammonia and caustic alkalis : the 

 solutions shew no absorption bands when examined spectro- 

 scopically. They are further said to account for the usually 

 dark colour of normal herbivorous urine and of urine after the 

 cutaneous absorption of carbolic acid and several other aromatic 

 compounds. 



5. Urinary melanin. 



Certain tumours are not infrequently observed which from 

 their extremely dark pigmentation are spoken of as 'melanotic,' 



