URINE. 491 



became black soon after it was passed. A portion of this urine 

 was examined by Dr Prout, who gave the following account of 

 it:* 



The residue remaining after the urine is evaporated to dry- 

 ness contains no uric acid, and no urea can be detected in it by 

 the usual tests. Although the addition of dilute acids produced 

 no immediate change of colour in this urine, yet, on standing 

 some time, a black precipitate slowly subsided, leaving the super- 

 natant fluid transparent and but slightly coloured. 



The black precipitate was nearly insoluble in water and alco- 

 hol, whether hot or cold. It dissolved in concentrated sulphuric 

 and nitric acids, forming a deep brownish-black solution ; but on 

 adding water the black substance precipitated unaltered. It dis- 

 solved readily in the fixed alkalies, and in their carbonates ; but 

 acids precipitated it unaltered. When ammonia was employed 

 as a solvent, and the excess driven off by evaporating to dryness, 

 a deep-brown matter remained, composed of the black matter 

 and ammonia. This compound was very soluble in water, and 

 when heated with caustic potash, gave out the smell of ammonia. 

 It would not crystallize. From the aqueous solution of this 

 brown matter chloride of barium and nitrate of silver threw down 

 copious brown precipitates ; as did also protonitrate of mercury 

 and nitrate of lead. Corrosive sublimate produced no immedi- 

 ate precipitate, and that obtained from acetate of zinc was of a 

 pale-brown colour. 



From these experiments Dr Prout inferred that the urine ow- 

 ed its black colour to a compound of the black matter with am- 

 monia. The black matter he considers as an acid, which he dis- 

 tinguishes by the name of melanic acid. No experiments have 

 been made to determine the nature of this acid, or the relation in 

 which it stands to uric acid. 



17. Some very cruel experiments were made upon dogs by 

 M. Collard de Martigny. He starved the poor animals to death. 

 In the urine of a dog thus treated he could detect no urea.f 

 The same remark was made by Magendie with respect to the 

 urine of dogs fed on sugar, gum, or olive oil, which in fact died 

 of starvation.} 



Annals of Philosophy, (2d series), iv. 71. 



j- Jour, de Physiologic, via- 157. \ Ibid. ii. 487. 



