MELANIN. 3() ( J 



rigid chemical investigation. From Virchow's investigations it is, 

 however, apparent that the physician must also lend his help for 

 the advancement of pathological and physiological chemistry ; for 

 without the aid of pathological histology, without a judicious appli- 

 cation of the microscope, the chemist could not have succeeded in 

 discovering hsematoidin any more than in detecting oxalate of lime 

 in normal urine ; without such aid the chemist could never have con- 

 ceived an idea of the metamorphosis of the pigments in the 

 animal body. As long as the physician contents himself with 

 borrowing mere hypotheses from chemists, without being himself 

 practically familiar with chemical science, he can never hope to 

 gain the advantages which it is capable of affording ; in this respect 

 he resembles the agriculturist, who can never expect to raise his 

 pursuit to the dignity of a science until he has learned the practical 

 application of the principles of chemistry. 



MELANIN. 



Chemical Relations. 



Properties. Melanin forms either a black, cohesive mass, or a 

 blackish-brown powder ; it is devoid of smell and taste ; when 

 stirred in water it continues to float for some time, but is insoluble 

 both in water and in alcohol, in ether, in dilute mineral acids, and 

 in concentrated acetic acid ; it dissolves, after prolonged digestion, 

 in a dilute solution of potash, from which it is again precipitated 

 with a light brown colour by hydrochloric acid ; it is decom- 

 posed when boiled with concentrated nitric acid, but it is not 

 affected even by the very prolonged action of chlorine. It is a 

 conductor of electricity, is incapable of fusing, may be ignited in 

 the air, and burns with a vivid light, the charcoal continuing to 

 smoulder till it is reduced to a whitish-yellow ash consisting of 

 chloride of sodium, lime, bone-earth, and a little peroxide of iron. 

 By dry distillation it yields an empyreumatic substance, and 

 carbonate of ammonia. According to Gmelin this pigment is 

 rendered paler, and is partially dissolved by chlorine- water, the 

 undissolved portion becoming again of a dark brown colour on the 

 addition of potash. 



Whether the black crystals which have been found by Macken- 

 zie,* Guillot,t and Virchow,J in melanotic masses are or are not 



* A Practical Treatise on Diseases of the Eye. Lond. 1835. p. 663. 



f Arch. gen. de Me'd. 4 St-r. T. 7, p. 166. 



Arch. f. pathol. Anat. u. s. w. Bd. 1 , S. 399. 



