xii MELANINS 583 



powdered they appear of a lighter colour, more brown ; a preparation 

 of Hensen and Nolke was ochre-coloured. They are insoluble in 

 water, neutral salt-solutions, alcohol, amyl-alcohol, ether, chloroform, 

 benzene, etc., and in dilute acids ; in 50 per cent acetic acid they are 

 soluble to a slight extent, and this soluble fraction possesses, according 

 to Morner, somewhat different properties. In alkalies, ammonia, and 

 the alkali-carbonates, melanins are readily soluble, and form in con- 

 centrated solutions black or brown-red, and on dilution yellow-brown 

 solutions. Examined spectroscopically, melanins do not show any 

 distinct bands ; there is a uniform darkening commencing at D which 

 becomes absolute at the latest by b. 



The colouring power of the melanin may be judged by the fact 

 that an average negro, according to Abel and Davis, 1 has in his skin 

 3 '3 grammes of pigmentary granules, of which amount only 1 gramme 

 consists of pigment, the other 2 - 3 grammes consisting of a colourless 

 substratum and much inorganic matter (Ca, Mg, Fe, silicic-, phosphoric-, 

 and sulphuric-acids). Urin containing O'l per cent of melanin has 

 the colour of dark beer (Hensen and Nolke). Nencki and Berdez 

 have obtained from one liver 300 grams of melanin. 



From their alkaline solutions melanins are precipitated by acidi- 

 fication, and likewise by the addition of barium hydrate, lead acetate, 

 and by saturating the solution with magnesium sulphate. To extract 

 the melanin from tumours, the tissues are extracted with water, which 

 converts the pigment into a fine suspension, which latter is readily 

 carried down by precipitating phosphates. The pigment is then 

 purified by repeatedly dissolving it in alkalies, and precipitating it 

 by acids. 



In some of the cases mentioned above, the melanin was also found 

 in the urine, either as such or as 'melanogen,' which by oxidation is 

 converted into the dark melanin. Urine containing melanogen shows 

 the normal colour, but assumes the dark melanin-colour on the addition 

 of nitric acid ; potassium bichromate + sulphuric acid ; bromine water 

 or ferric chloride. Miura has been in some cases successful in demon- 

 strating melanogen in the urine of rabbits after having injected melanin 

 into the peritoneal cavity. 



Wolff obtained two pigments from a melanotic liver, one of which 

 was soluble in soda-solution, while the other one was insoluble in 5 

 per cent cold soda-solution, but it could be made soluble by heating 

 to 50 or 60, becoming at the same time denaturalised. The soluble 

 pigment gave lower carbon-values than most of the melanins. From 



1 Abel and Davis, Journ. Exper. Med. 1. 361 (1896). 



