MELANIN COLOR FORMATION. 321 



melanogenesis " may be thought of as having begun with studies 

 in the production of artificial melanins, and the accompanying 

 search for the (melanin) chromogen in the albumen molecule. 

 This work was shared by many workers : Stadelmann ('90), 

 Gmelin ('94), Nencki ('95), Schmiedeberg ('97), Chittenden and 

 Albro ('99), Hofmeister (see v. Fiirth, '04), v. Fiirth ('99, '01, 

 '04), Hopkins and Cole ('oi, '03), Schneider ('01), Samuely 

 ('02) and others. Through these workers it was made known, 

 first, that melanins artificially produced are essentially the equiva- 

 lents of natural melanins ; and second, that tyrosin and related 

 aromatic compounds are the chromogens concerned. 



The second step in the progress of this knowledge was con- 

 cerned with the nature of the process by which the melanin is 

 formed from the chromogen. Hlasiwetz and Habermann ('73) 

 had first recognized oxidative processes as necessary for the 

 formation of the artificial melanins. Landolt ('99) extended this 

 fact to the natural pigment of the choroid. 



Bertrand then discovered ('96) an oxidizing enzyme tyrosi- 

 nase which was able to transform tyrosin into melanin-like 

 bodies. Bertrand found the enzyme in certain plants. It has 

 since been found to be of wide distribution, having been found 

 by Biedermann ('98) in the contents of the alimentary canal of 

 meal worms ; by Leptnois ('99) and Gessard ('oi) in the adrenal 

 glands ; by Gonnermann ('oo) in beet roots ; by v. Fiirth and 

 Schneider ('oi) in the haemolymph of insects; by Przibram (see 

 preceding, 'oi) in the ink-sacs of cephalopods (Sepia); by 

 Ducceschi ('oi) in the blood of Bombyx ; by Gessard (o2a, 'o$a, 

 '03^) in the ink-sacs of Sepia, in the integuments of insects, and 

 in melanotic tumors of horses ; by Dewitz ('02) in the blood of 

 certain insects ; by Durham ('04) in the skins of mammals and 

 birds ; by Weindl ('07) in the skin, eyes, ink-sacs and eggs of 

 Loligo ; and by Bertrand and Mutermilch ('07) in wheat bran, 

 v. Fiirth and Schneider ('oi) concluded that " tyrosinase-like 

 ferments are widely distributed in the animal organism, and prob- 

 ably always appear wherever and whenever a physiological or 

 pathological formation of melanin occurs." 



Meanwhile, another advance in our knowledge of melano- 

 genesis was made when Dewitz ('02) demonstrated the role of an 



