794 THE SKIN AND ITS SECRETIONS. 



The difficulties which attend the isolation and purification of the 

 melanins have not been overcome in certain cases, while in others it is 

 questionable whether the final product obtained has not another com- 

 position from the original coloring matter, owing to the energetic chemical 

 processes resorted to in its purification. The elementary composition 

 shows widely varying results in the different melanins, namely, 48-60 

 per cent carbon and 8-14 per cent nitrogen. Under these circumstances 

 and as no doubt we have a large number of melanins having different 

 composition, it seems that a tabulation of the analyses of the different 

 preparations can be of secondary importance only. 



So little is known about the structural products of the melanins or 

 melanoids that it is impossible to give the origin of these bodies. As 

 undoubtedly there are several distinct melanins, their origin must also be 

 distinct. The ferruginous melanins should be considered as originating 

 from the blood-pigments until further research proves otherwise. Others, 

 on the contrary, cannot have this origin; for example, the pigments 

 of the hair and choroid, which are free from iron and which do not yield 

 hsemopyrrol according to SPIEGLER. Several melanins and this is also 

 true of the melanoids produced from proteins on cleavage with acids 

 (SAMUELY l ) yield indol or skatol and a pyrrol substance on fusion 

 with alkali, while hippomelanin, according to v. FURTH and JERUSALEM, 

 gives a fecal odor on this treatment, but does not yield any indol or skatol. 

 More characteristic than the last two mentioned bodies is a phenol-like 

 substance, which occurs to a slight extent, and gives a bluish-black 

 color with ferric chloride (v. FURTH). 



The cyclic complexes of the proteins are rightly considered as the 

 mother-substance of the melanins (SAMUELY and v. FURTH and others), 

 and this view has received support by the behavior of tyrosine with 

 oxidases. It has been found that by the action of a plant oxidase, 

 BERTRAND'S tyrosinase 2 , upon tyrosine, colored products and then 

 melanin-like substances are formed, v. FURTH with SCHNEIDER and 

 PRIBRAM, GESSARD, NEUBERG, DEWITZ and others 3 have shown that 

 similar acting tyrosinases also occur in the animal kingdom, in insects 

 and sepia, in melanotic tumors and in pigmented skin, and v. FURTH 

 and JERUSALEM have prepared an artificial melanin from tyrosine 

 which shows great similarity to hippomelanin. Finally NEUBERG 4 has 

 also prepared an extract from the melanotic metastases of a primary 

 adrenal tumor which formed a dark-brown pigment from adrenalin 

 and p-oxyphenylethylamine, but not from tyrosine. As indicated 



1 Hofmeister's Beitrage, 2. 



2 Compt. rend., 122. 



3 The literature can be found in v. Fiirth and Jerusalem, Hofmeister's Beitrage, 10. 



4 Virchow's Arch., 192. 



