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MELANINS. 841
Melanins. This group includes several different varieties of amorphous
black or brown pigments which are insoluble in water, alcohol, ether.
chloroform, and dilute acids, and which occur in the skin, hair, chorioidia,
in sepia, in certain pathological formations, and in the blood and urine
in disease. From the true native melanins we must differentiate the
humus-like products obtained on boiling proteins with mineral acids
and which have been called melanoidins or melanoidic acid (Schmiedeberg)
and whose relation to the true melanins is still unknown.
The melanoidins are readily soluble in dilute alkali while the melanins
show a different behavior in this regard. Of the melanins a few such as
Schmiedeberg’s sarcomelanin, and that from the melanotic sarcomata
of horses, the hippomelanin (Nencki, Sieber, and Berdez), which are
soluble with difficulty in alkalis, while others, such as the coloring matter
of certain pathological swellings in man, the phymatorhusin (Nencki and
Berdez) are readily soluble in alkalies. The melanins, as above stated,
are in general insoluble in dilute mineral acids; from black sheep-
wool Gortner l
has isolated a melanin which was soluble in acetic acid
and in dilute mineral acids (see below).
Among the melanins there are a few, for example the choroid pig-
ment, which are free from sulphur (Landolt and others); others, on the
contrary, as sarcomelanin and the pigment of the hair (Sieber) are rather
rich in sulphur (2-4 per cent), while the phymatorhusin found in cer-
tain swellings and in the urine (Nencki and Berdez, K. Morner) is
very rich in sulphur (8-10 per cent). Whether any of these pigments,
especially the phymatorhusin, contains any iron or not is an important
though disputed point, for it leads to the question whether these pigments
are formed from the blood-coloring matters.
According to Nencki and Berdez the pigment, phymatorhusin, isolated by
them from a melanotic sarcoma did not contain any iron, and according to them
is not a derivative of haemoglobin. K. Morner and later also Brandl and L.
Pfeiffer found, on the contrary, that this pigment did contain iron, and they
consider it as a derivative of the blood-pigments. The sarcomelanin (from a sar-
comatous liver) analyzed by Schmiedeberg contained 2.7 per cent iron which
was partly in organic combination and could not be completely removed by
dilute hydrochloric acid. The sarcomelanic acid prepared by Schmiedeberg
by the action of alkali on this melanin contained 1.07 per cent iron. The sar-
comelanin investigated by Zdarek and v. Zeynek also contained 0.4 per cent iron.
Recently Wolff 2
prepared two pigments from a melanotic liver, of which one
was no doubt modified. The other, which was soluble in a soda solution, con-
1
Gortner, Journ. of biol. Chem., 8, and Bioch. Bulletin, 1, 1911.
i
Zdarek and v. Zeynek, Zeitschr. f. physiol. Chem., 36; Wolff, Hofmeister’s Beitrage,
5. The literature on the melanins may be found in Schmiedeberg, " Elementarformeln
einiger Eiweisskorper, etc." Arch. f. exp. Path. u. Pharm., 39; also in Robert, Wiener
Klinik, 27 (1901), and Spiegler, Hofmeister’s Betrage, 4, and especially v. Furth,
Centralbl. f. allg. Path. u. Path. Anat., ,15, 1907, 617.
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