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MUCINS. 1(39
solutions, or solutions prepared by the aid of a traee of alkali, arc mucilagi-
nous, ropy, and give a precipitate with acetic acid which is insoluble in
excess of acid or soluble only with great difficulty. The mucoids do not
show these physical properties, and have other solubilities and precipit-
ation properties. As we have intermediate steps between different pro-
tein 1 todies, so also we have such between true mucins and mucoids, and
a sharp line cannot be drawn between these two groups.
It is just as difficult at present to draw a sharp line between the pro-
teins and the mucins or mucoids, since we have been able to split off
carbohydrate complexes from several proteins, and as proteins have
been isolated from white of egg which yield more or less glucosamine.
The very variable amounts of glucosamine obtained under various con-
ditions from the crystalline ovalbumin seem to indicate that we are
dealing with a contamination with a glycoprotein.
True mucins are secreted by the larger mucous glands, by certain
mucous membranes, and by the skin of snails and other animals. True
mucin also occurs in the navel-cord. Sometimes, as in snails and in
the membrane of the frog-egg (Giacosa) and perch-eggs (Hammarsten l
),
a mother-substance of mucin, a mucinogen, has been found which may
be converted into mucin by alkalies. Mucoid substances are found in
certain cysts, in the cornea, the crystalline lens, white of egg, and in
certain ascitic fluids. ’
The so-called tendon-mucin, which, according
to the investigations of Levene and of Cutter, and Gies,2
contains
chondroitin-sulphuric acid or a related substance, cannot be classified
as a mucin, but must, like the chondromucoid and the osseomucoid,
be classified as chondroprotein. As the mucin question has not been
sufficiently studied, it is at the present time impossible to give any positive
statements in regard to the occurrence of mucins and mucoids, especially
as without doubt in many cases non-mucinous substances have been
described as mucins.
True Mucins. Thus far we have been able to obtain only a few
mucins in a pure and unchanged condition, because of the reagents used.
The elementary analyses of these mucins have given the following results:
c h n s
Mucin from mucous membrane (air-
passages) 48.26 6.91 10.70 1.40 (Fr. Muller «)
Mucin from submaxillary 48.84 6.80 12.32 0.84 (Hammarsten 5
)
Mucin from snail 50 . 32 6 . 84 13 . 65 1 . 75 (Hammarsten j
)
Synovial mucin 51.05 6.53 13.01 1.34 (v. Holst *)
1
Giacosa, Zeitschr. f. physiol. Chem., 7; Hammarsten, Pfluger’s Archiv., 36, and
Skand, Arch. f. Physiol., 17.
2
Levene, Zeitschr. f. physiol. Chem., 31; Cutter and Gies, Amer. Journ. of Physiol., 6.
3
Fr. Muller, Zeitschr. f. Biologie, 42; Hammarsten, Zeitschr. f. physiol. Chem.. 12,
.and Pfluger’s Arch., 36.
4
Zeitschr. f. physiol. Chem., 43.
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