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CONSTITUENTS OF THE NERVOUS SYSTEM. 605
The gray substance is only slightly richer in proteins than the white
substance; but as the neurokeratin, which forms the neurolgia, and as
a double sheath envelops the outside of the nerves, belongs in great
part, or according to Koch, entirely, to the white substance (Kuhne,
and Chittenden, Baumstark l
), the gray substance is actually richer
in protein. The same is true also for the nucleoprotein or at least for
the nucleins which v. Jaksch found in large amounts in the gray sub-
stance. The mixture of amino-acids obtained from the proteins of
the gray and white substances has about the same composition (Abder-
halden and Weil 2
). Glycocoll could not be detected in this mixture.
The so-called protagon has been considered as one of the chief con-
stituents, perhaps the only constituent (Baumstark), of the white
substance. This protagon, according to most investigators, is only a
mixture of phosphatides with cerebron or with a mixture of cerebrosides
(see below). Protagon belongs to the so-called brain lipoids, which
include three chief groups, phosphatides, cerebrosides and cholesterin and
which are contained to a greater extent in the white than in the gray
substance. Among the closely studied phosphatides the cephalin
seems to occur to the greatest extent in the brain. The lecithin, accord-
ing to Frankel,3
does not occur in the human brain and only in very
small quantities in other brains (of sheep and beef). Other brain
phosphatides especially described by Thudichum and by Frankel,4
have not been positively proved as chemical individuals. The same
is true for the jecorin and the sulphurized lipoids isolated from the
human brain and from ox brains. Cholesterin occurs chiefly in the
white substance. Fatty acids and neutral fats may be prepared from
the brain and nerves; but as these may be readily derived from a decom-
position of phosphatides, which exist in the fatty tissue between the
nerve-axes, it is difficult to decide what part the fatty acids and neutral
fats play as constituents of the real nerve-substance.
By allowing water to act on the contents of the medulla, round or oblong
double-contoured drops or fibers, not unlike double-contoured nerves, are formea.
These remarkable formations, which can also be seen in the medulla of the dead
nerve, have been called " myelins forms," and they were formerly considered a;s
produced from a special body, " myeline." Myeline forms may, however, be
obtained from other bodies, such as impure protagon, lecithin, and impure choles-
terin, and they depend upon a decomposition of the constituents of the medulla.
1
Koch, Amer. Journ. of Physiol., 11; Kuhne and Chittenden, Zeitschr. f Biologie,
26; Baumstark, Zeitschr. f. physiol. Chem., 9.
2
v. Jaksch, Pfliiger’s Arch. 13; Abderhalden and Weil, Zeitschr. f. physiol. Chem.
81 and 83.
3
Bioch. Zeitschr., 24.
4
Thudichum, Die chemische Konstitution des Gehirns des Menschen und der
Tiere, Tubingen, 1901; S. Frankel, and collaborators, Bioch. Zeitschr., 24 and 28.
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