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618 BRAIN AND NERVES.
great difficulty by pepsin-hydrochloric acid or trypsin solution, but are
soluble in dilute acids and alkalies in the warmth. Membranin of the
capsule of the lens contains 14.10 per cent N and 0.83 per cent S, and is
a little less soluble than that from Descemet’s membrane.
The principal mass of the solids of the crystalline lens consists of
proteins, whose nature has been investigated by C. Morner.1
Some of
these proteins dissolve in dilute salt solution, while others remain
insoluble in this solvent.
The Insoluble Protein. The lens fibers consist of a protein sub-
stance which is insoluble in water and in salt solution and to which
Morner has given the name albumoid. It dissolves readily in very dilute
acids or alkalies. Its solution in caustic potash of 0.1 per cent is very
similar to an alkali-alb uminate solution, but coagulates at about 50°
C. on nearly complete neutralization and the addition of 8 per cent NaCl.
Albumoid has the following composition: C 53.12, H 6.8, N 16.62, and
S 0.79 per cent. The lens fibers themselves contain 16.61 per cent N
and 0.77 per cent S. The inner parts of the lens are considerably richer
in albumoid than the outer. The quantity of albumoid in the entire
lens amounts on an average to about 48 per cent of the total weight of
the proteins of the lens.
The Soluble Protein consists, exclusive of a very Ftrall quantity of
albumin, of two globulins, a- and fi-crystallin. These two globulins differ
from each other in this manner: a-crystallin contains 16.68 per cent N
and 0.56 per cent S; /3-crystallin, on the contrary, 17.04 per cent N and
1.27 per cent S. The first coagulates at about 72° C. and the other at
63° C. Besides this, /3-crystallin is precipitated from a salt-free solu-
tion with greater difficulty and less completely by acetic acid or carbon
dioxide. These globulins are not precipitated by an excess of NaCl at
either the ordinary temperature or 30° C. Magnesium or sodium sul-
phate in substance precipitates both globulins, on the contrary, at 30° C.
These two globulins are not equally divided in the mass of the lens. The
quantity of a-crystallin diminishes in the lens from without inward;
/3-crystallin, on the contrary, from within outward.
A. Jess 2
has found that the different proteins of the crystalline lens
behave differently with Arnold’s protein reaction with sodium nitro-
prusside (page 100). The albumoid gives negative results with this
reagent. The a-crystallin gives it faintly, while the /3-crystallin gives a
strong reaction. The absence of this reaction, as observed by Weiss
in senile cataract, is connected with the fact as Jess has shown by his
investigations on the senile cataract in oxen, that the crystallin con-
1
Zeitschr. f. physiol. Chem., 18. This contains also the pertinent literature.
2 Zeit.srhr. f. Biol.. 01.
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