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11C THE PROTEIN SUBSTANCES.
a little more than 0.5 per cent pure crystalline cystine and on account
of the low cystine content as well as for other reasons the koilin differs
from the keratins.
Keratin is amorphous or takes the form of the tissues from which
it was prepared. It is insoluble in water, alcohol, or ether. On heating
with water to 150-200° C. it dissolves. It also dissolves gradually in
caustic alkalies, especially on heating. It is not dissolved by artificial
gastric juice or by trypsin solutions. Keratin gives the xanthoproteic
reaction, as well as the reaction with Millon’s reagent, although the
latter is not always typical.
In the preparation of keratin a finely divided horny structure is
treated first with boiling water, then consecutively with diluted acid,
pepsin-hydrochloric acid, and alkaline trypsin solution, and, lastly, with
water, alcohol, and ether.
Elastin occurs in the connective tissue of higher animals, sometimes
in such large quantities that it forms a special tissue. It occurs most
abundantly in the cervical ligament (ligamentum nuchae).
Elastin used to be generally considered as a sulphur-free substance.
According to the investigations of Chittenden and Hart, it is a question
whether or not elastin contains sulphur, as it may have been removed by
the action of the alkali in its preparation. H. Schwarz has been able
by another method, to prepare an elastin containing sulphur, from the
aorta, and this sulphur can be removed by the action of alkalies, without
changing the properties of the elastin; and Zoja, Hedin, Bergh,
and Richards and Gies } have found that elastin contains sulphur. The
most trustworthy analyses of elastin from the cervical ligament (Nos.
1 and 2) and from the aorta (No. 3) have given the following results,
which compare well with each other:
s o
.... 21.94 (Horbaczewski 2
)
.... 21.79 (Chittenden and Hart)
0.38 (H. Schwarz)
Zoja found 0.276 per cent sulphur and 16.96 per cent nitrogen in
elastin. Hedin and Bergh found different quantities of nitrogen in
aorta-elastin, depending upon whether Horbaczewski’s or Schwarz’s
method was used in its preparation. In the first case they found 15.44
per cent nitrogen and 0.55 per cent sulphur, and in the other 14.67 per
1
Chittenden and Hart, Zeitechr. f. Biologie,’ 25; Schwarz, Zeitschr. f. physiol.
Chem., 18; Zoja, ibid., 2’.l; Bergh, ibid., 25; Hedin, ibid.; Richards and Gies, Amer.
Journ. of Physiol., 7.
2
Zeitschr. f. physiol. Chem., 6.
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