Brunton to examine the slides, and he tested the globules with ether,
and found that they were dissolved. We may, therefore, conclude that
the secretion quickly dissolves casein, in the state in which it exists
in milk.
Chemically Prepared Casein. This substance, which
* Lecons, &c. tom. ii. page 151. [page 115]
is insoluble in water, is supposed by many chemists to differ from the
casein of fresh milk. I procured some, consisting of hard globules,
from Messrs. Hopkins and Williams, and tried many experiments with it.
Small particles and the powder, both in a dry state and moistened with
water, caused the leaves on which they were placed to be inflected very
slowly, generally not until two days had elapsed. Other particles,
wetted with weak hydrochloric acid (one part to 437 of water) acted in
a single day, as did some casein freshly prepared for me by Dr. Moore.
The tentacles commonly remained inflected for from seven to nine days;
and during the whole of this time the secretion was strongly acid. Even
on the eleventh day some secretion left on the disc of a fully
re-expanded leaf was strongly acid. The acid seems to be secreted
quickly, for in one case the secretion from the discal glands, on which
a little powdered casein had been strewed, coloured litmus paper,
before any of the exterior tentacles were inflected.
Small cubes of hard casein, moistened with water, were placed on two
leaves; after three days one cube had its angles a little rounded, and
after seven days both consisted of rounded softened masses, in the
midst of much viscid and acid secretion; but it must not be inferred
from this fact that the angles were dissolved, for cubes immersed in
water were similarly acted on. After nine days these leaves began to
re-expand, but in this and other cases the casein did not appear, as
far as could be judged by the eye, much, if at all, reduced in bulk.
According to Hoppe-Seyler and Lubavin* casein consists of an
albuminous, with
* Dr. Lauder Brunton, Handbook for Phys. Lab. p. 529. [page 116]
100