* Lecons phys. de la Digestion, 1867, tom. ii., p. 304. [page 124]
pepsin, but absorbs from it some albuminous impurity which induces
inflection, and which in large quantity is highly injurious. Dr. Lauder
Brunton at my request endeavoured to ascertain whether pepsin with
hydrochloric acid would digest pepsin, and as far as he could judge, it
had no such power. Gastric juice, therefore, apparently agrees in this
respect with the secretion of Drosera.
Urea. It seemed to me an interesting inquiry whether this refuse of the
living body, which contains much nitrogen, would, like so many other
animal fluids and substances, be absorbed by the glands of Drosera and
cause inflection. Half-minim drops of a solution of one part to 437 of
water were placed on the discs of four leaves, each drop containing the
quantity usually employed by me, namely 1/960 of a grain, or .0674 mg.;
but the leaves were hardly at all affected. They were then tested with
bits of meat, and soon became closely inflected. I repeated the same
experiment on four leaves with some fresh urea prepared by Dr. Moore;
after two days there was no inflection; I then gave them another dose,
but still there was no inflection. These leaves were afterwards tested
with similarly sized drops of an infusion of raw meat, and in 6 hrs.
there was considerable inflection, which became excessive in 24 hrs.
But the urea apparently was not quite pure, for when four leaves were
immersed in 2 dr. (7.1 ml.) of the solution, so that all the glands,
instead of merely those on the disc, were enabled to absorb any small
amount of impurity in solution, there was considerable inflection after
24 hrs., certainly more than would have followed from a similar
immersion in pure water. That the urea, which was not perfectly white,
should have contained a sufficient quantity of albuminous matter, or of
some salt of ammonia, to have caused the above effect, is far from
surprising, for, as we shall see in the next chapter, astonishingly
small doses of ammonia are highly efficient. We may therefore conclude
that urea itself is not exciting or nutritious to Drosera; nor is it
modified by the secretion, so as to be rendered nutritious, for, had
this been the case, all the leaves with drops on their discs assuredly
would have been well inflected. Dr. Lauder Brunton informs me that from
experiments made at my request at St. Bartholomew s Hospital it appears
that urea is not acted on by artificial gastric juice, that is by
pepsin with hydrochloric acid.
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