142 PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 
a more profuse elimination of mucilage, but also to the secretion of an acid liquid, 
which has the power of dissolving all bodies of the kind, namely, such as clotted 
blood, mill, albumen, and even cartilage. It has been experimentally established 
(for example) that small solid bits of cartilage placed on a leaf of Pinguicula 
vulgaris, whose mucilage shows no sign of an acid reaction, cause, after ten or 
eleven hours, the secretion of an acid liquid, and after forty-eight hours are almost 
entirely dissolved by it. At the end of eighty-two hours the bits of cartilage used 
in the experiment were completely liquefied, the whole secretion was reabsorbed, 
and the glands had become dry. When small insects such as midges alight from 
flight on a leaf of Pingwicula they remain glued by the mucilage, and their 
struggles to extricate themselves only cause them to sink deeper into it. Thus 
they generally perish in a very short time, are digested by the acid juice poured 
from the glands in response to the stimulus, and are absorbed with the exception 
of the wings, claws, and other parts of the skeleton, 
The acid liquid secreted by the glands is viscous, and when a number of glands 
are irritated it may exude so copiously as to fill the whole trough of the leaf. If 
the margin of the leaf alone is stimulated, as when a small creeping insect, or a 
midge alighting from above, gets upon the slightly up-curved margin of the leaf, 
not only do the marginal glands, which are comparatively infrequent, discharge 
their secretion, but in addition the edge curls over; the object of this movement 
being to cover, if possible, the prey whilst it is held fast by the sticky mucilage, or 
to push it into the middle of the flat channel, and so, in one way or another, to 
bring it into contact with as many glands as possible. The marginal glands alone 
could not produce the requisite quantity of acid liquid to effect solution, and, on 
this account, the glands on a wider area are summoned to assist in the manner 
described. The involution of the margin takes place very slowly; it is usually 
some hours before the animal sticking to the edge is enfolded, or, in the case of 
the larger specimens, is pushed into the middle of the leaf. After solution and 
absorption are accomplished, usually by the end of twenty-four hours, the leaf 
expands again, and its margins assume the position which they had before their 
involution. 
Besides small insects, pieces of plants, such as spores and pollen-grains brought 
by the wind, not infrequently fall on the viscid surfaces of Pinguicula leaves. 
These are subjected to the same fate as animal organisms, their protoplasts being 
dissolved and absorbed like the flesh and blood of insects. 
The action of the acid juice secreted by the glands of butterwort leaves upon 
albuminous bodies is identical with that of the gastric juice of animals. We may 
presume therefore that there are in it, as in the gastric juice, two kinds of sub- 
stance: firstly, a free acid, and, secondly, a ferment completely analogous to pepsin 
in its action; for, as is well known, it is by means of this combination that the 
juice of the animal stomach effects the solution of albuminoid compounds. Inas- 
much as the gland-cells of Pinguicula absorb all the soluble part of the prey, and 
re-absorb the solvent previously discharged by them, the action of this plant's leaves 
