on the discs of three leaves; these became moderately well inflected in
24 hrs., but began to re-expand after 48 hrs., and were fully
re-expanded in 72 hrs., always reckoning from the time when the bits
were first given. This substance, therefore, like fibrin, excites the
leaves for only a short time. The residue left on the leaves, after
they were fully re-expanded, was examined under a high power and found
much altered, but, owing to the presence of a quantity of elastic
tissue, which is never acted on, could hardly be said to be in a
liquefied condition.
Some areolar tissue free from elastic tissue was next procured from the
visceral cavity of a toad, and moderately sized, as well as very small,
bits were placed on five leaves. After 24 hrs. two of the bits [page
103] were completely liquefied; two others were rendered transparent,
but not quite liquefied; whilst the fifth was but little affected.
Several glands on the three latter leaves were now moistened with a
little saliva, which soon caused much inflection and secretion, with
the result that in the course of 12 additional hrs. one leaf alone
showed a remnant of undigested tissue. On the discs of the four other
leaves (to one of which a rather large bit had been given) nothing was
left except some transparent viscid fluid. I may add that some of this
tissue included points of black pigment, and these were not at all
affected. As a control experiment, small portions of this tissue were
left in water and on wet moss for the same length of time, and remained
white and opaque. From these facts it is clear that areolar tissue is
easily and quickly digested by the secretion; but that it does not
greatly excite the leaves.
Cartilage. Three cubes (1/20 of an inch or 1.27 mm.) of white,
translucent, extremely tough cartilage were cut from the end of a
slightly roasted leg-bone of a sheep. These were placed on three
leaves, borne by poor, small plants in my greenhouse during November;
and it seemed in the highest degree improbable that so hard a substance
would be digested under such unfavourable circumstances. Nevertheless,
after 48 hrs., the cubes were largely dissolved and converted into
minute spheres, surrounded by transparent, very acid fluid. Two of
these spheres were completely softened to their centres; whilst the
third still contained a very small irregularly shaped core of solid
cartilage. Their surfaces were seen under the microscope to be
curiously marked by prominent ridges, showing that the cartilage had
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