replaced on the leaves, which re-expanded after 10 days; and now
nothing was left except a very little transparent acid fluid.
Experiment 5. This experiment was slightly varied, so that the albumen
might be more quickly exposed to the action of the secretion. Two
cubes, each of about 1/40 of an inch (.635 mm.), were placed on the
same leaf, and two similar cubes on another
* In all my numerous experiments on the digestion of cubes of albumen,
the angles and edges were invariably first rounded. Now, Schiff states
( Lecons phys. de la Digestion, vol. ii. 1867, page 149) that this is
characteristic of the digestion of albumen by the gastric juice of
animals. On the other hand, he remarks les dissolutions, en chimie,
ont lieu sur toute la surface des corps en contact avec l agent
dissolvant. [page 94]
leaf. These were examined after 21 hrs. 30 m., and all four were found
rounded. After 46 hrs. the two cubes on the one leaf were completely
liquefied, the fluid being perfectly transparent; on the other leaf
some opaque white streaks could still be seen in the midst of the
fluid. After 72 hrs. these streaks disappeared, but there was still a
little viscid fluid left on the disc; whereas it was almost all
absorbed on the first leaf. Both leaves were now beginning to
re-expand.]
The best and almost sole test of the presence of some ferment analogous
to pepsin in the secretion appeared to be to neutralise the acid of the
secretion with an alkali, and to observe whether the process of
digestion ceased; and then to add a little acid and observe whether the
process recommenced. This was done, and, as we shall see, with success,
but it was necessary first to try two control experiments; namely,
whether the addition of minute drops of water of the same size as those
of the dissolved alkalies to be used would stop the process of
digestion; and, secondly, whether minute drops of weak hydrochloric
acid, of the same strength and size as those to be used, would injure
the leaves. The two following experiments were therefore tried:
Experiment 6. Small cubes of albumen were put on three leaves, and
minute drops of distilled water on the head of a pin were added two or
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