Notes. 
364 
while in the lower half some staining occurs. Thus, by the process of 
staining, the seat of the especially irritable tissue was clearly brought 
into view. I now commenced electrical experiments with the pul- 
vini. Two small pins (which were found not to injure the tissue to 
any appreciable extent) were inserted into the irritable tissue — one 
at each end, and fine wires from these pins communicated with the 
various electrical apparatus as required. When suitably stimulated 
with either a constant current, an induction shock, or a tetanising 
shock, the leaf fell immediately contact was made. With the single 
induction shock the breaking shock was found to be a stronger stimulus 
than the making. A small piece of stem with the pulvinus attached — 
the lamina and a portion of the petiole of the leaf having been pre- 
viously removed — was attached to a lever which wrote upon a revolving 
drum. On throwing in the electrical stimulus the pulvinus contracted 
and a curve was obtained. The pulvinus was then turned upside down, 
and, after recovery, was again stimulated and a second curve obtained. 
In both instances the pulvinus raised a weight greater than that of the 
leaf and leaf stalk. These experiments for the most part only con- 
firmed those of Cohn and Kabsch, except that they were carried out 
in further detail ; but one new and important observation was made, 
viz. that under the influence of a feeble tetanising current the period 
of recovery of the pulvinus could be materially shortened, and the 
leaf could be induced to assume the position before stimulation in 
less time than it would have taken under ordinary circumstances. 
The wonderful delicacy with which the irritable cells of the pulvinus 
at once reply to stimulation, the fact that in their reaction to the 
stimulus of electricity they obey the same laws as animal muscle, and, 
like certain muscles, may also be relaxed by a feeble tetanising current, 
go far to suggest that in dealing with the movements of the pul- 
vinus of Mimosa we have essentially to do with the phenomenon of 
contractility. 
Although the foregoing results may be said to favour the idea that 
in irritable organs movements are brought about by a definite 
contraction of the protoplasm of the cells of the irritable side, yet I felt 
that the matter could only be set at rest by still further strengthening 
the evidence, and if it were possible, by the actual observation of a 
cell contracdng under the influence of electrical or other, stimulation. 
I therefore turned my attention to the simple filamentous Algae, 
and among them to an organism which I believed would be peculiarly 
