Cuar. IL] THE EFFECTS OF REPEATED TOUCHES, 29 
glands, and afterwards those of the pedicels, are affected in a 
plainly visible manner by the pressure of minute particles, we 
shall have abundant evidence when we treat of the aggregation 
of the protoplasm. But the case is much more remarkable 
than as yet stated; for the particles are supported by the 
viscid and dense secretion; nevertheless, even smaller ones 
than those of which the measurements have been given, when 
brought by an insensibly slow movement, through the means 
above specified, into contact with the surface of a gland, act 
on it, and the tentacle bends. The pressure exerted by the 
particle of hair, weighing only 7,4,, ofa grain and supported 
by a dense fluid, must have been inconceivably slight. We 
may conjecture that it could hardly have equalled the 
millionth of a grain; and we shall hereafter sce that far less 
than the millionth of a grain of phosphate of ammonia in 
solution, when absorbed by a gland, acts on it and induces 
movement. A bit of hair, ;/, of an inch in length, and there- 
fore much larger than those used in the above experiments, 
was not perceived when placed on my tongue; and it is 
extremely doubtful whether any nerve in the human body, 
even if in an inflamed condition, would be in any way 
affected by such a particle supported in a dense fluid, and 
slowly brought into contact with the nerve. Yet the cells of 
the glands of Drosera are thus excited to transmit a motor 
impulse to a distant point, inducing movement. It appears 
to me that hardly any more remarkable fact than this has 
been observed in the vegetable kingdom. 
The Inflection of the Exterior Tentacles, when their Glands are 
excited by Repeated Touches, 
We have already seen that, if the central glands are 
excited by being gently brushed, they transmit a motor 
impulse to the exterior tentacles, causing them to bend; 
and we have now to consider the effects which follow from 
the glands of the exterior tentacles being themselves touched. 
On several occasions, a large number of glands were touched 
only once with a needle or fine brush, hard enough to bend 
the whole flexible tentacle; and, though this must have 
caused a thousand-fold greater pressure than the weight of 
the above-described particles, not a tentacle moved. On 
another occasion forty-five glands on eleven leaves were 
touched once, twice, or even thrice, with a needle or stiff 
