Cuar. II. INFLECTION DIRECTLY CAUSED. 33 
10 transmit a motor impulse throughout the whole 
length of the pedicel, consisting of about twenty cells, 
to near its base, causing this part to bend, and the 
tentacle to sweep through an angle of above 180°. 
That the contents of the cells of the glands, and after- 
wards 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 protoplasm. But the case is much more 
remarkable than as yet stated ; for the particles are sup- 
ported by the viscid and dense secretion ; nevertheless, 
even smaller ones than those of which the measure- 
ments 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 .,1,, of a 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 see 
that far less than the millionth of a grain of phos- 
phate of ammonia in solution, when absorbed by a 
gland, acts on it and induces movement. A bit of 
hair, ;4; of an inch in length, and therefore 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 
verve. 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. 
