OO eee bat 
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43 
for instance. If you touch the nettle lightly, it stings you; if you 
grasp it firmly, it has no effect upon you. This seems to me to 
show that the nerves of the nettle, or those particular nerves of the 
nettle which set the stinging machinery in operation, are in like 
manner excited by a slight touch, and not by a heavy one. But 
we need not go so far as the nettle for an illustration—we seem to 
have nerves of the same sort in our own frames. If you want to 
tickle a person on the face or on the soles of the feet, you take the 
tips of your fingers, or something delicate like a feather, and 
touch him as lightly as you possibly can. So doing, you tickle 
him ; if you lay on heavily, youcannot do it. Now the sensation 
of tickling, like every other sensation, comes from the nerves, and 
it, therefore, seems to me to show that we have in our own frames 
nerves which, like those of the plants in question, are excited by a 
slight touch, and not by a stronger one. 
The next point to which I desire to call your attention is 
this :—The insectivorous plants I have referred to swallow every- 
thing that comes, whether it be good to eat or whether it be not, 
and, constituted as these plants are, you will see that it is a 
necessity of their existence that they should do so. In a state of 
nature these plants take their chance—sometimes they get some- 
thing which is good to eat, sometimes something which is not, but 
upon the whole they get enough to eat. But if you were to take 
one of these plants and feed it, when it opened giving it a fly, and 
as soon as it had digested that and opened again, popping in 
another, and so on for a number of times in succession, the result 
would be that the plant would die from over-eating, because its 
digestive organs would be deprived of the interval of rest which 
_ nature provides by occasionally giving it something which is not 
good to eat. 
Now, sometimes even in a state of nature, these plants seem to 
die from over-eating, and it is not difficult to see how this may be 
so simply on the doctrine of chances. It may happen that the 
plant may get something good to eat every time for a number of 
_ times in succession, and so may, even in a state of nature, die 
_ from over-eating. 
