ximum growth in man.

In the second place, we find that when the grey matter is experimentally
removed from the brain of animals, the animals continue to live; but are
completely deprived of intelligence. All the lower nerve-centres
continue to perform their mechanical adjustments in response to suitable
stimulation; but they are no longer under the government of the mind.
Thus, for instance, when a bird is mutilated in this way, it will
continue to perform all its reflex adjustments--such as sitting on a
perch, using its wings when thrown into the air, and so forth; but it no
longer remembers its nest or its young, and will starve to death in the
midst of its food, unless it be fed artificially.

Again, if the grey matter of only one hemisphere be removed, the mind is
taken away from the corresponding (i. e. the opposite) side of the body,
while it remains intact on the other side. For example, if a dog be
deprived of one hemisphere, the eye which was supplied from it with
nerve-fibres continues able to see, or to transmit impressions to the
lower nerve-centre called the optic ganglion; for this eye will then
mechanically follow the hand waved in front of it. But if the hand
should hold a piece of meat, the dog will show no mental recognition of
the meat, which of course it will immediately seize if exposed to the
view of its other eye. The same thing is found to happen in the case of
birds: on the injured side _sensation_, or the power of responding to a
stimulus, remains intact; while _perception_, or the power of mental
recognition, is destroyed.

This description applies to the grey matter of the cerebral hemispheres
as a whole. But of course the question next arises whether it only acts
as a whole, or whether there is any localization of different
intellectual faculties in different parts of it. Now, in answer to this
question, it has long been known that the faculty of speech is
definitely localized in a part of the grey matter lying just behind the
forehead; for, when this part is injured, a man loses all power of
expressing even the most simple ideas in words, while the ideas
themselves remain as clear as ever. It is remarkable that in each
individual only this part of one hemisphere appears to be used; and
there is some evidence to show that left-handed persons use the opposite
side from right-handed. Moreover, when the side which is habitually in
use is destroyed, the corresponding part of the other hemisph