ere begins
to learn its work, so that the patient may in time recover his use of
language.

Within the last few years the important discovery has been made, that by
stimulating with electricity the surface of the grey matter of the
hemispheres, muscular movements are evoked; and that certain patches of
the grey matter, when thus stimulated, always throw into action the same
groups of muscles. In other words, there are definite local areas of
grey matter, which, when stimulated, throw into action definite groups
of muscles. The surface of the cerebral hemispheres has now been in
large measure explored and mapped out with reference to these so-called
motor-centres; and thus our knowledge of the neuro-muscular machinery of
the higher animals (including man) has been very greatly furthered. Here
I may observe parenthetically that, as the brain is insentient to
injuries inflicted upon its own substance, none of the experiments to
which I have alluded entail any suffering to the animals experimented
upon; and it is evident that the important information which has thus
been gained could not have been gained by any other method. I may also
observe that as these motor-centres occur in the grey matter of the
hemispheres, a strong probability arises that they are not only the
motor-centres, but also the volitional centres which originate the
intellectual commands for the contraction of this and that group of
muscles. Unfortunately we cannot interrogate an animal whether, when we
stimulate a motor-centre, we arouse in the animal's mind an act of will
to throw the corresponding group of muscles into action; but that these
motor-centres are really centres of volition is pointed to by the fact,
that electrical stimuli have no longer any effect upon them when the
mental faculties of the animal are suspended by anaesthetics, nor in the
case of young animals where the mental faculties have not yet been
sufficiently developed to admit of voluntary co-ordination among the
muscles which are concerned. On the whole, then, it is not improbable
that on stimulating artificially these motor-centres of the brain, a
physiologist is actually playing from without, and at his own pleasure,
upon the volitions of the animal.

Turning, now, from this brief description of the structure and leading
functions of the principal parts of the nervous system, I propose to
consider what we know about the molecular movements which go on in
different parts of th