the production of thought.

2d. In the medulla oblongata exists a nervous centre called the
vaso-motor centre, because of its close relations with the vaso-motor
nerves. Stimulation of this centre causes contraction of the
blood-vessels. Severing the same part causes paralysis of the vaso-motor
nerves and dilatation of the blood-vessels. The conditions of the brain
that have been most clearly shown to influence the circulation, are
those that can be proved to take an effect on this vaso-motor centre.
If, as is probable, different forms of cerebral action induce or depend
on different cerebral conditions, or involve different sections of the
cranial masses, this effect would necessarily be different, and the
influence on the circulation vary accordingly.

3d. No experimental proof has hitherto been obtained that stimulation of
the cerebral organs lying above the vaso-motor centre, and which include
those possessing the function of thought, ever paralyzes this centre;
but, as it is only by such paralysis that cerebral conditions can induce
dilatation of blood-vessels, it must follow that no _experimental proof_
at present exists that stimulation of the brain ever does cause such
dilatation--that is, ever does become a cause of haemorrhage. The
_clinical_ facts for such a supposition are those in which the
occurrence of an emotion is followed by flushing of the face,
acceleration of the pulse, hot or cold perspirations, phenomena all
indicative of dilatation of the blood-vessels, with temporary paralysis
of their nerves and of their vaso-motor centre. It is not proved,
however, that the emotions capable of causing these effects really
result from a stimulation of the brain. On the contrary, they are
generally accompanied by diminished activity of that cerebral function
that most certainly does depend on such stimulation--the function,
namely, of thought.

Now, since the power of thought and the power of the vaso-motor centre
are equally paralyzed under these circumstances, it is more probable
that the phenomena which most nearly resemble those of stimulation of
the brain are either confined to some special part of it, whose activity
is in antagonism to the rest, or else are really phenomena of
exhaustion, and therefore come under another category. But if these do
not, no facts exist to prove that stimulation of the intellectual
functions of the brain is in itself capable of producing vaso-motor
paralysis--that is, of be