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 becoming a cause of haemorrhage; or, in other words, stimulation of the brain cannot be likened in its effect to galvanic stimulation of a spinal nerve. But if stimulation of the brain does not paralyze, it must increase the tonicity of the vaso-motor centre, and hence the force and regularity of the circulation. Up to a certain point, these characters do indeed increase, with increase of pressure in the cerebral blood-vessels. They increase also during intellectual operations, unattended by emotion, in which a similar increase of pressure must take place, on account of the afflux of blood to the cerebral hemispheres, when these are aroused to activity.