An irritation which, in health, produces restlessness of the muscular system, accelerated respiration and pulsation and various mental phenomena within the normal limits, in the epileptic results in more intense phenomena in the same direction. The nervous irritability of the epileptic manifests itself in one direction especially. An important vaso-motor centre for the brain vessels exists, possibly diffused through an area somewhere between the thalamus and subthalamic region above the pyramidal decussation below. The irritability of this centre results in sudden arterial spasm in the carotid distribution (so characteristic a feature of the fit onset); simultaneously with the contraction of the vessel the pupil undergoes an initial contraction, and relaxation instantly results in both cases. The sudden interference with the brain circulation produces unconsciousness, and destroys the checking influence of the higher centres on the reflexes in a manner analogous to any shock affecting the nerve centres. In the meantime, while there has been a sudden deprivation of arterial blood and a sinking of intracranial pressure so far as the great cerebral masses are concerned, there has been as sudden an influx of blood to the unaffected district of the vertebral arteries whose irrigation territory is now the seat of an arterial hyperæmia. The result of this is that the great convulsion centre, the medulla, being over-nourished, functional excess, that is, convulsion, occurs unchecked by the cerebral hemispheres, which are disabled by their nutritive shock. The unconsciousness and coma of epilepsy more resemble shock than they do cerebral anæmia or syncope. The impeded return circulation of venous blood now comes into play. The contraction of the neck muscles explains this obstruction and especially the accumulation of venous blood in the cerebral capillaries of the medulla. True epilepsy presents an enormous number of sub-groups, exhibiting every variety of deviation from the ideal convulsive form, and the existence of these forms tends to demonstrate the views just expressed. In ordinary petit mal the initial arterial spasm has but to be confined to the surface of the hemispheres, leaving the thalamus ganglia undisturbed, and it can readily be understood how the momentary unconsciousness or abolition of cortical function can occur without the patient falling, his automatic ganglia still carrying on their functions. At the same time with the lesser spasm there would be a less extensive sinking of intracranial pressure with less consecutive collateral hyperæmia of the lower centres and therefore no convulsion.