But if the congestion occurs by means of a slow invasion, there is first a sanguineous infiltration into the cerebral matter (accompanied by convulsions and pains), a corresponding softening of this substance which, by admixture with the blood, alters in depth and agglutinates to form inert islets (hence paralyses) and finally a complete disorganization of the arteriovenous system in the cerebral parenchyma and often even in the arachnoid.