CH. XLVTIL] JACKSONIAN EPILEPSY 683 



of the supposed visual impulse. That such movements are reflex 

 and not direct is shown by the long period of delay intervening 

 between the stimulation and the movement. 



Extirpation of a sensory area leads to loss of the sense in question. 



The rougher experiments performed by nature in the shape of 

 diseases of the brain produce corresponding results. 



Some diseases are of the nature of extirpation. 



An instance of this is cerebral haemorrhage. If the haemorrhage 

 is in the region of the internal capsule, it cuts through fibres to the 

 muscles of the whole of the opposite side of the body, as they are 

 all collected together in a narrow compass, and the condition obtained 

 is called hemiplegia. The varieties of hemiplegia are numerous, 

 according as motor or sensory fibres are most affected, and in one 

 variety of hemiplegia, called crossed hemiplegia, the face is paralysed 

 on one side of the body, the limbs on the other ; this is due to injury 

 of the nerve-tracts in the bulb, subsequent to the crossing of the 

 fibres to the nucleus of the seventh nerve, but above the crossing of 

 the pyramids. 



If now the haemorrhage occurs on the surface of the brain, a much 

 more limited paralysis, called monoplegia, is the result ; if the arm area 

 is affected, there will be paralysis of the opposite arm ; if the leg 

 area, of the opposite leg ; if a sensory area, there will be loss of the 

 corresponding sense. 



Some diseases, on the other hand, act as the induction currents 

 do in artificial stimulation ; they irritate the surface of the brain ; 

 such a disease is a tumour growing in the membranes of the brain ; 

 if the tumour irritates a piece of the motor area, there will be 

 involuntary movements in the corresponding region of the body; 

 these movements may culminate in the production of epileptiform 

 convulsions commencing in the arm, leg, or other part of the body 

 which corresponds to the brain area irritated. It is these cases of 

 " Jacksonian Epilepsy " which have given the best results in surgery ; 

 the movement produced is an indication of the area of the brain 

 which is being irritated, and the surgeon after trephining is able to 

 remove the source of the mischief. If the area of . the brain which 

 is irritated is a sensory area, the result produced is a subjective 

 sensation, similar to what we imagine is produced in animals with 

 an electric current. 



We may now proceed from these general considerations to 

 particular points, and give maps of the brain to show the areas we 

 have been speaking of. 



Figs. 494 and 495 are views of the dog's brain. It is convenient 

 to take this first because it was the starting-point of the experimental 

 work on the subject in the hands of Hitzig and Fritsch. If the text 

 beneath the figure is consulted, it will be seen that the motor areas, 



