FUNCTION'S OF THE CEREBRAL HEMISPHERES 497 



intervals of from six to ten per second, but gradually getting slower 

 as the fit dies away. The tracing of such a contraction is given in 

 Fig. 227. 



The main phenomena of a fit, due to irritation ot any portion of the 

 motor area, were described by Hughlings Jackson in 1864, even 

 before the experimental proof of cortical localisation had been brought 

 forward by Fritsch and Hitzig. A similar condition may occur in 

 the human subject as a result of irritative lesions of this part of the 

 cortex, such as that due to the presence of a tumour or a spicule of 

 bone pressing on the brain. Jackson showed that in this condition 

 the convulsive movements follow a certain order or ' march.' Thus 

 if the thumb area be the seat of stimulation, the fit begins by a contrac- 



FIG. 227. Tracing of muscular contractions during an epileptic convulsion 

 aroused by strong stimulation of the motor area. (HoRSLEY and 

 SCHAFER). 



tion of the thumb muscles, then spreads to the muscles of the hand, 

 fore-arm and shoulder muscles of the same side, and then to the face, 

 trunk, and leg. If it begins in the toes the order would be up the leg and 

 down the arm. The same ' march ' is observed in artificial stimulation of 

 the motor area. If the convulsions are very strong they spread to the 

 leg of the opposite side and then to the whole body. The spread to 

 the other side of the body is not prevented by division of the corpus 

 callosum, nor by isolating the centres from one another, so that the 

 sequence seems to be maintained through the mediation of the sub- 

 cortical centres. Complete excision of the cortical centre for any 

 given movement excludes this movement from participation in the 

 fit. In man this type of epilepsy is, in the milder cases at any rate, 

 generally unattended with loss of consciousness. In animals epileptic 

 convulsions can be excited by stimulation of any portion of the cortex, 

 though it is obtained by a weaker stimulus applied to the motor cortex 

 than from any other part. Jacksonian epilepsy is often preceded by a 

 sensation of numbness or tingling, the ' aura,' in the part in which 

 such convulsions begin. In ordinary idiopathic epilepsy tactile or 

 visual sensory aurae may precede the attack ; but in this case loss of 

 consciousness is always a prominent symptom, even in the milder form 

 of the disease. Universal epileptic convulsions can be excited in 



32 



