566 PHYSIOLOGY CHAP. 



during contraction, the skin of the foot is gently stroked, or the 

 motor area tetanised with a small current, the muscle relaxes, and 

 the contraction disappears entirely or partly (Figs. 288, 289). 

 These tracings show that the state of activity of the motor centres 

 of the cortex which is elicited by strong stimulation may be 

 abolished by a subsequent peripheral or central stimulation of an 

 exceedingly mild character, which in the resting state of the 

 centres would be incapable of producing any obvious effect. 



Brown-Sequard (1884) on exciting the non-motor region of the 

 cortex of dogs and rabbits with strong currents was able to abolish 

 the excitability of the motor area for some minutes. He termed 

 the part of the cortex which does not react by movements to 



FIG. 288. Inhibitory effects of reflex excitations. (Bubnoff and Heidenhain.) a represents a 

 reflex contraction of the muscle, a ft, caused by rubbing the skin of the belly ; at y' there is a 

 rapid relaxation, y' y, caused by tactile stimulation of the skin of the leg ; at S the contracture 

 S &' is reinforced after firm pressure of the leg ; at e the muscle relaxes suddenly and 

 completely, *', after gently stroking the skin of the leg. 



stimulation, inhibitory ; he denied its inexcitability, and held it to 

 be capable of activity, and of transmitting excitation to other 

 centres, along the association fibres, so as to inhibit their functional 

 activity. 



With a view to localising the inhibitory activity of the cortex, 

 Libertiui (1895) endeavoured to determine the reflex time of the 

 muscles in the dog's limbs, before and after destroying certain seg- 

 ments of the brain. He found that a few days after the excision 

 of one or both pre-frontal lobes there was a marked shortening of 

 the reflex time of the muscles of the fore-limb. The same effect 

 is not obtained or only to a much less extent, after excising one or 

 both occipital lobes, and does not occur after excision of the 

 temporal lobe. The reflex time of the muscles of the hind-limb 

 undergoes no perceptible variation before and after the operation. 



