266 Mr. Graham Brown and Prof. C. S. Sherrington. [Mar. 16, 



and similarly again four seconds later. Here, however, it must be noted that 

 the flexor at the time of the second and third repetitions of the F point 

 stimulation is exhibiting epileptoid contraction. 



Occasionally, as in fig. 12, the interpolation of brief stimulation of an 

 E point is followed by a somewhat increased response of the F point, but in 

 such cases it is, of course, difficult to decide whether this slight increase may 

 not be due to the precurrent stimulation of the F point itself which is neces- 

 sary as a control at the beginning of the observation. 



V. Influence of Certain Afferent Nerves upon the Ee action of the 

 Cortical Point. 



As the antagonistic pair of muscles under observation actuated the fore- 

 arm, it seemed that stimulation of an afferent nerve of the fore-arm might 

 influence the response of the observed muscles to stimulation of the cortical 

 points. That in the chloratised rabbit electrical stimulation of the skin of 

 the fore paw and of the fore limb cortex of the opposite hemisphere usually 

 summate has been shown by Exner.* And, recently, A. Uchtomsky has 

 carefully examined in the dog the mutual influence of the peroneal and other 

 limb nerves on the responses of the motor cortex for the limb, both ipsilateral 

 and contralateral. He finds marked mutual interaction, both facilitatory and 

 inhibitory, and that " im allgemeinen bei gegenseitiger Einwirkung der 

 kortikalen und der reflektorischen Innervationen der Beine die ersteren eine 

 weit iiberwiegende Eolle spielen." 



In our observations nervus ulnaris in the fore-arm was the nerve chosen 

 and it was stimulated by faradisation. It was ascertained that in the 

 decerebrate preparation (monkey) stimulation of this afferent nerve usually 

 evokes contraction of the flexor and inhibitory relaxation of the extensor 

 -when that nerve is the ipsilateral one, and conversely evokes contraction of 

 the extensor and inhibitory relaxation of the flexor when it is contralateral. 

 This is in accord with the general rule previously formulated chiefly from 

 cat and dog. 



It was expected, therefore, that when working with the muscles of the 

 left elbow the stimulation of the left ulnar nerve would reinforce the effect 

 of stimulation of an F point of the right hemisphere. And this was found 

 to be the case (fig. 13). Conversely, stimulation of right ulnar, as might be 

 expected, was observed to diminish the effect of the stimulation of the right 

 hemisphere's cortical F point (fig. 14). But the tracing here reproduced 

 illustrates a further result, namely, that the cortical F-point on restiniula- 



* ' Pfluger's Archiv,' 1882, vol. 28, p. 502. 



