206 Prof. C. S. Sherrington and Miss S. C. M. Sowton. [June 29, 



background contraction which is itself of rather weak intensity. If then the 

 intensity of the background contraction be increased by stimulating the 

 ipsilateral afferent more strongly, the inhibitory decrement produced by the 

 contralateral stimulus becomes less, i.e. produces a shallower notch in the 

 contraction myogram, in accordance with the above rule. If, however, the 

 intensity of the background contraction be increased still further beyond a 

 certain limit, which need not be very extreme, the effect of the intercurrent 

 stimulation of the contralateral nerve is changed from inhibition to excita- 



Fig. 4. — Decrease of background intensity changes the effect of a given intercurrent 

 reflex from a pressor influence to a depressor. Semitendinosus (cat, decerebrate). 

 Lower signal marks stimulation (faradic) of ipsilateral afferent (peroneal) ; the 

 stimulus is more intense in a (350 Kronecker units) than in b (50 Kronecker units). 

 Upper signal marks stimulation (faradic) of contralateral afferent (popliteal) and is 

 of the same intensity in a and b. In a it augments the contraction, in b it decreases 

 (inhibits) it. Time marked above, in seconds. 



tion, i.e. the contralateral afferent not only does not obviously diminish the 

 contraction but augments it (fig. 3, a and b ; fig. 4, a and b). 



Besides intensity, other conditions also attaching to the background stimu- 

 lation influence the effect of the contralateral nerve. In our experience the 

 background of reflex contraction obtained by use of the brief alternating 

 galvanic currents of the v. Kries rheonome for the ipsilateral afferent is more 

 readily and amply inhibited by the contralateral afferent than is the reflex 

 contraction furnished by ordinary faradism (fig. 5, a, b, c, d). Similarly, the 



