328 



Observations on Reflex Responses to Rhythmical Stimulation in 



the Frog. 

 By Kanshi Sassa, M.D., Tokio. 



(Communicated by Prof. C. S. Sherrington, Pres. R.S. Received July 1, 1921.) 



(From the Physiological Laboratory, Oxford.) 



The primary object of this investigation was the study of the relation 

 between the frequency and intensity of stimulation, and the resulting reflex 

 reactions. I first studied the effect of alteration of frequency at a given 

 intensity of stimulation and found that under these conditions the frequency 

 has an optimal value. With moderate and rapid frequency stimuli there is 

 also an optimal intensity value, though with those of low frequency this is 

 not the case. 



It was also hoped that some light might be thrown on the mechanism of 

 the spinal reflex centre by the comparison of the isometrically recorded reflex 

 tetanus, with the tetanus obtained directly by stimulation of the efferent 

 nerve at varying intensity and frequency of stimulation. In particular, an 

 attempt was made to settle the question as to whether stimulation of a nerve 

 can set into action the whole of the I'eflex centre to which it is afferent. 

 Camis (4) concluded that the cells of a spinal motor centre can be regarded 

 from a functional point of view, as divided into several independent groups, 

 though this division is not absolute. On thQ other hand, Dreyer and 

 Sherrington's (5) observations point rather to the physiological unity of the 

 spinal motor centre ; since they showed that the maximal mechanical power 

 of tetanic contraction, obtainable from a muscle under spinal reflex action, is 

 sometimes as great as that which can be evoked from it by direct faradisation 

 of the motor nerve itself. 



Method. — The semitendinosus reflex preparation of the spinal frog was used 

 in these experiments. The femoral vessels were ligatured in the middle of 

 the thigh so as to diminish loss of blood due to the operation. An afferent 

 nerve, the ipsilateral tibial, peroneal or sciatic nerve or sometimes one of 

 their small branches was employed. When reflex and direct tetanus were 

 compared, the roots of the sciatic nerve were previously exposed by removing 

 the musculature lateral to the urostyle. 



To record the muscular contraction, the lower portion of the semitendinosus 

 was isolated from the surrounding muscles, its tendon being fixed to the short 

 arm of a spring myograph. All the tendons of flexors and adductors inserted 

 around the knee-joint were detached, and sometimes the leg was disarticulated 



