South African Clawed Frog. 



49 



would suggest that these initial deflections of rapid rate are central in origin, 

 and either that they represent the muscular responses to successive discharges 



Fig. 7.- — Electrical variation evoked reflexly from the muscles of the hind-limb of the 

 decerebrate frog by mechanical stimulation of the heteronymous toes. The response, 

 at its commencement, shows waves at a rate of 206 per second. Eoom tempera- 

 ture, 20° C. Time marker and signal as in figs. 2 and 3. 



from motor neurones, or that one group after another of motor neurones has 

 been thrown into activity, the delay between the excitations of the groups 

 indicating that one synapse or two synapses respectively have to l^e traversed 

 in the course of this irradiation. As Sherrington (6) points out, grading of 

 intensity of reflex contraction within one and the same muscle group, and 

 even within one and the same individual muscle, seems not only possible 

 but probable, by the numerical implication of more or fewer motor cells, and 

 it seems not improbable that the rapid succession of deflections described 

 above is evidence of the successive implication of neurones in the spinal 

 centres. 



Conclusions. 



The reflex times of the homonymous and heteronymous reflexes in the 

 hind limbs of the spinal clawed frog have been measured at temperatures 

 ranging from 14° C. to 30° C. The average heteronymous times (sixty-six 

 observations) is 18-7 cr (0"0187 second). The average homonymous (sixty-eight 

 observations) is 14*9 a. That is to say, the crossed reflex time is longer than 

 the same-side reflex time by 3"8 cr. 



It is suggested that tlie experiments can be divided into two classes, the 

 chief determining factor being the general condition or " fitness " of the 

 spinal preparation. In the first class, where the preparation is normal and 

 the temperature fairly high, the average heteronymous time is 15"7 cr and 

 the average homonymous 14'3 a. Since the difference between the crossed 

 and same-side reflex times is here very brief, viz., 1-4 cr, and as in some 



VOL. xcii. — B. E 



