Responses to Rhythmical Stimulation in the Frog. 337 



III. The Comparison of Reflex Tetanus with Peripheral Tetanus oi varying 



Bates of Stimulation. 



To examine this point, the afferent nerve was faradised at the optimal 

 intensity for a given frequency-rate, and the resulting reflex tetanus 

 registered by a spring myograph. For comparison, a direct tetanus was 

 produced by faradisation of the motor nerve under the same condition of 

 stimulation. 



The differences in the observations of the previous workers (Marey, 

 Bohr, Bernstein, Kohnstamm, Wedensky, Hoffmann and others) on myal 

 and neuromyal tetanus produced at varying rates and intensities of stimu- 

 lation are to be explained by the different conditions under which the 

 problem was studied. Some observations necessary for the present inquiry 

 in this respect were repeated with the method which I have used in these 

 experiments. 



The extent of direct tetanus with increasing intensity of stimulation of 

 a given frequency-rate only increases up to a certain point, and thereafter 

 shows no further increase. The optimal intensity of stimulation for reflex 

 excitation is usually somewhat higher than the maximal intensity for direct 

 tetanus. A series of records of neuromyal tetanus, which was made with 

 progressively rising frequency-rate of stimulation of maximal strength, and 

 in which the stimulation was continued until the maximal contraction was 

 attained in each case, shows no significant increase in the power of con- 

 traction with increase of the frequency-rate of stimulation beyond about 

 50 per second. From these observations it appears that the maximal 

 tetanus produced by the maximal intensity of stimulation for a given 

 frequency greater than 50 per second can be regarded as the maximal 

 contraction of the muscle. 



On comparing reflex tetanus with direct tetanus produced at low 

 frequency-rates of stimulation (under 30 per second) with the same intensity, 

 the former is usually more abrupt and more powerful than the latter in the 

 early period of contraction. This fact shows that the discharge of impulses 

 from the reflex centre is at a higher rate than that of stimulation applied 

 to the afferent nerve, and further suggests that some of the component shocks 

 used as stimuli evoke from the spinal reflex centre repetitive volleys of 

 motor impulses, since it has already been shown that at low frequency-rates 

 the rhythm of repetition of volley discharges from the centre is synchronous 

 with the rate of stimulation. A similar conclusion was drawn by the 

 comparison of reflex contraction produced by a single strong momentary 

 stimulus applied to the afferent nerve with a direct twitch produced by 



