44 



Mr. W. A. Jolly. Rejiex Times in the 



delay of all the responses, thirty-three in number, is 10'7 a. The average 

 temperature is 21° C. 



It will be seen that a number of records have been obtained of what appear 

 to be reflex effects from the same-side limb, which have a very short delay. 

 It is evident from diagram (fig. 5) that there is a group of same-side responses 

 averaging 9 a-, and a group of crossed responses averaging 1 6"4 a. If these 

 homonymous responses are in reality reflex then the time difference between 

 homonymous and heteronymous reflexes is 7'4 cr. This is just double the 

 figure which we have found in the spinal frog to represent the delay at one 

 synapse, and we would conclude from this that the path of the impulse across 

 the spinal cord involves two synapses more than the homonymous path, or 

 three synapses in all, with a latency of 3'7 a at each synapse. 



As regards the brief delay, it is certainly surprising to find such short 

 reflex times as 9 a. At first one was inclined to think that they must be due 

 to direct stimulation as opposed to reflex action, and the strong squeeze is 

 undoubtedly capable of causing direct stimulation at times, but the latency 

 with direct stimulation is much shorter than 9 a. The following experiments 

 show clearly the difference in latency between the muscular response to 

 stimulation of a motor nerve in these decerebrate frogs and the group of 

 responses which we are considering. The sciatic nerve was isolated at the 

 back of the thigh, without being cut, and small vulcanite rods were placed 

 above and below the nerve. The nerve was then mechanically stimulated by 

 a light hammer tap on the upper rod, the signal circuit being closed at the 

 same moment. The wicks of the non-polarisable electrodes were attached 

 round uninjured skin, one below the knee, the other at the ankle. The latency 

 of the muscular activity at 20° C. was found to be 3"2 cr, after deducting 

 0"7 o- for nerve conduction at the rate of 34 metres per second through 2'3 cm. 

 of nerve intervening between the point stimulated and the gastrocnemius 

 muscle. In another decerebrate frog, twenty-one days after operation, the 

 latent period of the muscle was found by the same method to be 4 tr at 

 17° C. With electrical stimulation of the nerve by an induction shock the 

 latent period has been found to be as short as 2*40 a at 22° G. 



Since it is found in this way that the latent period of the muscles of the 

 decerebrate frog is so short, it is difficult to entertain the view that delays of 

 over 8 a, obtained by squeezing the toes in lively decerebrate preparations in 

 good condition, with the circulation intact and no operative interference at 

 the time of experiment, can be other than reflex effects. Under the conditions 

 of experiment one would not expect the muscle latency to be lengthened to 

 such an extent, and with the data at present available we must regard this 

 delay of 9 o- at 21° as a reflex time, which includes the delay at one synapse. 



