South African Clmved Frog. 



47 



hammer-tap or innocuous stimulus is sufficient to produce it, and there is 

 some evidence that the central delay is then longer than with the stronger 

 form of stimulus. My observations have not yet extended far in this 

 direction, as attention was concentrated in the case of the decerebrate frog 

 on the effort to obtain crossed reflexes with constancy, and to compare their 

 time with the homonymous reflexes elicited by the same form of stimulation. 

 This necessitates a strong squeeze. It would be advisable in future work to 

 compare the crossed reflex, evoked as here described, with the same-side 

 response to the innocuous stimulus. Even with the data before us, it may be 

 possible to recognise a form of homonymous reflex whose path involves two 

 synapses. If we disregard Group A in diagram (fig. 5) altogether for the 

 present, and average the remainder of the homonymous reflexes, we have 

 14'4 a for the homonymous reflex as against 18"5 a for the average of all the 

 heteronymous reflexes, and 14'4 a on analysis suggests delay at two synapses, 

 and the extra delay of the crossed reflex would then he attributable to the 

 interposition of one additional synapse. This would accord with previous 

 work on Eana. Thus Wundt (2) finds the extra time of the crossed reflex 

 to be 4o-, and Miss Buchanan (1) assumes that one extra synapse is interposed 

 in the path of the crossed reflex, whose delay is normally between lOcr and 

 20 cr, but may be reduced under the influence of strychnine to 4 a. This 

 author, however, assumes that thei'e is only one synapse in the path of the 

 same-side reflex with a delay of between 10 a and 20 a. We may compare 

 the delay at two synapses in the clawed frog, say 7'4 a, with the synapse 

 delay in the mammahan homonymous reflex, which has been shown to be 

 4*3 cr (3), or, according to Forbes and Gregg (7), even less. These authors find 

 the reduced reflex time in tlie flexion reflex of the cat to lie in general 

 between 3 a and 5 cr. 



Form of the Response in the Decerebrate Frog. 



Waves of different rates are observed in the electrical responses recorded. 

 Sometimes the record shows the presence of waves occurring before the 

 stimulus has been given, and these are presumably the electrical expression of 

 the tonic activity of the limb muscles, and when they are very distinct 

 indicate a condition of heightened tonus. Fig. 6 is an example. Here the 

 waves occur at the rate of 54 per second, at a room temperature of 19° C. 

 Other rates recorded are 35 at 16° 54 and 55-5 at 21-3°, 49 at 22°, and 53 

 at 25°. These waves are of rather a higher rate than those described by 

 Piper (8) in Eana, doubtless owing, to some extent, to the higher summer 

 temperatures in South Africa. Piper states that on throwing the quadriceps 

 femoris of the frog reflexlyinto contraction, one obtains an inconstant rhythm, 



