South African Clawed Frog. 



39 



interposed in the crossed path in this group of experiments, and conclude 

 that the heteronymous path employed here contains two synapses more than 

 the homonymous, or three synapses in all. 



It seems to depend upon the general condition of the frog as to whether 

 the short path is pervious or not. Thus in Experiments 16 and 17, where 

 the observations were made on the second and first days respectively after 

 section of the cord, and where the frogs may not entirely have recovered 

 from the haemorrhage and other immediate effects of the operation, and 

 where the wounds were not yet healed, the short path is apparently 

 impervious. In Experiments 14 and 15, where the frogs had been 

 decerebrated and preserved in the laboratory for several months before 

 the cord was cut, and where they were emaciated, with flabby muscles, the 

 long path appears to have been used. Even the high temperature used in 

 Experiment 15 does not diminish the extra delay of the crossed reflex, 

 although it reduces the time of each reflex. 



In diagram (fig. 1) the time differences in all the experiments are arranged 

 in order of magnitude, and a step-like appearance is shown. 



(J 

 9 



8 

 7 

 6 

 5 

 4 

 3 

 2 

 1 

 

 -1 

 -2 

 -3 

 -4 

















Fig. 1. 







14 I 



/16 



/ 



/ 



/ 

 1 









, — • — ' 



1 lO 4 ^ 



,-'12 ^ 







- /9 

 / 



_ • 



5 



L 









« 



Fig. 1. — Diagram giving in order of magnitude the time differences obtained by sub- 

 tracting the homonymous reflex times in the hind-limb of the spinal frog from the 

 heteronymous reflex times. The numbers are the numbers of the experiments and 

 the time differences are plotted in thousandths of a second {a). The diagram 

 exhibits a step-like character. A negative difference means that the heteronymous 

 reflex time is shorter than the homonymous. 



Tlie Form of tlie Electo'ical Besponse in the Spiiial Frog. 

 2 and 3 represent forms of variation recorded on homonymous 

 stimulation of the toes, fig. 4 on heteronymous stimulation. The electrical 

 variation at its commencement resembles that of a twitch, but the curve 



rigs. 



