Transmission-time of Reflexes in Spinal Cord of Frog 55 



delay can only be studied in one of the experiments [No. 48], since it was 

 only in this one (of the two which had the temperature altered) that a 

 crossed-reflex could be recorded, before, as well as after, the cooling. As 

 may be seen from the table, not only was the same-side reflex delay 

 lengthened by cooling in this experiment, but the difference between the 

 two cord delays was likewise lengthened, showing that the temperature 

 of the cord affects the extra cord delay in the same way as it affects the 

 same-limb reflex time.^ 



We have, therefore, in the case of the crossed reflex, a loss of time 

 additional to that obtaining in the same-limb reflex, which is of about the 

 same order, and which varies, or does not vary (as the case may be), in the 

 same way with external physical conditions ; but which, when these are 

 constant, may vary independently of this same-limb reflex cord delay. 



These facts suggest very strongly that there is interposed in the 

 conductive path, in the case of the crossed reflex, some element 

 of the same nature as the one which is alone interposed in the 

 path of the same-limb reflex. In other words, one can hardly 

 refrain from inferring that, whereas in the same-limb reflex 

 a single synapse has, in the case of each fibre, to be passed; in 

 the crossed-limb reflex two such synapses have to be passed in 

 turn by every individual fibre concerned. 



The one set of synapses in the case of the crossed reflex would be the 

 same, or would belong to the same set, as those which are alone concerned 

 in the simpler reflex. They may, therefore, be called the primary synapses. 

 The principal cells concerned in them would be presumably the motor cells 

 of the ventral cornua. The second set involved in the case of the crossed 

 reflex may be called secondary synapses. They would lie on the opposite 

 side of the cord, and in view of the most interesting experiments of 

 Baglioni with regard to the action of strychnine on the cord, the locating 

 of them somewhere in the dorsal part of the cord suggests itself. 



Whether the primary synapses involved are individually the same, and 

 necessarily so, in the two kinds of reflexes, is another question to which 

 my records suggest an answer. Certain experiments show in the records 

 a very striking difference in the muscle response in the two kinds of reflexes. 

 The difference in Exp. 53 (in which all the six same-side responses very 

 closely resembled the one of them reproduced in fig. 6, A, and all the eight 

 crossed-reflex responses the one of them reproduced in fig. 6, B) was chiefly 

 one in strength, and might either mean that each primary synapse cell was 

 giving a weaker discharge when the impulses arrived by way of the secondary 

 synapses, or that a smaller number of them were brought into play. But 

 in other experiments, e.g. Nos. 55 and 5G R (in both of which especially 

 weak exciting stimuli were being employed), the two kinds of reflex 

 responses were equally strong, and yet exhibited characteristic diflerences. 

 To illustrate this, I have had reproduced in fig. 12 the records of four 

 > I have now made several experiments wliicli confirm tliis [Nov. 1907]. 



