45O COMPARATIVE ELECTRO-PHYSIOLOGY 



With regard to the effect of temperature, I found that 

 cold reduced the velocity of transmission. Thus, in one 

 experiment, slight cooling reduced it to one-third, and when 

 carried still further, it abolished the conductivity altogether. 

 A rise of temperature, on the other hand, had the effect of 

 enhancing velocity of transmission. The following table 

 shows that a rise of temperature from 30 C. to 35 C. 

 doubled the velocity, and that at 37 C. the rate was 

 almost three times that at the first temperature. The 

 velocity was in this case determined in the centrifugal 

 direction. 



TABLE SHOWING THE EFFECT OF RISE OF TEMPERATURE ON VELOCITY. 

 Distance traversed by stimulus 4! mm. 



Transmission of excitation, as I have shown elsewhere, 

 and shall show again, is depressed or abolished by the action 

 of anaesthetics. We shall also see, further, that the polar 

 effects of currents on the velocity of transmission are the 

 same in the plant as in the animal, being opposite, accord- 

 ing as it is the anode or kathode. In the case of a so-called 

 * sensitive ' plant, by taking advantage of the motile indica- 

 tions afforded by the leaf or leaflet, it is possible to determine 

 the velocity of transmission of excitation and its modifica- 

 tions. With ordinary plants, however, no such indications 

 being available, it is obvious that we must find some other 

 means of detecting and observing the excitatory wave during 

 transit. One such I have described elsewhere as the Electro- 

 tactile Method. It is found that the passage of the excitatory 

 wave, even through an ordinary tissue, brings about minute 

 form -changes. These give rise to pressure-variations as 

 between two enclosing contacts. And this variation of 

 pressure, in turn, can be recorded by means of a sensitive 

 electrical device. 



