5oo 



COMPARATIVE ELECTRO-PHYSIOLOGY 



intensity of which is capable of careful adjustment. The 

 cork chamber is closed with a cover, through which passes 

 a thermometer, T, for the indication of the temperature 

 within. The tube /' is connected with an aspirator, and air 

 is thus sucked in by /, and, passing through the platinum 

 spiral, is warmed, and raises the temperature of the nerve in 



the chamber. This rise of tem- 

 perature is adjusted (i) by regu- 

 lating the electrical current which 

 heats the spiral, and (2) by con- 

 trolling the inflow of air. As 

 regards the first of these two 

 processes, the electrical heating- 

 circuit has a carbon rheostat 

 interposed, by which the rate of 

 rise of temperature may be 

 regulated. The movement of the 

 current of air, on the other hand, 

 is controlled by adjusting the 

 stopcock of the aspirator. By the 

 joint manipulation of both these 

 the rate of rise of temperature 

 inside the chamber may be made 

 perfectly uniform, and in my 

 experiments this rate was approxi- 

 mately i C. per minute. 



As already said, I selected a 

 piece of vegetable nerve and took 

 a balanced record. After this the 

 temperature of the thermal cell 

 on the right-hand side was raised 



continuously, the response-record being taken at each degree 

 of the rise, till a temperature of 50 C. had beenat tained. 

 From the record given in fig. 309 it will be seen that the 

 conductivity was always greater at temperatures up to 47 C. 

 than it was on the left-hand side, which was all the time 

 maintained at the constant temperature of 33 C. At 48 C., 



FIG. 308. The Cork Chamber 

 for Gradual Raising of the 

 Temperature of one Arm of 

 the Balance 



A and B, the two halves of the 

 chamber ; T, thermometer ; 

 / and /', inlet and outlet 

 tubes; H, thermal coil for 

 heating. 



