498 COMPARATIVE ELECTRO-PHYSIOLOGY 



velocity. When it rose from 30 C. to 35 C, for example, 

 the velocity was doubled. 



By employing the electrical method of response, however, 

 we are rendered independent of the use of sensitive plants, 

 and by means of the Conductivity Balance we are enabled to 

 demonstrate the slightest variation of conductivity, as between 

 the left arm of the balance, which is maintained at standard 

 temperature, and the right, which is subjected to the given 

 change. 



Thus in a definite experiment on a nerve of fern the 

 temperature of the room was 30 C. After first obtaining 

 the balanced record, the temperature of a portion of the 

 right arm of the balance was lowered. This one-sided 

 cooling was effected by supporting the right arm of the 

 nerve, through a certain length, in the concavity of a U-tube 

 through which cold water at 15 C. was passed. Stimuli 

 were now applied at intervals of one minute. Previously, 

 as will be understood, such stimuli, owing to balance, had 

 induced no resultant effect But now, on account of the 

 depression of conductivity on the right side, brought about 

 by cooling, the balance was disturbed, and the resultant 

 down-response seen in fig. 307 shows the diminished con- 

 ductivity of the right arm. On the cessation of the flow of 

 cold water the balance was gradually restored, in concomit- 

 ance with the return to the original temperature. 



I next investigated the results of a rise of temperature, and 

 here I specially desired to observe the conductivity variations, 

 not at any one degree, but throughout a graduated and con- 

 tinuous rise. I was confronted at the outset of this investi- 

 gation by the difficulty arising from the fact that there was 

 no convenient and satisfactory means for the local variation 

 of the temperature of the nerve, in definite and known 

 degrees. In connection with this there was also the further 

 difficulty that a sudden variation of temperature will, in 

 itself, act as a stimulus. Hence, in studying the effects of 

 temperature per se, it is essential that there should be no 

 such sudden variation. These difficulties were overcome by 



