602 COMPARATIVE ELECTRO-PHYSIOLOGY 



anomaly, in the response of living tissues, where a slight rise 

 of temperature increases conductivity, at the same time that 

 it appears to diminish excitability, inasmuch as it brings 

 about a lessened amplitude of response (Chapter XV.). 

 This latter, however, may not really be due to diminution of 

 excitability, since the same effect might equally well be 

 brought about by an enhancement of the force of recovery. 

 This view is supported by the further records given in 

 fig. 368. We see here that incomplete recovery became 

 complete, under the application of gentle heat. The next 

 response given by this slightly warmed substance is seen to 



FIG. 369. Photographic Record Showing Uniform Response of Alu- 

 miniun Powder to Uniform Stimulus of Electric Radiation. 



show complete recovery within a relatively short time, this 

 enhanced force of recovery bringing about at the same time 

 a diminution in the height of response. The temperature of 

 the substance was now again raised to a slightly higher 

 degree, and the next response shows a still further diminished 

 height and a considerably quickened recovery. When a 

 substance is in a normal condition of excitability, its succes- 

 sive responses to uniform stimuli are found to exhibit com- 

 plete recovery, and to be of equal amplitude. Figure 369 

 shows such a series obtained with powdered aluminium. 



We have seen that the increased molecular mobility con- 

 ferred by warming hastens recovery. A similar hastening of 

 recovery may be brought about by a mechanical tap, as has 

 already been shown (fig. 364) in the case of magnetic response. 



