1 88 RESPONSE IN THE LIVING AND NON-LIVING 



Diphasic variation. A diphasic variation is observed 

 in nerve, if the wave of molecular disturbance does not 

 reach the two contacts at the same moment, or if the 

 rate of excitation is not the same at the two points. 

 A similar diphasic variation is also observed in the 

 responses of plants and metals (figs. 26, 68). 



Effect of temperature. In animal tissues response 

 becomes feeble at low temperatures. At an optimum 

 temperature it reaches its greatest amplitude, and, again, 

 beyond a maximum temperature it is very much 

 reduced. 



We have observed the same phenomena in plants. 

 In metals too, at high temperatures, the response is very 

 much diminished (figs. 38, 65). 



Effect of chemical reagents. Finally, just as the 

 response of animal tissue is exalted by stimulants, 

 lowered by depressants, and abolished by poisons, so 

 also we have found the response in plants and metals 

 undergoing similar exaltation, depression, or abolition. 



We have seen that the criterion by which vital 

 response is differentiated is its abolition by the action 

 of certain reagents the so-called poisons. We find, 

 however, that ' poisons ' also abolish the responses in 

 plants and metals (fig. 117). Just as animal tissues 

 pass from a state of responsiveness while living to a 

 state of irresponsiveness when killed by poisons, so also 

 we find metals transformed from a responsive to an ir- 

 responsive condition by the action of similar ' poisonous ' 

 reagents. 



The parallel is the more striking since it has long 

 been known with regard to animal tissues that the 



