DIFFERENT TYPES OI' RESPONSE 121 



minutes, which made the fatigued Mimosa once more con- 

 tractile. Returning to india-rubber, we find that here also 

 a period of rest of ten minutes enables it to recover 

 its excitability, and once more exhibit its responsive con- 

 traction. 



From these facts it would appear that in order to explain 

 the phenomenon of response, and its various modifications by 

 fatigue and other factors, we have no option but to regard it 

 as an expression of the molecular responsiveness of matter 

 in general. 



We next turn to the converse phenomenon of staircase 

 response. Since response is an expression of molecular 



Fig. 63. Preliminary Staircase In' 

 crease, followed by Fatigue, in the 

 Response of Ga/cna to Hertzian 

 Radiation 

 (Conductivity variation method) 



Fic;. 64. Preliminary 

 Staircase Increase, fol- 

 lowed by Fatigue, in 

 the Response of Style 

 of Eitcharis « 



derangement, it follows that its extent will, other things being 

 equal, depend on the degree of molecular mobility. This 

 being so, it is conceivable that a substance, at first in a 

 sluggish condition, may, by the impact of successive stimuli, 

 have its molecular mobility gradually increased, with a corre- 

 sponding enhancement of its response. In fig. 63 we have an 

 example of this staircase effect, in the responses of Galena. 

 It is to be noticed that this effect occurs at the beginning of 

 the series of responses, as we should expect. After the 

 attainment of maximum mobility, the phenomenon of over- 

 strain is seen, with its accompanying diminution of response, 

 or fatigue. I have obtained similar results in the longitudinal 



