60 COMPARATIVE ELECTRO-PHYSIOLOGY 



the tissue or negative : that is to say, done by the tissue. 

 The outward manifestations of these two processes are 

 respectively expansion and contraction. The positive, as we 

 shall see, is not the result of hydrostatic disturbance as such, 

 but is the effect of energy transmitted hydraulically. 



The indirect effect of stimulus, then, gives rise to positive 

 turgidity-variation, and increases the internal or potential 



FIG. 45. Record of Response of Mimosa Leaf, taken on a fast- 

 moving drum 



Stimulus applied at moment a, on point of stem diametrically opposite to 

 responding leaf. Hydro-positive erectile response occurs at ^, '6 second 

 after application of stimulus. True excitatory response of fall takes 

 place at c, 3*45 seconds after application of stimulus. Time-marks 

 represent fifths of a second. 



energy of the organ. A positive turgidity-variation is thus 

 concomitant with an increase of internal energy and 

 a negative turgidity-variation with the reverse. In observing 

 the mechanical response, we saw that the expression of 

 positive turgidity-variation, due to the indirect effect of 

 stimulus, consisted of an erection, and was therefore of 

 opposite sign to that of the negative turgidity-variation, 

 caused by true excitation, and expressing itself in a fall, of 



