xxii COMPARATIVE ELECTRO-PHYSIOLOGY 



CHAPTER XXVIII 



RESPONSE OF RETINA TO STIMULUS OF LIGHT 



PAGE 



Response of retina Determination of true current of rest Determination 

 of differential excitabilities of optic* nerve and cornea, and optic nerve 

 and retina The so-called positive variation of previous observers 

 indicates the true excitatory negative Retino-motor effects Motile 

 responses in nerve Varying responsive effects under different conditions 

 Reversal of the normal response of light due to (i) depression of 

 excitability below par ; (2) fatigue The sequence of responsive phases 

 during and after application of light Demonstration of multiple 

 responses in retina under light, as analogous to those in vegetable 

 tissues Three types of after-effect Multiple after-excitations in human 

 retina Binocular Alternation of Vision Demonstration of pulsatory 

 response in human retina during exposure to light 'f'-^-.'. .' . . 415 



CHAPTER XXIX 



GEO-ELECTRIC RESPONSE 



Theory of Hydrostatic Pressure and Theory of Statoliths Question regarding 

 active factor of curvature in geotropic response, whether contraction or 

 expansion Crucial experiment by local application of cold Reasons for 

 delay in initiation of true geotropic response Geo-electric response of 

 shoot Due to active contraction of upper side, with concomitant gal- 

 vanometric negativity Geo-electric response of an organ physically 

 restrained . . -,.',.. ,. , , . , , . . . . -;, _. 434 



CHAPTER XXX 



/'* DETERMINATION OF VELOCITY OF TRANSMISSION OF 

 EXCITATION IN PLANT TISSUES 



Transmission of excitation in plants not due to hydromechanical disturbance, 

 but instance of transmission of protoplasmic changes Difficulties in 

 accurate determination of velocity of transmission A perfect method 

 Diminution of conductivity by fatigue Increased velocity of transmission 

 with increasing stimulus Effect of cold in diminishing conductivity- 

 Effect of rise of temperature in enhancing conductivity Excitatory 

 concomitant of mechanical and electrical response Electrical methods 

 of determining velocity of transmission Method of comparison of longi- 

 tudinal and transverse conductivities Tables of comparative velocities in 

 animal and plant -Existence of two distinct nervous impulses, positive 

 and negative . . , -", ' V ' t * '' "" t ' t 444 



