1 8 COMPARATIVE ELECTRO-PHYSIOLOGY 



recording drum. This spot of light, hitherto quiescent, shows, 

 by its sudden deflection, the occurrence of the excitatory 

 change. 



To show the concomitance of the mechanical and elec- 

 trical responses, and in order to detect with certainty the 

 exact moment of the initiation of the former, a magnifying 

 arrangement is obtained by attaching the end of the leaf to 

 an Optical Lever. The pull exerted by the falling leaf rotates 

 the fulcrum-rod, carrying a light mirror. The spot of light 

 from this mirror moves in a vertical direction, and that 

 of the galvanometer horizontally or laterally. For the 

 purpose of simultaneous record, it is necessary to have the 

 two in one direction. The up and down movement of 

 the spot from the Optic Mirror is therefore converted into 

 lateral, by means of reflection from a second mirror, suitably 

 inclined. 



Stimulation may be effected in the neighbourhood of 

 the pulvinus by means of the electro-thermic stimulator, 

 which has the advantage of producing no mechanical dis- 

 turbance. This consists of a V-shaped platinum wire, 

 suddenly heated by the momentary passage of an electric 

 current. On applying stimulus in this manner it is found 

 that the two responses mechanical and electrical take 

 place at the same moment, the mechanical fall of the leaf ^ 

 being practically coincident with the induced electrical 

 variation. As regards the sign of this electrical change, the 

 excjted point is found to become galvanomctrically negative : X 

 that is to say, the electro-motive variation induced in the 

 excited vegetable, is the same as that observed in animal 

 tissues. I give below a series of these simultaneous records 

 of mechanical and electrical response (fig. 13), obtained from 

 Biophytum, whose lateral leaflets give motile indications. It 

 will be seen that the responsive fall of the leaflet, and the 

 subsequent recovery, are synchronous with the electrical 

 variation of galvanometric negativity, and its subsequent 

 recovery. For convenience of inspection. I shall always, 

 unless specially stated to the contrary, represent the normal 



