1914] on Plant-Autographs and their Revelations is? 



very sluggish under fatigue ; when excessively tired it temporarily 

 loses its power of perception. In this condition the plant requires at 

 least half-an-hour's absolute rest to regain its equanimity. 



Excitatory brpuLSE ix Mimosa, 



We next take up the question of the function of transmission 

 of excitation. It has hitherto been supposed that in Mimosa the 

 impulse caused by irritation is merely hydro-mechanical, and quite 

 different from the nervous impulse in the animal. According to 

 this hydro-mechanical theory, the turgid plant tissue is imagined to 

 be like india-rubber tube filled with water. The application of 

 mechanical stimulus is supposed to squeeze the tissue, in consequence 

 of which the water forced out delivers a mechanical blow to the 

 contractile organ of the plant. The propagation of mechanical 

 disturbance is thus occasioned by the bodily transfer of fluid material 

 in a pipe. In strong contrast to this is the transmission of nervous 

 impulse, which is a phenomenon of passage of protoplasmic disturb- 

 ance from point to point. The molecular disturbance, constituting 

 excitation, passes along the conducting nerve, and this point-to-point 

 propagation of molecular upset is known as the transmission of 

 excitatory or nervous impulse. If by any means the physiological 

 activity of a portion of the nerve be enhanced, then excitation will 

 pass through the particular portion with quickened speed. Such 

 favourable condition is brought about by the application of moderate 

 warmth. If a portion of nerve, on the other hand, be rendered 

 physiologically sluggish, then the speed of nervous impulse through 

 that portion will be slowed down. There are certain agents which 

 paralyse the nerve for the time being, causing a temporary arrest of 

 the nervous impulse. Such agents are known as anaesthetics. There 

 may, again, be poisonous drugs which destroy the conducting power. 

 Under the action of such poisonous agents the nervous conduction is 

 permanently abolished. 



We are now in a position to distinguish between mechanical and 

 nervous transmission. The mechanical conduction of water through 

 a pipe will in no way be affected by warmth or cold ; the pipe will 

 not lose consciousness and stop the flow of water, if it be made to 

 inhale chloroforui ; nor will its conducting power be abolished by 

 applying round it a bandage soaked in poison. These agents will, 

 on the other hand, profoundly affect the transmission of excitation. 

 The nature of an impulse may thus be discriminated by several 

 crucial tests. 



If physiological changes affect Vie rate of conduction, then the 

 impulse must be of a nervous character ; absence of such effect, on the 

 other hand, proves the mechanical character of tlie impulse. 



Of the various physiological tests, Pfeffer employed that of the 

 narcotic drug. Chloroform applied on the surface of the stem of 



