PHYSIOLOGICAL RESPONSE IN PLANT AND ANIMAL 745 



and that reversal of these normal effects which is liable to 

 occur under fatigue, or under excessively strong electro- 

 motive force, is the same in the one case as in the other. In 

 addition, moreover, to the contractile effects of kathode-make 

 and anode-break, the plant exhibits a responsive expansion 

 at anode-make and kathode-break, which is also seen in 

 animal tissues. 



Turning next to such tissues as are characterised by the 

 property of rhythmicity in a marked manner, we have seen 

 that this effect as exhibited by the plant cannot be distin- 

 guished from that in the animal. The rhythmic tissues of the 

 plants Biophytum and Desmodium are characterised by the 

 possession of relatively long refractory periods, a peculiarity 

 which also marks the rhythmic cardiac muscle of the animal. 

 The response of rhythmic tissues in both plant and animal is 

 found to be on the ' all or none ' principle. In both alike the 

 rhythmic tissue is incapable of tetanus ; and in both, when 

 at standstill, a single moderate stimulus gives rise to a single 

 response, and stronger stimulus to a multiple series of 

 responses. In Desmodium, again, as in the cardiac muscle, 

 increased internal hydrostatic pressure renews pulsation in 

 a tissue at standstill. In rhythmic tissues, again, whether 

 animal or vegetable, under favourable tonic conditions, per- 

 sistent pulsatory movements take place which are apparently 

 automatic ; and these rhythmic pulses are found to exhibit the 

 same types of cyclic variation in the plant as in the animal. 

 The effects of temperature on both are exactly the same — 

 that is to say, its rise increases the frequency and diminishes 

 the amplitude of pulsation. And still more striking, finally, 

 is the identity of the modifications induced by drugs in the 

 rhythmic responses of animal and vegetable. 



But this unity of rhythmic responses in plant and animal 

 is not merely a question of their fundamental characteristics. 

 They sometimes appear also to subserve functions somewhat 

 similar. Thus the rhythmic cardiac tissue of the animal 

 maintains the circulation, and we have seen that the rhyth- 

 mic tissue of the plant maintains the ascent of the sap. 



