238 RESEARCHES ON IRRITABILITY OF PLANTS 



the pulsation was arrested towards diastole by the make 

 of anode. The break of anode was immediately attended 

 by an abrupt termination of the standstill. A pulse of 

 systolic contraction followed, and was succeeded by the 

 renewal of ordinary pulsation. It is thus seen that while 

 the make of kathode and break of anode induce contraction, 

 the make of anode and break of kathode induce the reverse 

 effect of expansion. 



The contrasted effects of anode and kathode, and of 

 make and break, are also exhibited by induced variations 

 of excitability. These are well seen in characteristic 

 differences of effects induced by a constant current in a 

 muscle-and-nerve preparation, these being modified by 

 the strength of current. Thus employing a feeble current 

 it is found that both ascending and descending currents in the 

 nerve induce excitation of the terminal muscle at make but 

 not at break. With strong currents, on the other hand, 

 excitation only takes place at the make of the descending 

 current and break of the ascending current. We shall 

 presently see how these different effects are explicable on 

 the assumption of the contrasted effects of anode and 

 kathode, and of make and break. 



The obscurity of the subject lies in the fact that there 

 is no visible indication of an excitatory change in the nerve. 

 The case would have been different had the conducting- 

 tissue been provided with indicators which could signal the 

 passage of excitation. Such a conducting-tissue is provided 

 by the petiole of Biophytum, where the successive closures 

 of the lateral leaflets indicate the transmission of excitation 

 through the central conducting-strand. We shall see how 

 the effects visually manifested in Biophytum elucidate 

 the characteristic effects observed in the nerve-and-muscle 

 preparation. 



Fig. 121 shows arrangements of parallel experiments 

 in nerve of frog and conducting petiole of Biophytum. The 

 polarising electrodes are applied to the right, the terminal 

 motile organ, muscle or leaflet, being to the left. The series 



