ELECTRICAL STIMULI 89 



Corresponding observations were previously made by Velten 1 . Accord- 

 ing to Klemm the inner plasmatic membrane is destroyed before the 

 outer, and in the last stage of disorganization the protoplasm swells 

 and becomes highly vacuolated. This is because the action of the 

 electricity is such as to cause various solid substances to become soluble 

 and dissolve. These phenomena are not, however, connected with stream- 

 ing or with the presence of oxygen, for they are produced in the absence 

 of the latter, and also in chloroformed cells. 



Hermann 2 investigated more exactly the phenomena of electrical 

 excitation, and more especially the internal electrical changes which 

 follow stimulation. The experiments were performed exclusively with 

 Nitclla, and by laying the cells across insulating strips of vaseline and 

 using non-polarizable electrodes, Hermann made certain that the whole 

 of the current passed through a portion at least of the cell, and that no 

 other effect than the electrical one was produced upon it. This use of 

 vaseline is to be recommended in all cases in which the objects are of 

 sufficient size, except when the conjoint effects of thermal and electrical 

 stimuli are being investigated. 



Hermann found that after the stoppage of streaming by the 

 application of a galvanic current had been repeated once or twice, a 

 weaker current sufficed to produce the same effect. This he ascribes 

 to an increased excitability of the cell, and states that ultimately it 

 becomes wearied and responds less readily. Dutrochet and Becquerel 

 (1. c., p. 38) observed that streaming might recommence in Chara while 

 the current was still passing, and that a decrease or break of the current 

 caused another temporary stoppage. Those results have been extended 

 by Hermann, who finds that in Nitella a weak current produces a 

 temporary stoppage over the entire cell after a latent period of one 

 to seven or eight seconds, whereas with strong currents, at make streaming 

 temporarily ceases at the kathode, and remains slower there all the time 

 the current is passing (katelectrotonic excitation). On breaking the 

 circuit, a temporary stoppage occurs at the anodal end only. Hence, 

 according to Hermann, the production of katelectrotonus and the disap- 

 pearance of anelectrotonus constitute stimuli exciting a stoppage of 

 streaming just as they do in producing a contraction in muscle-fibre. 

 With weak currents the katelectrotonic and anelectrotonic excitations 

 spread over the entire cell, whereas strong currents diminish the excitability 

 at the anode on making the circuit, and at the kathode on breaking it. 

 Hence the stimulus is confined to the kathode in the first case and to 

 the anode in the second. 



Bewegung nnd Bau des Protoplasmas. Flora, 1873, p. 122. 

 Protoplasmastiomung bei den Characeen. Jena, 1898. 



