ORIGIN AND DETECTION OF ELECTRO-MOTIVE CHANGES 391 



electrical conditions. On the other hand, it requires a special arrangement 

 of the parts to enable the chemical actions involved in metabolism to 

 produce differences of potential sufficient to maintain perceptible external 

 currents. Changes of metabolic activity will naturally affect these currents 1 , 

 but might conceivably take place in such fashion as to leave the difference 

 of potential unaffected. The absence of oxygen, changes of temperature, 

 the action of chloroform and ether all produce a distinct effect upon the 

 external currents led off from a plant, not only because of their general 

 action on metabolism, but also when locally applied. The local application 

 of anaesthetics or of poisons, as well as local injuries, may not only influence 

 a pre-existent electrical current, but may also cause difference of electrical 

 potential to appear in regions which were previously isoelectric 2 . 



Similar phenomena are shown by adult organs in which, when kept 

 under otherwise constant conditions and in air saturated with moisture, the 

 removal of oxygen or a change of temperature mainly affects the metabolic 

 activity. When, however, movement takes place, as in a stimulated leaf of 

 Dionaea, the resulting movements of water and of the tissues as a whole 

 may produce a certain amount of electricity. Under similar conditions 

 symmetric points on a leaf or stem are usually isoelectric, and the same 

 may even apply to organs which are morphologically and functionally 

 dissimilar. The reversal of the normal current of action during life or 

 under special conditions shows that the polarity of the organ does not 

 involve any fixed electrical polarity. Currents can usually be obtained 

 between any two points after appropriate treatment, provided that the 

 surfaces are not covered by non-conducting cork layers. Hence the pro- 

 duction of electricity, like the production of heat, is a property common to 

 all living organisms, and not one possessed by a few, as is for instance the 

 property of luminosity. 



The difference of potential between different surfaces on an intact or 

 injured organ is usually less than o-i to 0-14 of a volt 3 , which is the same as 

 exists in resting muscle between the longitudinal and transverse surfaces. 

 The total amount of electricity produced is quite uncertain, and even when 

 the conductivity of the different tissues and of the different parts of the 



1 The relationships here are the same as when growth and movement are affected by external 

 stimuli, and hence no sharp distinction can be drawn between currents of rest and currents of action. 

 Cf. Biedermann, I.e., p. 331. 



3 [Waller (Journ. Linn. Soc., 1904, Vol. xxxvn, p. 32) finds that as the result of electrical 

 stimulation a 'blaze' current, lasting a few minutes or longer, is produced in the adult tissues of 

 most plants. The direction of this current may be the same or opposite to that of the exciting 

 current, and it is in some cases of quite appreciable intensity, the difference of potential produced 

 amounting to -^ volt. In some cases where a compensating current was used to balance the action 

 current or injury current of the object tested, the 'blaze' current obtained was simply due to 

 a decrease of resistance allowing the compensating current to produce a deflection of the galvano- 

 meter.] 



3 Cf., in addition to the works already quoted, Biedermann, Elektrophysiologie, 1895, p. 441. 



