CHAPTER XL 



INADEQUACY OF PFLUGER'S LAW 



Reversal of PflUger's Law under high E. M.F. Similar reversals under feeble 

 E.M.F. Investigation by responsive sensation Experiments on living 

 wounds Under moderate E.M.F., intensity of sensation enhanced at kathode, 

 and depressed at anode Under feeble E.M.F., sensation intensified at anode 

 and depressed at kathode Application of electrical currents in medical 

 practice. 



IN studying polar variations of excitability in nerves, in 

 the last chapter, we found that, during the passage of the 

 current, it was the anode which enhanced excitability and 

 the kathode which induced depression. Now this conclusion, 

 as will be remembered, is directly opposed to what is known as 

 PflUger's Law, the universal applicability of which has 

 hitherto been regarded as beyond dispute. Pfliiger's Law 

 lays it down that the kathode excites at make, and the anode 

 at break ; and that, moreover, during the passage of a 

 constant current, excitability is raised at or near the kathode, 

 and depressed at or near the anode. We are next, then, led 

 to inquire : Under what conditions is this law applicable, and 

 when does it fail to hold good ? Now, as regards the effects 

 at make and break, I have shown elsewhere, in the course of 

 experiments on plants, that these are not determined by 

 anode and kathode alone, but also by the intensity of the 

 acting electro-motive force. Thus, in the case of the sensitive 

 Biophytum, in a given experiment it was found that, using the 

 moderately strong E.M.F. of 24 volts, the excitatory wave at 

 make was found to be initiated at kathode, and to travel in 

 both directions, causing depression of nine pairs of leaflets. 

 The forward half of this wave of excitation, stopped only at 



