CHAPTER XIX 



ON ELECTROTONUS 



The anode acts as a block to the transmission of stimulus — Opposite effect of 

 kathode — Experiments on Biopkytum, showing variations of conductivity by 

 anode and kathode respectively — Experiments on Mimosa, showing increase of 

 motile excitability at or near the kathode, and diminution of motile excitability 

 at or near the anode — Curious ' development ' of response, near the kathode. 



We have seen in the last chapter that on account of the 

 diminished molecular mobility caused by physical and 

 chemical agents, the response underwent a diminution. It 

 was also seen that this reduction of molecular mobility found 

 expression in the diminution of conductivity and excitability. 

 External agents, like cold and ether, produce a temporary 

 reduction of mobility, after which there is a revival to the 

 original condition on the removal of the depressing agents. 

 But certain other agents, such as poisons, produce permanent 

 immobility, from which there is no recovery of response. The 

 tissue is then said to be ' killed.' 



Returning now to the molecular model, described in the 

 last chapter, we see that while stimulus causes molecular 

 upset, yet, at the same time, the force which restores the 

 molecule to its equilibrium position, or, in other words, that 

 which determines its stability, resists such an upset. Let us 

 then first imagine the molecular model to be under the 

 moderate directive action of the earth's magnetism. The 

 stability of the individual molecule will thus be neither too 

 great nor too small, and we shall call this, for convenience, 

 the normal stability. This stability may further be increased 

 by increasing the external directive force with the help of an 

 auxiliary magnet, arranged in a suitable manner. Or it may 



