EFFECT OF IRRITATION OF A POLARIZED NERVE. 419 



was produced when a solution of the glucoside saponin was substituted, 

 for the ammonia. With these substances hemiplegia was not always 

 produced, though the injection was made into the same portion of the 

 brain. In some cases a sort of hemi-chorea, and in others general con- 

 vulsions, were produced. 



From these experiments we must believe that hemiplegia results from 

 an irritation (or i)olarization ? ) and not from the destruction of motor 

 centres. How are these, the varying results following irritation of the 

 same part of the brain, to be explained ? 



Ammonia or saponin applied to a nerve tubule * really acts by polar- 

 izing this structure. The impulse causing the animal to make volitional 

 movements comes from the periiDheral centres, and is no doubt similar 

 to an irritation in its etfects on the central nerve tubules. Now, it was 

 seen that in a polarized nerve the effect of the irritating current is in- 

 creased or decreased as the relation between the proportions of the two 

 currents is changed. A polarizing current of a certain strength applied 

 to the fibres in the vicinity of the corpus striatum will diminish or totally 

 "inhibit" an ordinary volitional impulse ;t but when we increase the 

 strength of this irritation or impulse, as we undoubtedly do under strong 

 excitement, other proportions between the two currents result, and con- 

 sequently we have other effects. 



Again, under other circumstances a lesion of the same portion of the 

 brain will i^roduce convulsions. Here we have the proportions between 

 the sti-engths of the two currents again changed. The polarizing cur- 

 rent now increases instead of decreases the effect of the irritating current. 



In conclusion, I would say that the reason why a lesion in the same 

 portion of the brain at one time produces jiaralysis, at another has no 

 effect, and in a third instance i^roduces convulsions (or tremors), is to 

 be found in the proijortion, which exists in each individual case, between 

 the current developed in the nerve tubule by the lesion and that which 

 proceeds from the lierixjheral centres in the production of volitional im- 

 pulses. 



* A nerve tubule uudoubtedly lias the same properties whether it be of intercentral 

 or peripheral significance, 

 t A hemiplegic person has the will to move the paralysed limbs, but not the power, 



