190 life's beginning on the earth 



In the nerve the impulse travels at approximately the 

 speed limits of an automobile, varying somewhat according 

 to the size of the nerve fiber. 



Although not identical with an electrical current the 

 impulse is nevertheless electrical in nature, since sensitive 

 electrical instruments demonstrate that a negative elec- 

 trical charge travels along the nerve fiber simultaneously 

 with this impulse. What is meant here by electrical 

 charge and how can it travel along the nerve fiber? 



The charge in question is quite similar to that of a lead 

 battery in an automobile, which — as is well known — often 

 needs recharging. This battery consists of lead plates im- 

 mersed in sulfuric acid. The charge is effected by sending 

 a direct electric current through the battery which brings 

 about certain chemical changes at the surface of the lead 

 plates. These chemical changes constitute the charge. If 

 the battery is discharged by connecting with the starter or 

 with the lights, the chemical changes are reversed. 



In order to form a conception of what may occur in the 

 nerve fiber, we should imagine a lead-battery plate drawn 

 out to a thin wire, surrounded on all sides by a thin layer of 

 sulfuric acid. We then imagine this wire to be charged at 

 one end by connecting it to the negative pole of a battery 

 and by connecting the surrounding layer of sulfuric acid 

 with the other pole of the battery, so that a current flows 

 only through one end of the wire and the acid at the same 

 end. One end of the wire would thus be charged and the 

 rest remain uncharged, in a manner indicated diagrammati- 

 cally in Figure 75. Assuming that such a wire acts in the 

 same manner as a nerve-fiber, the following changes would oc- 

 cur automatically after disconnection of the charging battery. 

 The charged end of the wire would generate a local current 

 which flows through the adjacent uncharged petition, as 

 indicated by a dotted line in the diagram. The adjacent 



