504 Dynamic Theory. 



will be felt, but the muscular contraction or pulsation will not take 

 place. Under the strongest irritation of a peripheral nerve it is impos- 

 sible with the strongest microscope to discover the nature of the change 

 that takes place in it, although, since the irritation passes through the 

 nerve and irritates the muscle, it stands to reason that a change does 

 take place in the nerve. If the calf muscle of the frog, with the sci- 

 atic nerve connecting to it, be used for experiment, the pulsation of the 

 muscle may be produced by the irritation of the nerve mechanically, by 

 pressure or constriction with a thread, or by cutting it ; or chemically, 

 by putting upon it alkaline matter or an acid, or it may be irritated by 

 heating, another sort of mechanical irritant ; or it may be irritated by 

 electricity. All the chemical and mechanical irritations are abnormal, 

 and soon destructive of the irritability of the nerve at the point irri- 

 tated. But the electrical stimulus may be applied repeatedly without 

 immediately destroying the irritability of the nerve. < ' It therefore ap- 

 pears that in this respect a nerve acts exactly as does a muscle. " That 

 is, it wears better under an electrical stimulus than under any other 

 sort, showing it to be adapted best to that sort of stimulation, and by 

 implication, therefore, to have been built up by that sort of a stimula- 

 tion rather than by physical or mechanical jars. In experimenting with 

 the cortex 1 of the cerebrum, no sort of mechanical irritation was ever 

 found to have any effect whatever. It might be subjected to chemical 

 stimulation, it might be heated or cut or pinched without exciting either 

 sensation or motion. But the introduction, by Fritsch and Hitzig in 

 1870, of the galvanic current into their studies of the cerebrum, at once 

 led to the unlocking of its secrets. The galvanic pile in the hands of 

 the physiologist, takes the place of the normal will of the individual 

 owning the brain. The electrodes, or poles, applied to different parts 

 of the exposed cortex, cause the movement of the different muscles with 

 which the brain is in connection. 



A single inductive shock through a nerve produces a single pulsation 

 in the muscle, and if a continuous series of shocks is applied, the result 

 is tetanus in the muscle. The irritation of the nerve must be made at 

 some distance from the muscle. If the nerve be cut, the effects cease 

 and it cannot be mended by placing the parts in juxta-position, however 

 well done, and although the nerve may appear to be uninjured, it wont 

 work. If a thread is drawn tightly around the nerve it spoils it. After 

 the thread is removed the crushed spot is an impassable barrier to the 

 electrical stimulus. But the stimulus may be applied below the injured 

 spot and the effects will be complete again. 



It is proved by experiment on the nerves of frogs that the stimulation 

 passes along the nerve, so that the longer the nerve the longer it takes 



1 The bark or outside surface of the brain. 



