CHAP. IX.] NERVOUS FORCE NOT MERE ELECTRICITY. 243 



them, and is separated from their central axes by the insulating 

 structure. And were the electric current, passing through such 

 minute conductors as nerve-fibres, of sufficient intensity to magnetize 

 a needle, it is scarcely possible to conceive that it would be com- 

 pletely or perfectly insulated by the delicate membranes which 

 invest the central axis. Yet, without some provision for very com- 

 plete insulation of the several conductors in such a bundle as a 

 nervous trunk, it is obvious that disturbances must continually arise 

 from the secondary currents induced in neighbouring fibres by the 

 electricity passing through those in action. 



The proofs, therefore, of the passage of an electric current through 

 the nerve-fibres during nervous action must be held to be altogether 

 defective. Not only is experimental evidence wanting to support 

 the electrical theory, but certain facts are admitted which greatly 

 invalidate it. Of these, a very important one has been adduced in 

 the preceding paragraph. The following may be added, some of 

 which have already been adduced by Miiller. 



1. The firm application of a ligature to a nerve stops the propa- 

 gation of the nervous power below the points of application, but not 

 of electricity. The nervous trunk is as good a conductor of electri- 

 city after the application of the ligature as before it. 



2. If a small piece of a nervous trunk be cut out, and be re- 

 placed by an electric conductor, electricity will still pass along the 

 nerve, but no nervous force, excited by stimulus above the section, 

 will be propagated through the conductor to the parts below. 



3. Nervous fibre is not a better conductor of electricity than 

 other tissues. Matteucci assigns to muscle a conducting power 

 four times greater than that of nerve or cerebral matter; and 

 Weber states that no substance in the human body is so good a 

 conductor as the metals. From our own observations on this sub- 

 ject, made with the most delicate instruments, we are led to state 

 that both nerve and muscle are infinitely worse conductors than 

 copper, and that we have failed in detecting any appreciable 

 difference in the conducting power of these two animal sub- 

 stances. In fact, their power of conduction does not rank 

 above that of water holding in solution a small quantity of saline 

 matter. 



From the preceding review of the arguments for and against the 

 theory of the identity of the nervous force and electricity, we are 

 lod rather to reject than to adopt it. The same reasons induce us 

 to regard the nervous force as a power developed in the nervous 

 structure under the influence of appropriate stimuli ; as muscular 



