CHAP. XI. 



ON NERVE FORCE. NOT CURRENT FORCE SHEWN BY 

 THE GALVANOMETER J THE GALVANOSCOPIC FROG, 

 AND THE MAGNETIC NEEDLE. A POLAR FORCE. 



Is nerve force a polar force? If so, in what 

 respects does it differ from other polar forces? or 

 what evidence have we that it is a polar force at all ? 

 These are questions which no doubt arise in the 

 minds of many physiologists of the present day. 

 Without entering into any detailed account of the 

 various opinions that are entertained in regard to 

 the nature of nerve force, it may be fairly considered, 

 that those who entertain the opinion that nerve 

 force is a polar force, are called upon, in the present 

 state of the question, to give some direct experi- 

 mental evidence in support of their conclusion : the 

 onus probandi evidently rests upon their shoulders. 

 We cannot remain satisfied with the vague notions 

 that animal life and electricity are identical, or that 

 nerve force and electric force are identical, or that 

 nerve force differs entirely from electric force, or 

 that vital forces are totally distinct from inorganic 

 forces. The mind will not and cannot rest satisfied 

 with these vague assertions; it requires something 

 more definite. We want to know, if possible, how 

 far they agree, and in what respects they differ. 

 To answer these questions satisfactorily, it will 



