THE PHYSIOLOGY OF NERVE 259 



physiology ; it is hardly necessary to quote the instances of 

 electropathic battery belts, the claim that nerve contracts on 

 excitation ( l ), and the " records " of the electrical response in 

 metals ( 3 ), to show that folly of a kind that one moment's reflection 

 should dissipate finds a ready acceptance with those who consider 

 the experimental facts of animal electricity too dull for their 

 enlightened minds. 



There is, however, one quite genuine difficulty in the study of 

 our present subject that makes it less interesting than it will be 

 in the future. None of the theories are in any way complete, and 

 we come across many facts which appear to conflict with the best 

 arranged of these explanations. All that can be done in such a 

 case is to record these facts in the hope that later on the proper 

 place may be found for them ; the simple and easy receipt for the 

 manufacture of hypotheses by the inclusion of favourable instances 

 and the exclusion of everything that contradicts the theory is one 

 that does not lead to a result on which much reliance can be 

 placed. 



PRELIMINARY NOTES 



It is unnecessary to do more than briefly recapitulate the 

 experimental facts that have been made out concerning excised 

 medullated nerves that are still in a surviving condition, yet as 

 they form the starting point of what follows it may not be 

 out of place to give a short summary of the most important 

 phenomena. 



After the nerves have been excised from the body they are 

 best kept in an approximately isotonic solution of NaCl, to which 

 a small quantity of glucose may with advantage be added. When 

 the effect of the excision has passed off, such nerves are isoelectric, 

 that is, they give no current in the galvanometer, and they have 

 apparently (except in certain known particulars) resumed the con- 

 dition they were in before they were removed from the body. 



Three main varieties of electrical phenomena directly connected 

 with function can be observed in such nerves (1) Current of 

 injury ; (2) current of action or negative variation ; (3) electro- 

 tonic currents ; giving to each the usual name. Excellent reasons 

 can be given for the disuse of each of these terms, but as their 

 significance is perfectly clear, it seems better for our present 

 purpose to use words with which the student is already familiar 



