

CHAPTEK X 



ELECTROMOTIVE ACTION IN NERVE 



I. CURRENT OF " EESTING " NERVE 



Du Bois-PtEYMOND communicated his first observations on galvanic 

 action in the divided nerve in 1843, after many vain attempts 

 on the part of Matteucci and others to demonstrate its existence. 

 A complete historical account of all the preliminary researches 

 may be had in the second volume of du Bois-Eeymond's classical 

 work. Modern methods have facilitated the recognition of the 

 " law of the nerve current " in each excised particle of cold- or 

 warm-blooded nerve which law, apart from differences of in- 

 tensity in the resulting effects, coincides in every particular with 

 that of the muscle current. In both cases, each point of the 

 natural, uninjured surface (the "natural longitudinal section ") is 

 positive to all points of an " artificial transverse section " ; in 

 both the difference of potential is greatest when the " equator " 

 is connected with the cross-section by the leading-off circuit, such 

 P.D. being greater or less according as the points of the long 

 section are less positive to the cross-section, i.e. are more closely 

 approximated to it; each point nearer the equator being also 

 positive to each more distant point (weak longitudinal current). 

 As in muscle, we must assume each single nerve-fibre to be 

 equally electromotive with the entire nerve-trunk. 



Du Bois-Eeymond determined the absolute E.M.F. of the nerve 

 current as 0'022 Dan. in frog, 0'026 Dan. in rabbit. The follow- 

 ing table from Fredericq (1) shows the E.M.F. of medullated nerve 

 in the frog to be much the same as in various warm-blooded 

 animals, while the nerves that are composed of non-inedullated 

 fibres in both vertebrates and invertebrates are characterised 



