CHAPTEE X 



ELECTKOMOTIVE ACTION IN NERVE 



I. CURRENT OF "BESTING" NERVE 



Du BOIS-KEYMOND 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-medullated 

 fibres in both vertebrates and invertebrates are characterised 



