ELECTROMOTIVE ACTION IX NERVE 251 



and muscle physics " (where it long enough blocked the way) 

 the one-sided physical conception of vital phenomena so recently 

 disproved in all departments of physiological investigation. There 

 is, on the other hand, no sufficient reason for regarding the nerves 

 on which Boruttau experimented as really dead, with no re- 

 mainder of physiological excitability ; as will be admitted by every 

 one who has seen how even warm-blooded nerves (e.g. vagus), 

 when divided, and completely isolated by lifting them out of the 

 wound, so that they cannot be normally nourished, may be suc- 

 cessfully excited many hours afterwards, provided only that the 

 peripheral organ (heart, respiratory centre) be in good condition. 

 Under all circumstances, the failure of indirect and even of direct 

 muscular excitability in no way establishes the complete death of 

 the nerve belonging to it, and, notwithstanding Boruttau's protest, 

 we may still legitimately classify the action current, as well 

 as the negative variation of all excitable tissues, under one 

 category. 



III. ELECTROMOTIVE CHANGES PRODUCED BY STIMULATION 



OTHER THAN ELECTRICAL 



The galvanometer, by recording the negative variation of 

 the nerve, is thus (supra) a reliable indicator of the state of 

 its excitability, without further reference to the alterations 

 of the peripheral end-organ. It must be admitted to afford 

 indubitable evidence of conductivity in both directions. If 

 the peripheral end of a motor nerve is stimulated, a negative 

 variation appears on leading off from the central cut end, and 

 vice versa. Again, on exciting a purely centripetal (sensory) 

 nerve, the negative variation may be demonstrated at any point 

 peripheral to the seat of excitation. From this point of view it 

 becomes essential to test the negative variation with excitation 

 other than electrical. "We are already familiar with the fact that 

 nerves which are dissimilar in function do not react alike to 

 identical stimuli, but exhibit marked differences. Grutzner (22), 

 e.r/.j showed that centrifugal and centripetal nerves react quite 

 differently to thermal excitation, the latter becoming, with few 

 exceptions, highly excitable at a temperature of 40 to. 50 C., 

 while the former (with the exception of the vaso- dilators) do 

 not seem to be excited. Strictly speaking, however, these 



