526 NERVE. 



the response of the end organs with which this is associated. Thus the 

 non-medullated nerves which innervate the muscles of Anodon are 

 excited by the longer galvanic currents far more effectively than by 

 the rapid induced currents, as evidenced by the motor responses, and 

 in these the excitatory electrical change is observed with the former 

 method of stimulation rather than the latter. 1 



The discovery of these excitatory electrical effects formed a notable 

 advance in nerve physiology, since their presence affords the only 

 positive data derived from nerve itself as to the characteristics of the 

 alteration which the tissue undergoes when it passes from a condition 

 of rest into one of activity. 



It must not, however, be assumed that the electrical change is the 

 whole excitatory alteration ; nor indeed, in the present state of our 

 knowledge, are we justified in the less sweeping assumption that it is 

 a complete or absolutely faithful record of such alteration. It has 

 already been pointed out that the arrest of the circulation and the 

 excision of an efferent nerve are followed by profound changes in 

 excitability and conductivity, as estimated by the response of the 

 muscle to which it is distributed. When, in consequence of this arrest, 

 muscular responses have ceased to be evoked by indirect excitation, the 

 nerve will still give the resting difference on cross section ; but a more 

 remarkable feature is that, as long as structural continuity is unimpaired, 

 such a nerve may also give the excitatory negative variation. Thus 

 Hermann, Fredericq, and others 2 found the excitatory electrical change 

 to be present for many hours in the excised sciatic of the rabbit, as 

 indeed is also and more notably the case in the same nerve of the cat. 3 

 Steinach 4 noticed that the frog's sciatic gave the excitatory effect when, 

 having been dried, it was soaked again in 0'6 per cent. NaCl, and 

 Boruttau 5 observed electrical changes on mechanical stimulation of the 

 same nerve eight days after its excision, and in the vago-sympathetic of 

 the dog two days after its removal from the body. It must, however, 

 be remembered that the muscular response to indirect excitation requires 

 the functional activity of the nerve-endings. It is therefore not im- 

 probable that this manifestation should completely fail, and yet the 

 nerve fibres themselves maintain, to some extent, their functional 

 attributes. Still the facts above mentioned warrant the caution that, 

 although the electrical change is a concomitant of the real excitatory 

 process, the two are not identical, and the former may be perceptible 

 when other evidence of the existence of the latter fails. 6 



In order to accentuate the difference between the vera causa 

 and its excitatory electrical concomitant, the latter will in these 

 pages be now referred to as the excitatory electrical response of the 

 nerve. 



1 Biedermann, Sitzungsb. d. k. Akad. d. Wissensch., Wien (3), Bd. xciii. 



2 Hermann, "Handbuch," 1879, Bd. ii. S. 120; Fredericq, Arch. f. Physiol., Leipzig, 

 1880, S. 65. 



3 Gotch and Horsley, Phil. Trans., London, loc. cit. 



4 Steinach, Arch. f. d. ges. Physiol., Bonn, Bd. Iv. 



5 Boruttau, ibid., 1894, Bd. Iviii. S. 29. 



6 Quite recently Gotch and Burch have obtained evidence of the dissociation of the 

 electrical response from the excitatory process. In the sciatic nerve of the frog it is 

 possible with two stimuli in rapid succession to obtain only one electrical response near 

 the seat of excitation which has been cooled, whilst two such responses occur in a more 

 peripheral warmer region. "Proc. Physiol. Soc. , " Journ. Physiol., Cambridge and London, 

 1899, vol. xxiii. ; 1899, vol. xxiv. 





