THE INFLUENCE OF ANESTHETICS. 



491 



failed completely, whilst excitability is still present, though dimin- 

 ished. 1 



The influence of anaesthetics. — It is the peculiar property of this 

 class of chemical substances (ether, chloroform, carbonic acid, etc.) that 

 they can diminish the functional attributes of living nerve fibres without 

 causing any permanent impairment, and can do this when reaching the 

 tissues through the blood, by inhalation, etc. The degree to which they 

 affect the two main attributes of nerve fibres, excitability and con- 

 ductivity, has been comparatively recently investigated in isolated nerve, 

 and the results obtained by different observers are in some instances 

 conflicting. The method for determining their direct action upon motor 

 nerves is that first employed by Griinhagen in determining the effects 

 of G0 2 gas. 2 This consisted in enclosing the middle portion of the 

 sciatic nerve of a muscle-nerve preparation of the frog in a small 

 chamber through which the gas could be passed (Fig. 258). The nerve 

 could be excited either in the chamber or on the central side, and it 

 was found that the passage of C0 2 gas caused the excitation by the 

 induced current at X 2 within the chamber to be ineffectual, whilst 

 similar excitation of the central end at Xj still evoked the muscular 

 response. Similar experiments by Luchsinger, 3 in which the vapours 

 of ether, chloroform, alcohol, and ammonia, as well as C0 2 , were employed, 

 showed results which 

 varied with the dura- 

 tion of the action of 

 the vapour or gas. In 

 the early stages the 

 nerve in the chamber 

 could no longer be 

 excited so as to evoke 

 a muscle response by 

 an intensity of stimu- 

 lus which aroused it before the passage of the vapour, whilst 

 excitation on the central side was unaffected ; a subsequent stage was 

 reached, in which even the strongest excitation of the central portion 

 failed to evoke the response, whilst such strong excitation of the nerve 

 in the chamber was still effective. This stage could be reached by 

 C0 2 after fifteen to twenty minutes. Hirschberg repeated these 

 experiments with C0 2 gas, but did not obtain the failure to the strong 

 central excitation. 



It is evident that the experiment is one of considerable importance 

 in determining the extent to which excitability and conductivity 

 are independent. The whole subject has been investigated with great 

 care by Piotrowski. 4 His observations were made along the same lines 

 as the preceding, but were extended to include the action of several 

 different modes of excitation, whilst the alterations of the nerve functions 

 through the anaesthetic were determined in a variety of ways, including 

 the variation in the extent of the muscle response evoked by an un- 

 altered intensity of nerve stimulus, the variation in the intensity of the 

 minimal adequate nerve stimulus, and the alteration in the rate of 

 propagation of the nerve excitatory state. 



1 See Griitzner, Arch. f. d. ges. Phi/siol., Bonn, 1893, Bd. liii. S. 113. 



2 Ibid., Bd. vi. 3 Ibid., Bd. xxiv. 

 *Arch.f. Physiol., Leipzig, 1893, S. 205-290. 



Fig. 258. 



