ON THK MAMMALIAN NERVOUS SYSTEM. 413 



Etherisation. 



These nerve impulses may, as before stated, have two direct sources of origin, 

 namely, the excited mixed nerve or the grey matter in the cord, which the arrival of 

 afferent impulses may have thrown into functional activity. They may be conducted 

 along direct fibres from the lumbar nerves to the dorsal cord or to central mechanisms, 

 and from these either along continuous fibres to the area observed or along short 

 internuncial fibres to other cellular mechanisms, and so again to others and thus finally 

 reach the area. 



That the change is due to the presence in varying degrees of all these three factors 

 is extremely probable from anatomical considerations, since GA.TJLE* has shown that 

 the number of fibres in the Frog's cord can be satisfied by such a triple arrangement. 

 It is, moreover, clear, from the influence of profound etherisation upon the electrical 

 change, that, when an adequate strength of stimulus is employed, the galvanometric 

 effect varies in amount with the pronounced or slight character of the visible reflex 

 effect. This has been already referred to (p. 372), but its importance in connection 

 with the subject of this section warrants the introduction of some experimental 

 details. We therefore give as examples the following : In one case, on exciting 

 the sciatic of a profoundly etherised animal (Cat) with a weak but adequate 

 stimulus for 5 seconds, the galvanometric cord effect was 76 scale ; the animal was 

 then less etherised and the effect was 220 scale. On again deeply etherising the effect 

 with the same excitation sank to 130 ; upon the ether being then more or less removed, 

 the excitation produced an effect of 200 ; whilst on renewed profound etherisation 

 this was only 80. In all these cases very feeble reflexes or none were observed in 

 the profoundly etherised animal, but the reflexes were well marked when with less 

 narcosis the larger electrical changes were noted. 



These differences evidently point clearly to the fact that the electrical change may 

 not only be that due to the transmitted nerve impulses up direct tracts, but also to 

 the presence of interposed cellular mechanisms and their susceptibility of response 

 to the arrival of afferent impulses. In Chapter III. we have discussed the value 

 of the use of ether as a means of discriminating between the functional activity of 

 fibres and of fibres plus cells, to that chapter we refer the reader, merely remarking 

 now that we must not lose sight of the fact that etherisation, especially when very 

 profound, may affect the nature of the excitatory processes in the nerve fibres them- 

 selves, as in the experiments made on the nerve of the Frog by BIEDERMANN with ether 

 vapour. The differences between effects obtained with unvarying intensity of stimulus 

 but different degrees of narcosis are practically the same as those obtained with 

 different strengths of excitation and unvarying but not too profound anesthesia. 



* GAULE, ' Abhandl. Math.-Physik. Classe d. Kgl. Sachs. Gesellsch. d. Wiss.,' 1889 (vol. 15, No. IX. ; 

 ' Neurol. Centralblatt,' vol. 9, p. 3. 



