254 ELECTRO-PHYSIOLOGY < HAP. 



The negative variation of the nerve current is under all cir- 

 cumstances a far less sensitive excitatory reagent than the 

 reaction from the natural end-organ. Even in electrical excitation 

 the visible reaction from the muscle appears earlier, i.e. at a 

 greater distance of coil, than the negative deflection on the gal- 

 vanometer. The requisite interval of current intensity is invari- 

 ably much greater in warmed than in preparations of cooled 

 frogs. Steinach excited both sciatic nerves simultaneously with 

 induction currents, one nerve being connected with the leg, while 

 he led off from the other to the galvanometer. In a warmed 

 frog, tetanus first appeared with the coils 43 cm. apart, the 

 negative variation at 2 7 cm. ; in a cooled frog the distances were 

 respectively 39 and 38 cm. Granting that these experiments 

 are inconclusive as regards the presence of qualitative differences 

 in the nerve-fibres, the fact that the negative variation is some- 

 times very weak, or altogether absent, in electrical stimulation, 

 where all the fibres are simultaneously and equally excited, at 

 least suggests this inference. Fredericq (1) remarked upon the 

 insignificance of the negative variation in electrical excitation of 

 mammalian nerve, and Griitzner has recently notified the same 

 effect. No trace of negative variation can be obtained from an 

 artificially-cooled rabbit, although the same excitation of the sciatic 

 nerve causes a pronounced tetanus of the muscle. Apparently 

 the alterations fundamental to the negative variation are in this 

 case not transmitted, although the nerve as a whole is still 

 excitable, and able to conduct, at all points. The negative 

 variation may be observed in normal, uncooled, mammalian nerve, 

 always, however, in a strikingly inferior degree from that of frogs' 

 nerve. In this case a negative variation of 10 per cent of the 

 nerve current is readily obtained with maximal currents, while 

 the same stimulus only elicits a variation of 4 per cent in 

 mammalian nerve. 



In all these cases we have been concerned with excitation of 

 the nerve in its continuity. What, in the next place, is the 

 negative variation on stimulating the natural end-organ (central 

 or peripheral) of the nerve-jibre ? We are again indebted to 

 du Bois-Eeymond for the first observations on this point. In 

 strychnia-spasm he observed a distinct diminution of the longi- 

 tudinal-transverse current, on the frog's sciatic nerve still in con- 

 nection with the spinal column. In the conviction that the 



