x ELECTROMOTIVE ACTION IN NERVE -255 



negative variation was to be regarded as the galvanic expression 

 of excitation, du Bois-Reymond poisoned a conveniently arranged 

 frog with strychnia, and then, after ligaturing the iliac artery on 

 one side, divided the sciatic nerve of the same side at the knee, 

 and exposed it as far as the vertebral column. He then led off 

 to the multiplier from the peripheral end. If the strychnia- 

 spasm happened to coincide with the moment at which the needle, 

 after deflection by the nerve current, had returned to rest, it 

 swung back several degrees at the commencement of the spasm. 

 The experiment is, however, most uncertain, and depends upon 

 various irregular conditions. On the other hand, there is regu- 

 larly, on exciting the motor zone of the cerebral cortex, a 

 negative variation of the longitudinal-transverse current in the 

 spinal medulla, expressed on the capillary electrometer as a suc- 

 cession of rhythmical oscillations, occurring simultaneously with 

 epileptic spasms in the muscles. 



In opposition to the marked effects on leading off from longi- 

 tudinal and transverse sections of the spinal cord, there is, as was 

 shown by Gotch and Horsley (5), very little result from leading 

 off at the cut end of the sciatic nerve, during excitation of the 

 motor zone. According to Horsley's observations the excitation 

 diminishes on its way from the cord to the mixed nerve, by more 

 than 80 per cent. The same difference appears when the fibres 

 of the corona radiata, instead of the cortex, are directly excited. 



If it is thus established that efferent impulses from the 

 centres, however excited, produce a negative variation of the 

 nerve current, more recent observations seem to establish the 

 same for sensory impulses also. Du Bois-Reymond made experi- 

 ments to see whether excitation of the natural ending of a 

 sensory nerve by an adequate stimulus might not result in 

 movement of the multiplier-needle, instead of in sensation (just as 

 the motor nerve in the above experiment with strychnine had 

 displaced the magnet, and not the muscle). He obtained a 

 negative variation on the frog's sciatic when the leg, with the 

 skin in situ, was progressively scalded with boiling salt solution 

 from tendon to knee, or corroded and burned with concentrated 

 sulphuric acid (28). Yet, as du Bois-Eeymond himself pointed 

 out, this was rather " tetanising of the sciatic through its 

 cutaneous branches," than excitation of the sensory end-organs 

 of the skin. Kiihne (9.) in fact found that the negative variation 



