BT SHL MI CHAM, TDfiSBK. -> : 



with a, given current on a perfectly 

 re main fo 



effects will be found to be hi 



.'Hi? rariatum if dependent on fke 

 vital conditions f the neroe. 



CHAPTER XXTJIL 

 STIMU1 



OTHEE things being constant, we may now take 

 in the contraction of the muscle of a nerve-muscle preparation 

 as a measure of variations in the condition of the nerve. A 

 muscular contraction is a token of a nervous impulse passing 

 along the nerve, the extent and character of the one being & 

 measure of the extent and character of the other: a tetanus in 

 the muscle indicates a series of impulses in the nerves, follow- 

 ing each other with not less than a certain velocity. 



1 The Effects of the Constant Current. Obs. I. Ar- 

 range a nerve-muscle preparation in the moist chambei. 

 the nerve on non-polarizable electrodes, the muscle loaded 

 with 10 or 15 grammes, lever attached, recording surface pre- 

 pared, etc. 



Have a battery of two or more cells, and between the br, 

 and the el- introduce the rheochord (Chap. XIX 



VI II.). Let all the plugs be in, and the travelling mercury 

 cups close up. 



The resistance now offered by the rheochord, compared with 

 that offered by the electrodes, is practically nil ; consequently 

 none of fbe current from the battery will pass through the 

 latter; there will, therefore, be no contraction in the m ... - 



Remove one of the plugs, viz., that one the removal of which 

 throws the least resistance into the rheochord. A certain 

 fraction of the current will now pass through the electrodes on 

 account of the resistance thrown into the current through the 

 rheochord by the removal of the plug. If a contract: 

 the result, let it be recorded ; if none, let that fact be recorded 

 oting on the recording surface the plug removed. He- 

 move the plugs one by one, recording the result each time. 

 Replace the plugs one ly one, also noting the results. 



It will be found that a contraction of the muscle takes 

 place, a nervous impulse is originated, only at the moment 

 when the plug is withdrawn or replaced. It may be p. 



