120 PlIY.SlMl.'H.y OF MUSCLI> AM> NEBVES. 



bility at the \ari. -us points of t he nerve is cou.-eciit i\ , 1 v 

 determined in tin- way described above, it is generally 

 found tliat tlir r\ritaliility of the upper j art of the 

 nerve is greater tliaii that of the lower. Ihnv is. how- 

 ever, no great ivniilant y in this charact <T. Sometime- a 

 point is found in the centre of the nerve which is Irss 

 irritalilr. than those immediately above and below it. 

 Vn-y fVr(|iirntly the most excitable point occurs, not 

 immediately at the cut end, but at some little distance 

 from this; so that, on proceeding downward, it is found 

 to increase at tirst, and then, at a yet ]o\\n- point, to 

 decrease again. If such a nerve is observed for some 

 little Him-, its excitability at the various points being 

 tested every five min ut es. it is found that the excita- 

 bility alters especially soon at the upper end : it de- 

 creases, and in a short time is entirely extinguished, so 

 that no muscular pulsations can afterwards he elicited 

 from the, upper parts even by the most powerful 

 currents. The nerve is then said to be dead in its 

 upper parts, and this death proceeds gradually down- 

 ward in the nerve, so that pulsations can only be 

 obtained by irritating tin- p.-m >itna!rd nr.-n-est the 

 muscle, and at a little later period even this part, 

 lircoino dead. After the \\holr nn-\r is drad, pul- 

 sations may yet always be olitained ibr a timr bv 

 direct irritation of thr muscle. The mnscU- dors not, 

 usually die until much later than the nervo Yet in a 

 (|iiite fresh preparation of the nerve and mn>i-|r. t he 

 Latter i- always less ex-italile than the former, and 

 a much stiMii^er irritant is required to excite the 

 mii-elr diri'ctly, than indirectly through the n.-rve. 



In all these experiments the oerve must lie ca re- 

 full \ protected from drying up, a> oilurwise ilsexcita- 



