244 I'HYSIOLOGY OF MIM I.i'..S AND NF.KVKS. 



CHAPTER XV. 



1. Connection of IHTVC and muscle; 2. Isolated excitement of 

 individual muscle-fibres; I!. Discharge-hypothesis; 4. Principle 

 of the dispersion of forces; 5. Ind<-| cndrnt irritability of muscle- 

 Mil'Stancr ; <'.. Curare; 7. Clu-mira! irri'ants ; S. Theory of tlie 

 activity >!' the n< r\ s, 



1. Ill till' foregoing chapters We have examined the 



characters of muscles and nerves separately. Tin- 

 muscle is distiiiiMiislird l>y its jiowcr of shortening ami 

 thereby accomplishing work. The nerve 1ms imt this 

 power: it is only able t<> incite the nmscle to activity. 

 We must now inquire how this incitement, this trans- 

 fnvnct' of activity from the nerves <,> tli,. mu c 1 -. 

 occurs. 



To understand tin act j.ni of a machine, of any piece 

 of mechanism, it is necessary to learn its structure and 

 the relative positions of ite separate parts. In our ca-. . 

 microscopic observation can alone aH'>rd the explana- 

 tion. If we (rare the course of the nerve within the 

 mu-cle, we tind that the separate til >re<, which enter 

 the inii-i-le in a c.iniieeted luiiidle, separate, run among 

 the muscle-fibres, and sjiread throughout the muscle. 

 It then appear- t hat the single nerve-fibres divide, and 



this explains the fact that each mn>-h-iil>re is eventu- 

 ally pro\ id. d wit h ;' ner\e-lilire IMH- ne,-\-e-til.res . ven 

 \\ilh two although the numlier of nerve-libres which 

 tin muscle is generally much less than the 



