OF FUNCTION ; OK, HOW WE ACT. 27 



The views recently proposed by Pfliiger, in refer- 

 ence to the effects of electricity applied to the nerves, 

 are strikingly in harmony with this general idea. 

 He finds all the phenomena best explained by the 

 conception of a tension-force and a controlling force 

 as existing within the nerve, the balance of which 

 the electrical agencies variously disturb. 



If we pass from the nervous to the muscular 

 system, we find abundant confirmation of our posi- 

 tion. Of the means by which the decomposition of 

 the muscle causes its contraction in length, and so 

 results in motion, there is as yet no certain know- 

 ledge ; but chemical action is one of the best known 

 sources of motor force, and one of the most frequently 

 employed. The flight of a bullet and the motion of 

 the arm are phenomena of a similar kind. The ap- 

 pearances presented by muscles during contraction 

 have been carefully observed. All muscles consist 

 of fibres, of which 10,000 on an average would about 

 occupy an inch. Each fibre runs the whole length of 

 the muscle, and is connected with the tendons in which 

 almost all muscles commence and terminate. These 

 fibres are of two kinds, simple in the involuntary 



