244 PHYSIOLOGY OF MUSCLES AND NERVES. 



CHAPTER XV. 



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

 individual muscle-fibres; 3. Discharge-hypothesis; 4. Principle 

 of the dispersion of forces ; 5. Independent irritability of muscle- 

 substance ; G. Curare; 7. Chemical irri'ants; 8. Theory of the 

 activity of the nerves. 



1. In the foregoing chapters we have examined the 

 characters of muscles and nerves separately. The 

 muscle is distinguished by its power of shortening and 

 thereby accomplishing work. The nerve has not this 

 power : it is only able to incite the muscle to activity. 

 We must now inquire how this incitement, this trans- 

 ference of activity from the nerves to the muscles, 

 occurs. 



To understand the action of a machine, of any piece 

 of mechanism, it is necessary to learn its structure and 

 the relative positions of its separate parts. In our case, 

 microscopic observation can alone afford the explana- 

 tion. If we trace the course of the nerve within the 

 muscle, we iind that the separate fibres, which enter 

 the muscle in a connected bundle, separate, run among 

 the muscle-fibres, and spread throughout the muscle. 

 It then appears that the single nerve-fibres divide, and 

 this explains the fact that each muscle-fibre is eventu- 

 ally provided with a nerve-fibre — long nerve-fibres even 

 with two— although the number of nerve-fibres which 

 enter the muscle is generally much less than the 



