NERVE TERMINALS. 513 



That contraction follows in all four cases, with medium stimu- 

 lation, is explained by assuming that the depression of the func- 

 tional activity of the nerve is not sufficient to affect its conduct- 

 ivity. 



The want of response to a making shock, in the case of the 

 strong descending current, depends upon the fact that the part 

 of the nerve near the muscle, around the anode, is in a state of 

 lowered activity, and is, therefore, unable to conduct the impulse 

 which has to pass through this region from the cathode, where 

 the stimulation takes place, in order to reach the muscle. 



The absence of contraction at the breaking of a strong descend- 

 ing current, is caused by the same lowering of the conductivity 

 of the nerve between the point of stimulation and the muscle, 

 because at the cessation of strong catelectrotonus, the region near 

 the cathode rebounds from exalted to depressed activity, and at 

 the moment of stimulation the greater part of the intrapolar 

 region is an electrotonic. 



The specific use of nerve fibres in the body of the higher 

 animals may be thus briefly stated. They form a means of 

 extremely rapid intercommunication between distant parts. The 

 protoplasm of the axis cylinder has undergone a special modifi- 

 cation, by which it is enabled to conduct impulses much more 

 quickly than ordinary protoplasm does. Even the most nearly- 

 related substance, muscle tissue, transmits impulses about thirty 

 times more slowly than a nerve fibre. A highly organized animal 

 body, without nerve fibres, would be in a worse condition than 

 a highly organized state without a telegraph or even a postal 

 system. 



NERVE CORPUSCLES OR TERMINALS. 



These are the real actors in the nervous operations, while the 

 fibres are merely their means of communicating with one another. 

 One great set of terminals is placed on the surface of the body, 

 and is adapted to the reception of the various external influences 

 which are brought to bear on it from without by its surroundings. 

 These receivers of extrinsic stimuli are necessarily much varied 

 so as to be capable of appreciating all the different kinds of stim- 

 ulation presented to them. They are either distributed over the 



