CHAPTEE HI. 



GENERAL PROPERTIES OF THE NERVES. 



Nervous irritability Different means employed for exciting the nerves Disap- 

 pearance of the irritability of the motor and sensory nerves after exsection . 

 Nerve-force Non-identity of nerve-force with electricity Rapidity of 

 nervous conduction Estimation of the duration of acts involving the nerve- 

 centres Action of electricity upon the nerves Contrasted action of the 

 direct and the inverse current on closing and opening the circuit Voltaic 

 alternations Induced muscular contraction Galvanic current from the 

 exterior to the cut surface of a nerve Effects of a constant galvanic cur- 

 rent upon the nervous irritability Electrotonus, anelectrotonus, and cathe- 

 lectrotonus Neutral point Negative variation. 



experiments have been made, especially upon 

 the cerebro-spinal nerves, with regard to their action under 

 different kinds of stimulation, the probable nature of the 

 nervous agent, or nerve-force, the extent and duration of 

 their excitability and sensibility, etc., which have developed 

 facts of more or less physiological interest and importance. 

 As far as the nerves of general sensibility are concerned, the 

 phenomena of conduction of impressions are essentially the 

 same in all, if we except certain variations in different 

 nerves as regards the degree of sensibility. The motor 

 nerves all respond in the same manner to stimulation ; and 

 it is upon this portion of the nervous system that the most 

 important observations have been made. This being the 

 case, it is evident that the cerebro-spinal nerves, in their 

 behavior under the experimental conditions above enumer- 

 ated, possess certain general properties, and that the functions 

 of special nerves are to be studied, after a full consideration 



