DISEASES OF THE NERVOUS SYSTEI\r. L'83 



CONVULSIONS AND SPASMS. 



The term convulsion, in its most extended sense, indicates 

 any spasmodic contraction beyond the control of the animal. 



Convulsions may affect a single muscle, or a group of 

 muscles, a limb, or the whole or one half of the body. 



They vary in intensity, from a mere ' tremor' or ^trem- 

 bling ' of a single muscle to the most violent contortions of 

 the whole body. 



Convulsions may be considered under three groups : 



1. Tremors. — Tremors may accompany voluntary move- 

 ments, or may occur independently. The tremors from cold 

 or mercurial poisons are good examples of the latter. 



2. Choreic Movements. — The disease termed chorea 

 furnishes the most typical example of this kind of convul- 

 sion. Choreic movements are characterized mainly by their 

 abruptness and irregularity, and by the fact that when 

 engrafted on any voluntary movement, they interrupt its 

 progress by a series of contractions which are not then 

 necessarily limited to the limb or organ which is making 

 the effort (Bristow). 



3. True Convulsions. — They may arise from direct irri- 

 tation of the nerve-centres, and also from irritation in 

 remote parts. 



Convulsions are clonic or tonic. 



Clonic convulsions are intermittent and irregular, and 

 those occurring in epilepsy will serve as an example. Tonic 

 spasm consists in more or less sudden muscular contraction, 

 and is exemplified in tetanus and strychnia poisoning. 



MOTOR PARALYSIS— PARESIS. 



By paralysis is meant the impairment of that power which 

 the various motor centres normally exercise over the move- 

 ments of the muscles. 



