DISEASES OF THE NERVOUS SYSTE>r. 501 



intiinsic epilepsy has sometimes given way to the salts of silver, 

 zhic, or iron. 



CHOREA. 



Definition. — A serious of automatic muscular movements, 

 rarely seen except in the dog ; clonic spasms, sometimes affect- 

 ing the muscles of the face only, but generally involving those 

 of the head, neck, and fore extremities ; due to alterations in the 

 spinal cord, or to disease of the facial nerve when affecting 

 the face only. 



The pathological conditions which give origin to the peculiar 

 twitching or comailsive action of the muscles, characteristic of 

 chorea or St. Vitus' dance, are not exactly determined, many 

 pathologists who have investigated cases of the disease having 

 failed to detect any definite morbid appearances. Consequently 

 it has been regarded as an entirely functional disease, or as a 

 disease due to an altered condition of the blood, the precise 

 nature of such alteration not being known, and also as a symp- 

 tom of some diseases of the heart. 



In the dog, it may with good reason be said to be first due to 

 an altered condition of the blood, generally brought about by, 

 or giving origin to, the disease called distemper, of which it is 

 so often a distinguishing feature ; whilst in the horse, spasmodic 

 contractions of the thoracic and cervical muscles, of the nature 

 of chorea, are often associated with cardiac diseases of a 

 rheumatic type. 



Si/vijjfonis in the Bog. — The convulsions may be confined to 

 one fore leg or shoulder, of which there is a peculiar jerking 

 action, like a series of pulsations. At other times both fore 

 legs are affected, when there is a nodding or depressing of 

 the head and neck. In many cases it is restricted to a constant 

 jerking of the head and lower jaw, with marked twitchings of 

 the superior cervical muscles ; the muscles of the eyelids, and 

 sometimes the muscles of the eye itself, are also affected. The con- 

 vulsions do not cease whilst the animal is lying down, but they 

 generally, although not uniformly, cease during sleep. In some 

 cases the dog will remain otherwise healthy for an indefinite 

 period ; but if the chorea attacks it whilst in a debilitated 

 state, the expenditure of muscular action, and the general rest- 

 lessness, slowly undermine the remaining strength ; the dog 

 l.iecomes emaciated, subject to fits, and finally paralysis and 

 death supervene- 



