PBELIMINABT EEMAEKS. 373 



It is by means of the brain and its nerves, the spinal cord 

 and its nerves, and the sympathetic system, that the relations 

 I have stated are maintained. 



The sympathetic nervous system is distributed to the heart, 

 and to the blood vessels throughout the body ; and also to 

 those various organs, the aggregate of which constitutes what 

 is called the organic sphere of the animal's body. 



The brain and its nerves, and the spinal cord and its nerves, 

 preside over the sensational and locomotive spheres of the 

 animal ; while, in addition, the two systems exchange filaments 

 with each other, and thus the whole is balanced in every part 

 in a manner which cannot fail but excite the wonder and admi- 

 ration of every beholder. 



The diseases and derangements of the braiu, the spinal cord, 

 and the nerves thence proceeding, I have alone to treat upon 

 in the present section. 



The nervous structures of the horse do not manifest such a 

 numerous class of diseases as those which affect the correspond- 

 ing class of structures of the human being ; nevertheless, those 

 which have been observed in the former are closely similar, 

 both iu the mode by which they invade the system and in their 

 general course and terminations. 



The blood vessels of the membranes investing the brain and 

 the spinal cord are prone to congestion, and to the effusion of 

 serum amid their tissues. 



The- substance of the brain and the spinal cord are prone to 

 softening and to other changes within their tissues, which are 

 the immediate causes of certaia forms of disease, some of which 

 are of a violent and dreadful character. 



Injuries of a direct character inflicted upon the spinal cord 

 may destroy aU voluntary power in two or more of the limbs ; 

 or a similar effect may result to a single limb, or a single muscle 

 of a limb. 



