HYPEREMIA OF THE BRAIN 435 



by mental disturbances, the brain may be regarded as 

 being the seat of the lesion. If, on the other hand, no 

 mental disturbances are noted, it is assumed that the lesion 

 is in the cord. Further, the portion of the animal affected 

 will often point to the origin of the disturbance. Hemi- 

 plegia, or paralysis of one-half of the body, and monoplegia, 

 paralysis of a single organ or part, indicate that the disturb- 

 ance is of cerebral origin, while paraplegia, a paralysis of a 

 portion of both sides, indicates spinal paralysis. 



HYPEREMIA OF THE BRAIN. 



Congestion of the Brain. 



Definition.— Hyperemia is a condition in which there is 

 an engorgement of the vessels of the brain. The engorge- 

 ment may be active or passive. 



Etiology.— Active hyperemia, or congestion of the brain, 

 may be caused by anything which affects the cerebral 

 arterial circulation. Violent exercise, excitement, espe- 

 cially in young animals, blows and concussion on the head, 

 are causes. It may accompany eruption of the permanent 

 teeth, or abnormal heart action as in hypertrophy of the left 

 ventricle. Excessive heat, as direct sunlight upon the head 

 in hot weather, will also produce active hyperemia. 



Infective hyperemia of the brain appears secondarily to 

 some of the infectious diseases, the most common being 

 rabies and distemper. 



Passive Hyperemia. — The causes of passive hyperemia of 

 the brain are chiefly mechanical, and may be anything 

 which impedes the outflow of the blood from the brain. 

 Tight collars will compress the jugular veins and produce 

 it. Tumors and enlarged thyroid glands (goiter), valvular 

 insufficiency of the left heart, chronic diseases of the lungs 

 as interstitial pneumonia, may produce a passive hyperemia. 



Pathology.— In severe hyperemia of the brain, the dura 

 mater or outer covering will be found injected and in cases 

 of long standing may be adherent to the bones of the cranial 

 cavity. The pia mater or inner membrane is hyperemic 

 and the bloodvessels engorged. The gray matter varies 



