408 HEALTH AND DISEASE 



slight, and probably attracts very little attention; the driver may notice 

 that the horse occasionally shakes his head, or turns it to one side as though 

 he were annoyed by something which had entered the ear; after a short 

 time the animal ceases to behave strangely, and finishes the journey with- 

 out any further indication of disturbance. Nothing more may be thought 

 of the matter until the recurrence of the attack after the lapse of a week or 



Fig. 178. — Vertigo or Megrims 



more, and even then no suspicion of megrims is probably excited until 

 a more severe attack occurs. 



Post-mortem examinations have been made of horses which have 

 suffered from chronic vertigo, the fits occurring at intervals of a few weeks 

 or months during several years of the animals' lives. The results of 

 such examinations were in some cases unsatisfactory; in others calcareous 

 nodules and tumours, varying in size from a pin's head to a pigeon's egg 

 or larger, have been found in the plexus of vessels in the lateral ventricles 

 of the brain. Frequently, however, the search for morbid appearances in 

 the brain and spinal cord has been attended with disappointment. 



Attacks of vertigo may sometimes happen in consequence of injury 

 to the head; a blow accidentally or intentionally inflicted may produce 



