DISEASES OF THE BRAIN. 301 



associated with general plethora, or with any interference 

 with the general arterial or capillary circulation. 



Megrims occurring in harness or draught-horses, except 

 when due to organic cerebral disease, is almost always due 

 to mechanical impediment to the flow of the blood from the 

 brain, occasioned by the pressure of too tightly or badly 

 fitting harness. 



By some megrims is believed to be due to inflammatory 

 action, but there does not appear to be any grounds for this 

 supposition. 



It is said also that megrims may be produced by ex- 

 posure to the rays of the sun, or by driving fast after a 

 heavy meal. 



These causes certainly may increase the tendency to this 

 aff'ection, but it is very improbable that they alone can 

 cause it. As already pointed out, however, indigestion is liable 

 to be caused by fast driving after heavy meals, and may 

 induce vertiginous symptoms, which might easily be con- 

 fused with megrims depending upon actual congestion. 



Symptoms. — There are generally no premonitory sym- 

 ptoms, the attack being sudden in its onset. 



The animal slackens its speed, or stops suddenly, and 

 moves its head from side to side or up and down. Some- 

 times its head is turned to one side. 



The vessels of the face and throat are engorged, the eyes 

 stare, the nostrils are dilated, and the breathing is rapid. 

 The skin may be bedewed with perspiration, and the 

 cervical and facial muscles twitch convulsively. 



If the collar causing the obstruction be removed, the 

 symptoms abate, and the animal soon recovers. 



When the symptoms are very severe, there is great 

 excitement, the convulsions become still more severe, and 

 the animal falls prostrate to the ground. 



Morbid Anatomy. — The brain is found congested. 



