THE HORSE, ITS DISEASES. 407 



certain manifestations in one horse will produce different ones in another, 

 so that it may be readily inferred that the varying symptoms do not mark 

 different types of disease but mere difference of degrees ; and that the 

 jBame general causes act throughout. 



The immediate cause is clearly pressure on the brain, resulting from 

 unusual flow of blood to the head. This is doubtless in some instance* 

 the result of a constitutional tendency — a predisposition to epilepsy — . 

 that is brought to manifest itself on occasion of excitement, over-exertion, 

 or geiieral ill condition of the digestive apparatus. In others it is most 

 probably a watery suffusion of the brain — the blood being subjected to 

 some sort of decomposition in its passage through the head and leaving 

 the serum or watery portion to collect there. 



The brain requires a proportionately far greater amount of blood than 

 any other organ ; but while ample means are provided for supplying it, 

 nature guards against doing this with that velocity which would endanger 

 it by overloading and rupturing. The arteries make their way through 

 the head in a peculiarly circuitous manner, and they enter through minute 

 bony holes that will not admit of much distension. When the horse is 

 overheated, however, or when the return of the blood is impeded, this 

 fullness takes place. In great heat the arterial passages are enlarged to 

 their utmost capacity, and the rapidity with which the now uncommonly 

 heated and the thinner fluid makes its way into the brain is not counter- 

 balanced by a similarly rapid return, and the effect is produced to which 

 the various names referred to have been given. Impeded return of the 

 blood from the extremities, through the veins, is caused by a tight collar, 

 pressing, during the act of pulling, upon the large or jugular vein, on 

 one or both sides of the neck ; by a tight throat latch, producing a similar 

 compression of the jugular ; or by a check-rein drawn so short as to 

 brines down the head, and bend the neck to the extent of crowdino; its 

 parts together and interfering with the circulation. By this compression, 

 though the blood may not be forced to any undue arterial activity, the 

 large veins will be too long distended by reason of the sluggishness of 

 return, and the small veins running through the substance of the brain 

 will be so increased as to press upon the nerves at their points of origin 

 and produce loss of power and of consciousness. 



The immediate cause, or pressure upon the brain, is doubtless some- 

 times to be found in tumors, arising from blows on the head, as well as 

 in congestion, or too great fullness. 



Other remote causes besides those already named may be found in a 

 diseased stomach and intestines. Inflammation of all the organs of 

 digestion and secretion may be brought on by the retention of great 

 masses of indigestible food, and this clogged state superinduces conges- 



