474 HEALTH AND DISEASE 



which will excite inflammation in the vessel wall or diminish its vitality 

 may determine the coagulation of blood within it. It is also a consequence 

 of degenerative changes in the structure of the vessel, and of arrest of the 

 circulation from aneurism (fig. 196), or any other cause which induces the 

 blood to stagnate. 



ILIAC THROMBOSIS 



The most notable example of thrombosis in the horse is that which is 

 seen now and again in the iliac arteries the vessels into which the abdom- 

 inal aorta breaks up beneath the lumbar spine, and whose branches are 

 distributed to the hind-quarters and extremities. 



Causes. For the most part thrombosis of the iliac vessels is the result 

 of sprain inflicted upon them by some violent backward stretching of the 

 hind-limbs, such as would result when a horse falls short in jumping and 

 slips down the bank of a drain, or when his legs fly back from under him, 

 or " spread-eagle", while drawing a heavy load over a slippery surface, or 

 out of deep heavy ground. The writer has also known it to be occasioned 

 in the course of the struggles of a horse while cast in a railway box, and 

 in another instance the disease followed upon a hunter being " hung up" 

 across a gate. In all these positions there would be sudden and severe 

 stretching of the vessels and injury to their coats. 



Symptoms. The symptoms of iliac thrombosis will vary with the 

 stage of the disease, but, when well established, they are very diagnostic. 

 At first the patient displays slight stiffness of one or both hind-limbs, more 

 especially on rising from the recumbent posture, or when first led out of 

 the stable. This, however, will pass away with a little exercise, to re- 

 appear again from time to time in a more and more marked form. It may 

 be accompanied by slight swelling of the limbs. As the arteries become 

 more and more blocked, and the circulation obstructed, the legs are found 

 to be cold, and the large veins are distended. This distension of the veins 

 results from the absence of force to move on the blood within them, con- 

 sequent upon the blocking up of the arteries, and is most strikingly seen 

 during rest. When the animal is made to move, the blood disappears from 

 the veins, and returns but slowly. The horse's movements are observed 

 to be somewhat unsteady behind, especially during work. In the more 

 advanced stages of the disease exertion brings on a rolling gait behind, 

 and, if continued, results in paralysis of the posterior part of the body, 

 At this time the animal breaks out into a profuse perspiration, the 

 breathing is hurried, the muscles quiver, and the pulse is much acceler- 

 ated. In some cases the affected animal strikes the belly, looks round 

 to the flank, and shows signs of acute pain, as if the subject of colic. 



