Pathogenesis. In the larger arteries (aorta, radical stump of the mesenteric artery) clots (as from strangles) rarely produce dangerous obstruction. In the smaller vessels stenosis is complete and anæmia and gangrene are liable to occur unless the blood supply is partially maintained by anastomotic vessels. When the embolism affects a number of smaller arteries or capillaries in a vascular organ like the lungs, the blood filters in from the adjacent capillaries, in which circulation is still carried on, and this passes through the softened and ruptured capillary walls so that the tissue is charged with globules and constitutes a black infarction. In the lung this usually affects one or several lobulettes, forming a pear shaped mass corresponding to the distribution of the obstructed vessel. The cut surface is black, compact and granular. The lymph thrown out around it forms an organized fibrous sac, and the unclosed sequestrum undergoes a slow necrobiosis, blanching and liquefaction into a pus-like fluid which is removed by absorption. Such results are met with in the parenchymatous organs (lungs, liver, spleen, kidneys, etc.) and less frequently in the limbs. The symptoms will correspond to the particular organ invaded.
In the fore or hind limbs the result is usually less radical. The vessels below the obstructed trunk are connected more or less freely by anastomosing branches, so that the circulation in the tissues below, though somewhat restricted, remains active enough to sustain a fair measure of nutrition. Apart from the suffering, attendant on the preliminary inflammation, the morbid phenomena are largely confined to the absence of pulsation in the lower part of the limb and the inability of the muscles to sustain active contraction.
Chronic Embolism of the External Iliac or Femoral Artery. In this condition the pulsations in the digital arteries are imperceptible, if it has been of long standing there may be obvious atrophy of the muscles of the thigh, but when standing quietly or walking there is usually no lameness. In continuous rapid walking and above all in the trot, however, he soon begins to halt on the affected limb, and this rapidly increases, the joints bending under his weight, the toe dragging and the animal threatening to drop altogether. If stopped and allowed to rest for ten or fifteen minutes he gradually recovers and may be led quietly back to his stable without a sign of lameness. But if again trotted fifty or one hundred paces the lameness develops anew and disappears in the same way when left at rest. The circulation in the muscles is enough for a moderate nutrition but altogether inadequate to sustain active work.
Chronic Embolism of the Internal Iliac Artery. In this case the control of the muscles of the limb may be perfect but there is some indication of paresis of tail, bladder, rectum and anus. Impaction of the rectum is liable to occur. By examination through the rectum the pulsations are felt to be strong in the aorta and external iliac, but imperceptible in the internal iliac blocked by the embolus.
Chronic Embolism of the Axillary Artery. Here there are the same general symptoms, the absence of the radial and digital pulsations, the wasting of the muscles of the forearm, and the intermittent lameness, developed rapidly by exercise and recovering promptly under rest.
Acute Embolism of the Mesenteric Arteries. This will be fully treated under the title of verminous colic in solipedes. The blocking of the branches, usually of the anterior mesenteric artery, leads to derangement of the innervation, congestions, spasms, involutions and other disorders. The presence of the strongyli in the fæces, the general symptoms of intestinal worms, and the recurrence of the indigestions and spasms would serve to indicate the nature of the complaint.
Treatment of Chronic Embolism. As affecting the arteries of the limbs the repair must be largely left to nature, and we must place the patient in condition, favorable to such repair. Except in the early stages absolute rest is not necessary. Gentle exercise stimulating to a freer circulation solicits a slow enlargement of the anastomosing vessels (arterial or capillary), and when this has reached a given stage, weak pulsations may again be felt in the vessels beyond and the muscles will once more stand moderate work without lameness. Alkalies and iodide of potassium may be given to solicit solution of the clot, but this can rarely be counted on to the extent of rendering the vessel once more pervious. A small paddock in which the patient can move around quietly is desirable, and in a few months a tolerable recovery may have taken place.
Embolism in other organs must be treated on the same general expectant method, and a considerable time is usually necessary to secure a fair recovery.
ANEURISM.
Definition. Divisions, true, false, dissecting, arterio-venous, mixed, traumatic, spontaneous. Causes, violence, rupture, debilitated vascular walls, strains, stretching, force of blood current, overloaded intestine, strongyli, contiguous inflammation, embolism, microbian invasion of the walls, arteritis, concussion. Symptoms, soft tumor pulsating with the heart, a double rushing sound, diagnosis from abscess, nervous disorders through pressure, cramps, palpitations. Treatment, when desirable, rest, moderate, laxative diet, iodides, bromides, icebags, compression, ligature, galvano-puncture, wire coils, injections.