Definition. Causes: presence of sclerostoma in arteries, form, habit, nature, immature, biology, life in bowel, in submucosa, in arteries, outside the mammal, pathogenesis, blood-sucking, verminous cysts, verminous aneurisms, seats of latter, coagula, embolism, stagnation of blood, œdema and thickening of intestine, mesentery, fermentations, tympany, infective inflammations, blood extravasations, infection of liver and spleen. Symptoms: sudden attack, violent colics, reckless movements, frequent defecation followed by its arrest, palsy of peristaltic movement, of pain, prostration. Course: two to twenty-four hours, death from indigestion, tympany, obstruction, hemorrhage, poisoning, recovery, sequelæ, laminitis, intestinal catarrh or atony, debility. Treatment: aneurism worms beyond reach, treat lesions, venesection, anodynes, stimulants of peristalsis, antiseptics, compresses, sinapisms. Prevention: expel intestinal worms, exclude embryos, tartar emetic, iron sulphate, arsenic, phenol, pure water, occasional vermifuges. _Definition._ Congestion and spasms of the intestines in connection with blocking (thrombus or embolism) of the mesenteric arteries, and verminous aneurism. _Causes._ The essential cause is the migration of the sclerostoma equinum (strongylus armatus, Rud.) into the mesenteric arteries in its agamous condition. It seems appropriate therefore to here notice the life history of this parasite. The =sclerostoma equinum= (_strongylus armatus_) is one of the common pin worms of the horse. It is distinguished by its dull gray or reddish brown body, thickest at the cephalic end and tapering off toward the caudal, but ending in a blunt point; by the round, open mouth furnished with several firm chitinous rings, of which the _outer_ bears six short symmetrically arranged papillæ, an _intermediate_ row of rounded blunt tooth-like projections, and the _innermost_ a row of fine, closely aggregated and very sharply pointed teeth for penetration of the mucosa. Male ¾ to 1½ inches long, with caudal membranous alæ in two lateral lobes, joined by a rudimentary central lobe: two delicate spicula. Female ¾ to 2 inches long, blunt pointed tail, vulva in posterior half of the body. Eggs ovoid with slightly raised ring around the centre: oviparous. _Habitats._ They are found in solipeds in two stages of existence, the _mature worms_ in the cæcum and colon, and the _immature_ in the same organs encapsuled in little pellets of manure, and in cysts in the mucosa but also apart in the arterial system especially in the anterior mesenteric artery and other gastric or intestinal trunks.