WOKM-ANEUEISMS. 



131 



so complete, the conditions produced naturally differ ; but even when 

 less serious, they often become fatal to the host through long con- 

 tinuance. 



Perhaps it is well at this stage to note the so-called " worm-aneur- 

 isms," which are of such frequent occurrence in the mesenteric arteries 

 (especially the anterior) of the horse 

 that they can hardly be sought for 

 in vain (according to Bollinger, only 

 in 6 to 10 per cent.). There can 

 be no doubt that these formations 

 are caused by the parasitism of 

 Strmigylus s. Sderostomum eqiiinum, 

 which, when quite small (p. 64), 

 enters the intestinal canal of the 

 horse from outside, but soon migrates 

 thence into the circulatory system, 

 and there gives rise to the formation 

 of aneurismal sacs. The manner 

 in which these aneurisms (Fig. 79) 

 are gradually developed cannot be 

 determined in the absence of the 

 necessary data, but the general sup- 

 position is, that as soon as the worms 

 reach the blood-vessels, they begin 

 to bore into the arterial coats, 

 and thereby cause a swelling and 



loosening of the walls, so that the lumen of the vessel is con- 

 stricted, and the aneurismal enlargement produced. ^ It is true that 

 afterwards the worms, which have now attained a length of 18 mm., 

 are found chiefly among the masses of albumen in the aneurismal 

 sac, but this situation is probably a secondary one. In some cases 

 new aneurisms are formed in other parts by the wandering thither of 

 the larger worms. That the existence of these aneurisms must 

 often be followed by other diseases is very evident, from the fact that 

 the anterior mesenteric artery in which they are usually situated is 

 the source of blood for a long portion of the intestine, not less 

 than 26 to 27 metres in length. It has indeed been proved by the 

 researches of Bollinger^ that the so-called colic of horses, which is 



• The Bupposition that the worms give rise to the aneurisms by means of their oral 

 armature, rests upon complete ignorance of the circumstances of the case, since this oral 

 armature is developed only shortly before the arrival of the parasites in the intestine — 

 that is to say, when the pathological changes of the artery have long before been com- 

 pleted. See Vol. II. 



= Bollinger, "Die Kolil^^,-^|g^jP,'j,^g^O^0, 



Fig. 79. — Worm aneurism of the hors^. 



