CALCULI. 



437 



give rise to intestinal concretions, which are hardly ever found 

 among animals Avhose food is carefully looked after. 



An oat-hair concretion would appear to result chiefly from the 

 mechanical adhesion of undigested particles of food to the moist 

 covering of a nucleus whose presence on the mucous membrane had 

 caused a certain amount of irritation. The formation of a mixed 

 calculus- would probably be effected both by chemical and me- 

 chanical agencies. 



An unhealthy condition of the intestines is not seen as a rule at 

 post-mortem examinations of horses affected with calculus, and, 

 therefore, it cannot be regarded as a cause of this complaint. 



SYMPTOMS. — There is no characteristic symptom by which to 

 tell the presence of a calculus in the digestive canal ; although 

 there are several common to the disturbance brought about by it. 



Fig. 144. — Dust ball. 



and to other disorders. The only certain means — which is not always 

 within our power to put in practice — to determine the existence 

 of such a body in the abdomen, is feeling it, which we can generally 

 best do by introducing the hand into the rectum. These balls may 

 attain a large size without causing death, or even without giving 

 rise to any marked symptoms of ill-health, in which case it may be 

 inferred that they continue to remain in some portion of the intes- 

 tine, where, owing to the. large diameter of the gut, or to the fact 

 of their having made for themselves a pocket in it, they do not 

 cause obstruction to the passage of food, until they become greatly 

 increased in bulk. If, however, they happen to become dislodged, 

 as for instance, by the action of a purgative, they may, very pos- 

 sibly, set up fatal obstruction by getting wedged in some narrower 

 portion of the large intestine, which varies greatly in size along its 

 course. It appears that calculi cause colic far more frequently by 

 the fact of their shifting, than by their being large. The ordinary 

 (though by no means characteristic) symptoms of the presence of 



