CALCULI. 435 



though they may, in exceptional oases, be as heavy as 16 lbs., or 

 even more. The term " calculus " {calx, chalk) should, correctly 

 speaking, be restricted to this variety ; and the other two might 

 be called " concretions." When a phosphatic calculus is found in 

 the stomach, we may feel certain that it has been passed into that 

 organ from the intestines ; because the acid nature of the gastric 

 juice would prevent its formation in the stomach. (2) Oat-hair 

 calculi or dust-balls (Fig. 144:), which are formed of closely packed, 

 undigested vegetable matter. (3) Mixed calculi, which are made 

 up of earthy and vegetable constituents. 



Phosphatic calculi seem invariably to have been formed round 

 some indigestible object, such as a piece of metal or fragment of 

 stone which acts as a nucleus. Although not so apparent as in 



Fig. 143 — Phosphatic calculus. 



the phosphatic kind, it is probable that a nucleus generally exists 

 in dust-balls and mixed calculi. 



CAUSES.^ — ^Experience amply proves that the presence, in the 

 horse's food, of indigestible particles, especially if they be of an 

 irritating nature, is a fertile cause of calculus. The frequency of 

 this complaint in the stables of many large firms, has been greatly 

 diminished by the adoption of means for the removal of such pos- 

 sible nuclei. One of the best preventives is the use of an auto- 

 matic separator provided with magnets, which attract and thus 

 remove all particles of iron and steel from the corn passed over 

 them. In small stables, the careful use of a sieve is imperative. 

 In foreign corn, among other sources of danger, are to be found 

 great numbers of nails and heads of nails employed to tack down 

 the canvas that lines the holds of vessels which carry corn in bulk. 



28* 



