438 DISEASES OF DIGESTION. 



calculi or dust-balls (Fig. Hi), 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 

 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 natm'e, 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. 

 Mr. llogerson has pointed out that in foreign corn, among other 

 sources of danger, are to be found great numbers of nails and 

 heads of nails which are employed to tack down the canvas that 

 lines the holds of vessels which carry corn in bulk. We may 

 surmise that the presence of such an object set up, in the first 

 instance, irritation of the mucous membrane of the bowel, with 

 the result of its becoming surrounded with mucus, to which other 

 undigested objects, passing by, would be liable to adhere. Or the 

 irritation might cause the precipitation from the dissolved food 

 of earthy salts. I think we may safely say that the tendency to 

 calculus depends on the fact of indigestible and irritating sub- 

 stances being taken into the stomach. Mr. Hunting mentions 

 that the indiarubber ring of a mineral water bottle formed the 

 nucleus of a calculus which he examined on one occasion. 



I have shown in " Stable Management and Exercise " that dry 

 bran is an admirable food for horses, and that it is much more 

 digestible than oats. I have already said that wet bran (bran 

 mash) is more a medicine (a laxative) than a food. 



From an examination of a phosphatic calculus, we cannot help 

 being struck by the fact that the deposition of its earthy con- 

 stituents must have taken place from a fluid which had held them 

 in solution. We may therefore regard consumption of food rich 

 in phosphates (like bran and maize) to be a predisposing, though 

 not an exciting cause. Another predisposing cause might be a 

 condition of the digestion, in which these earthy salts would be 

 more liable to be deposited from the alimentary fluid, than in a 

 state of health. 



