300 HEALTH AND DISEASE 



It is generally believed by veterinarians that horses in the possession 

 of millers and bakers are more frequently the subjects of these formations 

 than those employed by other persons. Various reasons have been 

 rendered for this exceptional liability to stone formation. While some 

 attribute it to largely feeding on bran and other offal, others find an 

 explanation in the presence of grit in the sweepings of the mill and 

 bakehouse which the horses of these traders are said to receive. Before 

 special machinery came into use for the removal of foreign matters from 

 hay and chaff a considerable mortality from this cause prevailed in the 

 studs of railway companies, contractors, and other large proprietors. 



Where this cleansing process is not adopted obstruction of the bowels 

 by calculi is still a common occurrence. 



CONCRETIONS 



These formations differ from calculi in the fact that they are made 



up of masses of vegetable and earthy matter agglomerated together, while 



the latter consist exclusively of salts which 



have crystallized out of the fluids of the 



bowels around a central nucleus. 



Concretions, like calculi, are rounded in 

 form, but vary in composition, and also in 

 their structure and external character. 



Two kinds of concretions are found in 

 the horse, known as mixed concretions or 

 dung balls, and oat-hair concretions. The 

 former are composed of earthy - looking 

 masses of salts, such as go to make in- 

 xed or conglomerate calculus testiiial calculi, loosely incorporated with 

 materials of food — hay, straw, dung, the 

 husk of oats, &c. &c. Mixed concretions (fig. 109) have an irregular, 

 nodulated appearance. They are dark in colour, and much less dense and 

 hard than calculi. When divided they present a rough surface, of loose 

 texture, and in structure resemble calculi in being made up of concentric 

 layers, but of a much thicker and coarser character. 



Oat-hair concretions are composed of the fine downy hairs which cover 

 the kernel of the oat, and not, as is universally stated by veterinary writers, 

 of the " beard of oats and other grains ". 



This formation, like the others, is also rounded, but its surface is 

 regular, and of a soft velvety character. It sometimes occurs that the 

 hairy surface of the concretion becomes covered by a layer of earthy 



