RAREFYING OSTEITIS. OSTEOPOROSIS. OSTEOMA- 

 LACIA OF THE HORSE. BIG HEAD. 



Definition. Distinction from rachiti.s. Process of rarefaction, cell pro- 

 liferation, congestion, solution of earthy salts and fibrous matrix, osteo- 

 clasts, Howship's lacunte. Dried bone light, spongy, friable, though 

 enlarged in repaired cases, dense, heavy. Face lesions. Dyspnoea. Drop- 

 ping teeth. Causes : microbian hypothesis, disturbance of bone nutrition, 

 fault)^ food, lack of bone salts, cellar stables, floor on ground, malaria, cold, 

 damp soils, city life, early life, breed, asses and mules, breeding. Nature. 

 Symptoms : illness, inappetence, lifelessness, early fatigue and perspiration, 

 stiffness, lameness, distortions, stumbling, knuckling, arthritis, tender 

 puffed joints, thickened softened bones, facial swellings, narrowing of in- 

 termaxillary space, chisel teeth, difficult mastication, shedding teeth, 

 emaciation, marasmus. Phosphates in urine when disease is active. Re- 

 lation to exostosis. Prevention and treatment. Hygienic, move from cellar 

 stable, or ground floor, secure air space under floor, ventilation, warmth, 

 sunshine, grain feeding, pasture, change food, rest, salicylates, salicin, salol, 

 phenacetin, blisters, phosphates, bone dust, phosphorus, bitters, iron, 

 barium chloride. 



Defi)iition. A form of osteomalacia occurring in the mature 

 as well as in the growing horse, characterized by the absorp- 

 tion of earthy salts from the walls of the cancelli and Haver- 

 sian canals with excessive production of the organic basis and 

 cell elements and enlargement, .softening, lightness and fragility 

 of the bones. 



It differs from rachitis e.ssentially in this that while the latter 

 attacks the young growing bone at the chief .seats of growth, 

 under the periosteum and in the epiphyseal ligament, and there- 

 fore especially on the surface of the true bony tissue, osteo- 

 porosis attacks the formed and often the mature bone in its interior, 

 producing attenuation of the walls of its va.scular canals and 

 caucellar cavities and increase of their fibro-cellular contents. 

 Both result in enlargement of the bone, but in rachitis this is 

 determined largely by deposition on the surface while in cs- 

 teoporosis it takes place by expansion from within. The fur- 

 ther distinction that rachitis appears enzootically and osteopor- 

 osis sporadically applies only to localities in which the latter is 



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