506 CHAPTER 65. 



But the more aggravated cases will continue to present fungoid eleva- 

 tions and morbid secretions, and will require repeated dressings with 

 powerful caustics. The dressing should be changed every day or nearly 

 every day, as after a few aj^plications the same remedy seems to lose its 

 eflEect. Chromic, sulphuric, and other acids may be used in turn. 



Care, however, must be taken not to continue for too long the use of 

 strong caustics, or the whole sensitive sole will be destroyed and necrosis 

 of the bone induced, followed by great sloughing and perhaps death of 

 the patient. After a time therefore, in lieu of the above, burnt alum, 

 sulphate of copper, terchloride of iron, chloride of zinc, and other astrin- 

 gents may be tried. Carbolic acid may also be used. Most cases im- 

 prove under firm pressure, but in others, long-continued pressure seems 

 to stimulate the diseased action and the growth of fungus. It is scarcely 

 possible to lay down a positive rule. The symptoms of each case must 

 be carefully watched and treatment applied accordingly. In all cases, 

 except for the first two days, the dressing should be removed daily. 



The general health must be carefully attended to. A purgative will 

 probably be beneficial in the first instance, followed after a time by 

 tonics. Good dry food, fresh air, great cleanliness, and a dry stable 

 and bedding are essential. 



1021. Navicular Disease. 



Navicular disease in its primary stage is infiammation of the navicular 

 bone, which lies at the back of the coffin bone, or bone of the foot. 

 Plate 47, fig. 0. 



After a time the neighbouring parts, viz. the tendon, which passes 

 under the bone, as a rope under a pulley (Fig. k), and its cartilage and 

 bursa, become inflamed. 



1022. Further changes. 



The inflammation which has been set up in the bone, leads to a variety 

 of changes both in its external and internal .structures. In some cases 

 the bone gradually wastes away, until at last it becomes liable to fracture 

 from any trivial cause. In other cases an ossified deposit takes place on 

 the outside of the bone. This deposit limits the free play of the tendon, 

 and it gradually becomes adherent to the bone, and its bursa becomes 

 absorbed. In other cases the fibres of the tendon split up, partly from 

 friction against the roughened surface of the diseased bone, but more 

 often from degeneration of its structure from the iaiflammatory action, 

 which extends to it from the bone. In the end the tendon may give way 

 altogether. 



As the disease goes on the concavity of the foot increases, and the frog 

 becomes either hardened and elevated from the ground, or softened by a 

 discharge from its cleft and surface. These changes however, are not 

 due to the disease, but to the decreased use which the horse makes of 

 the heel on account of the disease existing in the foot. 



