DISEASES OF THE JOINTS 437 



term a weak navicular bone. In this connection Colonel 

 Smith says : * Though it is far from present in every case 

 of the disease, still I consider it a factor of great importance.' 



5. A Defective or Irregular Blood-siq)})!}; to the Bone. — 

 This, Colonel Smith considers, is brought about by excessive 

 and irregular work, and by the opposite condition — rest. 

 The author points out that the bloodvessels passing to and 

 from the navicular bone run in the substance of the inter- 

 osseous ligaments, or in such proximity to them that it is 

 conceivable that under certain circumstances mechanical 

 interference may occur to the navicular circulation. He 

 further points out a fact that is, of course, well known to 

 every veterinarian, that in periods of work the circulation 

 of the foot is hurried, and that in rest there is always a 

 tendency to congestion ; and he says in conclusion : ' I 

 cannot help thinking that irregularities in the blood- 

 supply in a naturally weak bone must be a factor of some 

 importance, especially when the kind of work the horse is 

 performing is a series of vigorous efforts followed by rest.' 



6. Senile Decay. — With approaching age the various 

 tissues lose their vigour, and are prone to disease. The 

 navicular bone and surrounding structures are not exempt. 

 With the other and more active causes we have described 

 acting at the same time it is not surprising that navicular 

 disease is seen as a result. 



In conclusion, it is well, perhaps, to say that, no matter 

 to which particular theory of causation we may lean, we 

 should make up our minds to consider them as a whole. 

 While one cause may be exciting, the other may be pre- 

 disposing, and the two must act together before evil results 

 are noticed. It may be that even more than two are con- 

 cerned in bringing on the disease, and to each the careful 

 veterinarian will give due consideration. 



SymjJtoms and Diagnosis. — In the early stages of navicular 

 disease the symptoms are obscure. Pointing of the affected 

 limb is the first evidence the animal gives. This, however, 

 more often than not, goes unnoticed, and the first symptom 

 usually observed by the owner or attendant is the lameness. 



