THRUSH. 



165 



48), 111 the event of a horse under these abnormal conditions 

 falling lame, an ignorant or careless observer may, not unlikely, 

 assume the ailment to be navicular disease. When thrush is caused 

 by wet, the frog becomes soft and pulpy. In the absence of 

 moisture acting on the feet, there may be little or no discharge 

 from the cleft of the frog, which will be then more or less filled 

 with soft, degraded horn of, as I have already said, a cheese-like 

 consistence. In this case, the frog will be more or less shrivelled 



Fig. 48. — Foot with contracted heels and thrush. 



Up. The presence of the disease is always accompanied by an 

 offensive and peculiar smell. 



Pressure on the frog causes an increased growth of epithelium 

 (p. 154). Hence, when the frog is exposed to continual pressure, 

 it becomes strong and well developed ; but, if it be deprived of this 

 natural stimulus, it becomes diseased and contracted in size. The 

 skin of our own hands and feet is as dependent on continued pres- 

 sure for its strength and hardness, as is the frog of the horse. 



Horses which are worked (as in riding schools), or stabled, on 

 tan, are very liable to get thrush on account of the tan becoming 



