648 HYPODERMOSIS. 



Each larva is surrounded by a thick wall, forming a cavity, which 

 communicates with the outer air by a minute aperture. 



When the swelling is sufficiently advanced the larva may be extri- 

 cated by pressing with the fingers around the base of the warble. A 

 few days before it leaves its shelter the larva enlarges the little opening 

 by thrusting its last rings into it. Soon after the larva has escaped 

 the discharge of pus ceases, and the skin wound heals. 



Diagnosis. The times at which the swellings appear and the larvae 

 are present render the diagnosis easy. 



Prognosis. This is seldom grave, for the larvae rarely cause death 

 In cases where they are present in very large numbers, however, they 

 may set up purulent infection. 



Treatment. No really effective treatment against warbles is known. 

 Curative treatment consists in squeezing out or killing the larvae 

 when in the subcutaneous tissue, but this is practically useless, as 

 the dead larvae then set up prolonged suppuration. 



