PSOROPTIC MANGE — SHEEP SCAB, 



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Experience has shown that in some cases apparently healthy sheep 



ive hecome infected in places where no sheep have been kept for four, 



ight, twelve, or even twenty-four months. The conditions underlying 



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this infection are not thoroughly understood. Possibly some of the 

 eggs have retained their vitality a long time and then hatched out ; 

 possibly the vitality of the fecundated female has also played a role ; 



