PSOROPTIC MANGE — SHEEP SCAB. 



615 



Experience has shown that in some cases apparently healthy sheep 

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

 eif^ht, 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; 



