154 SHEEP DISEASES. 



for, is final results. The time to explain how 

 to prevent a recurrence of the trouble is after 

 the epizootic has been brought under control or 

 eradicated. 



In the sheep raising section on the western 

 range only five parasites are common; two ex- 

 ternal, the common scab mite and the sheep tick; 

 three internal, the stomach worm, the liver-fluke 

 and the "gid" or "turnsick." 



A. EXTERNAL PARASITES. 

 1. Sheep Scab. 



Common scab; mange; itch; scurf; St. An- 

 thony's fire; wildfire; erysipelas; dry scab; dry 

 rot, and ringworm. 



Sheep scab is caused by the Psoroptes communis 

 ovis; order Acarina; class Arachnida. 



The scab mite is a nearly round, rather light 

 colored parasite, the female measuring about 

 one-fortieth of an inch in length, and the male 

 nearly one-fiftieth. By placing the mites on a 

 sheet of black carbon paper and holding this 

 in the sunlight, they can be seen easily. 



After mating, the female deposits about a 

 dozen eggs at the base of the wool fibers. These 

 eggs hatch in three or four days; in a week the 

 young will have matured, and in three or four 

 days more they will have mated and the female 

 laid her eggs. Grerlach estimates that the en- 

 tire life cycle of the psoroptes mite is completed 

 within fifteen days. Using these figures as a 

 basis for calculation, it has been estimated that 



