390 MANAGEMENT AND FEEDING OF SHEEP 



classes and ages. Unlike the mite that produces head 

 scab, it works underneath a covering of wool, and appar- 

 ently preferably where the wool is longest. Consequently 

 the autumn and winter are the most favorable to its dis- 

 tribution. Other influences that favor rapid multiplica- 

 tion in the mites are such as pertain to old age, to lack of 

 stamina generally and to insanitary surroundings. 



The indications that point to the probable presence 

 of scab are the rubbing of the sheep against external ob- 

 jects and the attempts to bite themselves. Soon the coats 

 become rough, taggy and ragged. Examination may 

 show the insects themselves. At first when attacked by 

 the scab mites minute elevations appear on the skin 

 slightly more white or yellow than the surrounding skin. 

 These become so numerous at length as to unite. From 

 the summit of each a watery serous fluid exudes which 

 leads eventually to covering the skin with a yellowish 

 scaly layer under which the parasites hide. These sur- 

 faces continually enlarge by the mites working outward. 

 The mites usually begin their attacks along the back and 

 carry to the neck glands and rump. They congregate 

 most around the edges of the scabs. 



The losses from scab to flockmasters through the 

 presence of scab in the aggregate are very great. These 

 losses occur: (i) Through ill-doing on the part of the 

 sheep ; (2) through loss by death which may result from 

 scab directly or indirectly through disease favored by the 

 enfeebled condition resulting because of the presence of 

 scab ; and (3) through the cost of the curative methods 

 that are necessary to free the flock from the presence of 

 the mites. The suffering endured by the sheep thus at- 

 tacked is exceedingly great. The mites are communicated 

 by contact with tufts of wool torn from the bodies of in- 

 fected sheep. In these the mites which are exposed even 

 to low temperatures may live for 20 days. (For treat- 

 ment see Chapter XXI). 



The sheep louse of the genus Trichodectes is not very 



