82 
Parasites of Cattle and Sheep. 
can, however, be no question but that its presence is detri- 
mental to the sheep, which it irritates and robs of blood. It 
is destroyed by most applications advised for scab ; but, as 
the larvae are not so readily killed as the mature “ ked,” two 
applications, within two or three weeks, are usually necessary. 
It is probable that its reappearance after a single dipping and 
its almost constant presence in sheep is due to this survival 
of the pupae. 
Sheep Scab. — “Scab,” “shab,” “rubbers,” “ sceal,” “tetter,” 
and other terms have been, from the earliest times, applied 
to a disease of the sheep’s skin. Anglo-Saxon records show 
that this disease was prevalent in Great Britain in the distant 
past, while the fact that in the year 1893 it was known to exist 
in at least eighty-six out 
of the ninety-six counties, 
speaks clearly as to more 
recent times. 
Though always regarded 
as a troublesome and loath- 
some affection, it was not 
often allowed to be fatal, and 
had come to be looked on as 
something “ which always 
did exist, and always would 
exist ” ; indeed, it had for 
centuries been known to be 
preventable and curable, but 
had been borne so long that 
its very familiarity had caused 
its effects to be held in con- 
Photo by Jf. Jt . Sheathe,*. ) tempt. As our sheep have 
Fig. 6.— Female Acarus causing Sheep Scab, become more valuable and 
called for greater care, and 
perfection and rapid maturity have become matters of greater 
importance, stock owners have realised the injurious and 
annoying effects of the disease and have co-operated in the 
call for compulsory measures towards its prevention. At the 
present time the result of measures recently adopted indicates 
the possibility of eradicating the malady entirely, a promise, 
the accomplishment of which appears mainly dependent on 
the thoroughness with which those measures are carried out 
by sheep owners. 
Cause . — The mature acarus or mite ( Dermatodectes ovis 
or Psoroptes communis , var. ovis), which causes sheep scab, 
though minute of an inch long), is just visible to the naked 
eye (see Fig. 6). If wool is plucked from the outer edge 
of the scab and warmed, the parasite may be seen on a wool 
