70 THE COMMON SHEEP-SCAB. 
This estimate of their rapid multiplication, which is by 
no means exaggerated, but is a very moderate one, plain- 
ly proves that the farmers keeping sheepcan not be toocare- 
ful to prevent the scab from infecting their flocks. Mites, 
and their eggs as well, if removed from their abodes and 
placed upon a moist piece of blotting paper, or if kept in a 
moist atmosphere, can exist from fourteen days to four weeks, 
butin dry surroundings they willsoon perish. Thisshows the 
necessity of preventing healthy sheep from sleeping upon 
moist soil upon which diseased animals have been resting. 
All such scab-mites seem to become more active in warm 
stables, and thus cause more violent itching. In the case of 
the human itch-mite it has been observed that the mites leave 
their tunnels at night, if the patient is in a warm bed, and 
commence to make new tunnels, hence the increased itching 
at that time. 
The skin disease caused by the common scab-mite has a 
different appearance upon different breeds of sheep. Upon 
some breeds, characterized by wool nearly free from fat, the 
disease can spread over the wholebody. Starting from small 
and isolated spots the scab extends slowly but steadily. In 
Merino sheep the disease is not so readily communicated, 
and affects mainly spots free from long wool. The firstindi- 
cation of the disease is violent itching, which the infested 
animals show by rubbing against all sorts of objects and 
by biting the infested spots. This itching sensation becomes 
more evident when the animals become heated by exercise. 
The sensation produced by rubbing against posts, etc., 
is evidently of a pleasant character to the sheep, as is 
shown by a trembling motion of their lips, as well 
as by the rapid opening and closing of their jaws. 
The spots of skin infested usually upon the back 
—show small yellowish knots, which soon change 
to little pus balls filled with lymph. Later this 
fluid is discharged and dries, forming small yellowish- 
brown scabs. The wool upon the invaded spots becomes 
paler and dry, is slightly lifted, but usually remains in posi- 
tion, being glued to the skin by the drying lymph. Very 
often these first indications are very slight, and escape de- 
