26 
SHEEP SCAB. 
to a temperature of 5 degrees or lower did not hatch in any case. 
It seems probable that the eggs will not bear a temperature as 
low as 0 and live. 
Whether or not exposure will kill one of these eggs prob- 
ably depends upon, at least, three things, viz., the degree of 
cold, the duration of the exposure and the stage of incubation 
of the egg when exposed. 
Period of Incubation — When carried in the pocket, the long- 
est time that eggs have lived and hatched after being removed 
from a sheep has been nine days. One egg known to have been 
laid November 3, was kept in a warm pocket and the mite 
emerged on November 8. Time of incubation evidently depends 
much on temperature. In their natural position on the skin of 
the sheep and protected from the cold by a heavy coat of wool, 
it is probable that the eggs hatch in from three to five days. 
Where the Eggs are Placed — The eggs of these mites are not 
glued to the fibers of the wool, neither are they inserted beneath 
the surface of the skin, but are placed directly upon the moist 
skin or upon light scab. 
EFFECT OF EXPOSURE ON THE MITES. 
It is also a matter of much importance to know how long 
the mites can live off the sheep. How soon after scabby sheep 
have been turned out of a corral or field will it be safe to put 
healthy sheep in them without danger of their becoming dis- 
eased? The following experiments bear upon this point, but it 
must be remembered that I have been able to study the condi- 
tions during cold weather only. 
EXPERIMENTS IN WHICH THE MITES WERE KEPT WARM. 
In these experiments the mites were placed on wool in small 
vials and carried in an inside pocket during the day and were 
kept at a temperature of about 60 degrees during the night. 
Lot 1 — Fourteen mites of different ages, taken November 3. 
November 4, all seemed active; November 5, five were ac- 
tive and nine quiet; November 6, only two were active; No- 
vember 7, there were no signs of life. 
Lot 2 — Thirty-six mites of all ages, taken October 31. 
November 2, eighteen seemed dead and eighteen were active; 
not examined again. 
Lot 3 — Fifteen mites taken November 5. 
November 6, seven appeared dead and eight alive; Novem- 
ber 7, only two showed any signs of life. 
Lot 4 — Seventeen mites taken November 6. 
