PARASITES OF ANIMALS. 49 
appearance of a tortoise, and are ordinarily sluggish, yet they 
are capable of leaping to a considerable distance. They bury 
themselves in the human skin, especially in the more delicate 
and less exposed parts, and excavate minute galleries for them- 
selves, in a manner something like that 
Figure 47. in which moles excavate galleries in 
7 the soil. These galleries are at first 
perpendicular, and then go off horizon- 
tally to some distance. The females 
lay their eggs in these galleries: as 
they progress. 
These mining and boring operations 
cause much irritation of the nerves of 
the skin and induce an intolerable itch- 
ing, and the inflammation that they 
cause produces pustules, filled with a 
watery exudation. The insects them- 
selves are not found in the pustules but 
in their minute galleries, off to one 
side, the pustule generally marking the place where they en- 
tered. The itch is contagious, simply because the insects, 
especially in their young and more active state, pass from one 
person to another, or are transmitted by clothing. They are 
most active at night and, therefore, sleeping with an infested 
person is pretty sure to be attended by the transfer of the 
insects., The longer the parasites are neglected, the more 
numerous they become. The increase is, however, quite slow 
at first, owing to the small number of eggs. There are 
various remedies for this disease, but the different preparation 
of sulphur are no doubt the best and safest. The solutions 
of sulphuret of potassium, described on page 109, is probably 
the simplest and most efficacious preparation for this purpose. 
Its use should be accompanied by a thorough change of gar- 
ments and bedding, and it should be used by all the members 
of an infected family simultancously. It should be appliedat 
Figure 47.—Itch-inseet (Sarcoptes scabiet Latreille), female, upper side, much 
enlarged. From Guerin. 
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