PARASITES OP ANIMALS. 



49 



Fie-nre 47. 





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 

 in which moles excavate galleries in 

 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 simultaneously. It should be appliedat 



Figure 47. — Itch-insect {Sarcoptes scahiei Latreille), female, upper side, much 

 enlarged. From Guerin. 



7 



