48 



BOAED OP AGRICULTUEE. 



Mange-insect of the Horse (^Psoroptes equi Gervais). 



This insect is readily visible to the naked eye and swarms 

 on horses afifiicted with the mange, which is a disease anala- 

 gous to the itch in man. It has a soft, depressed body, spiny 

 beneath at the base of the legs and on the thorax. One or 

 both of the two posterior pairs of feet bear suckers, and all 

 are more or less covered with long slender hairs. 



Figure 45. 



riff. 46. 



This insect may be destroyed by the same remedies used for 

 lice and for the human itch. The best remedy is probably the 

 solution of sulphuret of potassium, described on page 109. 



The Itch-insect (^SarcojJtes scabiei Latr.). Figure 47. 

 This is a very minute, whitish species, barely visible to the 

 naked eye, unless on a dark surface. It has been, in former 

 times, the subject of many lengthy discussions, in reference 

 to its causing the itch. It is, however, at the present time 

 fully ascertained to be the sole cause of the ordinary itch, 

 though other species of similar parasites may cause different 

 varieties of itch. The body is rounded and soft, with small 

 round pustules on the middle of the back, and with radiating 

 lines or ridges, the sides of the body and legs bearing long 

 bristle-like hairs. The mandibles are needle-like. The 

 female is largest and has the two pairs of hind legs but little 

 developed, ending a bristle ; in the male they are well devel- 

 oped and terminate in a slender sucker. These creatures, as 

 seen under the microscope, have something of the unwieldy 



Figure 45. — Psoroptes equi Gervais, female ; ventral side, mucli enlarged. 

 Figure 46. — Head of the same, more magnified. Both from Cuvier. 



