292 INSECTS AND MAN 



is attained, then the adults leave the burrows and travel to 

 the surface of the skin to mate ; afterwards the females 

 make fresh burrows in which to lay their eggs. 



Somewhat akin to Sarcoptes scabei is the copra itch 

 mite, Tyroglyphus longior, castellani, a variety of the 

 cheese mite. This minute animal, as its name implies, causes 

 intense irritation to the skin of hands, arms, legs ; in fact, 

 the whole body, except the face, of Coolies and Europeans 

 who are brought into close contact with the dried coco-nut 

 kernels, known as copra. In Ceylon, the home of this 

 mite, kernels are removed from fresh coco-nuts and dried in 

 the sun for two days. At the end of this time a portion 

 of the kernels crumbles away ; this is the copra dust, which 

 swarms with the mites. 



Little or nothing is known of the life-history of these 

 minute animals. They closely resemble the cheese mite in 

 appearance, being eight-legged and well armed with stiff 

 bristles, and, though they cause the intense itching character- 

 istic of the common itch mite, they do not burrow into the 

 skin, and, for some unexplained reason, they never attack 

 certain individuals. Other mites causing severe dermal irri- 

 tation and eruptions in man are Glycyphagus domesticus, 

 causing grocers' itch, and Rhizoglyphus parasiticus, the 

 cause of water itch in the Coolies employed on Indian tea 

 plantations. 



A mite of curious habit, Demodex folliculorum var. 

 hominis, was discovered by Simon of Berlin, more than 

 seventy years ago, in " blackhead " pustules. It is now 

 known that these worm-like, eight-legged mites are quite 

 common in the sweat glands of the face, chiefly those of 

 the nose, chin, and forehead ; whilst in the hair follicles 

 they often occur in large numbers, with their heads point- 

 ing away from the surface of the skin. In order to see 

 these creatures, the white oily substance, extracted by 

 pressure on the sides of the sweat glands, should be 

 examined in a drop of oil, spirit or xylol, under the 



