THE ITCH MITE 337 



parts which are largely formed by the chelate cheliceras. They are chiefly of 

 importance because of their being occasionally found in urine, faces, etc., and being 

 striking objects, the question of pathogenicity arises. The T. longior has been 

 associated with intestinal trouble (probably a coincidence, patient having eaten 

 cheese containing these mites). 



Glyciphagi are found in sugar and are the cause of what is known as "grocers' 

 itch." Rhizoglyphus parasiticus is reported to be the cause of an itch-like affection 

 of the feet of coolies on tea plantations. To distinguish: the dorsum of Glyciphagus 

 is hairy or plumose; Tyroglyphus has both claws and suckers on tarsi, while Rhizo- 

 glyphtis has only claws. 



Sarcoptidae 



These are small eyeless mites with a transversely striated cuticle. They live 

 on the epidermis of man and various animals. The rostrum is chiefly made up of 

 chelate chelicerae with quite short three jointed, rather adherent palpi. It is the 

 female that makes the tunnels in the skin between the fingers, on penis, flexor surface 

 of forearm, etc. The male dies off after copulation. The female passes through four 

 stages: i. larva; 2. nymph; resembles adult, but has no sexual organs; 3. the pubes- 

 cent female; 4. the egg-bearing female. A pair of itch mites may produce 1,500,000 

 descendants in three months. Transference of eggs, larvae or pubescent females 

 does not seem to transmit scabies. It is the egg-laden female only. The human 

 itch mite, Sar copies scabiei, is an oval mite, the male is 250 X 150/^5 the female is 

 about 400 X SOOJL*. Besides the difference in size, the male may be distinguished 

 from the female by the fact that the third and fourth pairs of legs in the female have 

 bristles, but in the male, the fourth pair has suckers. The tunnels made by the 

 female have the egg-bearing female at the blind end; scattered all along are fasces, 

 eggs, larvae; the eggs being next the mother and the more mature young at the en- 

 trance to the gallery. A diagnosis can be made from the finding of either eggs or 

 larvae. The eggs are 140;* long and hatch out in four to five days. A female becomes 

 mature in about two weeks. 



In treating itch with sulphur preparations the adult females and immature itch 

 mites are killed; the eggs, however, are not affected. Hence a second treatment 

 about ten days after the first is necessary to kill the young mites, which have devel- 

 oped subsequent to the first treatment. Different animals have different species of 

 itch mites. 



Demodicid (Hair Follicle Mites) 



Demodex folliculorum. This is a vermiform acarine about 400 JU long; the eggs 

 are about 75/z long; they chiefly live in the sebaceous glands of nose and forehead. 



Tarsonemidae 



This acarine family shows a complete sexual dimorphism. The Pediculoides 

 ventricosus is oval and about 125 X 75M for the male which has claws at the extremi- 

 ties of the anterior and posterior pairs of legs; the two other pairs have booklets and 

 a sucking disc. The female is about twice as long but of the same breadth as the 

 male, and has claws only on the anterior legs. 



