5 22 



THE ANIMAL PARASITES OF MAN 



Family. Demodicidae (Mites of the Hair-follicles). 



Small Acarina, elongated in worm-like fashion, with annulated abdomen, and 

 without eyes or tracheae. The mouth parts consist of a suctorial proboscis and 

 three-jointed palpi ; the legs are short, and have three segments with small terminal 

 ungues. The anus is situated on the anterior border of the abdomen ; oviparous ; 

 the laivce have six stumpy legs. These mites live in the hair-follicles of mammals. 



Genus. Demodex, Owen. 

 Demodex folliculorum, Simon, 1842. 



Syn. : Acarus folliculorum, Sim., 1843; Demodex folliculorum^ Owen, 1843; 

 Macrogaster platypus, Miescher, 1843; Simonea folliculorum, P. Gervais, 1844; 

 Steatozoon folliculorum, Wilson, 1847. 



As in Sarcoptes scabiei, numerous varieties of this species are 

 known ; the form parasitic on man lives in the hair-follicles, the 

 meibomian and sebaceous glands, and hardly ever causes incon- 

 venience; the male measures 0*3 mm. in length and 

 the female about 0-4 mm. in length. The eggs 

 0*06 to croS mm. in length, 0*04 to 0^05 mm. in 

 breadth, and are thin-shelled. The creatures are 

 always attached with the head end downwards in 

 the parts mentioned ; they are most frequent in 

 the sebaceous glands of the face, by the nose, lips 

 and forehead, but they may be present on the 

 abdomen and on other parts of the body. They 

 may occasionally obstruct the excretory gland ducts, 

 thus causing inflammation of the gland (comedones) ; 

 their agglomeration in the meibomian glands sets 

 up inflammation of the margins of the eyelids. 

 There are generally only a few specimens in a gland. 

 According to some statements Demodex occurs in 

 50 per cent, of mankind and even in children ; they 

 survive the death of their hosts by several days. 



FIG. 370. Demo- 

 dex folliculorum of 

 the dog. (After 

 Megnin.) 



The variety living in the dog (D. folliculorum var. cants) 

 is smaller than the variety living in man, and produces a skin 

 disease resembling scabies in these animals. According to 



Ziirn they may also live on man ; nevertheless, no other investigator has recorded 

 a similar observation, and attempts at artificial infection have proved negative. 1 



[Ten distinct species of Demodex are given by Canestrini and 

 Kramer (" Demodicidae und Sarcoptidae," Das Ticrreich, 1899, vii). 

 The species are certainly distinct. 



[The species living on the dog (D. canis, Leydig, 1844) is cosmo- 

 politan. According to the British Medical Journal (February 22, 1913, 



1 [This mite causes what we know in England as red mange in dogs. F. V. T.] 



