14 



Arachnid a and Myriopoda 



very minute (length of female of D. folliculorum 380 ^ *), and the 

 hody is elongated, giving the mite a rather worm-like appearance, 

 the posterior part of it being transversely striated (annulated). 

 Demodex folliculorum, Simon, lives in the sebaceous glands of 

 man, and is a very common parasite, being found in the skins of 

 a large proportion of the human race. The anterior part of the 

 dorsal surface is about a third of the total length 

 of the body in this species of Demodex parasitic 

 in human beings, and the egg is heart-shaped. 

 The mite does not usually give rise to any skin- 

 disease, and, owing to this fact and to its minute 

 size, it is not noticed unless specially looked for. 

 Hence many people harbour this parasite without 

 being aware of it. Specimens can often be 

 obtained by squeezing out the contents of black- 

 heads (due to acne) on the face, and examining 

 the material thus obtained under the microscope. 

 Sometimes also they can be found in wax from 

 the ear. According to Borrel, mites belonging to 

 this species are especially abundant in cancerous 

 lesions of the skin, and he also suggests that the 

 germs of leprosy may perhaps be carried from a 

 person suffering from this disease to a healthy 

 individual by this mite. Lefebvre states, how- 

 ever, that the idea that Demodex is an active 

 propagator of leprosy must be abandoned. Be- 

 sides the human species, other species of Demodex 

 occur in various animals ; that of the dog is the 

 cause of the serious disease called follicular or 



Fig. i. 



Demodex follicu- 

 lorum, G. Simon. 

 Greatly magni- 

 fied. (After 

 Berlese.) 



demodic mange. 



Demodex caninus, Tulk. 



A case of Demodex caninus affecting human beings has been 

 recorded by Zurn, and another rather doubtful case by Babes in 

 1902. Lewandowsky has described a skin-eruption occurring in 

 several patches on the face of an Italian workman in 1906. He 

 found numerous examples of a Demodex in the affected parts of 

 the skin ; judging from the proportions of its body and the 

 spindle-shaped eggs, he points out that it must be D. caninus. 



fj. — one thousandth of a millimetre. 



