STUDIES ON ACART. 



No. 1. The Genus Demodex. 



FEEQUENCY OF OCCURRENCE AND EFFECTS OF THE PARASITISM. 

 OF DEMODEX ON THE HOST. 



The species of Demodex usually seem quite innocuous, their 

 presence apparently causing no inconvenience to their host. These 

 parasites can be found in perfectly healthy animals — for instance, 

 specimens have been collected by the author from mice, dormice, 

 rabbits, a sheep, field mice, hedgehogs, etc., which showed no signs 

 of skin-complaint. Very numerous specimens were found in the skin 

 of a hibernating dormouse, the fur of which was nevertheless in perfect 

 condition *. 



Demodex and Man. — It has been pointed out by Gmeiner and many 

 other specialists that D. folliculorum is very frequently met with in 

 human beings but does not usually cause any disease. In the course 

 of his researches Gmeiner examined over two hundred corpses besides 

 living persons, and is of opinion that Demodex occurs in the skin of 

 practically every human being. In America, Allen has published a case 

 of a skin-eruption resembling molluscum contagiosum in which speci- 

 mens of Demodex were very numerous, and Fordyce and Holder have 

 recorded two instances of acne rosacea in which great numbers of the 

 same parasite were present. De Amicis and others in Italy have 

 considered Demodex to be associated with a pigmentary affection 

 resembling tinea versicolor. Dubreuilh also has found these mites in 

 a case of localised pigmentation of the skin, and Darier found numerous 



* Acknowledgment is due to the following gentlemen for their kindness in presenting 

 material utilised in this little memoir : The Belgian Government and M. R. van Saceghem 

 for specimens of D. bovis from the Belgian Congo; Lt.-Col. A. W. Alcoek, F.R.S., for 

 specimens of D. pJiylloides (from the pig) ; and Lieut. Leslie Linzell for examples of 

 D. equi and D. raiti, and for supplying me with much valuable information on the 

 Demodeclic mange of the horse. Mr. M. A. C. Hiuton has also kindly helped me in 

 collecting Mammals and in other ways. 



Thanks are also due to Messrs. Taylor & Francis for kindly allowing the reproduction 

 of Figs. 39, 41, 42a, 4G and 47, which have appeared in the ' Annals & Magazine of 

 Natural History.' 



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