22l8 



THE DERMATOZOIASES 



named it A cams in his ' Systema Naturae,' calling it Acarus exulcerans, but 

 earlier in ' Entomologia Faunae Suecicae ' he termed it Acarus humanus siao- 

 cutaneus, and in the thirteenth edition of the ' Systema,' 1788, Acarus siro is 

 separated from A cams scahiei. It was described by Schaefier in 1766, by 

 De Geer in 1778, by Fabricius in 1780, by O. F. Miiller in 1776, and by Latreille 

 as Sarcoptes hominis; by Baker in 1744, by Casal in 1762, by Wichman in 

 1786, and by Adams in 1905. Adams says that in Madeira there is a disease 

 due to ou9oes which is not itch, being associated with fever, but is due to a 

 small animalcule. Excluding the observations [sic) of Gal6s we next come to 

 Gras' pamphlet which appeared in 1834, and to Raspail's work which was also 

 published in the same year, and wMch established firmly the belief in the 

 arachnid. 



In 1861 Fuerstenberg wrote a monumental work on the subject 

 entitled ' De Kratzmilben der Menschen und Thiere.' Finally, 

 in 1915, Charles Singer wrote an interesting history of the small 

 animalcule. Notwithstanding all this scientific work, the derma- 

 tologists were for long sceptical as to the causal action of the small 

 parasite — e.g., Bateman — ^but Erasmus Wilson, in 1842, was quite 

 clear on this point. 



Climatology. — Scabies is known all over the world, and jhas local 

 names in all localities. It is very common in the tropics, and is more 

 frequently met with in the low country than in the hills. 



Etiology. — The causal agent is the mite Sarcoptes scahiei var. 

 hominis (Linnaeus, 1758), which lives on the surface of the skin, but 

 after impregnation the female burrows into the epidermis, making 

 a little orifice marked by slight fraying of the horny layer. From 

 this orifice it slowly works its way more or less parallel to the skin, 

 but penetrating deeper and deeper. In so doing it deposits faeces 

 and eggs along the burrow, while the mite itself lies buried in the 

 horny layer at the far end of the burrow and just beyond a small 

 vesicle, which often marks its position. It may be obtained by 

 opening the burrow by means of a fine needle until it reaches the 

 grey speck which marks the mite, which can then be extracted. 

 The female finally dies in the burrow, and the males are believed to 

 expire after copulation, but the species is kept in existence by the 

 eggs, which produce six-legged larvae in some four to eight days. 

 These moult several times, and then become the eight-legged nymph, 

 without fully developed sexual organs, which finally becomes the 

 sexually mature mite. The adult female is 330-450 microns in 

 length, but the male is smaller. 



More rarely ' scabies ' may be caused by the mite belonging to an 

 animal, but the infection in this instance does not last long. 



The vesicles and the irritation are thought to be caused by ex- 

 cretions from the mite. 



Infection generally takes place by contact, and hence is more 

 common among the poor, who are crowded together, whereas in the 

 better classes it usually begins about the generative organs, and is 

 usually thought to be spread by sexual intercourse. 



Symptomatology. — The primary symptom is itching, especially 

 when warm and when in bed, while the first clinical sign is a small 

 line on the surface of the skin, and which may be reddish. If this 



