300 ARACHNOIDEA. 



CASE but irritation of a kind quite different from any less continuous 

 and minute shaving. But then we have different symptoms pro- 

 duced by different species ; the scurfy inflamed surface of the S- 

 scabiei ; the coarse leprous crust of the S. scabiei-crustosse j the 

 deep ulcers of Glyciphagus hippodos ; and so on. It is possible 

 that there may be some difference in the kind and degree of me- 

 chanical irritation to produce such different results ; but it is also 

 possible that there be some special poisonous or irritant virus 

 in the bite of the different species, to account for the variation in 

 the phenomena observed in each. 



There are several other species of itch mite. One of the most 

 formidable (producing a much worse complaint than the common 

 itch) is the following : — 



Sarcoptes scabiei-crustos^ {Furstenherg Kratzmilben). — The Norwegian 

 itch mite. 



This is very like the common species, but smaller and some- 

 what darker. It likewise is attached to man, but fortunately 

 is much more rare. It was first described from Christiana in 

 Norway, and seems to be more particularly special to that 

 country, although examples of the disease have occurred in other 

 countries. 



It was first noticed by MM. Boeck and Danielssen in Chris- 

 tiana, in their Treatise on the *' Spedalskhed," Elephantiasis, &c., 

 published in 1848. Among the diseases of the outer skin they 

 found a kind of tubercles covered with thick brownish crusts, in 

 which they discovered an Acarus, which presented itself in 

 millions, not only on the surface of the tubercles, but even in 

 the softened tubercular mass. When the mass was examined 

 with a lens, it appeared to consist of nothing but small white 

 round points, which, placed under the microscope, proved to be 

 Acari in every stage of development. The tubercular mass 

 consisted of softened tissue, and on the inner surface of the crust 

 an innumerable crowd of the little animalcules appeared. The 



