74 



DIRECT INJURIES CAUSED BY INSECTS. 



From the above facts it seems fair to infer that this animal 

 is not invariably the cause of scabies, but that there are cases 

 with which it has no connection. Now, from this inference, 

 would not another also follow, that the disease produced by 

 the insect is specifically distinct from that in which it cannot 

 be found? Sauvages and Dr. Adams are both of this 

 opinion ^, the former assigning to it the trivial name of ver- 

 micularis, and the latter proving, by very satisfactory argu- 

 ments, that it is different from the other. If they were botli 

 animate diseases, but derived from two distinct species of 

 animals (for it seems not impossible that even our common 

 itch may be caused by a mite more minute than the other, 

 and so more difficult to find), they would properly be con- 

 sidered as distinct species 5 much more, therefore, if one be 

 animate and the other inanimate. Nay this, I should think, 

 would lead to a doubt whether even their genus were the 

 same. I shall dismiss this part of my subject with the 

 mention of a discovery of Dr. Adams, which seems to have 

 escaped both Linne and De Geer, that the Acarus Scahiei is 

 endowed with the faculty of leaping (in this respect re- 

 sembling the insect found by Willan in Prurigo senilis men- 

 tioned above), for which purpose its four posterior thighs are 

 incrassated.^ 



But besides these Acarine diseases, there seems to be one 

 (unless with Linne we regard the plague as of this class ^) 

 more fearful and fatal than them all. You will, perhaps, 

 conjecture I am speaking of that described by Aristotle and 

 Sir. E. Wilmot as the Phthiriasis, and your conjecture will be 

 right. But some think, and those men of merited celebrity, 

 that mites have nothing to do in these and similar cases, for 

 that maggots were the parasites mistaken for lice. This, 

 from the passage above quoted, appears to have been Dr. 



1 This opinion Dr. Bateman thinks probably the true one. Cutan. Dis. 197. 



2 It may be mentioned here as a remarkable fact, that the Acarus Scahiei 

 was discovered by M. Latrielle upon a New Holland quadruped {Phascolomys 

 fusca GeofFr. ) of the Marsupian tribe. A^. Diet, d' Hist. Nat. xxi. 222. Much 

 light has recently been thrown on the history of Acarus Scahiei by M, A. Duges, 

 who regards it as forming the distinct genus Sarcoptes {Ann. de Sci. Nat. 2d. Serie, 

 iii. 255.), and by MM. Bande, Rennucci, Sedillot, and Blainville, the last of 

 whom has given a critical history of this parasite in his report in the Nouv. Ann. 

 du Mus, iv. 213. See also Raspail's Memoire Comparatif sur VHist. Nat. de 

 rinsecte de la Gale, ^ Amcen. Ac. ubi supr. 101. 



