DIRECT INJURIES CAUSED BY INSECTS. 49 



men as John Hunter, Dr. Heberden, Dr, Bateman, Dr. Adams, and Mr. 

 Baker, should never, in this country, have been able to meet with it ? 

 Did it indeed exist in our common scabies, it seems impossible that it 

 could have escaped the observation of the two last of these gentlemen ; 

 Dr. Adams being so well qualified to detect it from his observations in 

 Madeira, and Mr. Baker from his expertness in microscopical researches. 

 Dr. Bateman, in the letter above quoted, says, " I have hunted it with a 

 good magnifier in many cases of itch, both in and near the pustules, and 

 in the red streaks or furrows, but always without success." In his work 

 on Cutaneous Diseases, he tells us, however, that he has seen it, in one 

 instance, when it had been taken from the diseased surface by another 

 practitioner. And though Dr. Willan, in his book, speaks of the Acarus 

 as the concomitant of this disease, yet his learned friend just men- 

 tioned observes, that he admitted that it was not to be found in ordi- 

 nary cases, and indeed never seemed to have made up his mind upon the 

 subject. When I was at Norwich, in 1812, Dr. Reeve very kindly accom- 

 panied me to the House of Industry there, to examine a patient whose 

 body was very full of the pustules of this disorder; but though we used a 

 good magnifier, we could discover nothing like an insect. I must observe, 

 however, that our examination was made in December, in severe weather, 

 when the cold might, perhaps, render the animal torpid, and less easy to 

 be discovered. 



From the above facts it seems fair to infer that this animal is not invari- 

 ably 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 1 , the former assigning to it the trivial name of vermicularis, and 

 the latter proving by very satisfactory arguments that it is different from 

 the other. If they were both animate diseases, but derived from two 

 distinct species of animals (for it seems not impossible that even our com- 

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

 more difficult to find), they would properly be considered as distinct 

 species ; 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 Scabiei is endowed with the faculty of leap- 

 ing (in this respect resembling the insect found by Willan in Prurigo seni/is 

 mentioned above), for which purpose its four posterior thighs are in- 

 crassated. 2 



to the Linnean Society, that in the north of Scotland, the insect of the itch is well 

 known, and easily discovered and extracted. 



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 Scafo'ei was dis- 

 covered by M. Latreille upon a New Holland quadruped (Phascolomys fusca Geoffr.) 

 of the Marsupian tribe. N. Diet. d'Hist. Nat. xxi. 222. Much light has recently 

 been thrown on the history of Acarus Scabiei by M. A. Duges, who regards it tin 

 forming the distinct genus Sarcoptes {Ann. de Sci. Nat. 2nd. Serie, iii. 255.), and by 

 MM. Bande, Rennucci, Sedillot, and Blainville, the last of whom has given a critical 





