458 DISEASES OF SENSATION. SECT. XXXIII. 2 . 



their arms by the contact of variolous matter in 

 lifting their patients ; and that when patients, who 

 have formerly had the fmali pox have been inocu- 

 lated in the arm, a phlegmon, or inflamed fore, has 

 fucceeded, but no fubfequent fever. Which (hews, 

 that the contagious matter of the fmall-pox has not 

 loft its power of ilimulating the part it is applied 

 to, but that the general fyftem is not affeded in 

 confequence. See Sect. XII. 7. 6. XIX. 10. 



9. From the accounts of the plague, virulent ca- 

 tarrh, and putrid dyfentery, it feems uncertain, 

 whether thefe difeafes are experienced more than 

 once ; but the venereal difeafe and itch are doubtlefs 

 repeatedly infedlious \ and as thefe difeafes are never 

 cured fpontaneoully, but require medicines, which 

 act without apparent operation, fome have fufpecl:- 

 cd, that the contagious material produces fimilar 

 matter rather by a chemical change of the fluids, 

 than by an animal procefs ; and that the fpecific me- 

 dicines deftroy their virus by chemically combining 

 with it. This opinion is fuccefsfully combated by 

 Mr. Hunter, in his Treatife on Venereal Difeafe, 

 Part I. c. i. 



But this opinion wants the fupport of analogy,, 

 as there is no known procefs in animal bodies, which 

 is purely chemical, not even digeftion ; nor can any 

 of thefe matters be produced by chemical procefles. 

 Add to this, that it is probable, that the infects, 

 obferved in the puftules of the itch, and in the (tools 

 ot dyfenteric patients, are the confequences, and 

 not the caufes of thefe difeafes. And that the fpe- 

 cific medicines, which cure the itch and lues vene- 

 rea, as brim (lone arid mercury, adt only by increaf- 

 ing the abforption of the matter in the ulcufcles of 

 thofe difeafes, and thence clifpofmg them to heal'; 

 which would other wife continue to fpread. 



Why the venereal difeafe, and itch, and tenia, or 

 fcald head, are repeatedly contagious, while thofe 



contagions 



