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this kind. The fmall-pox, meafles, cy- 
nanche parotidaea, the pian in the human 
fubjedt, and the ftrangles in horfes, and 
diftempers in dogs, are fufficiently illuftra- 
tive of this fadt. 
Certain difeafes never return if their 
firft attack be violent, or if they do, are 
of a much milder charadter. This is par¬ 
ticularly obfervable of the plague. Thu¬ 
cydides fpeaking of that which reigned in 
his time, fays, “ verum illi praecipue mo- 
rientium, laborantium que miferabantur 
qui ipli evaferant, quippe id jam antea 
experti, ac de fe fecuri: neque enim bis 
eundem morbus corripiebat, ut extingue- 
ret.” (Lib. 2.) 
If ever they experience any fmptom of 
it, it is in the enlargement of fome lym¬ 
phatic gland, which, notwithftanding, is 
not produdtive of any ill confequence, and 
they may live without danger or apprehen- 
fion in a country where the plague com¬ 
mits the mod dreadful depredations. 
If 
