208 ENQUIRY into tue CAUSE or 
and extenfive furface of moift ground expofed to the ac= 
tion of the fun, and of courfe to the generation and exha- 
lation of febrile miafmata. ‘The hiflory of epidemics in 
foreign countries, favours this opinion of the caufe of their 
increafe in Pennfylvania. The inhabitants of Egypt are 
always healthy during the overflowing of the Nile. Their 
fevers appear only after the recefs of the river. It is re= 
markable that a wet feafon is often healthy in low, while 
it is fickly in hilly countries. The reafon is obvious. In 
the former the rains entirely cover all the moift grounds, 
while in the latter, they fall only in a fufficient quantity 
to produce thofe degrees of moifture which favour febrile 
exhalations. The rains which fall in the fummer are ren= 
dered harmlefs only by covering the whole furface of 
marfhy ground. ‘The rains which fall in our ftate after 
the middle of September, are fo far from producing fevers, 
that they generally prevent them. The extraordinary 
healthinefs of the laft autumn, | believe was occafioned 
by nothing but the extraordinary quantity of rain that fell 
during the autumnal months. ‘The rain probably aéts at 
this feafon by diluting, and thus deftroying, the febrile 
miafmata that were produced by the heat and moifture of 
the preceding fummer. In fupport of the truth of this 
third caufe of the increafe of fevers in Pennfylvania, I have 
only to add a fa&t lately communicated to me by Dr. 
Franklin. He informed me that in his journey from Pafly 
to Havre de Grace, laft fummer, he found the country 
through which he travelled, unufually fickly with fevers. 
Thefe fevers it was generally fuppofed, were produced by 
the extraordinary dry weather, of which the public papers 
have given us fuch melancholy and frequent accounts. 
I come now to fuggeft a few hints for obviating and 
preventing fevers, and for rendering our country again 
healthy. For this purpofe I beg leave to recommend in 
the firft place, the planting of trees around all our mill- 
ponds, (befides cleaning them occafionally) in order to 
prevent 
