PROTECTION AGAINST MALARIA. 
155 
Maury’s experiments have been repeated in Italy. Large 
plantations of sunflowers have been made upon the alluvial 
deposits of the Oglio, above its entrance into the Lake of Iseo 
near Pisogne, and it is said with favorable results to the health 
of the neighborhood.* In fact, the generally beneficial effects 
of a forest wall or other vegetable screen, as a protection against 
noxious exhalations from marshes or other sources of disease 
situated to the windward of them, are very commonly admitted. 
It is argued that, in these cases, the foliage of trees and of 
other vegetables exercises a chemical as well as a mechanical 
effect upon the atmosphere, and some, who allow that forests 
may intercept the circulation of the miasmatic effluvia of 
swampy soils, or even render them harmless by decomposing 
them, contend, nevertheless, that they are themselves active 
causes of the production of malaria. The subject has been a 
good deal discussed in Italy, and there is some reason to think 
that under special circumstances the influence of the forest in 
this respect may be prejudicial rather than salutary, though 
this does not appear to be generally the case.f It is, at all 
events, well known that the great swamps of Virginia and the 
Carol in as, in climates nearly similar to that of Italy, are healthy 
even to the white man, so long as the forests in and around 
them remain, but become very insalubrious when the woods 
are felled.:): 
The Forest , as Inorganic Matter , tends to mitigate Extremes. 
The surface which trees and leaves present augments the 
general superficies of the earth exposed to the absorption of 
* II Politecnico , Milano, Aprile e Maggio, 1863, p. 35. 
f Salvagnoli, Memorie suite Maremme Toscane , pp. 213, 214. 
I Except in the seething marshes of the tropics, where vegetable decay 
is extremely rapid, the uniformity of temperature and of atmospheric hu¬ 
midity renders all forests eminently healthful. See IIohenstein’s obser¬ 
vations on this subject, Per Wald , p. 41. 
There is no question that open squares and parks conduce to the salu¬ 
brity of cities, and many observers are of opinion that the trees and other 
vegetables with which such grounds are planted contribute essentially to 
their beneficial influence. See an article in Au% dcr Natur , xxii, p. 813. 
