TREES AS A PROTECTION AGAINST MALARIA. 155 



in Italy where the interposition of a screen of trees preserved 

 every tiling beyond it, while the unprotected gronnds were subject 

 to fevers." Few European countries present better opportuni- 

 ties for observation on this point than Italy, because in that king- 

 dom the locaHties exposed to miasmatic exhalations are numerous, 

 and belts of trees, if not forests, are of so frequent occurrence 

 that their efficacy in this respect can be easily tested. The belief 

 that rows of trees afford an important protection against malai'i- 

 ous influences is very general among Italians best qualified by in- 

 telligence and professional experience to judge upon the subject. 

 The commissioners, appointed to report on the measures to be 

 adopted for the improvement of the Tuscan Maremme, advised 

 the planting of three or four rows of poplars, Populus alba, in 

 such directions as to obstruct the currents of air from malarious 

 locaHties, and thus intercept a great proportion of the pernicious 

 exhalations." * Maury beheved that a few rows of sunflowers, 

 planted between the "Washington Observatory and the marshy 

 banks of the Potomac, had saved the inmates of that estabhsh- 

 ment from the intermittent fevers to which they had been for- 

 merly liable. 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.f 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 fohage 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 in- 

 tercept 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 pro- 

 duction of malaria. The subject has been a good deal discussed 



* SAiiVAGNOLi, Bapporto ml Bonificamento delle Ma/remme Toacane, pp. xli. 

 124. 

 f B PoUtecnico, Milano, Aprile e Maggio, 1863, p. 35. 



