TKEES FOE SHADE AND SALUBRITY. 279 



shade and protection are those which relate to salubrity ; 

 though we must bear in mind that trees are not in all 

 places and situations promotive of health and comfort. 

 It is well known that the inhabitants of our Southern 

 cities, during ^the sickly season, or from June to October, 

 resort to the "pine barrens" for health and recreation. 

 The air in these woods is perfectly salubrious ; even the 

 half-inundated lands communicate no disease when cov- 

 ered with wood. There is something connected with large 

 assemblages of trees that prevents the formation of malaria 

 in the atmosphere, or at least deprives it of its power of 

 communicating disease. Mr. Marsh records the fact, that, 

 in certain unhealthy districts of Italy, " the interposition 

 of a screen of trees preserved everything beyond it, while 

 the unprotected grounds were subject to fevers " ; and he 

 adds, " the belief that rows of trees afford an important 

 protection against malarious influences is very general 

 among Italians best qualified by intelligence and profes- 

 sional experience to judge upon the subject." 



How many of the seemingly capricious movements of 

 epidemics might be traced to the presence or absence of 

 trees and woods, if our experience were enlightened by 

 special investigation, cannot be determined. An increase 

 of knowledge on this subject may refer these things to 

 some yet unsuspected action of trees in the economy of 

 nature. It is not yet known whether the salubrity of 

 forests be caused by some chemical action of the foliage 

 upon the atmosphere, destroying or absorbing noxious 

 effluvia, or whether the trees act simply as a bulwark 

 against the access of malarious currents of air. Indeed, 

 the principal cause of their salubrity may be the dense 

 mass of foliage with which the ground is covered, espe- 

 cially under a pine wood, preventing the escape of malaria 

 from the soil. An improved knowledge of the chemistry 

 of the atmosphere may at some future time reveal the 



