Influence of Forests on Health. 165 



The natural respiration of the trees when in leaf may also exert important 

 influence in purifying the atmosphere by their powers of absorption and di- 

 gestion, or assimilation. 



Especially in tropical countries, and even in sub-tropical and lower tem- 

 periite regions, the usual forestal condition of moisture and decaying veget- 

 able matter, .accompanied by heat, are believed to give rise to that enigmati- 

 cal but universally accepted condition called malaria — a most unsatisfactory 

 term, and a more unsatisfactory condition of our atmosphere. 



The rich low lands of these Western States, which were once heavily tim- 

 bered, were found to be very sickly and to abound in fevers when the hardy 

 pioneers first opened their farms, though these lands, since being cleared and 

 drained, have become entireh' salubrious, their sanitary conditions have been 

 changed by the complete removal of the forests. 



The unhealthfulness of the dense forests, especially on the lower levels 

 within the tropics, is too well known to need a reference to localities by way 

 of illustration. 



It has been supposed that certain trees gave forth exhalations Ihat were in- 

 salubrious. The fabled Upas tree is familiar to every school boy, but the re- 

 ports of modern travelers and the lights of modern science have united to 

 dispel the fable. There is such a tree as the Upas, known to botanists as the 

 Antiaris toxicaria, and it belongs to a family many of which contain a pois- 

 onous principle, chiefly found in their milky juices, but there is no evidence 

 of poisonous exhalations from the tree that could affect the atmosphere, as 

 set forth in the fable. Many trees exhale carbonic acid at night, and unpleas- 

 ant ettects might be produced by exposure to a confined atmosphere sur- 

 charged with such a gas. 



Many trees exhale a heavy perfume when in blossom that has been found 

 prejudicial to the health of delicate persons, and some are really poisonous 

 in their aura, as the Rhus venouita of our Xorthern swamjis. The noble and 

 valuable AUanthus glandidosa, from the Farther East, which may yet play an 

 important role in our Western forestry, just now bears the weight of odium 

 on account of its exhalations. True, it belongs to a p)oisonous family, and does 

 aftect some sensitive persons injuriously. This, however, is exceiDtional, and 

 is rather a matter to be referred to the peculiar idiosyncrasy of individuals. 

 To most persons this tree, though unjileasant, is not poisonous nor injurious. 



The opportunity can not be permitted to pass without the remark that in 

 this country the prevailing haste of our people has induced them to adopt 

 this, and some other trees, for planting in their streets and avenues, on ac- 

 count of their rapid growth, without duly considering their compatibility or 

 otherwise for such a purpose. The ailanthus has, indeed, an important place 

 to fill, where it w'ill prove eminently satisfactory, but that place may, per- 

 haps, not be as a shade tree in city or village. »■ 



The various species of Eucdlyptus that have been introduced from Aus- 

 tralia, though unfitted for our latitudes, have proved valuable acquisitions in 

 hotter regions, especially on account of their rapid growth and valuable tim- 



