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hills, the attenuated streams will fill their banks again — and yield us a better fish supply 

 — and will cease to drown the valleys with floods after every rain. 



Trees, I believe, chemically alter the atmosphere in such a way as to increase its 

 salubrity. They are living, breathing organisms and, under the stimulus of sun-light, 

 they exhale a great quantity of oxygen. A portion of oxygen thus exhaled, assumes 

 that allotropic form which the chemists have named ozone. By virtue of its powerful 

 oxidizing powers, ozone pi'obably conduces to health in a high degree. It is produced in 

 the forest not only by exhalation from the leaves, but also by the slow oxidation of 

 essential oils such as lend their perfume to aromatic plants and fragrant flowers. It is 

 produced, also, wherever slow oxidation or fermentation takes place, and especially where 

 turpentine or terebinthinate compounds are oxidized in the presence of water. For these 

 reasons the air of forests, particularly of pine forests, is charged with a large amount of 

 ozone, while the air of towns has absolutely none. 



Ozone disinfects decomposing animal matter and is capable of destroying miasms and 

 disease-germs, and constantly conduces to health. 



And now, having so far advocated our thesis that the more trees the more health, com- 

 mon scientific fairness requires us to entertain the reverse side of the question and enquire 

 if ever, under any circumstances, trees are injurious to health. 



The popular opinion regards the woods as the breeding-place of malaria. The popu- 

 lar opinion in this embodies a vulgar error. All the conditions for breeding malaria are 

 not known ; it is a fickle crop and will not grow where all known essential conditions 

 seem to be present. But we know that air, moisture and abundant sun-light are essential 

 and in the dark, primeval woods of all countries, the malarial fevers are almost unknown. 

 About the margins of streams and rivers, in half-dried swamps, and especially where salt 

 and fresh waters meet in brackish swamps, the malarial poison is most concentrated and 

 malignant. It is very true that the pioneers who were woodmen, were great sufferers 

 from ague and intermittent and remittent fevers. But this, I think, was not because 

 they lived in the woods, but because they were compelled to clear away the forest and 

 admit the sun-light, and turn the virgin soil. Freshly exposed soil is unfortunately the 

 favourite nidus of the malarial poison. The draining of ponds, and necessary excavations 

 for streets, roads and railways, have in hundreds of instances developed severe endemics 

 of this sort. But the connection of shaded soil and malarial diseases, has no scientific 

 justification. 



And we may even go further and declare that plant life is absolutely antagonistic to 

 malaria. In this region where there are many of its isolated breeding-places, it cannot 

 escape notice that even a thin or narrow belt of woods will defend a strip of territory 

 from the malarial influence. In some mysterious way the poison is neutralized in travers- 

 ing the woods, and health prevails on one side as surely as disease reigns on the other. 



Bowditch, of Massachusetts, in 1862, presented facts which led almost to a demon- 

 stration that soil-moisture develops pulmonary consumption, and by him we should be 

 warned. It is possible that on damp, tenacious soils trees may be so massed about dwel- 

 lings as to keep the soil too damp. Supposing a house to stand on good rolling soil, well 

 drained and underdrained, this would be impossible, but, out of abundant caution it 

 would be well to keep dense masses of shade some little distance from dwelling-houses. 

 Let the trees that come into closest conxpanionship and look into oiar windows be few • 

 let them come not too near. And let them be lofty, so that their shadows may sweep 

 over long arcs as the sun swings round his daily course. Then the dangers of damp soil 

 and damp walls will be wholly forestalled. 



While they should not come too near, there is one good sanitary reason why trees 

 should come somewhat near our homes. Civilization requires and creates fixed homes 

 and the social instinct tends to bring these homes into groups. From this it comes ta 

 pass that the soil about our dwellings becomes saturated and oversaturated with oro'anic- 

 matter. The defilement of the surface soil with vast quantities of slops and suds and 

 scraps of organic matter is an evil, but the continual pollution of the sub-soil, is a far 

 more serious matter. Superficial filth may be removed, and, if not removed, is capable 

 of oxidation, so as to become innocent in time. But subterranean filth can neither be 

 traced nor removed, and is beyond the influence of oxidizing influences of the air. 

 13 (F. G.) 



