44 



PARAGRAPH XV. 



THE HYGIENIC INFLUENCE OF THE FOREST. 



The hygienic influence of the forest is explained by the presence 

 of ozone and the absence of bacteria and dust in the forest air. 



Ten acres of forest exhale, in the course of a day, as much 

 oxygen as is needed for the life of sixteen men. 



The air in the forest, nevertheless, is no richer in oxygen than 

 the air over the field, with the exception of the edge of the forest 

 and of the crown space where a slight surplus of oxygen is found. 



The amount of ozone, however, suspended in the air is greater 

 in the forest than over the field, and exceeds by far the ozone 

 in the city air. The latter fact is apt to be due more to the 

 number of fires in the city than to the absence of trees. 



Ten acres of forest exhale, in the course of a year, as much 

 oxygen as is required for the burning of twelve tons of coal. 



The influence of the forest on fever-breeding bacteria is denied 

 by some medical authorities and affirmed by others. At the 

 present moment, it is impossible to see clear. The ecological 

 conditions of bacterial life are not understood sufficiently. 



Ebermeyer attributes the protection against fevers which, in 

 his opinion, the forest offers, to the conditions of the forest soil. 

 The vegetable components of the forest soil contain less matter 

 nutritive to bacterial growth than the soil in the field. The 

 acidity of the humus is antagonistic to pathogenic bacteria. So 

 far, no microbes have ever been found in forest soil; a gramm 

 of soil in the field contains from two to three hundred thousand 

 bacteria. 



The absence of dust in the forest is explained by the fact 

 that there is less wind in the forest, and that the carpet on the 

 ground does not allow any dust to form. The bacteria &re 

 carried about not by the air, but by the particles of dust suspended 

 in the air. 



As a sanitary filter of drinking water, the forest, or rather 

 the soil under the forest, is unexcelled. 



