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(XIV.) UTILITY OF THE FOREST. 



The utility of the forest is two-fold: 



First: Direct utility, or utility to the owner (money earned). 

 Second: Indirect utility, or utility to the commonwealth (money 

 saved — losses prevented). 



The indirect utility of the forest has been and is in dispute 

 among scientists. 



The indirect value of the forest lies in: 



(a) The hygienic influence of the forest (§XV.). 



(b) The influence of the forest on temperature of soil and air. 

 (§XVI.). 



(c) The influence of the forest on moisture conditions (§XVII 

 to §XIX.). 



(d) The influence of the forest against the mechanical action of 

 water, wind, avalanches, etc. (§XX.) 



Historical data relative to the indirect utility of the forest must 

 be read with care. The advocates of forestry have attributed to the 

 forest the origin of all the good things which Heaven bestows on 

 mankind. 



(XV.) THE HYGIENIC INFLUENCE OF THE FOREST. 



The hygienic influence of the forest is explained by the presence 

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



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

 oxygen as is needed for the life of sixteen men for one day. 



The air in the forest, however, is no richer in oxygen than thj 

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

 crown space, where a slight surplus of oxygen is found. 



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

 greater in the forest than over the field, and far exceeds 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 evaporate in the course of a year as much 

 oxygen as is required to burn twelve tons of coal (the average family 

 consumption). 



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, since the ecological conditions 

 of bacterial life are not sufficiently understood. 



Ebermeyer attributes the protection which, in his opinion, the 

 forest offers against fevers, to the conditions of the forest soil; the 

 vegetable components of the forest soil containing less matter nutri- 

 tive to bacterial growth than the soil in the field. The acidity of the 



