HYGIENIC EFFECT OF FORESTS. 



45 



and especially of towns. Professor Ebermayer gives the 

 following results, the maximum contents of ozone being 

 indicated by 10 and complete absence by : — 



The difference between forest countries and towns is 

 greatest during winter, which seems to show that the presence 

 of ozone does not depend on the action of the leaves. It was 

 also found that the air in the interior of forests, near the 

 ground, contained slightly less ozone than along the edges of 

 the woods, which may be due to the presence of large quantities 

 of decaying matter (humus) in the forest. 



As forests produce oxygen and ozone and protect human 

 habitations against injurious air currents, they have been held 

 to exercise a beneficial effect upon the healthiness of adjoining 

 lands. Instances are not wanting, where forests are said to 

 have given protection against the germs of malaria, but there 

 are others, where they are believed to have had the opposite 

 effect. As far as India is concerned, in some cases the medical 

 authorities of military cantonments ordered forests to be 

 planted and in others to be cut down. According to modern 

 investigations, ozone is believed to have no hygienic effect ; 

 more especially its presence or absence is said not to influence 

 the development of epidemic diseases. If this is so, the 

 salutary effect of forest air is probably due to the absence of 

 dust, smoke and injurious gases, to the small number or total 

 absence of microbes and the greater tranquillity of the human 

 mind. 



