16 FORESTS, WOODS, AND TREES 



matter in the floor of the forest (8). The occurrence of 

 ozone in the air of forests, of mountains, and of seaside 

 places, and its absence from the air of streets in towns and 

 of inhabited houses, has given rise to the idea that this gas 

 has some health-giving properties. It may purify the air 

 by oxidising animal or vegetable matter in the course of 

 decay and by uniting with the gases produced by their 

 decomposition ; but the minute quantity of ozone found in 

 the air of forests can have little effect of this kind, and is 

 evidently of no hygienic importance. Recent experiments 

 have shown that ozone is useless as a disinfectant, since 

 the quantity necessary to kill pathogenic bacteria is very 

 irritating to the lungs and proves fatal to animals 

 experimented on. Hydrogen peroxide also exists in minute 

 quantities in the air of forests ; but there is considerable 

 difficulty in distinguishing by its effects this substance from 

 ozone. 



Forests depress the level of the underground water ; and 

 drainage can often be done effectually by planting trees. 

 Diseases like phthisis, bronchitis, rheumatism, neuralgia, 

 might then be diminished in forest areas. In damp marshy 

 soils, pools are common, and serve as breeding grounds for 

 mosquitoes. The planting of Eucalyptus trees in the Cam- 

 pagna Romana diminished malaria undoubtedly, by the 

 permanent lowering of the subsoil water, which dried up 

 the pools that bred the mosquitoes. The role of the forest 

 in draining marshy places, where water stagnates for some 

 months of the year, is not doubted by the French, who have 

 seen this effect in the pine forests of the Landes and Sologne. 

 In the forest of Mondon near Nancy the level of the under- 

 ground water is throughout the year at least 12 inches 

 lower than in the cultivated land adjoining, to cite only one 

 of the extensive series of observations that were carried out 

 by Prof E. Henry of the Nancy School of Forestry. Similar 

 results have been established by Ototzky in the forests of 

 the steppes of Voronej province in Southern Russia. 



The most important hygienic asset of the forest is the 

 purity of the air therein. Smoke, particles of dust, injurious 



