THE FOREST AS A CONDITION. 79 



especially with regard to malarial diseases. These 

 are not produced by bacilli, but by parasitic pro- 

 tozoa {Plasmodium, malarice), which seem to thrive 

 in the swamp conditions. As long as the water 

 covers the soil, there is no danger, but as soon as 

 the water recedes, the plasmodia develop, and with 

 the assistance of mosquitoes or by other means are 

 communicated to man. ^i^-^ 

 ^A further indirect sanitary mfluence must not be 

 overlooked in our modern economy of city life. The 

 recuperation of bodily energy and of spirit which 

 an occasional sojourn in the cool, bracing, and in- 

 spiriting forest air brings to the weary dweller in 

 the city must not be underestimated as an element 

 in the general health conditions of a people. In 

 addition, the question of a good water supply is 

 being recognized as more and more dependent 

 upon the condition of the sources of supply. 



Knowing that a large number of diseases are 

 bred in soils, it becomes essential that the drinking 

 water carry as little soil particles as possible, and 

 although, by artificial means of filtration and sedi- 

 mentation, the river water may be freed of sand 

 and bacilli, we would have more assurance of 

 freedom from disease, if the water came from a 

 well-forested region, where, as we have seen, no 

 pathogenic bacteria are produced, and if the wash- 

 ing of the soil into the river on the way to the 

 reservoirs were prevented by proper attention to 

 preventing the erosion along its banks. 



