SANITARY INFLUENCE OF FORESTS. 21 



(4) The well-kept forest floor, better tbaii even tlie close sod of a 

 meadow, prevents erosion and abrasion of the soil and the washing of 

 soil and detritus into brooks and rivers. 



This erosion is especially detrimental to agricultnral interests as 

 well as water flow in regions with this surface and impenetrable sub- 

 soils, and where rains are apt to be explosive in their occnrrence, as in 

 our western and southern country. The best soil of tlie farms is often 

 washed into the rivers, and the water stages of the latter by the accu- 

 mulations of this soil are influenced unfavorably. 



(5) Water stages in rivers and streams which move outside the 

 uionntain valleys are dependent upon such a complication of climatic, 

 topographic, geological, and geographical conditions at the headwaters 

 of their afHuents that they withdraw themselves from a direct correla- 

 tion to surface conditions alone. Yet it stands to reason that the con- 

 ditions at the headwaters of each afHuent must ultimately be reflected 

 in the flow of the main river. The temporary retention of large amounts 

 of water and eventual change into subterranean drainage which the 

 well-kept forest floor produces, the consequent lengthening in the time 

 of flow, and esijecially the prevention of accumulation and carrying of 

 soil and detritus which are deposited in the river and change its bed, 

 would at least tend to alleviate the dangers from abnormal floods and 

 reduce the number and height of regular floods. 



SANITARY INFLUENCE OF FORESTS. 



(1) The claimed influence of greater purity of the air due to greater 

 oxygen and ozone production does not seem to be significant. 



(2) The protection against sun and wind and consequent absence of 

 extreme conditions may be considered favorable. 



(3) The soil conditions of the forest are unfavorable to the produc- 

 tion and existence of pathogenic microbes, especially those of the 

 cholera and yellow fever, and the comparative absence of wind and 

 dust, in which such microbes are carried into the air, maybe considered 

 as the principal claim for the hygienic significance of the forest. 



We may summarize that the position (»f the forest as a climatic factor 

 is still unceitain, at least as to its practical and quantitative imi)or- 

 tance, but that its relation to water and soil conditions is well estab- 

 lished. As a climatic fact«u' it would appear that the forest of the 

 plain is of more importance than that of the mountains, where the more 

 potent influence of elevation obscures and reduces in significance the 

 influence of their cover; as a regulator of water conditions the fcnest 

 of the mountains is the inqK)rtant factor; and since this inlluence 

 makes itself felt far distant from the location of the forest, the claim for 

 attention of Government activity and for statesmanlike jiolicy m ith 

 reference to this factor (»f national welfare may be considered as well 

 founded. Every civilized government must in time own or control the 



