The Earth as Modified by Human Action eBook

The literature of this subject is now very voluminous.  For observations with high microscopic power on this subject, see Beale, Disease Germs, their supposed Nature, and Disease Germs, their real Nature, both published in London in 1870.

The increased frequency of typhoidal, zymotic, and malarious diseases in some parts of the United States, and the now common occurrence of some of them in districts where they were unknown forty years ago, are startling facts, and it is a very interesting question how far man’s acts or neglects may have occasioned the change.  See Third Anual Report of Massachusetts State Board of Health for 1873.  The causes and remedies of the insalubrity of Rome and its environs have been for some time the object of careful investigation, and many valuable reports have been published on the subject.  Among the most recent of these are:  Relazione sulle condizioni agrarie ed igieniche della Campagna di Roma, per Raffaele Pareto; Cenni Storici sulla questione dell’ Agro Romano di G. Guerzoni; Cenni sulle condizioni Fisico-economiche di Roma per F. Giordano; and a very important paper in the journal Lo Sperimentale for 1870, by Dr. D. Pantaleoni.

There are climates, parts of California, for instance, where the flesh of dead animals, freely exposed, shows no tendency to putrefaction but dries up and may be almost indefinitely preserved in this condition.  Is this owing to the absence of destructive animalcular life in such localities, and has man any agency in the introduction and naturalization of these organisms in regions previously not infested by them ]

CHAPTER III.

The woods.

The habitable earth originally wooded—­General meteorological influence of the forest—­Electrical action of trees—­Chemical influence of woods—­Trees as protection against malaria—­Trees as shelter to ground to the leeward—­Influence of the forest as inorganic on temperature—­Thermometrical action of trees as organic—­Total influence of the forest on temperature—­Influence of forests as inorganic on humidity of air and earth—­Influence as organic—­Balance of conflicting influences—­Influence of woods on precipitation—­Total climatic action of the forest—­Influence of the forest on humidity of soil—­The forest in winter—­Summer rain, importance of—­Influence of the forest on the flow of springs—­Influence of the forest on inundations and torrents—­Destructive action of torrents—­Floods of the Ardeche—­Excavation by torrents—­Extinction of torrents—­Crushing force of torrents—­Transporting power of water—­The Po and its deposits—­Mountain slides—­Forest as protection against avalanches—­Minor uses of the forest—­Small forest plants and vitality of seeds—­Locusts do not breed in forests—­General functions of forest—­General consequences of destruction of—­Due proportion of woodland—­Proportion of woodland in European countries—­Forests of Great Britain—­Forests