“The old proverb――‘Man is the son of his environments’――is a translation of a truth scientifically demonstrated, proving the weather’s influence. It is true that it means the law of adaptation, but the environments of man depend entirely upon the meteorological conditions. According to this law we could, perhaps, live even under bad conditions of weather, but such condition would bring an unhealthy condition of life, too. “Professor Dexter, of the University of Illinois, studying the mental and physiological influence of the meteorological conditions, in one of his books, gives a comprehensive study of the question, proving the weather’s influence on the organic and intellectual life, the emotions, the literary sentiments, the individual conduct. He proves principally that the change of meteorological conditions affects the health more than anything else. “Under bad meteorological conditions we never would have the necessary reserve of energy for the complete activity of life. “And good meteorological conditions can be guaranteed only by the preservation of forests, that, unhappily for our future, does not receive from the people the deserved attention.” Since the colonial time many Brazilians have been considering the forests from a sanitary viewpoint. The patriarch of our independence José Bonifacio in 1815 wrote these phrases: “What other productions of Mother Nature ought to deserve greater attention from the philosophers and statemen than the forests and trees? Trees, wood and timber: Only these words, well meditated upon and understood, are enough to awaken our whole sensibility.” Besides other reasons there is a powerful one that makes necessary the protection of forest――its great influence upon health. Health is all, and upon it reposes the happiness of people and the greatness and prosperity of the countries. On account of a rapid progress we must not sacrifice the forests as it has been done in many new countries. Any progress detrimental to the vital forces of nature, is negative, ephemeral; if one generation profits by it, the following one fatally will suffer its consequences. This axiom, in my humble opinion, translates better the decline and disappearance of some nations that figured in antiquity than any explanation given by the modern philosophy for the fact; and forethought advises to profit by the practical lesson contained within it, preserving our natural resources in order not to sacrifice to a temporary greatness the best means of preserving life, which means are represented by the forest.