In describing a tropical forest, Humboldt says, “Under the bushy, deep, green verdure of trees of stupendous height and size, there reigns constantly a kind of half daylight, a sort of obscurity, of which our forests of pines, oaks, and beech trees afford no example; forming a carpet of verdure, the dark tint of which augments the splendour of the aërial light.” With this luxuriance of vegetation is combined a corresponding abundance of animal life. The earth and air teem with living creatures. “The mould,” observes the same distinguished traveller, “contains the spoils of innumerable quantities of reptiles, worms, and insects. Wherever the soil is turned up we are struck with a mass of organic substances, which by turns are developed, transformed, and decomposed. Nature in these climates appear more active, more fruitful, we might say more prodigal of life.” The air is still more alive than the land. Insects fill the lower strata of the atmosphere to the height of fifteen or twenty feet, like a condensed vapour. It is estimated that a cubic foot of air is often peopled by a million of winged insects, which contain a caustic and venomous liquid, several species being nearly two lines (1.8) long. When two persons who have their home in these regions meet in the morning, the first questions they address to each other are, “How did you find the zancudoes during the night?” “How are we to-day for the mosquitoes?” An ancient form of Chinese politeness, showing the ancient state of that country, was—“Have you been incommoded in the night by serpents?” It appears that there are still inhabited places in which the Chinese compliment on the serpents might be added to that of the mosquitoes. Proportionate to this prodigality of organic life is the amount of organic decomposition, the products of which are poured into the atmosphere and suspended in the surrounding vapour and fog,[11] to which they give a decided and often a highly offensive odour. Footnote 11: See note, p. 16. “On fixing our eyes on the tops of the trees,” describes Humboldt, “we discovered streams of vapour wherever a solar ray penetrated and traversed the dense atmosphere, exhaling, together with the aromatic odour yielded by the flowers, the fruit, and even the wood, that peculiar odour which we perceive in autumn in foggy seasons. It might be said, that notwithstanding the elevated temperature the air cannot dissolve the quantity of water exhaled from the surface of the soil and of the vegetation.”