among the heaviest of gaseous bodies, and it is readily absorbed by water; consequently, floating within a short distance from the surface of the earth, a large quantity is dissolved by the waters spread over it. A considerable portion is removed by the vegetable kingdom; indeed, the whole of that produced by animals, and by the processes of combustion, eventually becomes part of the vegetable world, being absorbed with water by the roots, and separated from the air by the peculiar functions of the leaves. However, this heavy gas unites with the lighter atmospheric fluid in obedience to that law which determines the diffusion of different specific gravities through each other. The leaves of plants may be regarded as performing similar offices to the lungs of animals. They are the breathing organs. In the animal economy a certain quantity of carbon is necessarily retained, in combination with nitrogen and other elements, to form muscle; but this is constantly undergoing change; the entire system being renewed within a comparatively limited period. The conditions with plants are somewhat different. For instance, the carbon is fixed in a tree, and remains as woody fibre until it decays, even though the life of the plant may extend over centuries. Animals, then, are constantly supplying carbonic acid; plants are as constantly feeding on it; thus is the balance for ever maintained between the two kingdoms. Another condition is, however, required to maintain for the uses of men and animals the necessary supply of oxygen gas. This is effected by one of those wonderful operations of nature’s chemistry which must strike every reflecting mind with admiration. During the night plants absorb carbonic acid; but there is a condition of repose prevailing then in their functions, and consequently their powers of effecting the decomposition of this gas are reduced to their minimum. The plant sleeps, and vital power reposes; its repose being as necessary to the plant as to the animal. With the first gleam of the morning sun the dormant energies of the plant are awakened into full action; it decomposes this carbonic acid, secretes the carbon, to form the rings of wood which constitute so large a part of its structure, and pour out oxygen gas to the air. The plant is, therefore, an essential element in the conditions necessary for the support of animal life. The animal produces carbonic acid in an exact proportion to the quantity of carbonaceous matter which it consumes. Fruit and herbage contain a small quantity of carbon in comparison with muscle and fat. But let us confine our attention to the human race. Man within the Tropics, where the natural temperature is high, does not require so great an amount of chemical action to go on within him for the purpose of maintaining the requisite animal heat; consequently his Maker has surrounded him with fruits and grains which constitute his food.