This slow wasting takes place in any damp place under ground, and the ferments assume the form of vapour when such places happen to be warmer than the open air; it is in this state that the odour is so sensible to us after a hot dry day or during cold nights. There is no smell in rainy or damp weather. It is in the spring and autumn months when ferments from slow combustion abound, aided by the amount of heat and moisture which then prevail, and by the floating of plants. The poison thus generated is known to be the product of a ferment, and like many such products, possesses the quality of fermenting other organic compounds with which it may come in contact. Introduced into the living system of man, it finds in certain individuals the material already disposed to pass into fermentation. It incubates, and this incubation is measured as to time by a variety of circumstances I need not enumerate. In cold countries the incubation is slow, extending over many months; not that the ferment differs, but its action is modified by the existing condition of the accessories to its action and power. The ferment introduced into the blood in autumn may not show its full action on the living fluids until the following spring, or early in summer: in hot countries it is different; there the ferment, aided by numerous adjuncts, acts almost immediately; fever sets in, causing violent reaction of the conservative powers of nature; delirium, coma, vomiting, death. The mass of the blood has undergone a change in all its constituents, and dissolution and putrefaction are swift in reducing the frame, even whilst life is still present, to that state to which all that lives must come at last; whilst the physician loses himself in vague theories of an “unknown poison”--a malaria, a something not strictly a gas, a matter or influence differing from all chemical or other agents known, the scientific chemist steps in, and shows that the subtle matter they so anxiously endeavour to discover, is a process constantly going on before their eyes; a chemical process, universal; the process, in short, on which in a great measure depends the disposal of the dead and effete remains of the organic world; the growth, the nourishment, the renovator of each successive generation of the same world.