CHAPTER VI. AIR VITIATED BY ADMIXTURE WITH EFFLUVIA ARISING FROM THE DECOMPOSITION OF VEGETABLE MATTER ON THE SURFACE OF THE EARTH. It is not only from such sources as those already treated of, that effluvia or gases arise, to contaminate the atmosphere, and to spread disease among men and beasts. Effluvia likewise spring from the putrefaction of vegetables; and, in many instances, from circumstances favourable to their development and action, they so vitiate the atmosphere, that its respiration induces some of the most virulent diseases, and, where the effects are not so serious, a state of slow sickness and great suffering is often the lot of the sufferer, during the whole course of his miserable existence. The situations of these effluvia will shortly be pointed out, along with the respective diseases incident to them. But let us for a moment consider the changes on which these effluvia depend. Putrefaction of vegetable matter is one of the many wise provisions which the Almighty has instituted for the accomplishment of his comprehensive plan of the creation. The surface of the earth is covered with vegetation, to supply man with food, and likewise to support the various animals placed below him in the scale of creation, so necessary to his comfort and existence. They are consumed, and, by means of digestion, become component parts of animals; and when these, in their turn, die, they go down to the earth, whence they originally sprung. Mixed there, with other matters composing the soil, the carcasses of animals afford nourishment to vegetation again, and once more they are found as the component principles of vegetable forms. Thus the animal is constantly supplying food to the vegetable world, which, in its turn, supplies food to the other again. In life, we found them performing functions useful to each other, and mutually correcting their unwholesome effects; in death, they are no less useful: the one is converted into the other. All animated creation is the scene of endless changes, and is the object of successive transformations. ’Tis one mighty circle, of a thousand parts, constantly revolving,—one part occupying now this, now that place,—and each taking the place of that next it, till at length it completes the entire circle; and even then the race is not yet run, the revolution must be performed again and again, to the very end of time. The immediate agency by which these wonderful changes are effected, is putrefaction. We have alluded to it shortly, in connection with man in health, in disease, and in death. We have now to speak of putrefaction in connection with dead vegetable matter, in marshy situations, &c., where it is the occasion of much disease.