which I have already studied, from the same point of view, variola, scarlatina, and typhoid fever; and a truth, which the simple observation of facts had already rendered evident, "receives from microscopic study complete confirmation.
"The air we breathe, the water we drink, are full of spores and organic germs, all of which seem to have a purpose to serve in the economy of things. If any one doubts the statements of scientific men regarding the presence of these germs, they have only to become acquainted with the use of the microscope to convince themselves of their entire truthfulness. Separate from the bark of the common maple-tree a bit of the adhering dry lichen, or moss, as it is called, moisten it with water, and place over it a glass slide. The spores or seeds which lie dormant, when the lichen is dry, immediately become vitalized, and rising into the air are caught upon the glass, and with a power of four hundred diameters can be seen and studied. This simple experiment will illustrate the origin and nature of what are called spores, and the air is filled with thousands of varieties, arising from as many sources.
"Dr. Smith and Mr. Dancer, of Manchester, England, have recently been examining the air of that city, and have found it loaded with them. The air was first washed by shaking it in a bottle with distilled water, and in a drop of the water it was reckoned that there were about two hundred and fifty thousand spores. In the quantity of air respired by a man in ten hours there would be more than thirty-seven and a half millions. All these germs, floating in the air, are ready to spring into activity, whenever the conditions of growth are favorable. The varieties and sources of fungoid growths from which the spores arise are wonderful. A fungus is known which develops only on the corpses of spiders; another, which grows only on the hoofs of horses in a state of decomposition. The isaria has as yet been observed only on certain night butterflies; there are other species which invade the larvae and chrysalides. Hooker has discovered a fungus which attains considerable dimensions (from ten to twelve centimeters), but which is found absolutely only on the neck of a certain caterpillar in tropical countries. It vegetates on the animal, fructifies on it, and the caterpillar buries it with itself in the ground, whence it springs like a funeral plume. Still more, a singular vegetable is known, the racodium cellare, which has never been found except
