mals, and receive oxygen (an action which, by the way, they also exhibit by day), and emit carbonic acid. These facts do not affect the main point at issue, which is the direct use by the plant of animal waste, and a very pretty cycle of operations would thus appear to have been established when botanical research showed the interactions to which we have just alluded.
Going a step further in the same direction, we may find that this utilization of animal waste is by no means limited to the mere reception and decomposition of carbonic-acid gas by green plants. It may be shown that the economical routine of Nature is illustrated in other phases of the common life of the world. The general food of plants is really animal waste. We fructify our fields and gardens with the excretions of the animal world. The ammonia which plants demand for food is supplied by the decay of living material, largely animal in its nature; and even the sordid fungi flourish-amid decay, and use up in the system of natural economy many products for which it would be hard or impossible to find any other use. What we, in ordinary language, term "putrefaction" or "decay," is really a process of extermination of the decomposing matter. No sooner does an organism—animal or plant—part with vitality and become as the "senseless clod," than thousands of minute organisms—the "germs" of popular science make it their habitation and their home. The process of putrefaction, unsavory as it may be, is really Nature's way of picking the once living body to pieces, of disposing of it in the most economical way. So much of it is converted into gas, which, mingling with the air, feeds the green plants as we have noted. So much of the dead frame is slowly rendered into nothingness by the attack of the microscopic plants which are the causes of decomposition. Nature says to these lower organisms: "There is your food. In nourishing yourselves, accomplish my further work of ridding the earth of yon dead material." And so much, lastly, of the once living frame—assuming it to have been that of the higher animal—as is of mineral nature, and therefore resists mere decay, will in due time be dissolved away by the rains and moisture, and be carried into the soil, to enter into new and varied combinations in the shape of the minerals which go to feed plants. Shakespeare must surely have possessed some inkling of such a round of natural economics when we find him saying:
"Imperial Cæsar, dead and turned to clay,
Might stop a hole to keep the wind away:
Oh, that that earth, which kept the world in awe,
Should patch a wall t'expel the winter's flaw!"
Continuing the study, we may see yet further glimpses of the great system of general regulation which guards Nature from overdrawing her accounts in connection with the arrangement of living things. Not only in beings of high degree, but in animals of low estate, do we meet with illustrations of the economy of power and the
