The Marvelous Human Machine which we call the body. All the inventions and devices ever constructed by the human hand or conceived by the human mind, no matter how delicate, how intricate and complicated, are simple, childish toys compared with that most marvelously wrought mechanism, the human body. Let us proceed to take this wonderful machine in pieces and study its various parts and the manner in which they are put together. The Two Objects of Human Existence.--The objects of this wonderfully formed mechanism are two: 1. The maintenance of an individual life; 2. The production of similar individuals which shall also have the power of maintaining individual lives. The same may be said of every plant that grows, and every animal. Each tree, plant, and shrub has some useful service to perform while it lives, in addition to the production of seed from which other plants may grow. For example, the object of the majestic oak which towers high and broadly spreads its leafy branches is not to produce acorns merely, but to give place for birds to build their nests, to present an inviting shade for cattle, and to afford protection in a variety of ways to numerous living creatures which need such aid. The same may be said of all vegetable growths, each particular plant having its peculiar purposes to fulfill, and all together acting as purifiers of the air for the benefit of man and lower animals. The principle is equally true as applied to lower animals, as is evidenced by the numerous ways in which domestic animals are utilized. Indeed, it seems that the prime purpose of life, not only with all lowly living creatures, as plants and animals, but with man as well, is to live and act as individuals. But the important function of reproduction, or producing other similar individuals, though incidental, is necessary to the perpetuation of the race or species. In order that an individual human being may live and develop, it is necessary that he should eat, drink, digest, and assimilate, and that he should be able to move about, to perceive,--that is, to hear, see, feel, smell, taste, determine weight and distinguish temperature,--to think, and to express ideas in language. In order to keep his vital machinery in order, it is necessary that the body should also be able to repair injuries which may occur in consequence of wear or accident, and to remove out of the way wornout material which would otherwise obstruct the working of the delicate machinery of which his body is constructed. Each of these functions requires special organs and apparatuses to carry on the work; and these we will now briefly consider:--