2. What Physiology should Teach us. The study of physiology is not only interesting, but it is also extremely useful. Every reasonable person should not only wish to acquire the knowledge how best to protect and preserve his body, but should feel a certain profound respect for an organism so wonderful and so perfect as his physical frame. For our bodies are indeed not ourselves, but the frames that contain us,—the ships in which we, the real selves, are borne over the sea of life. He must be indeed a poor navigator who is not zealous to adorn and strengthen his ship, that it may escape the rocks of disease and premature decay, and that the voyage of his life may be long, pleasant, and successful. But above these thoughts there rises another,—that in studying physiology we are tracing the myriad lines of marvelous ingenuity and forethought, as they appear at every glimpse of the work of the Divine Builder. However closely we study our bodily structure, we are, at our best, but imperfect observers of the handiwork of Him who made us as we are. 3. Distinctive Characters of Living Bodies. Even a very meagre knowledge of the structure and action of our bodies is enough to reveal the following distinctive characters: our bodies are continually breathing, that is, they take in oxygen from the surrounding air; they take in certain substances known as food, similar to those composing the body, which are capable through a process called oxidation, or through other chemical changes, of setting free a certain amount of energy. Again, our bodies are continually making heat and giving it out to surrounding objects, the production and the loss of heat being so adjusted that the whole body is warm, that is, of a temperature higher than that of surrounding objects. Our bodies, also, move themselves, either one part on another, or the whole body from place to place. The motive power is not from the outside world, but the energy of their movements exists in the bodies themselves, influenced by changes in their surroundings. Finally, our bodies are continually getting rid of so-called waste matters, which may be considered products of the oxidation of the material used as food, or of the substances which make up the organism.