_A._ And are you so heretical, dear Isabel, as to class this science, on the score of utility, with Arithmetic and Geography--the alpha and omega of common school education? _I._ Yes. It is important, inasmuch as it is necessary that we know how to preserve the fearfully delicate fabric which our Creator has entrusted to our keeping. We gather many wholesome rules and cautions from maternal lips; we learn many more from experiencing the painful results that follow their violation. But this kind of knowledge comes tardily; it may be when an infringement of some organic law, of which we were left in ignorance, has fastened upon us painful, perhaps fatal, disease. _A._ We may not always avoid sickness and premature death by a knowledge and observance of these laws; for there are hereditary diseases, in whose origin we are not implicated, and whose effects we cannot eradicate from our system by "all knowledge, all device." _I._ But a knowledge of Physiology is none the less important in this case. If the chords of our existence are shattered, they must be touched only by the skilful hand, or they break. _E._ Were it not for this, were there no considerations of utility in the plea, there are others sufficiently important to become impulsive. It would be pleasant to be able to trace the phenomena which we are constantly observing within ourselves to their right causes. _I._ Yes; we love to understand the springs of disease, even though "a discovery of the cause" neither "suspends the effect, nor heals it." We rejoice in health, and we love to know why it sits so strongly within us. The warm blood courses its way through our veins; the breath comes and goes freely in and out; the nerves, those subtle organs, perform their important offices; the hand, foot, brain--nay, the whole body moves as we will: we taste, see, hear, smell, feel; and the inquiring mind delights in knowing by what means these wonderful processes are carried on,--how far they are mechanical, how far chemical, and how far resolvable into the laws of vitality. This we may learn by a study of Physiology, at least as far as is known. We may not satisfy ourselves upon all points. There may be, when we have finished our investigations, a longing for a more perfect knowledge of ourselves; for "some points must be greatly dark," so long as mind is fettered in its rangings, and retarded in its investigations by its connection with the body. And this is well. We love to think of the immortal state as one in which longings for moral and intellectual improvement will _all_ be satisfied. _A._ Yes; it would lose half its attractions if we might attain perfection here. _E._ And now permit me to bring you at once to our subject. What is this life that I feel within me? Does Physiology tell us? It ought. _I._ It does not, however; indeed, it cannot. It merely develops its principles. _E._ The principles of life--what are they?