No physiological truth is more firmly established than the fact that we can modify the action of our physical organs towards the special objects related to them, by the way in which we use our organs. By long-continued and careful study of the apparatus and processes of digestion, the physiologist has discovered the general plan by means of which food is converted into the substance of the body, and the part which each portion of the complicated digestive system takes in the maintenance of daily life. He does not stop, however, with this discovery of the general plan by which food is converted into flesh. He studies the way in which our habits of eating and drinking may destroy or improve the power of digestion, and recognises the effects which various kinds of food and drink may exercise upon the character of the individual and the race. The physiologist, therefore, proceeds to investigate, as a direct branch of necessary human physiological inquiry, the influence which the consumption of flesh or fruit, of alcohol or water, of warm or cold articles, of quantity or quality, etc., exerts upon the unique organization of the human being, in producing health or disease in mankind; or upon the power of self-control or endurance, with the promotion of ferocious or genial tendencies in Man. Both human strength and human character can be affected by enlarged knowledge and control of the uses which belong to the digestive system. What is true of the effects of food is equally true of the effect of every other physical condition of human life. It is, therefore, a special work of the rational physiologist to discover the higher uses of our varied human faculties. We only see at present the beginning of this great work of applied physiology in enabling us to comprehend the full effects of food, air, exercise, climate, etc., upon human character. We possess only vague knowledge of the great facts of the hereditary transmission of diseased or healthy tendencies; and we give, as yet, no due consideration to the important results which follow from such transmission. We only faintly realize the transforming power of habit or mind in healthy growth and in morbid degeneration. These investigations form a distinct branch of applied physiology; and such investigation and application of physiology is the especial duty of the rational or Christian physiologist who sees clearly that creative force is a beneficent power; and this perception cheers and guides him in the perplexed paths which lead towards human growth and perfection.