It is therefore certain, that in meteorology one has only to observe the earth and her position with regard to the sun, together with the currents of air and the position of land and water. Other phenomena of the atmosphere may be entirely omitted. PART VII. OUR ARTICLES OF FOOD. CHAPTER I. THE RAPID RENEWAL OF THE BLOOD IS AN ADVANTAGE. Our articles of food are also called _articles of life_, and very properly so; for that which lives in us is, indeed, nothing but food transformed into ourselves. According to this, it is very easy to determine what a man must eat in order to live; what kind of food can best maintain his health; what constantly renews his working-power; what compensates for the loss he experiences by emission of breath, perspiration, and excretions. This easy task many have proposed to themselves. They believe they have solved the problem, if they can but prove that all parts of the human body are fed by the blood; and, the constituents of the blood being well known, they believe they have done enough, if they designate that food as the most proper for man which contains the constituent parts of the blood, or which, by digestion, may be changed into blood. As a general thing this is true; yet it is not sufficient to give the necessary information about the principal articles of our food. The poor Irishman, who lives almost exclusively on potatoes, has as much blood in his body as the Englishman, whose workmen threaten him with a strike, if they do not earn enough to have a piece of meat and a good glass of beer for breakfast. The Irishman's blood contains quite the same elements that the Englishman's does, and yet their food is very different; and the Irishman is as justly called "poor," as the Englishman is said to be "well fed." It is evident that the blood alone does not account for this, nor can it do so. There must be other additional items; and these we shall try to learn before we speak of the different articles of food and their worth. The first principle which we must set up before all others, runs thus: Nutrition does not depend on the blood, but rather on its quick renewal. The blood resembles the capital which a man possesses. No one can live on his capital without consuming it; he must live on the interest of the capital; he must live by constantly turning the capital over. And so must it be with the blood. The comparison seems so perfect, that we can illustrate our idea best by an example.