The human body is a machine, not an iron and steel machine, but a blood and bone machine, and just as it is necessary to understand the mechanism of the iron and steel machine in order to run it, so is it necessary to understand the mechanism of the blood and bone machine in order to run it. If a person understanding nothing of the business of a _chauffeur_ undertook to run an automobile, doubtless he would soon come to grief; and so likewise if a person understands nothing of the needs of his body, or partly understanding them knows not how to satisfy them, it is extremely unlikely that he will maintain it at its normal standard of efficiency. Under certain conditions, of which we will speak in a moment, the body-machine is run quite unconsciously, and run well; that is to say, the body is kept in perfect health without the aid of science. But, then, we do not now live under these conditions, and so our reason has to play a certain part in encouraging, or, as the case may be, in restricting the various desires that make themselves felt. The reason so many people nowadays are suffering from all sorts of ailments is simply that they are deplorably ignorant of their natural bodily wants. How much does the ordinary individual know about nutrition, or about obedience to an unperverted appetite? The doctors seem to know little about health; they are not asked to keep us healthy, but only to cure us of disease, and so their studies relate to disease, not health; and dietetics, a science dealing with the very first principles of health, is an optional course in the curriculum of the medical student. Food is the first necessary of life, and the right kind of food, eaten in the right manner, is necessary to a right, that is, healthy life. No doubt, pathological conditions are sometimes due to causes other than wrong feeding, but in a very large percentage of cases there is little doubt that errors in diet have been the cause of the trouble, either directly, or indirectly by rendering the system susceptible to pernicious influences.[1] A knowledge of what is the right food to eat, and of the right way to eat it, does not, under existing conditions of life, come instinctively. Under other conditions it might do so, but under those in which we live, it certainly does not; and this is owing to the fact that for many hundred generations back there has been a pandering to sense, and a quelling and consequent atrophy of the discriminating animal instinct. As our intelligence has developed we have applied it to the service of the senses and at the expense of our primitive intuition of right and wrong that guided us in the selection of that which was suitable to our preservation and health. We excel the animals in the possession of reason, but the animals excel us in the exercise of instinct.