2 Doctors of medicine who have been custodians of the people's health for many centuries have seldom been food scientists. Most of them attempt to combat disease with drugs. Now we are beginning to learn the truth about the origin of disease and in considering the body as a human engine, to take into consideration the all-important question of fuel. [Sidenote: Tendency of the modern physician toward food science] That the most learned physicians are drifting more and more toward scientific feeding and natural remedies is a matter of common knowledge. This splendid army of laborers in the great field of human suffering is made up largely of what is termed the _Modern Doctor_--the man who is brave enough to think and to act according to his better judgment. Just to the extent that we understand the origin of drugs, and the drugging system of treating dis-ease, we turn instinctively _from them_, and instinctively _toward_ food, for in drugs we find an ancient system of guesswork, while in food we find fundamental principles and primary causes. The majority of causes are removed when the diet is made to fit our physical condition and environment, and we then become normal by the process of animal evolution, Nature merely bestowing upon us our birthright because we have obeyed her laws. 3 The true science of human nutrition can be evolved only from an accurate knowledge of both food chemistry and of physiological chemistry. [Sidenote: Why food chemistry and physiological chemistry have not been united] The science of physiological chemistry has been known and taught for more than one hundred years, while the science of food chemistry is of recent origin. These two branches have been kept separate because they grew up at different periods of time. United they constitute the greatest science known to mankind, because they affect his health, his happiness, his life, and above all they measure the period of time he will live. Physiological chemistry tells what the body is and its needs--food chemistry tells how to supply these needs. Recognizing these facts, I have merely united these hitherto unapplied branches of science, and have made of the union the science of Applied Food Chemistry, which makes practical that which has heretofore been confined mainly to theory. LESSON II SIMPLE PRINCIPLES OF GENERAL CHEMISTRY [Sidenote: Relation of chemistry to food science] If the student is versed in chemistry, this lesson will serve merely as a review; if not, somewhat close attention must be given to facts which at first may seem uninteresting. Patience should be exercised, for, while all the information herein given does not, taken as a whole, bear directly upon the subjects of health and dis-ease, yet with this knowledge it will be much less difficult to understand the principles which are applied later when we take up the chemistry of the body and the chemistry of food.