But if this is so, why have not our parents been able to be boys with us instead of old men at fifty? Because they did not understand; never had the plain points shown them; physicians have not always considered this side of boyhood development, and because physiology as taught in the public schools was not that physiology needed by youths and boys. We shall not here bother with the old style and schoolbook physiology. I am going to present to you the simple, common-sense facts about the body and how it must be handled to get the best out of it. If you have an automobile, the first thing you do is to understand it; its different working parts, how they are dependent upon each other, how much fuel is needed and how applied, what will make the engine run smoothly, what will injure it and what kind of usage is necessary to keep it always in good running order, what will cause it to break down and become an old rattling thing and send it to the scrap heap. The finest built machine is of no value if any of the parts which have gone into it are faulty; it will break down when a strain comes. It is just so with man; for when you really come to understand the machinery within you, you will realize that you are the most delicate and at the same time toughest piece of mechanism ever produced. Muscular power, brain force, will, mental ability, all depend upon the PHYSICAL condition of man――the parts and condition of the machine in him. The higher power in us that makes the human body a mere medium for development we shall not here say much about, but so related is it to the body itself, that a poorly adjusted or diseased body will affect this higher power, the soul, the conscience, the morals of the man. That is, a diseased or weak body――not merely muscular weakness, but a general weakness due to neglect of nature’s laws――will show a weak will, a lack of determination and a further falling away from a high moral standard――in other words make a failure of a man. But why should this be so? Is man to be blamed for being physically weak, to be punished because he has not that full strength of body that others have? Yes; I think so. But suppose he inherits a weak body, inherits disease? Is he to be blamed for something over which he has no control? Not exactly that, for there _is only one disease you can inherit_, and that is a punishment for your parents’ or grandparents’ sins――or in most cases, ignorance. When you thoroughly understand your own body, the little _tendencies_ to weakness or predisposition to certain diseases can all be overcome. The distressing effects of venereal diseases seen in children whose parents have been ignorant of the facts you will be given in this book, have been a blessing to mankind, insomuch as you can all avoid them after the knowledge concerning them and your body is yours.