You know the poem of the "One Hoss Shay," which was so perfectly built in every part that it ran for fifty years and then collapsed all at once in a heap. But the human body is not built that way. It always has one or more places which are weaker than the others, and which first show the effects of strain. In one person it will take the form of dyspepsia, in another it will be headaches, in another colds, in another decaying teeth, in another hardening of the arteries or stiffening of the joints. But whatever the symptoms may be, the fundamental cause is always the same, an abnormal condition of the blood-stream, and a consequent lowering of the body's tone. Therefore, studying any disease and its cure, you have first the emergency question, are there any germs lodged in the body, and if so, how can you destroy them? As part of the problem, you have to ask whether your blood-stream is normal, and if not, what are the methods by which you can make it normal and keep it so? Also you have to ask, what are the reasons why your trouble manifests itself in this or that particular organ? Is there some weakness or defect there, and can the defect be remedied, or can your habits be changed so as to reduce the strain on that organ? Are there any measures you can take to increase the flow of blood to that organ, and to promote its activity? In the study of your health, you will find that circumstances differ, and the importance of one factor or the other will vary; but you will seldom find any problem in which all these factors do not enter, and you will seldom find an adequate remedy unless you take all the factors into consideration. CHAPTER XIX EXPERIMENTS IN DIET (Narrates the author's adventures in search of health, and his conclusions as to what to eat.) Students of the body assure us that every particle of matter which composes it is changed in the course of seven years. It is obvious that everything that is a part of the body has at some time to be taken in as food; so the problem of our diet today is the problem of what our body shall consist of seven years from now, and probably a great deal sooner. I begin this discussion by telling my own personal experiences with food. I am not going to recommend my diet for anyone else; because one of the first things I have to say about the subject is that every human individual is a separate diet problem. But I am going to try to establish a few principles for your guidance, and more especially to point out the commonest mistakes. I tell about my own mistakes, because it happens that I know them more intimately.