In conclusion, we wish jointly to express our obligation to Mr. Horace Fletcher, to Dr. J. H. Kellogg, to Professor Russell H. Chittenden, to Professor Lafayette B. Mendel, and to Professor Irving Fisher for advice, criticism and generous help afforded in the preparation of some of the chapters of this book. The authority of these scientists, physicians and investigators, and of others like Metchnikoff, Pawlow, Cannon, Curtis, Sager, Higgins and Gulick, whose works we have studied, is the foundation upon which we rest on all questions of fact or scientific statement. They are the pathbreakers and the roadbuilders,—we claim to be simply guides and companions along the journey to the fair land of health. The journey is not long, and the road is a highway open to all. I THE BATTLE OF THE BLOOD The new ideas of living which are the subject of this book have proceeded from investigation of the human body with the high-power microscope. The discoveries made, which have to do, not so much with the body itself as with the countless billions of minute organisms which inhabit the body, may be best set forth by a description of the blood. “The blood is the life,” says Exodus, and modern science has confirmed this statement. From the blood proceeds the life of all the body, and in its health is the body’s health. If you should prick your finger and extract a drop of your own blood, and examine it under a microscope, you would make the fascinating discovery that it is the home of living creatures, each having a separate and independent existence of its own. In a single ounce of blood there are more of these organisms than there are human beings upon the face of the globe. These organisms are of many kinds, but they divide themselves into two main groups, known as the red corpuscles and the white. The red corpuscles are the smaller of the two. The body of an average man contains something like thirty million of millions of these corpuscles; a number exceeding the population of New York and London are born in the body every second. They are the oxygen conveyers of the body; the process of life is one of chemical combustion, and these corpuscles feed the fire. No remotest portion of the body escapes their visitation. They carry oxygen from the lungs and they bring back the carbon dioxide and other waste products of the body’s activities. They have been compared to men who carry into a laundry buckets of pure water, and carry out the dirty water resulting from the washing process. The other variety of organisms are the white cells or leucocytes, and it is concerning them that the most important discoveries of modern investigators have been made. The leucocytes vary in number according to the physical condition of the individual, and according to their locality in the body. Their function is to defend the body against the encroachments of hostile organisms.