This is the era of preventive medicine. It is no longer a speciality in the hands of the medical officer of health - it has spread into the domain of private practice. There is an increasing tendency to depend less upon drugs and more upon hygienic methods, less upon therapy of any kind, and more upon such attention to the laws of health as will prevent the inception of disease. Not that the possibilities of curative medicine are by any means exhausted, but that the infinite potentiality of preventive medicine is now being fully recognised.

In no branch of this vast subject has greater advance been made than that of dietetics, until it has now attained such proportions that there are not wanting those who exalt its practice as the only necessity of health. Some have even begun to inquire whether by the adoption of a suitable diet it might not be possible so to improve mankind, by building the bodily edifice of a more enduring and resistant material, as to confer a degree of immunity upon it that would render other branches of preventive medicine ultimately nugatory. I can scarcely subscribe to such a Utopian faith. Nevertheless, I consider the subject of dietetics of incomparable importance, and pregnant with possibility for the future regeneration of the human body. Such a multiplicity of counsellors have, however, appeared on the field seeking for favourable consideration, and the diverse character of their advice is so bewildering, that a full presentation of the subject is necessary for the guidance of those who have not made dietetics their special study.

In the following pages I deal with practically all the important systems of diet which are entitled to serious consideration. Although the book is written primarily for the medical profession, and especially for students of dietetics, it is hoped that it may commend itself to all who are interested in the question, containing as it does little, with the exception of the first two chapters, which cannot be readily understood by any intelligent person.

In the discussion of the various conflicting problems my one object has been to present the truth as it appeared to me. Where I express adverse views to those held by the authors of the different theories, I have endeavoured to couch my opinion in language which, I hope, will commend itself to all for its moderation. Where I have felt it incumbent to express my views more emphatically than usual, it has been more with the view of cautioning the reader than on account of any personal or partisan feeling against the author.

My material has been collected from the most diverse quarters. I have not scorned even to avail myself of the valuable assistance which may sometimes be obtained from laymen, but in every such instance I have supplied a corrigent in the shape of the views expressed by scientific men. This has necessarily entailed much study and correspondence. To all who have been obliging enough to send me information or reprints I hereby acknowledge my indebtedness, although in most instances I have recorded this in the bibliography at the end of the book. Where no such acknowledgment has been made it has been because the reference could not be traced, or because the facts have more or less become part of the general stock of medical information.

I am specially indebted to the editor of the British Medical Journal for permission, so willingly granted, to use the following articles contributed by me at various times: "The Limitations of a Purin-free Diet," "A Personal Investigation into the Dietetic Theories of America," "The Limitations of Curdled Milk Therapy."

Here and there throughout the book a sentence or two occurs in quotation marks without any obvious reference. These have been extracted from my recently published volume, "The Laws of Life and Health," and I am under a great debt of obligation to the publisher, Mr. Andrew Melrose, for permission to use them.

Dr. Fraser Harris, Dalhousie Professor of Physiology in the University of Halifax, Nova Scotia, was good enough to revise the first two chapters of "Theories of Metabolism," and I desire here to record my grateful thanks for this service.

Dr. E. P. Cathcart, Lecturer on Physiological Chemistry at the University of Glasgow, very kindly undertook the revision of the whole manuscript at an early stage in its production, and I have taken full advantage of his many invaluable suggestions, emendations, and references to original authorities.

I much appreciate the kindness of Dr. J. H. Kellogg, Superintendent of Battle Creek Sanitarium, the largest vegetarian establishment in the world, who frankly, but temperately, criticised the chapter on "Vegetarianism," and I hope that the information he has placed at my disposal has tended to make that chapter more useful and interesting.

Finally, and in particular, I beg to tender my sincere thanks to Dr. Leonard Hill, Lecturer on Physiology at the London Hospital Medical School, for numerous hints as to the best manner of enlarging the scope of the book, and adapting it more suitably to the purpose of the practical dietist.

I have occasionally considered it expedient to repeat a statement which has found expression in a previous chapter. This has been done advisedly to make the argument more complete.

I shall be amply repaid for the labour involved in writing the book if it will help any one to settle for himself or others the vexed problem of diet.

ALEXANDER BRYCE. Moseley, Birmingham.