At the present moment of writing (October, 1903) there are quartered at New Haven, Connecticut, twenty privates of the Hospital Corps of the United States Army and three non-commissioned officers, under the command of Assistant Surgeon, Lieutenant Wallace DeWitt. These men and officers, while they are under regular army discipline and are performing duty in conformity with their oath of enlistment, are yet volunteers. They are from the same corps, if they are not the same men, which furnished volunteers to investigate the causes of yellow fever in Cuba, whose heroism resulted in stamping the fever out of the islands and in that more effectually protecting our coast states from its yearly incursions. These are the same men who generously refused to accept the offered bounty. This latter expression of exalted manhood is evidence of what humanity is whenever there is real need for heroes to serve the general good. They refused to _sell_ themselves as risks for money, but they freely _offered_ themselves as subjects of scientific investigation for the benefit of their fellows and of mankind at large. * * * * * The duty that the soldiers are engaged in at Yale has no element of risk, and need not have any feature of monotony or tediousness in it, much less has it the romance of sacrifice, for it deals with an attempt to restore normality and does not consort with disease. But the service being rendered by these guardians of our health, these soldiers of hygiene, is even more important than was the service rendered in stamping out yellow fever, for it deals with an enemy much more subtle, treacherous, common, and deadly than Yellow Jack. Yellow fever calls for a halt and an immediate attempt at cure, and further, for stringent defence to extermination; but indigestion and the American plague, _dyspepsia_, work their evils slowly but surely to cut off our best men and loveliest women in their prime and to rob us of their richest product and of their maturest wisdom. * * * * * The investigation at Yale is a link in a chain of effort that has developed in logical sequence and has been planned to effect a cure of the common ignorance and practice relative to right human nutrition in its relation to profitable thinking and doing; and to discourage the personal neglect which has been responsible for the existing ignorance, this book is issued to show what may easily be done and what has been done, so far, in this direction. It is a compilation of important knowledge which has been born of recent scientific research but which is hidden away from common comprehension in scientific publications; and it relates the story of the development of which this book is an exponent. Herein are given the reasons why the government and the most eminent scientists in the line of researches in nutrition are coöperating so earnestly and so unusually in a commonweal inquiry.