To the students of the University who volunteered as subjects of experiment our acknowledgments are due for their intelligent co-operation, keen interest, and hearty compliance with the conditions imposed. PREFACE There is no subject of greater physiological importance, or of greater moment for the welfare of the human race, than the subject of nutrition. How best to maintain the body in a condition of health and strength, how to establish the highest degree of efficiency, both physical and mental, with the least expenditure of energy, are questions in nutrition that every enlightened person should know something of, and yet even the expert physiologist to-day is in an uncertain frame of mind as to what constitutes a proper dietary for different conditions of life and different degrees of activity. We hear on all sides widely divergent views regarding the needs of the body, as to the extent and character of the food requirements, contradictory statements as to the relative merits of animal and vegetable foods; indeed, there is great lack of agreement regarding many of the fundamental questions that constantly arise in any consideration of the nutrition of the human body. Especially is this true regarding the so-called dietary standards, or the food requirements of the healthy adult. Certain general standards have been more or less widely adopted, but a careful scrutiny of the conditions under which the data were collected leads to the conclusion that the standards in question have a very uncertain value, especially as we see many instances of people living, apparently in good physical condition, under a _régime_ not at all in harmony with the existing standards. Especially do we need more definite knowledge of the true physiological necessities of the body for proteid or albuminous foods, _i. e._, those forms of foods that we are accustomed to speak of as the essential foods, since they are absolutely requisite for life. If our ideas regarding the daily quantities of these foods necessary for the maintenance of health and strength are exaggerated, then a possible physiological economy is open to us, with the added possibility that health and vigor may be directly or indirectly increased. Further, if through years and generations of habit we have become addicted to the use of undue quantities of proteid foods, quantities way beyond the physiological requirements of the body, then we have to consider the possibility that this excess of daily food may be more or less responsible for many diseased conditions, which might be obviated by more careful observance of the true physiological needs of the body.