A medium-sized man at out-of-door work, fully oxidizes all waste of the system and he requires a higher protein diet—125 grams. In such event he does not require so much starch and sugar. If, on the other hand, he were to take but 106.8 grams of protein, as above, he would require more carbohydrates. One working or exercising in the fresh air breathes more deeply and oxidizes and eliminates more waste, hence he has a better appetite, which is simply the call of nature for replacing the waste. Experiments in the quantity of food actually required for body needs, made by Prof. R. H. Chittenden, of the Sheffield Scientific School, Yale University, have established, beyond doubt, the fact that the average individual consumes very much more food than the system requires. In fact, most tables of food requirements, in books on dietetics, are heavy, yet the amount of food required as a result of Professor Chittenden’s experiments would seem to be too light for a continuous diet. Professor Chittenden especially established the fact that the average person consumes more protein than is necessary to maintain a nitrogenous balance. It was formerly held that the average daily metabolism and excretion of nitrogen through the kidneys was sixteen grams, or proportionate to about one hundred grams of protein or albuminoid food. Professor Chittenden’s tests, covering a period of six months, shows an average daily excretion of 5.86 grams of nitrogen, or a little less than one-third of that formerly accepted as necessary; 5.86 grams of nitrogen corresponds to 36.62 grams of protein or albuminoid food. Professor Chittenden’s experiments concerning the amount of foodstuffs actually required by three groups of men, one group of United States soldiers, a group from the Yale College athletic team, and a group of college professors, all showed that the men retained full strength, with a higher degree of physical and mental efficiency, when the body was not supplied with more protein than was liberated by metabolic activity, and when the quantity of carbonaceous food was regulated to the actual requirements for body heat and energy. It may be well to call attention here to the fact that most of the food elements, called on for work, are not derived from those foods just consumed or digested, but from those eaten a day or two previous, which have been assimilated in the muscular tissues. Dr. W. S. Hall gives the rations for different conditions, as shown in the following tables: TABLE XI RATIONS IN DIFFERENT CONDITIONS