We see here an increase of 495 calories per day in heat production, due to metabolism of the food ingested. In other words, with a basal energy exchange of 2022 calories, the average of the five fasting days, energy equivalent to 495 calories was expended in taking care of the ingested food. It should be added, however, that the daily ration here was somewhat excessive, 4193 calories being considerably in excess of the requirements of the body. Finally, it should be stated that of the several classes of foods, proteids cause the greatest increase in metabolism and fats the least. In studying heat production in the body under varying conditions, one of the important aids in drawing conclusions as to the character of the body material burned up is the respiratory quotient. This is the relationship, or ratio, of the oxygen absorbed to the oxygen of the carbon dioxide eliminated, viz., CO_{2}/O_{2}. Carbohydrates (C_{6}H_{12}O_{6}, C_{12}H_{22}O_{11}) all contain hydrogen and oxygen in the proportion to form water, H_{2}O, and in their oxidation they need of oxygen only such quantity as will suffice to oxidize the carbon (C) of the sugar to carbon dioxide (CO_{2}). Carbohydrates, starch and sugars, have a respiratory quotient of 1.00. Fat, on the other hand, has a respiratory quotient of 0.7, and proteid, 0.8. Hence, it is easy to see that the respiratory quotient will approach nearer to unity as the quantity of carbohydrate burned in the body is increased. Similarly, the respiratory quotient will grow smaller the larger the amount of fat burned up. Practically, we never find a respiratory quotient of 1.0 or 0.7, because there is always some oxidation of proteid in the body. If, by way of illustration, we assume that the energy of the body under given conditions comes from proteid to the extent of 15 per cent, while the remaining 85 per cent is derived from the oxidation of carbohydrate, the respiratory quotient will be 0.971. If, however, the 85 per cent of energy comes from fat, the respiratory quotient will change to 0.722. In the resting body, as in the early morning hours, after a night’s sleep and before food is taken, the respiratory quotient is generally in the neighborhood of 0.8. When, however, as sometimes happens, the quotient at this time of day approaches 0.9, it must be assumed that sugar is being burned in the body, presumably from carbohydrate still circulating from the previous day’s intake.