In considering these figures bearing on the output of carbon dioxide under the conditions specified, we note at once a correspondence with the total energy exchange, as indicated in the preceding table. As previously stated, we are at present dealing simply with generalities, and the important point to be observed here is that muscular work--7 A. M. to 7 P. M.--in the work experiments, increases enormously the output of carbon dioxide. We see clearly emphasized a connection between the total energy exchange of the body, as expressed in calories or heat units, and the oxidation of carbonaceous material, of which carbon dioxide is the natural oxidation product. We note that on the cessation of work--7 P. M. to 7 A. M.--the output of carbon dioxide tends to drop back to the level characteristic of the corresponding period in rest, with or without food. In the experiment with “extra severe muscular work,” the results are different simply because here the subject worked sixteen hours, necessitating a portion of the work being done at night-time. Finally, it should be mentioned that the differences in output of carbon dioxide in these experiments are somewhat greater than in many experiments of this type, although all show the same general characteristics. This may be explained, as stated by the authors from whom the data are taken, “by the fact that J. C. W. was a larger and heavier man than any of the others; that the differences in diet were wider, and that the amounts of external muscular work were larger in these experiments than in those with the other subjects.” If we pass from experiments of this type, conducted in a calorimeter, to those cases where competitive trials of endurance are held by trained athletes, _i. e._, where external muscular activity is pushed to the extreme limit, we then see even more strikingly displayed the effect of work in increasing the energy exchange of the body. One of the best illustrations of this type of experiment is to be found in the observations made in connection with the six-day bicycle race held in New York City, at the Madison Square Garden, in December, 1898.[39] The observations in question were made upon three of the athletes, one of whom withdrew early in the fourth day, while the others continued until the close of the race--142 consecutive hours--winning the first and fourth places, respectively. The following table gives the computation of energy of the material metabolized, exclusive of body-fat lost: [39] See W. O. Atwater and H. C. Sherman: The effect of severe and prolonged muscular work on food consumption, digestion, and metabolism. Bulletin No. 98, Office of Experiment Stations, U. S. Department of Agriculture.