the output of carbon dioxide was proportional to the load. At the end of each experiment the pulse-rate was taken, but in no case was it unusually high, indicating that the work was not excessive. Exactly the same type of apparatus was employed by Johansson and Koraen" to study the effect of static work upon metabolism. No. TABLE 3.-Carbon-dioxide production during muscular work. 4 Speck, ibid., p. 69 folg. 5 Speck, ibid., p. 80. 6 Hanriot and Richet, Comptes rend. de l'académie des sciences, 1887, 115, p. 78. 7 Katzenstein, Pflüger's Archiv f. d. ges. Physiol., 1891, 49, p. 359; carbon dioxide computed by Sondén and Tigerstedt. 8 Katzenstein, loc. cit., p. 367; carbon dioxide computed by Sondén and Tigerstedt. A most interesting series of experiments was carried out under Rubner's direction by Wolpert in the Hygienic Institute in Berlin. Using a large respiration chamber designed by Rubner, Wolpert studied the actual daily work of men and women employed in different occupations, his subjects including a seamstress, a writer, a tailor, a lithographer, a sewing-machine operator, a draftsman, a mechanic, and both a man shoemaker and a woman shoemaker. Only the production of carbon dioxide was observed. In an investigation upon the influence of the temperature of the air on the quantity of carbon dioxide produced by man during severe muscular work, Wolpert, employing an ergostat, found that every gram of carbon dioxide corresponded to approximately 300 kilogrammeters of work, consequently that every kilogrammeter corresponded to 33 milligrams of carbon dioxide. Employing this factor in his studies on the work of different laborers, he computed the hourly external muscular work of the different subjects as ranging from 900 kilogrammeters for the seamstress to 8,000 kilogrammeters for the man shoemaker. Using the Pettenkofer-Voit respiration chamber in Berlin, Rubner made experiments with a subject who took a large quantity of carbohydrate in one period and of protein in another, performing each day 100,000 kilogrammeters of work. By measuring the resting requirement, Rubner found that the increase in energy due to this amount of work when sugar was taken a Johansson and Koraen, Skand. Archiv, 1902, 13, p. 229. c Rubner, Sitzber. K. Preuss. Akad. Wiss., 1910, 16, p. 316. was 845.3 calories and when protein was ingested, 855.6 calories. Since the heat equivalent of the work performed was 234 calories, the data give opportunity for computing the mechanical efficiency of the body. a The first report of researches carried out by Atwater and his associates " with the respiration chamber at Wesleyan University, Middletown, Connecticut, included three experiments on muscular work in which a block of iron weighing 5.7 kilograms was raised and lowered by means of a rope passing over a pulley attached to the top of the respiration chamber. The movements of raising and lowering the weights brought into play not only the muscles of the arms but also the legs and other parts of the body, the idea being to induce severe muscular activity with no attempt to isolate any group of muscles. With this apparatus the subject did severe work for 8 hours on each experimental day. Throughout the working period he perspired very freely, and at the end he was thoroughly tired. The experiments were made on three successive days, during which time the subject remained in the respiration chamber the entire 24 hours. Later, by means of a stationary bicycle, the rear wheel of which was connected by a belt with a small dynamo, Atwater and Benedict made an experiment on muscular work with a subject inside the respiration chamber. At that time the chamber had been sufficiently tested as a calorimeter to be used for measuring exactly the heat produced by the body. As in the earlier experiments, the muscular work period lasted 8 hours, the number of revolutions of the wheel being counted by means of a cyclometer attached to the bicycle. The heat equivalent of the external muscular work was estimated to be not far from 250 calories per day. This same bicycle ergometer, with its rear wheel belted to a small dynamo, was used by Atwater and Benedict in a work experiment which was published in 1902. The results of four additional experiments were also given in which a modified form of the ergometer was used. As modified, the rear wheel of the bicycle was applied directly to a pulley fastened to the shaft of the dynamo, which was mounted on a rocking base, the necessary tension being secured by means of a spiral spring which kept the pulley of the dynamo pressed against the tire of the bicycle wheel. The detailed description of the apparatus and the method of calibration were not, however, given until a later publication in which additional work experiments were published. This form of ergometer was calibrated before and after each experiment by running the dynamo as a motor and likewise by connecting another motor with the armature shaft and measuring the energy required to rotate the wheel of the apparatus. Employing a new form of bicycle ergometer, Benedict and Milner report a large number of muscular-work experiments, covering several days. These were all carried out inside the respiration calorimeter at Wesleyan University, Middletown, Connecticut, the subject remaining in the chamber the entire 24 hours, the working periods usually being 8 hours in length. Certain of the experiments were designed to study the relative efficiency of fats a Atwater, Woods, and Benedict, U. S. Dept. Agr., Office Expt. Stas. Bul. 44, 1897, p. 51. b Atwater and Rosa, U. S. Dept. Agr., Office Expt. Stas. Bul. 63, 1899. In this description of the respiration calorimeter, Atwater and Rosa cite one of the experiments on muscular work (p. 76). See also Atwater and Benedict, U. S. Dept. Agr., Office Expt. Stas. Bul. 69, 1899, p. 47. Atwater and Benedict, U. S. Dept. Agr., Office Expt. Stas. Bul. 109, 1902, p. 21. a Atwater and Benedict, loc. cit., pp. 94-120. e Atwater and Benedict, U. S. Dept. Agr., Office Expt. Stas. Bul. 136, 1903, p. 30. Benedict and Milner, U. S. Dept. Agr., Office Expt. Stas. Bul. 175, 1907. and carbohydrates for muscular work, but the apparatus was chiefly used as a means of securing a large and accurately known amount of muscular work. A description of this new form of bicycle ergometer was given in a publication by Benedict and Carpenter which appeared in 1909." The experiments reported in the same publication were primarily designed for the study of the efficiency of the body as a machine, and included a series of experiments with a professional bicycle rider in which an enormous amount of external muscular work was performed by means of this ergometer. In the calibration of the apparatus certain abnormal factors were observed which ultimately became the subject of a special investigation in which the influence on the magnetic field of the rotation of a copper disk was accurately studied. In this research, two ergometers constructed upon the same principle were observed; these instruments were, as a matter of fact, those subsequently employed for the study of the metabolism during muscular work which is reported in this publication. METHODS AND APPARATUS USED IN THIS RESEARCH. GENERAL PLAN OF THE RESEARCH. A critical examination of all the literature bearing upon the relationship of muscular work and metabolism brings out two striking facts: First, that while many investigators have studied the influence of muscular work upon the character of the material katabolized in the body to find whether or not there is a selective combustion incidental to severe muscular activity, it nevertheless remains a fact that there is a wide diversity of opinion on the subject. Second, that the relationship between the actual amount of external work performed and the energy equivalent of the materials katabolized is by no means established, the results obtained by the various investigators differing within wide limits. Even in the more recent work, the divergence of opinion on both these points is very noticeable. Thus, Chauveau and the members of the French school are strongly inclined to maintain that there is a selective combustion of carbohydrate material during muscular work. On the other hand, Zuntz and his associates are thoroughly convinced that muscular work does not alter the character of the metabolism. Similarly, in discussing the efficiency of the body as a machine, the values found by the French investigators are noticeably different from those of Zuntz and his associates, and there is likewise a wide difference between the values found with the respiration chamber at Middletown, Connecticut, which have been reported by Benedict and Carpenter, and those of Zuntz and Durig and their associates. An examination of the experiments made in this laboratory for a number of years past shows that the diversity of results obtained and reported by other investigators has not been observed here, since our values indicate in a general way a uniformity in the effect of muscular work upon metabolism. In view of the development of an extremely accurate bicycle ergometer which a Benedict and Carpenter, U. S. Dept. Agr., Office Expt. Stas. Bul. 208, 1909, p. 11. Benedict and Cady, Carnegie Institution of Washington Publication No. 167, 1912. has recently been calibrated with especial care, together with the development of a new form of respiration apparatus capable of measuring accurately the large amounts of carbon dioxide produced and oxygen consumed during severe muscular work, it was considered that this laboratory was peculiarly well fitted for undertaking an investigation on the influence of severe muscular work upon not only the character of the material katabolized, but also upon the amounts of material katabolized. Moreover, the striking disagreement between the results for the mechanical efficiency of man obtained on the one hand by Benedict and Carpenter and on the other by Zuntz and his associates made further experiments on this subject necessary. The study reported here was intended to amplify the results of the earlier investigations. The research was primarily designed to secure evidence with regard to the influence of severe muscular work upon the character of the metabolism, as well as evidence with regard to the efficiency of the body as a machine. The experiments were for the most part carried out with a professional bicyclist riding a carefully calibrated ergometer with an electric brake." While no calorimetric measurements were made, the carbon dioxide produced and the oxygen consumed were determined by means of the new form of respiration apparatus, which was especially modified to meet the exacting requirements of experiments with severe muscular work. The experimental periods were all of such length as to overcome the criticism that has previously been made with regard to the short experiments of earlier investigators. In order to obtain values for use as a base-line, a large number of experiments were made in which the resting metabolism of a subject without food was determined while he lay quietly upon a couch. Studies were also made of the resting metabolism while the subject sat quietly upon the bicycle seat, with his feet in position for riding, but without movement. In the muscularwork experiments, the work varied from very light to extremely severe, i. e., the heat equivalent of external muscular work was 2 calories per minute or 850 kilogrammeters per minute; in some experiments the subject rotated the pedals without load; in others, he kept his feet upon the pedals while they were rotated by a motor; in the majority of the work experiments, the subject rode with a load which was varied from light to heavy according to the character of the experiment. All of the experiments were made when the subject had been at least 12 hours without food. The majority of the work experiments were preceded by rest experiments. To carry out successfully a series of experiments of this kind it was necessary to have a well-trained subject capable of severe and prolonged muscular exertion. We were extremely fortunate in securing a subject who coöperated very intelligently with us in the conduct of the experiments, and while the muscular work was frequently very severe, it was at no time beyond or even equal to the endurance or ability of the subject. DETERMINATION OF THE BASAL METABOLISM. The basal metabolism was established by studying the respiratory exchange when the subject lay quietly at rest on a couch and at least 12 hours after the last food. Under these conditions we obtained what may be termed the minimum metabolism of the subject when awake. Inasmuch as this a Benedict and Cady, Carnegie Institution of Washington Publication No. 167, 1912. resting metabolism was determined on a great many days, the evidence secured supplies a basis for comparison as to the constancy of values obtained under these conditions as well as evidence regarding the normal drafts upon the body-material when the subject was lying quietly without food and awake. From the respiratory quotient the character of the material burned, and therefore the character of the draft upon the body-material can be approximately computed. Furthermore, the base-line with regard to the measurement of the total metabolism under these conditions can be quite definitely established. Experience in this laboratory has shown that there is a marked difference between the metabolism when the subjects are sound asleep and when they are awake, even though they are well trained and capable of the greatest muscular relaxation. It can be seen, therefore, that our base-line determined in the morning without breakfast is by no means the minimum metabolism of the subject, but represents the minimum metabolism when awake. On purely theoretical grounds it might have been of value to obtain the minimum metabolism of the subject when sound asleep, but this was impracticable. It is perhaps needless to state that during the course of the winter the subject became extremely automatic in his relations to the experiments, and hence if there was any evidence regarding the value of training for an experiment or of training to decrease the incidental muscular activity which might be voluntarily controlled, we should expect to find it here. As a matter of fact, from the very start the subject was not affected in any way, psychologically or otherwise, by the simple routine of the experiments, and we have every reason to believe that the minimum metabolism when the subject was awake was accurately determined. Since the minimum metabolism under these conditions does not represent the true minimum metabolism of the subject, and since such a base-line is arbitrarily taken for purposes of comparison, it seemed advisable to secure data with regard to base-lines under other conditions. For example, the subject when riding must sit upright on the seat of the bicycle ergometer with the feet on the pedals. Inasmuch as this calls for an increase in the metabolism above that of lying quietly, exactly as lying awake calls for an increased metabolism over lying quietly asleep, it seemed logical likewise to determine the metabolism in the sitting position. This was done in a number of instances. Again, the legs must move in rotating the wheel, and experiments were made in which, by belting a motor to the rear wheel of the ergometer, it was possible to drive the ergometer and thus rotate the legs of the subject at the various speeds employed in the regular work experiments. The values obtained under such circumstances would obviously form still another base-line. Then again, as the subject must in rotating the wheel overcome the ordinary small friction of the machine, a series of experiments was made in which the subject simply rotated the pedals by riding without load. Furthermore, the load was varied so that a series of experiments was carried out with a very low load and increased step by step to the maximum load. Each of these different values can all logically be taken as a series of base-lines for comparison with the highest loads, and thus afford the greatest possibility for variations in the subsequent comparisons. Finally, since there is much contradictory evidence regarding the aftereffect of muscular work on metabolism, a number of experiments were con |