Brezina and Kolmer1 report that the height of the initial respiratory quotients obtained during periods of mechanical work are proportional to the intensity of the work accomplished. When 1.6 calories represented the total metabolism per minute the R. Q. was 0.83, and when the metabolism rose to 10 calories the R. Q. was 0.99. Formation of acid, with the consequent elimination of carbon dioxid from the blood itself, in part explains the high quotient obtained. Increased ventilation, and carbohydrate utilization are also undoubtedly contributory. An increased acid formation tends to cause the conversion of liver glycogen into sugar (see p. 421).

1 Brezina and Kolmer: "Biochemische Zeitschrift," 1914, lxv, 16.

Although from Zuntz's work it seems proved that, in furnishing power for mechanical work, carbohydrates and fat are replaceable one for the other according to their dynamic values, there is a well-founded belief that work may be obtained in larger quantity from an individual if carbohydrates be available.

Schumburg1 finds that ingestion of carbohydrates enables a fatigued muscle to contract more powerfully. Hellsten2 states that in doing mechanical work in the morning before breakfast, an improved capacity occurs thirty to forty minutes after ingesting sugar.

The ready exhaustion of diabetics who cannot burn glucose confirms this observation.

Lee and Harrold3 have found evidences of great fatigue in the excised muscles of a cat from which the readily combustible sugar had been removed by rendering the cat diabetic with phlorhizin. Another cat similarly treated, the body of which, however, had been flooded with sugar by ingestion before the animal was killed, showed a much larger capacity for muscular contraction.

The writer4 while injecting phloretin solutions into the jugular vein of fasting rabbits, diabetic through phlorhizin, noticed that seven out of eight rabbits had convulsions, while normal rabbits were not so affected. Four died and three lost motor control of the muscles of their limbs. In these three there was an increased glucose elimination in the urine on account of the passage of the glycogen content of the organs into the blood, which glycogen would normally be immediately available for muscular activity (p. 107). The animals which survived the convulsions regained control of their muscles in two to four hours. This indicates a slow preparation from fat of materials available for the production of muscle work.

1 Schumburg: "Archiv fur Physiologie," 1896, p. 537. 2 Hellsten: "Skan. Archiv fur Physiologie," 1904, xvi, 139. 3Lee and Harrold: Proceedings of the American Physiological Society, "American Journal of Physiology," 1900, iv, p. ix.

4 Lusk: "Zeitschrift fur Biologie," 1898, xxrvi, 109.

Schumburg1 finds that coffee and tea have no recuperative power over the muscles of a fatigued organism except when taken with other foods, and that the stimulating action of alcohol is only temporary. Hellsten,2 exercising before breakfast, finds that the effect of taking tea is almost negligible, and that the effect of alcohol is at first to increase the muscle power, but that after twelve to forty minutes there is a decrease in power which lasts for two hours. No such depression occurs after taking sugar. It is obvious that alcohol is not beneficial when muscular work is to be accomplished.

The carbon dioxid produced as a result of mechanical work is quickly eliminated through the lungs. Higley and Bowen3 find that the increased elimination begins twenty seconds after the commencement of bicycle riding and reaches its maximum in about two minutes. At this point it remains constant from minute to minute, provided the same amount of work is done. This principle has been frequently demonstrated by Zuntz and his pupils. It is evident, however, that the quantity of carbon dioxid excretion for the unit of work accomplished will be less during starvation and on a fat diet than when carbohydrates are ingested, by reason of the higher heat value of fat carbon.4

Johansson and Koraen5 have caused a man to raise a weight of 21.7 kilograms ½ meter high, each movement lasting one second, and there being in different experiments 300, 600, 720, and 900 movements per hour. In the trained individual the quantity of increase in the carbon dioxid expired was exactly proportional to the number of the movements in the unit of time. The experiments were performed when food was absent from the intestines.

1 Schumburg: hoc. cii.

2 Hellsten: Loc. cii.

3 Higley and Bowen: "American Journal of Physiology," 1904, xii, 335.

4 Johansson and Koraen: "Skan. Archiv fur Physiologie," 1902, xiii, 251.

5 Johansson and Koraen: Ibid., 1903, xiv, 60.

It has already been shown (see p. 318) that 25 per cent, of the total energy of the increase above the resting metabolism as caused by work is converted into mechanical energy by a person turning the wheel of an ergostat with his arms.

Katzenstein1 has shown a still more economical utilization of the fuel when the work accomplished is climbing, about 35 per cent, of the total increase in metabolism being then converted into mechanical effect. Walking, the commonest muscular exercise, is accomplished with the greatest mechanical efficiency.

A great many interesting details have been worked out in Zuntz's laboratory by his pupils. The following epitome of long investigations shows the comparative energy equivalents necessary for dog, horse, and man to move 1 kilogram of body weight 1 meter with a given rapidity along a horizontal plane or to lift 1 kilogram of body weight 1 meter high.2 The experiments were made by placing the individual on a moving platform, the speed and incline of which could be varied.