The elements of the science of nutrition / by Graham Lusk.

  • Lusk, Graham, 1866-1932.
Date:
1928
Catalogue details

Licence: In copyright

Credit: The elements of the science of nutrition / by Graham Lusk. Source: Wellcome Collection.

    34/668 (page 34)
    Crawford concluded that the heat above produced was due to the transformation of pure air into fixed air (carbon dioxid) and water. The methods of Crawford, though primitive, were based on fundamental principles, for according to the modern com- putation of Zuntz the values of heat production where i liter of oxygen is used to burn the different food-stuffs in the body are very nearly identical (see p. 62). In 1823 the French Academy awarded a prize for the best essay on the subject of animal heat. Depretz and Dulong competed for the prize and it was awarded to the ' former. Depretz^ calculated the amount of heat which would have been liberated in burning the carbon and hydrogen of the metabolism to carbon dioxid and water, and compared this with the amount of heat given off by the animal. The heat as calculated was only 74 to 90 per cent, of what was found, a discrepancy due to faults in the method employed (see p. 43). So Depretz concluded that although the respiration was the principal source of animal heat, food, the motion of the blood, and friction yielded the remainder. Interpretation along the lines of the law of the conservation of energy was obviously beyond the ideas of the time. Dulong’s^ experiments also led to the same conclusion, that oxidation was insufficient to explain the cause of animal heat, and that there must be other sources of it. Regnault and Reiset, writing in 1849 regarding the com- putation of heat production from the oxygen absorbed by an animal, remark, ‘^The phenomena are evidently so complex that it is scarcely probable that one will ever be able to submit them to calculation.” About 1842 James P. Joule supplied the chief experimental data which established the mechanical equivalent of heat. In 1845 J- Mayer laid down the law of the conservation ^ Depretz: “Journal de Physiologie,” 1824, iv, 143. 2 Dulong: Ibid., 1823, iii, 45.