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

  • Lusk, Graham, 1866-1932.
Date:
1917
Catalogue details

Licence: In copyright

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

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    Interpretation along the lines of the law of the conservation of energy was obviously beyond the ideas of the time. Dulong’s1 experiments also led to the same conclusion, that oxi- dation 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 computation 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. R. Mayer laid down the law of the conservation of energy, and in 1847 Helmholtz independently made the same discovery. Both contri- butions were rejected by the leading German scientific journal of the day.2 This should encourage all workers to rest assured of the ultimate recognition of work that is worth while. Energy cannot arise from nothing, nor can energy disappear into nothing. Where energy is active it must have been elsewhere potential. The sum total of energy remains constant in the universe, but energy may vary in kind. The kinds include mechanical energy, heat, electricity, magnetism, and potential energy. The source of energy on the earth is the sun, excepting the energy of the tides, which is due principally to the moon. The sun unevenly warms the atmosphere, producing winds which drive ships and windmills. The sun’s heat lifts the vapor of water into the atmosphere, producing rain, in consequence of which rivers are made to turn machinery. The sunlight acts upon a mixture of hydrogen and chlorin gas, caus- ing them to unite with a loud explosion, and the sun acts upon the green leaf of the plant, causing it to unite carbon dioxid and water, with the production of formic aldehyd, which is built up into sugar, oxygen being given off in the process. The sun’s energy required to build up the compound becomes latent or potential in it. Whenever and wherever this sugar is again converted into carbon dioxid and water by oxidation, exactly the same quantity of energy taken from the sun and made potential in the sugar is set free. This sugar in the plant may be further converted into starch, cellulose, fat, and pos- sibly into protein. Plants furnish wood and coal as fuel for the 1 Dulong: J. de Physiol., 1823, 3, 45. 2 Exner, S.: Wiener klin. Wchnschr., 19T4, 27, 1529.