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

  • Graham Lusk
Date:
1917
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Licence: In copyright

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

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    that at a temperature of 30° C., under which condition all thermal stimu- lus to the organism ceased, two guinea-pigs of different sizes still produced heat in proportion to their skin areas. A similar fact was noted by Frank and Voit,1 who found that the administration of curare, which paralyzes the voluntary muscles, scarcely affected the carbon dioxid output of a dog as compared with what was eliminated during ordi- nary muscular rest, provided the temperature of the animal was maintained at the normal by keeping him in a warmed chamber. The mass of living cells preserved the same metabolism as before, even though a pathway of heat increase had been cut off through paralysis by curare of the motor nerve-endings in the muscles. Keeping the animal in a warmed chamber was necessary in this case, for Roehrig and Zuntz2 had shown that curarized animals at the ordinary room temperature lost the power of maintaining their body temperature and that their metabolism decreased accordingly. The removal of the chemical regulation caused a behavior toward external temperature similar to that of cold-blooded animals. In the light of these older experiments the discovery that immersion of a human being in a warm bath (330 to 38°) does not alter his metabolism3 is quite to be expected. Although the effect of cold on the skin (inducing chemical regula- tion) is of itself demonstrably insufficient to account for the “law of skin area,” Rubner4 argues that even at 30° C., when the body is losing heat by means of the dilatation of the blood-vessels and the evaporation of water (physical regulation), the law is still a necessity if the general mechanism for loss of heat in the various animals is the same in all. An infant produces 90 calories per kilogram in twenty- four hours; an adult, 32 calories. Were the metabolism of an adult 90 calories per kilogram, the means of heat elimination through his comparatively smaller surface would have to be materially modified if a normal temperature were to be maintained with comfort. Though Rubner realized in 1902 that the level of basal metabolism could not be caused by the influence of cooling on the body, yet he believed that the phenomenon of the Law of Surface Area was the result of accommodation to the action of cold to which animals in former ages had been exposed. 1 Frank, O., and Voit, F.: Z. f. Biol., 1901, 42, 309. Confirmed by Tangl, F., and Verzar, F.: Biochem. Z., 1918, 92, 318. 2 Roehrig, A., and Zuntz, N.: Pfliiger’s Arch, gesam. Physiol., 1871, 4, 57. '* Benedict, F. G., and Benedict, C. G.: Proc. Nat. Acad. Sc., 1924, 10, acK. 4 Rubner, M.: “ Energiegesetze,” 1902, p. 174.