How We Lose Heat

Manawatu Times, Volume 63, Issue 44, 22 February 1938, Page 3

How We Lose Heat

OLD IDEAS ERRONEOUS When physicists measure radiation they use a theoretical “black body,” and thus deduce laws which are applied in designing everything that sheds light or heat (writes the Science Editor of the New York Times). Physicians would like to know whether the laws apply to man, in order to be able to deal with chills and fevers more intelligently. Dr. James D. Hardy (Russell Sago Institute of Pathology and New York Hospital) came forward with the wanted information at the National Academy of Sciences meeting at Rochester. Into a respiration calorimeter (room which is carefully sealed and to which air can be supplied in measured amounts) he and his heavier colleague, Dr. Eugene Du Bois, went naked, with a blackened cylinder which could be filled with water kept at any desired temperature. Dr. Hardy found that he and Du Bois lost almost exactly the same amount of heat by radiation and convection (that is, heat physically carried off as a fan) as an inanimate “black body” of equal radiating area. Assuming that the heat of the body is carried to the surface by the circulatory system, it is possible to calculate the flow of blood in the skin. Dr. Hardy finds that as the temperature of a room drops to 72deg Fah. (at which a naked man will begin to shiver) the blood flow decreases and remains stationary, i Such adjustment in blood flow as we may be able to make to keep warm or cool seems to be limited to the higher temperatures. Nothing can bo done by tho circulatory system to keep the body warm at low temperatures —a discovery made ages ago by men who froze to death. No Chemical Regulation. With Dr. Du Bois (also of the Russell Sage Institute of Pathology), Dr. Hardy studied heat loses from their naked bodies in the temperature range 72deg. to 96deg. F. At 91 deg and higher the skin temperature changed but little, and the body cooled itself by dilating blood vessels and by sweating. But a change of only 3.6 deg F. in temperature increased sweating about 30 per cent., and the flow of blood in the skin about 20 per cent. Electric fans carry away considerable heat from the skin. But at summer temperatures (91deg F.) the cooling lasts only a few minutes. The whole business of freezing to death is pretty mysterious. The best that Drs Hardy and Du Bois can say by way of explanation is that “some mechanism as yet undetermined causes the onset of a chill.” Muscular activity (tensing or twitching) raises the body’s temperature and thus stops the chill. Then comes another paroxysm. And so it goes from cold to warm. The conclusion to be drawn from all this is that old theories must be abandoned. There is no chemical regulator, of the body ’s heat, as the text-books have t. We behave pretty much as if we were so much dead wood or metal, so far as heat radiation is concerned.