Outlines of physiology in its relations to man / by John Gray McKendrick.

  • John Gray McKendrick
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Outlines of physiology in its relations to man / by John Gray McKendrick. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    pliysical research and thonglit, which form the groundwork of ^^hysical science, and they must be recognized in dealing with the j)henomena of the living body just as clearly as in considering the facts of chemistry and physics. In its passage through the living body, matter cannot be created or destroyed ; if it apparently disappear, it is only trans- formed into another condition. The idea of force or energy is inseparable from that of matter; and we must also admit that energy can neither be created or destroyed. It can only be transformed. Energy may be in two conditions, actual and 'potential. When actual, energy is being trans- formed from one condition or state into another j when potential, it is stored u]). When energ}'^ appears in the actual state, it is as one or other of certain modes which are termed forces., and these forces may be transformed the one into the other. Thus mechanical movement may be converted into heat, and heat, on the other hand, may produce movement. The exact relation of two such forces can now be exj^ressed by what is known as the mechanical equivalent of heat, calculated by Mayer of Heilbronn, in 1842, and experimentally demonstrated by Joule of Manchester, in 1844. This equivalent may be stated at 425 kilogrammetres, or, in other words, the same force which elevates 425 kilogrammes of water 1 metre in height, in a second, will elevate the temperature of 1 kilo- gramme of water 1 degree centigrade. Difficulty of experi- mentation has hitherto prevented the accurate determination of the mechanical equivalent of light, electricity, or magnet- ism, but we have sufficient evidence of various kinds to entitle us to regard these also as modes of motion, which may be therefore transformed into each other. This great principle is known as the correlation of the physical forces. The ap])lication of these views regarding energy to living organisms will be shown hereafter.