On human muscle as a transformer of energy / John G. McKendrick.
- McKendrick, John G. (John Gray), 1841-1926.
- Date:
- [1891]
Licence: Public Domain Mark
Credit: On human muscle as a transformer of energy / John G. McKendrick. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![gramme of oxygen used in destroying fat, 3*370 calories are pro- duced ; in destroying starch, 3*797 calories; and in destroying dextrose, 3*695 calories. Lastly, for each gramme of carbonic acid exhaled, associated with the destruction of fat, 3*460 calories are set free; of starch, 2*750 calories; and of dextrose, 2*687 calories. It will be observed that each gramme of oxygen con- sumed produces almost the same amount of heat, whatever may be the nature of the substance oxidised in the body. Assuming a mixed diet, let us take the mean of these figures for oxygen, namely, 3*56, and multiply by 1,488. This gives 5,297*28 calories, a result approximately near that obtained by the other method of computation. From the physical point of view, therefore, it is clear, theo- reticallv, that a balance can be struck between the income and the output of energy in a living being like man. The chemical reactions occurring in the body are the source of the energy set free, either as heat or external mechanical work, or both. The physiologist, however, is not satisfied with the striking of this balance sheet. His science leads him to the study of the inter- mediary changes that occur between the chemical phenomena and the final production of thermal energy and of mechanical energy; and the tissue in which these changes may be most conveniently studied is muscle. Muscles work and produce heat. What is the relation existing between these two functions'? Are thev independent of each other; or is the heat set free in a muscle by chemical changes partly liberated as heat and partly converted into mechanical energy ? These are questions that have in recent years been very fully discussed both by physicists and by physi- ologists, and on the answer to be given depends our conception of a muscle considered as a motor or heat machine. Does the muscle resemble a heat machine which transforms heat into work ] This question was first put and answered in the affirmative by J. Mayer, but it has been answered in the negative by the majority of physicists and physiologists, because they do not find in muscle one of the essential conditions of all such machines—namely, a marked difference of temperature between one part and another. Let us consider shortly the arguments of those who uphold the hypothesis of the thermic origin of the mechanical energy mani- fested by a muscle.](https://iiif.wellcomecollection.org/image/b24930143_0012.jp2/full/800%2C/0/default.jpg)
