A treatise on food and dietetics : physiologically and therapeutically considered.

  • Pavy, F. W. (Frederick William), 1829-1911.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on food and dietetics : physiologically and therapeutically considered. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    outside the living system, the oxidation occurs ; the result is the same, as far as the amount of the force liberated is concerned, it being implied in the doctrine of the Conservation of Energy that it should constitute the equivalent of the solar force originally made use of. This is presuming complete oxidation to occur ; but in the processes of animal life, although fully oxidised compounds, like carbonic acid and water, are formed and discharged, yet others, like urea, are expelled in an imperfectly oxidised state, and carry with them a certain amount of latent or unutilised force. Thus it is that the various forms of force manifested in the ac- tions of animal life trace their origin to that emitted from the sun. Plants are media for fixing solar force—for converting actual into latent or potential energy. Animals re-convert latent into various forms of actual force. Thus, in the various forms of actual force liberated by the actions of animal life, we have the equivalent of that which has been fixed by plants from the sun. As there is a revolution of matter, so is there a revolution of force within and around us. In the liberation of actual force a complete analogy may be traced between the animal system and a steam-engine. Both are media for the conversion of latent into actual force. In the animal system, combustible material is supplied under the form of the various kinds of food, and oxygen is taken in by the process of respiration. From the chemical energy due to the combma- tion of these, force is liberated in an active state ; and, besides manifesting itself as heat, and in other ways peculiar to the animal system, is capable of performing mechanical work. The steam- engine is supplied with combustible material under the form of coal, which differs from our food in representing the result of the vege'tative activity of a former instead of the present epoch. Air is also supplied, and from the combination which occurs between its oxygen and the elements of the combustible material, heat is produced, which in part is dissipated as such, but in part is applied to the performance of mechanical work. According to Helmholtz, the animal economy, in respect of its capacity to turn force to account in the accomplishment of mechanical work, is a more perfect instrument than the steam-engine. His calculations lead him to conclude that whilst in the best steam-engine only one tenth of the force liberated by the combustion of its fuel is realis- able as mechanical work, the rest escaping as heat, the human