RELATION OF HEAT-PRODUCTION TO BODY WORK. 401 



entire amount of potential energy is transformed solely into heat, for 

 the work of the muscles of the circulatory, digestive, and respiratory 

 organs is transformed within the body into heat, and therefore is not 

 work transmitted outward. A man at work, however, in addition to the 

 production of heat, transforms potential energy into work. An equiva- 

 lent measurement will serve for the comparison of both activities, 

 namely, i heat-unit, that is, the energy that will raise the temperature of 

 i gram of water i C., which equals 425.5 grammeters. 



The following illustration will serve, first of all, to make clear the relation 

 between heat-production and work. If a small steam-engine, in which a given 

 amount of coal is burned, is placed within the inner chamber of a capacious calor- 

 imeter, heat alone will be produced from the coal so long as the engine is not 

 brought into working activity. The water in the calorimeter will indicate exactly 

 through the elevation of its temperature the number of heat-units furnished by 

 the burning coal. If this has been determined, the same amount of coal is burned 

 in the steam-engine in a second experiment, but at the same time by means of a 

 suitable device outside of the calorimeter work is performed by the engine, such 

 as the raising of a weight. This work must naturally be furnished by the potential 

 energy of the fuel and be transformed. If now the elevation of temperature at 

 the end of the experiment is noted it will be found that a smaller number of heat- 

 units have been transmitted to the water than in the first experiment, in which 

 the engine was heated, but performed no work. Comparative experiments of this 

 kind have demonstrated beyond doubt that in the second experiment the useful 

 working effect is almost proportional to the heat-deficit observed. 



If the processes in the organism be compared with this illustration 

 it will be seen that the resting human being generates between 2 J and 2-J 

 million calories from the potential energy contained in the ingested 

 food, while the amount of work performed by a laborer is estimated at 

 300,000 kilogram -meters. If the organism were exactly comparable 

 with the engine, just so much less heat would have to be formed within 

 the body as corresponds to the amount of work done. As a matter of 

 fact, the organism naturally can transform only a lesser amount of heat 

 from the same measure of potential energy when work is performed. 

 One point, however, should be taken into consideration in which the 

 laborer differs from the working engine. The laborer consumes in the 

 same time a far larger amount of potential energy than the resting indi- 

 vidual. A greater amount of combustion takes place in his body, and 

 it therefore comes about that the loss through the increased combustion 

 is not alone made good, but is even over-compensated. The laborer is, 

 by reason of his greater muscular activity, warmer than the resting 

 individual. The following may serve as an example of the relation in- 

 dicated: Him in 1858 took up at rest in the calorimeter-chamber 30 

 grams of oxygen in an hour, and produced 155,000 calories. When 

 subsequently he undertook in the chamber work transmitted outward, 

 to the amount of 27,450 kilogram-meters, he consumed 132 grams of 

 oxygen and furnished only 251,000 calories. 



In estimating the amount of work done only that transmitted outward as heat- 

 equivalent is to be considered, as, for instance, the lifting of a load, the throwing 

 of weights, the displacement of masses. Also the lifting up of the body is to 

 be included here. In ordinary walking the overcoming of the resistance of the 

 air and the activity of the muscles must be taken into consideration. In descending 

 from a height an increase in heat of the body is not to be looked for, for muscular 

 activity is required to prevent the body from falling down and from collapsing, 

 and to avoid a too precipitate descent. 

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