THE ENERGY EQUATION. 403 



stuffs is much more difficult. The work of the heart alone 

 has been estimated at from 20,000 to 60,000 kilogram-meters 

 in 24 hours. 3,000 Cal. of heat liberated would correspond 

 to 1,270,500 kilogram-meters of work; hence the heart work 

 in forcing the blood through the vessels may amount to as 

 much as 5 per cent of the whole metabolism. 



In respiration the \vork done is largely the expansion of the 

 thorax against the atmospheric pressure and the elastic ten- 

 sion of the rib cartilages and the lungs. The conditions for 

 estimation are perhaps more favorable than in the other case. 

 It has been calculated that 4 to 5 per cent of the whole metab- 

 olism is called for by this work. 



In maintaining the tonus of the great mass of skeletal mus- 

 cles of the body it is likely that a large metabolism is required. 

 The muscular part of the body is not far from 40 per cent 

 in the mean or 10 per cent of dry substance. In the body of 

 a man weighing 75 kilograms we have therefore about 7.5 

 kilograms of muscle substance. A large fraction of this falls 

 to the so-called skeletal portion which exists always in a pecu- 

 liar tense condition. In keeping up this condition without 

 doing outside work oxidation is necessary. Glycogen is split 

 up and water and carbon dioxide appear. The only visible 

 effect of this metabolism is the production of heat. When the 

 muscle does outside work, as in lifting a weight, although the 

 heat production may be greater in the sum, it is relatively 

 less in proportion to the oxygen consumption. A part of the 

 energy is consumed in lifting the weight. 



Heat Production Incidental. It is possible that the whole 

 heat liberation at times is but a result of the various kinds of 

 internal work done, and that no oxidation takes place for the 

 simple production of heat. This may be the case at relatively 

 high temperatures. At certain lower temperatures, on the 

 other hand, it is apparent that a part of the heat liberation is 

 called for independently of that transformed in the internal 

 work. A certain heat production is necessarily connected 

 with the performance of the various body functions and this 



