182 NUTRITIONAL PHYSIOLOGY 



temperature changes and supplemented by the heat loss 

 through evaporation) is a just representation of the total 

 energy set free. May there not be other forms of energy 

 than heat? What are the facts concerning muscular 

 work? We cannot say positively that no energy eludes 

 the calorimeter, but the impression is constantly being 

 confirmed that any such escape must be insignificant. As 

 to the energy of movement it can be shown that under most 

 conditions this will eventuate in heat. This is an import- 

 ant matter and deserves to be carefully illustrated. 



Let us take for an example the case of the heart. This 

 organ does a great deal of work in forcing the blood through 

 the vessels. Does this work appear as heat so as to be 

 arrested and recorded by the calorimeter? There is no 

 doubt that it does. The conversion is effected as the re- 

 sistance to the blood-flow is encountered and overcome. 

 The heart produces some heat within itself, and some addi- 

 tional heat due to its metabolism is made to appear in all 

 parts of the body. Wherever the blood is driven there is 

 friction, which is a means of transforming the energy of 

 motion into heat. The same statement applies to the 

 breathing movements. Work is done, in the physical sense 

 of the term, each time the ribs are lifted, but with their 

 return to the expiratory position this work is reconverted 

 into heat. So, too, all ordinary forms of exercise may be 

 shown to result in heat production. 



Nevertheless it is possible to devise conditions under 

 which a part of the metabolic energy will not be given to 

 the calorimeter. Suppose, for example, that the subject 

 within the apparatus is employed in taking books from the 

 floor and placing them upon shelves. As long as he pur- 

 sues this form of activity a share of his evolved energy will 

 become potential and be lost to direct observation. It 

 may be said to exist as "energy of position" in the mass 

 which he has elevated. In other words, it has been stored. 

 If, after a day of this labor, he should occupy himself in 

 removing the books from the shelves and laying them upon 

 the floor, he would be giving to the calorimeter more heat 



