INCOME AND OUTGO 331 



A man in a calorimeter, therefore, gives out a certain 

 quantity of heat which can be deduced from the warm- 

 ing effect on water circulating in coils and he is credited 

 with having produced an additional .quantity which is 

 estimated by ascertaining how much water has evapor- 

 ated from his skin and respiratory tract. We have said 

 that the latter quantity may be as much as 500 Calories. 

 The total will probably approach 2000 Calories for a 

 resting adult. If the body temperature is not the same 

 at the end of the experimental period that it was at 

 the beginning a correction has to be made for heat 

 retained or dissipated, as the case may be. For example, 

 if the body is equivalent to 50 kilograms of water as a 

 container of heat, and its temperature has risen 0.5C. 

 during the experiment, 25 Calories must have been stored 

 in it. This must be added to. the other quantities to 

 arrive at a correct estimate of the heat produced. 



The total daily production of heat by a full-grown man 

 is not likely to fall below 1500 Calories under any cir- 

 cumstances that can be called normal. The maximum 

 is in the vicinity of 10,000 Calories. These limits are 

 so widely separated that one seeks at once for a de- 

 termining condition and will probably draw a correct 

 inference as to what it is. No other factor influencing 

 metabolism approaches in importance muscular activity. 

 The heat production is nearly proportional to the work 

 performed. It is also true that the discharge of carbon 

 dioxid varies in the same sense. Since, as we have 

 already found, the excretion of nitrogen has no such rise 

 and fall we have here clear evidence in support of a 

 previous general assertion: that muscular contractions 

 are made at the expense of non-nitrogenous fuel. 



Someone may raise the question, does the calorimeter 

 give credit in Calories for energy expended in the per- 

 formance of mechanical work? It may be answered 

 that it does excepting under special conditions. Sup- 

 pose, for instance that the subject of an experiment 

 engages in sawing wood. The ultimate result of his 



