METABOLISM 537 



it is interesting to note that the actual heat given out when a definite 

 amount of alcohol or ether is burned in one of them exactly corresponds 

 to the amount as measured by the smaller bomb-calorimeter. All of the 

 energy liberated in the body does not, however, take the form of heat. A 

 variable amount appears as mechanical work, so that to measure in calories 

 all of the energy that an animal expends, cue must add to the actual cal- 

 ories given out, the calorie equivalent of the muscular work which has 

 been performed by the animal during the period of observation. This can 

 be measured by means of an ergometer, a calorie corresponding to 425 

 kilogram* meters of work. That it has been possible to strike an accurate 

 balance between the intake and the output of energy of the animal body, 

 is one of the achievements of modern experimental biology. It can be 

 done in the case of the human animal ; thus, a man doing work on a bicycle 

 ergometer in the Benedict calorimeter gave out as actual heat 4,833 C., 

 and did work equalling 602 C., giving a total of 5,435 C. By drawing up 

 a balance sheet of his intake and output of food material during this 

 period, it was found that the man had consumed an amount capable of 

 yielding 5,459 C., which may.be considered as exactly balancing the actual 

 output. 



It would be out of. place to give a full description of the respiration 

 calorimeter here. The general construction will be seen from the accom- 

 panying figure of the form of apparatus in use for patients in the Russell 

 Sage Institute, New York. One of the most interesting details of its con- 

 struction concerns the means taken to prevent any loss of heat from the 

 calorimeter to the surrounding air. This is accomplished in the following 

 way: The innermost layer of the wall is of copper; then, separated from 

 this by an air space, is another wall of copper, outside of which are two 

 wooden walls separated from each other and from the outer copper walls 

 by air spaces. The two copper walls are connected through thermoelectric 

 couples, so that an electric current is set up whenever there is any differ- 

 ence in their temperatures. The current is observed by means of a gal- 

 vanometer placed outside the calorimeter, and from its movements the ob- 

 server either heats up or cools down the outer copper walls so as to cor- 

 rect the difference of temperature causing the current. This is done by an 

 electric heating device .or by cold water tubes placed between the outer- 

 most copper and the innermost wooden walls. Since the temperature of 

 the two copper walls is the same, there can be no exchange of heat between 

 them, and consequently none of the heat that is absorbed by the inner cop- 

 per walls is allowed to be carried away. All the heat given out by the 

 animal is absorbed by the stream of cold water flowing through the coils 



*A kilogram mctrr is the product of the load in kilograms multiplied by the distance in meters 

 through which it is lifted. 



