148 GENERAL METABOLISM 



walls, ceiling and floor of the chamber are composed 

 essentially of four layers separated by air-spaces. The 

 outer two are of wood, the inner two of copper. The 

 copper walls are connected together in an electric circuit 

 in which is placed a thermo-electric junction and galvano- 

 meter. These register any difference of temperature between 

 the two walls. The temperature of the outer copper wall 

 can be varied by means of an electric heating apparatus. 

 When any difference of temperature occurs between the 

 walls it is annulled by heating or cooling the outer. There 

 is therefore practically no loss of heat by radiation from 

 the chamber. All the heat evolved by the subject is 

 absorbed by a circulation of cold water through the chamber, 

 and its amount calculated from the volume and rise in tem- 

 perature of the water. But this does not include all the 

 heat produced, for a certain amount is dissipated in convert- 

 ing water into water- vapour in the lungs. This is calcu- 

 lated by absorbing the water-vapour in the outgoing air 

 with sulphuric acid and estimating the latent heat of its 

 formation. 



The unit of energy employed is the amount of heat 

 required to raise one kilogramme of water through 1° C. 

 This is called the large Calorie (C). 



The accuracy of the apparatus, tested by burning a 

 known amount of some inflammable substance in it, is 

 found to be of a very high order. 



When the individual is at complete rest almost all 

 the energy is given ofE as heat. If it is desired to investigate 

 the effect of muscular acti^dty, a measured amount of 

 work is performed on a pedaUing machine. The work 

 recorded is reduct'.d to its heat equivalent, 1 Calorie being 

 equivalent to 425 kilogramme-metres of work. 



It is first necfsssary to determine whether the foodstuffs 

 Uberate the sanic amount of energy when metabohsed in 

 the body and w len oxidised in vitro. It is obvious at the 

 outset that acci^rate correspondence is not to be expected 

 unless the oxidation which occurs within the body is as 



