NUTRITION 



143 



The amounts of protein, carbohydrate and fat oxidised are 

 calculated, as previously described, from the excretion of 

 nitrogen, the respiratory quotient and the volume of oxygen 

 absorbed. 



In order to carry out a complete experiment of this nature 

 a respiration calorimeter is used. It consists of a closed 

 chamber in which the animal can be placed and the respiratory 

 gases measured and analysed. The food can be passed through 

 a trap door and the excreta obtained and analysed. 



FIG. 26. Diagram of Respiration Calorimeter. 



Surrounding the two casings shown in the diagram are several layers of wood, etc., which 

 are intended to protect the apparatus from being affected by variations in the surrounding 

 temperature. They have been omitted from the diagram so as not to confuse it by too 

 much detail. (Modified from Halliburton.) 



The energy output is not measured as the separate items, 

 but loss of heat from the chamber is prevented and the heat 

 set free is absorbed by a water circulating apparatus. Any 

 moisture condensed on the heat absorbing apparatus gives up 

 its latent heat and any uncondensed moisture is collected in 

 the gas analysis apparatus and its heat equivalent calculated. 

 The air is passed in at the same temperature at which it comes 

 out, hence this source of heat loss is eliminated. The 

 external work performed must be measured and its heat 

 equivalent calculated. 



The loss of heat from the calorimeter is prevented by having 

 two metal casings one inside the other. The temperature of the 

 outer casing is kept the same as the inner, thus there cannot be 



