696 



PHYSIOLOGY 



If we take into account the great difficulties of such an experi- 

 ment, we cannot but be impressed with the closeness of agreement 

 between the total output of energy reckoned as heat and measured by 

 the warming of a given volume of water and the total income of energy 

 as estimated from the chemical reactions involved in the metabolic 

 changes which had taken place during four days of the experiment. 

 The important result which comes out in such experiments is that 

 the food-stuffs produce the same amount of energy when oxidised 

 in the body as when burnt to the same end-products outside the 



Water 



FIG. 317. Diagram to show the principle of the Atwater-Benedict calorimeter. 



(After HALLIBURTON.) 



body, so that it becomes easy in any given research to sum accurately 

 the energy income of the body. 



The Atwater calorimeter has been improved to such an extent 

 by Benedict and his fellow workers that it has practically replaced 

 all other forms for physiological purposes. It consists of a room 

 or chamber with double non-conducting walls. All round the inner 

 wall of the room are fitted coils of pipes through which a stream 

 of water flows. The pipes are fitted with discs so as to take up 

 rapidly heat produced in the room. The current of water is accurately 

 adjusted so as to maintain the temperature of the inner wall constant. 

 As the inner wall and outer wall are kept at the same temperature, 

 no heat is lost to the exterior, the whole of the heat produced by 

 the animal or individual in the chamber being communicated to 

 the water passing through the chamber. The temperatures of the 

 entering and leaving water are taken by accurate thermometers 

 reading to a hundredth or a thousandth of a degree Centigrade. 

 Knowing the amount of water that has passed through in a given 

 time and the difference in temperature during the same time, it is 



