668 



PHYSIOLOGY 



foodstuffs in the body during the same time. In an earlier chapter I have 

 quoted the results of an experiment by Rubner on a dog, which demonstrated 

 this equivalence, as proving the important fact that the fundamental 

 doctrine of the Conservation of Energy applies to the organised as to the 

 inanimate world. Similar results have been arrived at by Atwater in a 

 series of experiments with a special calorimeter on man. It may be sufficient 

 here to give the figures from one such experiment : 



If we take into account the great difficulties of such an experiment, 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 givon 

 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 foodstuffs produce the same 

 amount of energy when oxidised in the body as when burnt to the same 

 end products outside the body, so that it becomes easy in any given research 

 to sum jMTiirali'ty the ener^v income of the body. 



Tin- Atwater calorimeter has been improved to such an extent by Bone- 

 diet and his fHlnw-wm-kvrs. tluit it has practically replaced all other forms 

 tor j)hvsi..loL!ir:i! purpnsrs. It consists of a room or chamber with double 

 non conduct inj walls. All round the inner wall of the room are fitted coils 

 of pipes thiou-h 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 \\all are kept at the same tem- 

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



