86 



PHYSIOLOGY FOR DENTAL STUDENTS. 



burned in one of them exactly corresponds to the amount as meas- 

 ured by the smaller bomb calorimeter. All of the energy liber- 

 ated 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 which an animal expends, one must 

 add to the actual calories given out, the calorie equivalent of 



Water to absorb heat 



Chamber for animol /" 

 window 



H m 



Fig. 8. Diagram of Atwater-Benedict Respiration Calorimeter. As the 

 animal uses up the O, the total volume of air shrinks. This shrinkage is indi- 

 cated by the meter, and a corresponding amount of O 3 is delivered from the 

 weighed Oa-cylinder. The increase in weight of bottles II and III gives the 

 C0 2 . 



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 kilo- 

 gramme 2 metres 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 experi- 

 mental biology. It can be done in the case of the human jini- 



2A kilogrammemetre is the product of the load in kilogrammes by the dis- 

 tance in metres through which it is lifted. 



