ii THE THEEMIC ECONOMY OF THE OEGANISM 57 



There are numerous and serious defects in this method, amongst which we 

 may mention the impossibility of measuring accurately the quantity of 

 water produced, since some of it ad- 

 hnvs to the pieces of ice and to the 

 siili - of the calori meter, and of renew- 

 ing the air for breathing, and finally 

 the considerable lowering of tempera- 

 ture to which the animal is subjected. 

 For these reasons physiologists have 

 recourse to other and more satisfac- 

 tory methods. 



B. We may divide the numerous 

 forms of calorimeter with a fluid 

 medium (water) into : (a] Methods in 

 which the man or animal is brought 

 into direct contact with the medium, 

 the bath method, which has numerous 

 defects and drawbacks ; (6) methods 

 in which the man or animal is separ- 

 ated from the calorimetric medium 

 by a space filled with air, methods 



which have numerous advantages FlG c ._i ce calorimeter of Lavoisier and Laplace, 

 and have been used in two different 



ways, in one of which the water is gradually heated, while in the other it is 

 kept as far as possible at the same temperature. 



The former plan is carried out in Dulong's calorimeter (Fig. 7), which is 



FIG. 7. Dulong's water calorimeter. 



suitable for small animals used for experimental purposes. It consists of two 

 concentric chambers having thin metal sides. The inner of these chambers, 

 B B', for the animal's cage, isj closed with an air-tight and water-tight lid, 



