582 



JOHN R. MURLIN 



rapid motion. By calibration of the apparatus with known sources of 

 heat it is possible to determine the heating effect of the live subject. 



Another group of these calorimeters have double-walls, between which 

 is a cushion of air. The effect of heat generated within the chamber is re- 

 corded by expansion of this air cushion. Among those employing this prin- 

 ciple of registering the effect of heat are the siphon calorimeter of Richet 

 (b) (Fig. 30) and the second calorimeter designed by Rubner (/) (Fig. 

 31). Both these calorimeters have rendered extremely important service 

 to physiological science for it was by means of the former that Richet made 

 his contributions on the relation of heat production to body size and it was 

 by means of the latter that Rubner first proved with a high degree of 



Fig. 30. Richet siphon calorimeter. For description see the text. 



precision that the law of the conservation of energy applies to the animal 

 body (see page 584). The siphon calorimeter is very simple in principle. 

 The space between the walls of the base and cover between which the rab- 

 bit in the figure is placed communicate by a common tube with a pressure 

 bottle containing about three liters of water. A siphon from this bottle 

 terminates in a funnel-like vessel which catches the overflow and delivers 

 it into a burette. By expansion of the air water is forced into the measur- 

 ing limb of the siphon or over into the burette. By calibration of the ap- 

 paratus with known sources of heat the heat of the animal body can be 

 determined. It should be noted that an apparatus of this sort takes no 

 account of the heat of vaporization. 



Rubner's apparatus is a respiration calorimeter. It is ventilated in 

 the same manner as the original Pettenkofer apparatus, and determines 

 directly only the water and carbon-dioxid. The heat-measuring device 



