58 



PHYSIOLOGY 



CHAP. 



thus limiting the air space with which the animal comes in contact. The 

 outer chamber, A A', contains a quantity of water, the calorirnetric medium, 

 sufficient to cover the chamber B B' entirely. In order that the air breathed 

 by the animal may be renewed, the inner chamber communicates with the 

 tube D, which supplies it with fresh air from outside, while the vitiated air 

 escapes through the tube D' by means of the coil S at the bottom of the cage 

 (shown in horizontal section in the figure) ; one opening E is in communica- 

 tion with the inner chamber, while E' is a continuation of D'. Thus the ex- 

 pired air before coming into the open air has time to acquire the temperature 

 of the water in the calorimeter. In order to distribute uniformly the heat 

 acquired by the water, the wing-shaped fan a b is set in motion. The rise in 



FIG. 8. D'Arsonval's compensation calorimeter. 



the temperature of the water due to the heat produced by the animal is indicated 

 by the two thermometers Q and Q'. 



This calorimeter is open to various objections, of which the most serious 

 is that inherent in the method, i.e. the raising of the temperature of the en- 

 vironment of the animal, which, as we now know, has a great effect upon 

 the regulation of temperature in the animal and the radiation of heat. For 

 this reason calorimeters in which the liquid is kept at the same temperature 

 are preferable. Of these methods the best is that of d'Arsonval, called the 

 compensation calorimeter. 



As will be seen by Fig. 8, it consists of two concentric cylinders of metal 

 confining two cavities, of which the inner one holds the animal to be experi- 

 mented on, and the outer one the calorimetric liquid (water, petroleum, etc.). 

 Through the liquid passes a coiled cooling tube, one end of which is con- 

 nected with a supply of cold water at 0, whilst the other end communicates 

 by means of an indiarubber tube 4 with the receptacle 0, arranged to receive 

 the water which escapes. 



