60 



PHYSIOLOGY 



CHAP. 



annular cavity of a receptacle having double walls, the animal to be experi- 

 mented on being placed in the inner cavity. 



Of the first class we may mention d' Arson val's anemocalorimeter, which, 

 though not very accurate, is in its simplicity admirably adapted to 

 physiological or clinical experiments on man. 



The principle on which this method is based is that hot air tends to 

 ascend, producing a current of air from below upwards the velocity of which 

 is in proportion to the quantity of heat produced. 



As will be seen by Fig 9, A, the apparatus consists of a tent of silk or 

 woollen material about two metres high, not touching the ground, but held 

 up by a three-legged support ; within it a man can stand upright. In the 



roof is a conical funnel, of which the 

 outlet is bent at a right angle and the 

 inlet is large enough to contain the 

 anemometer shown in Fig. 9, B. This 

 anemometer is a very light windmill ; 

 the eight aluminium sails placed at 

 an angle of 45" to the axis of rotation 

 are set in motion by the current of air, 



FIG. 9. D'Arsonval's anemocalorimeter. 



which, ascending from inside the tent, passes through the funnel. The 

 movement of the wings is transmitted and measured by the meter attached 

 below. 



In order to carry out researches with this apparatus, it must first of all be 

 tested and graduated. This is easily done by placing in it a constant source 

 of heat and noting the number of revolutions registered by the meter in 

 a given time five minutes for instance when the mill has reached its 

 maximum velocity. In experiments on man, a certain time ten minutes 

 will usually be long enough must be allowed to elapse between the 

 placing of the person in the apparatus and the starting of the meter in order 

 that the windmill may attain its maximum velocity and uniform motion. 



D'Arsonval was able without difficulty to convert this calorimeter into a 

 calorigraph, by placing the meter in an electric circuit which was closed when 



