ii THE THEKMIC ECONOMY OF THE OEGANISM 59 



The indiarubber tube, before reaching the receptacle, passes through the 

 regulator of the outflow B, which adjusts the escape of the liquid auto- 

 matically, so that the cold water only escapes when the temperature of the 

 calorimeter is higher than that of> the outer air. The automatic working of 

 this regulator will be readily understood from the illustration. By means of 

 tube 6 it is directly connected with the liquid in the calorimeter. If weights 

 be pi iced on the pan in such a way as to compress the indiarubber tube 4, 

 the liquid cannot escape through the tube. As soon, however, as the animal 

 is placed in the calorimeter, the liquid becomes hotter and therefore expands ; 

 this expansion, transmitted through tube 6 to the lower cylinder of the 

 regulator, raises the weight pan and thus allows a compensating escape of 

 cold water. It will be seen that in this way the temperature of the calori- 

 meter is kept uniform. 



The recipient (7, in addition to receiving and measuring the quantity of 

 water which escapes, affords also a graphic record, as will be seen from the 

 figure. 



The ventilation of the environment of the animal is secured by a current 

 of air which enters by tube A and makes its exit by tube S. 



In order to obtain reliable results the apparatus must of course be kept 

 from variations in the temperature of the outside air ; this condition can' 

 be obtained by covering the calorimeter with an outer isolating jacket, 

 or experimenting in a laboratory in which the temperature is kept 

 constant 



On the principle of this calorimeter with a uniform temperature Atwater 

 constructed the large calorimeter used in his well-known researches upon the 

 exchange of material and energy in man. It is a real room, in which the 

 person can spend days and nights, and which allows of the exercise of all his 

 functions. The inner free space measures 2*15 metres in length, 1*92 in 

 height, and 1-22 in width. It is shut off from the outside by a double wall 

 of metal, the inner one being copper, the outer zinc. Between the two walls 

 there is an air space about 7-6 cms. wide. To prevent the calorimeter being 

 affected by variations in the temperature of the outside air, it is encased 

 in two or three wooden covers, about 5 cms. apart. 



There is, for the purpose of keeping its temperature uniform, outside the 

 zinc wall and inside the first wooden one, a system of silver-plated wires and 

 iron tubes, the former for the purpose of heating the calorimeter by sending 

 an electric current through it, the latter for the purpose of cooling it by the 

 passage of a current of cold water. Provision having thus been made 

 against the loss or gain of heat through the walls of the calorimeter, it 

 remains to conduct away and measure the heat produced inside it by the subject 

 of the experiment. In order to do this, the temperature of the water in 

 entering and leaving the system of tubes in the calorimeter is recorded with 

 an extremely sensitive thermometer divided to T ^ 7 of a degree. In addition, 

 the quantity of water circulating through the system is measured with an 

 accurate meter. 



The room occupied by the subject of the experiment is ventilated by 

 means of a special apparatus. Both the ingoing and the outgoing air are brought 

 into equilibrium with the temperature of the calorimeter by means of 

 special contrivances. In order to make his researches still more perfect, 

 Atwater analysed the respiratory gases, and also the intake and output of 

 material, i.e. he studied not only the dynamic but also the material exchange, 

 wliich makes the prosecution of the plan of research far more complicated. 

 This will be realised from the fact that in each of his experiments the services 

 of at least twelve persons were required. 



G. There are two kinds of calorimeter having a gaseous medium (air) : (a) 

 those in which the air serving as the calorimetric medium comes into .direct 

 contact with the animal ; (b) those in which the calorimetric air is 

 not in direct contact with the source of heat, but is contained in an 



