602 EXPERIMENT STATIOIST EECOUD, 



course, provided with facilities for supplying the subject with food, 

 and for collecting the liquid and solid excreta. There is also pro- 

 vision for detennining body temperatures, respiratory movements, 

 and similar factors whenever experimental conditions necessitate it. 



It will be recognized that these measurements of heat, of carbonic 

 acid, and of water to be of value call for a high degree of accuracy, 

 and require a very delicate and finely adjusted mechanism, sensitive 

 to slight changes from within and protected from fluctuations with- 

 out. The manner by which this is accomplished is quite technical, 

 but some of the leading features may be readily understood. 



The respiration chamber, about 6^ by 6^ by 4 feet in size, is made 

 up of double metal walls, the inner one of copper and the outer one 

 of zinc, the two being separated by a small space. They are pro- 

 vided at frequent intervals with thermal junctions, or thermocouples, 

 which are arranged in series. The latter being composed of two dif- 

 ferent metals, any difference between the temperature of the inner 

 and outer walls sets up a current which is indicated by a gal- 

 vanometer outside the chamber. The new thermocouple has been 

 improved and made more efficient, and a simpler switch has been 

 devised to connect the various groups of thermocouples with the 

 galvanometer. 



Outside the zinc wall is an air space surrounded by a wall of cork 

 board 1-| inches thick, which is a very excellent heat insulator and 

 protects the inclosed air space from changes in the laboratory tem- 

 perature. The cork layer is protected in turn by an outer covering 

 of asbestos lumber, in place of the former wooden covering, put on in 

 panels and bound together with brass strips. The wooden frame- 

 work formerly used has been replaced by a skeleton of structural 

 iron to which the walls are attached, raised above the laboratory 

 floor, the whole structure being very rigid. Throughout the con- 

 striction attention has been given to details which make for sim- 

 plicity and convenience, and the outer covering is so arranged that 

 it may be easily removed, affording access to all parts of the zinc 

 wall and to the devices attached to it. 



To prevent the passage of heat through the zinc and copper walls 

 in either direction, the dead air space surrounding the zinc wall is 

 kept at practically the same temperature as the air within the cham- 

 ber, advantage being taken of the well-known fact that no passage of 

 heat occurs between two bodies having the same temperature. To 

 maintain this equilibrium the air space is provided with a system of 

 electric resistance wires for heating and of small water pipes for 

 cooling, as conditions may require. The numerous thermal junc- 

 tions between the inner (copper) and outer (zinc) linings show the 

 attendant at once by means of the galvanometer any difference in 



