12 A RESPIRATION CALORIMETER. 



The air is therefore again forced through sulphuric acid (not shown in 

 the diagram) and then enters a pipe leading back to the chamber. It 

 is now freed from carbon dioxide and water, but still deficient in oxy- 

 gen. The oxygen is replenished by admitting the requisite amount 

 from a steel cylinder of compressed oxygen through an opening in the 

 ventilating air-pipe, as shown in the diagram, and the air when restored 

 to a respirable condition reenters the respiration chamber. 



The metal walls of the chamber and the metal pipes confine the air 

 in a definite volume, and to allow for expansion or contraction of the 

 air volume as the result of barometric or thermometric fluctuations a 

 compensating device, consisting of two pans with flexible rubber covers, 

 is inserted in the ventilating air-pipe. 



The amounts of water and carbon dioxide absorbed by the sulphuric 

 acid and soda lime and of oxygen admitted to the system are obtained 

 by direct weighing on suitable balances. These weights give an approx- 

 imate estimate as to the carbon dioxide, water, and oxygen involved in 

 the transformations which have taken place in the body. There may 

 be, however, considerable variations in the composition of the air in the 

 system from time to time, especially as regards the oxygen content, 

 which are not detected in this way. Since the volume of air in the 

 closed circuit is comparatively large, even a slight variation produces a 

 considerable error. It is therefore necessary to know the composition 

 of the air at the beginning of an experiment, and also of the residual 

 air at the end of each experimental period. Apparatus suitable for 

 this purpose has been especially devised and is described in connection 

 with the respiration apparatus. 



From these data as a whole, with suitable corrections to be explained 

 in detail, it is possible to compute accurately the amounts of oxygen 

 absorbed and carbon dioxide and water eliminated by the subject during 

 an experiment. 



THE RESPIRATION CHAMBER. 



The respiration chamber is an airtight, constant-temperature room, 

 2.15 meters long, 1.22 meters wide, and 1.92 meters high, with a total 

 volume of about 5,000 liters. It is lighted by a window on the east 

 side, and has several other openings for the admission and removal of 

 food, air, etc. It is furnished with a table and bed, both of which 

 may be folded against the walls when not in use, a chair, a telephone, 

 and, in certain classes of experiments, with a bicycle ergometer. A 

 view of the interior taken from the window is shown in figure 7, and 

 in figure 8 a cross-section of the chamber showing the location of some 



