HORMAL PROCESSES OF ENERGY METABOLISM 521 



ment less the gain in weight of the absorbers gives the amount of oxygen 

 absorbed. 



2. Closed Circuit Type of Apparatus. In most of the open-circuit 

 types of apparatus thus far described the determination of oxygen is in- 

 direct, being based upon the loss of body weight of the subject. The absorp- 

 tion of oxygen can be determined directly, however, provided the subject is 

 enclosed in an air-tight system of known capacity. The simplest system 

 of this sort consists of a respiration chamber only of largo enough capacity 

 to supply oxygen and permit respiration of ordinary atmospheric air with- 

 out discomfort for at least an hour. By analysis of a sample of air at the 

 beginning and the end of an observation it is possible to learn from the 

 changed composition the amount of oxygen absorbed and the amount of 

 C0 2 given off. 



Fig. 3. Haldane respiration apparatus. Ch, chamber ; 1 and 2 absorbers for 

 ingoing air; 3, 4, and 5, absorbers for outgoing air; M, meter; J, safety bottle; P, 

 air puinp. 



A more physiological arrangement, however, is to provide for the ab- 

 sorption of the carbon dioxid approximately as rapidly as it is produced 

 and its replacement by oxygen. The observations can then be prolonged 

 for many hours. 



a. The Apparatus of Regnault and Reiset. This is the original closed- 

 circuit apparatus. The respiration chamber consists of a glass bell of 45 

 liters capacity (A, Fig, 4). The bell is fitted by an air-tight seal into a 

 metal base which serves at the same time as the base for the surround- 

 ing water jacket. Entrance to the chamber is gained by means of a circu- 

 lar opening in the base. The top or handle of the bell is perforated by 

 several tubes one of which connects with a mercury manometer (a, b, c) 

 for recording the pressure inside the chamber. A second connects with a 

 sampling apparatus d'. Two others connect with the CO 2 absorbers C and 

 C', and a fifth with the oxygen supply (the flasks N, W and N"). The 

 CO 2 absorbers have a capacity each of about three liters. The absorbing 

 fluid is an assayed solution of KOH. Movement of air from the chamber 

 to the absorbers is accomplished by alternately raising and lowering the 

 absorbers. For example, when C is raised as in the figure the fluid runs 



