544 METABOLISM 



air in the system. Beyond this and the pump is a specially constructed 

 bottle containing concentrated H 2 S0 4 , then one containing soda lime, and 

 lastly another H 2 S0 4 bottle. The first H 2 S0 4 bottle absorbs all the water 

 vapor contained in the air coming from the chamber; the soda lime bottle 

 absorbs the C0 2 , and the second H 2 S0 4 bottle absorbs water that is pro- 

 duced in the chemical reaction involved in the absorption of the C0 2 by 

 the soda lime (2NaOH+C0 2 =H 2 0+Na 2 C0 8 ). By weighing these ab- 

 sorption bottles before and after an animal has been for some time in the 

 chamber, the weight of H 2 and of C0 2 given out can be determined. An- 

 other side tube leads to an oxygen cylinder, the valve of which is manip- 

 ulated so as to cause oxygen to be discharged into the system at such a 

 rate as to compensate exactly for that used up by the animal, as indicated 

 by the behavior of the meter. The amount of oxygen required is de- 

 termined either by weighing the oxygen cylinder before and after the ob- 

 servation or by measuring the volume of oxygen used by passing it through 

 a carefully calibrated and very sensitive water meter inserted on the side 

 tube that connects the 2 cylinder with the main tubing of the system. 

 Since muscular activity causes pronounced changes in the rate of me- 

 tabolism, means are usually taken to secure graphic records of any move- 

 ments made during the observation. 



The growing importance in clinical investigations of measurements of 

 the respiratory exchange and the necessity for having methods that are as 

 simple as is consistent with accuracy, have led to the introduction of 

 several other forms of apparatus, of which those of F. G. Benedict and of 

 Tissot* are the most important. In the former a tightly fitting mask, 

 applied over the nose and mouth is connected, by a short T-piece, with 

 the same tubing as that used in the respiration calorimeter. The patient 

 thus breathes in and out of the air stream that is passing along the tubing 

 without any of the obstruction experienced when the breathing has to be 

 performed through valves, as in the older (Zuntz) forms of portable 

 respiratory apparatus. It is particularly for studies on man that this 

 apparatus has been devised. The Tissot and Douglas methods are shown 

 in Figs. 179 and 180.* 



To complete the investigation, it is necessary that the urine and feces 

 be collected and the nitrogen excretion measured. "When the respiratory 

 excreta are measured over a considerable period of time, as in the large 

 calorimeter, the urine is collected for the same period, but when shorter 

 respiratory measurements are made, the urine of the twenty-four hours 

 is usually taken. 



Principles Involved in Calculating 1 the Results. Provided with the an- 

 alyses furnished by the above methods, we proceed to ascertain the total 



"The Tissot method will be found described in full elsewhere (page 554). 



