330 HUMAN PHYSIOLOGY 



partly from the breathing passages and partly from the 

 skin of the imprisoned volunteer. 



The dry air from the sulphuric acid still contains the 

 carbon dioxid which it has gained through being re- 

 spired. To remove this it is conducted through a 

 container in which alkali is used to retain the carbon 

 dioxid. Special precautions are taken to hold back the 

 moisture which might be carried out of the alkaline 

 mass at this point. The gain in weight registered by 

 the alkali cylinder during an experiment is taken to 

 equal the output of carbon dioxid. The air thus freed 

 from water and carbon dioxid is returned to the chamber. 



It will be recognized that the scheme, so far as it has 

 been described, keeps down the humidity and the carbon 

 dioxid in the air breathed by the subject but does not 

 compensate for oxygen consumed. This is secured as 

 follows: A tank of pure oxygen is at hand and con- 

 nected with the chamber. As the oxygen originally 

 available is diminished by respiration and the result- 

 ing carbon dioxid is absorbed by the alkali the volume 

 of the air in the compartment will tend to contract. By 

 an automatic arrangement any measurable shrinkage 

 of the air in the apparatus will automatically admit 

 oxygen from the tank, while the admission will cease 

 as soon as the initial volume and density have been 

 restored. 



The oxygen tank is weighed from time to time. 

 The- diminution in weight indicates how much oxygen 

 has passed into the chamber to take the place of that 

 consumed by the subject. So, with a chamber of this 

 pattern, three figures are obtainable: the water loss, the 

 carbon dioxid elimination, and the oxygen consumption. 

 If the urine and the feces are collected for the same 

 period we may consider that we have a fairly complete 

 knowledge of the body's discharges. Of course, the 

 task is much less simple than it has been made to appear. 

 There are preliminary and subsequent analyses of the 



