This apparatus is designed much after the principle of the
Regnault-Reiset apparatus, in that there is a confined volume of air in
which the subject lives and which is purified by its passage through
vessels containing absorbents for water and carbon dioxide. Fresh oxygen
is added to this current of air and it is then returned to the chamber
to be respired. This principle, in order to be accurate for oxygen
determinations, necessitates an absolutely air-tight system and
consequently special precautions have been taken in the construction of
the chamber and accessories.