In a recent publication1 I described a gas analysis apparatus suitable for rapid and accurate laboratory work. This apparatus is, however, somewhat cumbrous, and cannot easily be conveyed from place to place, as is very often required in investigations relating to questions of hygiene. It also occupies a good deal of working space in a laboratory, as it cannot be moved from its place without a good deal of trouble. On the other hand the already existing forms of portable gas analysis apparatus for technical work are too inaccurate for many of the requirements of work in hygiene and physiology. I have therefore designed an apparatus with a view to meeting these defects as far as possible2.