The research described in this report was planned on the following lines:— In October, 1918, portable Haldane analysers and other apparatus were installed in the Research Sub-section of the Welfare and Health Section of the Ministry of Munitions, and the three authors carried out a considerable number of determinations upon themselves, both with the object of acquiring or regaining familiarity with the experimental technic and in order to determine what form of respiratory apparatus would be most suitable for use in the study of factory conditions. Ultimately, a system was evolved which conforms to the rules afterwards laid down for the guidance of investigators by the Metabolism Research Sub-Committee of the Royal Society Food (War) Committee. Having acquired the necessary experience, it was decided to proceed on the following general lines:—Permission having been granted to make observations in a national projectile factory in the north-east of London, we arranged to make measurements upon women engaged on the various operations of the factory, while attention was coincidently directed to the cooling power of the air in the workrooms; or, more exactly, in each experiment on a worker, the cooling power of the air was ascertained in a position as near as possible to the worker during the experiment, that is to say, for the purpose in view, practically in an identical position. The respiration apparatus used was a modification of the Douglas bag combined with a face mask (approved by the Metabolism Research Sub-Committee) and needs no special description.