HISTORICAL A respiration calorimeter is an apparatus designed for the measurement of the gaseous exchange between a living organism and the atmosphere which surrounds it, and the simultaneous measurement of the quantity of heat produced by that organism. The first contrivance of this nature was described by Lavoisier in 1780. It will be remembered that Lavoisier was the first to comprehend the significance of the then newly discovered oxygen. Primitive though the apparatus, yet intellectually inspiring was the mind which so early grasped the principles and understood many of the difficulties. Apparatus for the measurement of the respiratory exchange was perfected before that for the measurement of heat production. Thus, Regnault and Rieset1 in 1850 designed an air-tight apparatus in which an animal was placed; the carbonic acid formed in it was removed by pumping the air into flasks filled with potash, and oxygen was added