An Improved Electrical Conductivity Method for Accurately Following Changes in the Respiratory Quotient of a Single Biological Sample.

It is not possible to follow the 02 consumption and the CO2 production of a single sample of biological material by conventional volumetric or manometric techniques. A recent paper by LASER and LORD ROTHSCHILD (8) calls attention to the need for a device to measure the respiratory quotient (R.Q.) of a single biological sample. They achieved this end with a quite elaborate manometric apparatus which we feel is too complicated for general use. Means of continual CO2 measurements independent of simultaneous 02 determinations include the katharometer method of STILES and LEACH (17),.the infrared method of McALISTER (11), the mass spectrometer method of BROWN, NIER, and VAN NORMAN (2), and electrical conductivity techniques. The latter seem the most suitable for routine work, judged on the basis of cost, convenience, and technical skill required. Measurement of CO2 by observation of the electrical conductance of an absorbing solution was described by CAIN and MAXWELL (3) and first used for biologically produced CO2 by SPOEHR and McGEE (16). A number of modifications have been published. The literature is summarized by NEWTON (12) who also treats the theory of the general method. FENN (6) described a respirometer vessel containing electrodes for conductivity measurement. The tissue was placed in a central cup surrounded with Ba (OH)2 solution. The vessel was kept at constant temperature and shaken to mix the alkali. It was necessary to stop the shaking to read the conductance, which can be inconvenient. LEDEBUR (9) described a respirometer vessel which incorporated a conductivity inset containing Ba(OH)2 and which could be shaken continuously. The conductivity inset was a glass thimble on the bottom of the respirometer vessel in which electrodes were suspended from a removable stopper on the top of the vessel. It is probable that the cell constant was dependent upon the precise orientation of this