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Continued from page 296.) UNIFORMITY OF DUPLICATE MEASUREMENTS IN REGARD TO RESPIRATION APPARATUS AND BREATHING APPLIANCE.In any research, as well as in clinical application of the results, the investigator is concerned with two problems, viz., what are the actual variations involved and how closely can the method used measure these variations.Naturally, two factors enter into any consideration of these problems, i.e., the duplication of the physiological condition and the adequacy of duplicate measurements for the purpose concerned if the conditions remain constant. The possibility of duplication of results in relation to time is considérée! later. In this research we have attempted to arrange the duplicate determinations in such a manner that the question of time of day, breathing appliance, or respiration apparatus would in no way affect our conclusions. We had two respiration apparatus and three breathing appliances, and thus the possibility of six combinations. We employed six different sequences of experimenting. Owing to technical difficulties it was not possible at times to carry out our original plan of using three subjects with each of the six sequences of periods. From previous experience with respiration apparatus in general16 and the results obtained here, we feel that the data presented in our tables are in no way affected statistically or physiologically by the deviation from our original plan. Table V has been prepared primarily Avith reference to technical possibilities of duplication of results. The values in the table are arranged first as to respiration apparatus; sec-ond, breathing appliance as used with either respiration apparatus; third, averages of first and second periods: fourth, averages of individual differences between first and second periods. The table therefore involves differences in respiration apparatus and differences in breathing appliances as far as the average uniformity is concerned between the measurements in two periods with the different respiration apparatus and breathing appliance.Carbon-Dioxide Elimination. The agreement of the duplicate averages with each breathing appliance, regardless of respiration apparatus employed, is all that could be expected, with the exception of those for the mask in combination Avith the respiratory-valve apparatus. The averages of the individual differences between the first and second periods are highest with the portable apparatus and nosepieces and lowest with the respiratory-valve apparatus and the mask. The average of the individual differences between the first and second periods with the respiratory-A'alve apparatus and mask corresponds more closely with the differences be-tAA-een the averages of the first and second periods than Avith any other combination of breathing appliance and respiration apparatus.Oxygen Absorption. The data for oxygen consumption shoAv that the best agreement on the average between two measurements is with the portable apparatus and mask and the next best is with the nosepieces' and either apparatus. The...