ALVEOLAR CARBON DIOXIDE. 487 



tions. While the agreement of these values with a large number of the 

 subjects is perhaps all that could be expected, certain instances, such 

 as the variation with Mon of 43.2 to 50.1 mm., is rather wider than one 

 would normally expect, likewise that with Gul from 41.6 to 48.5 mm., 

 with Pea from 39.9 to 49.9 mm., with Pec from 40.2 to 47.2 mm., with 

 Spe from 35.1 to 44.8 mm., and with Vea from 31.9 to 49.4 mm. On 

 the whole the values lie considerably above 43 mm., which is about that 

 ordinarily found with normal individuals. It seems important, also, 

 to find if the variations from day to day were inherent in the method or 

 were actually existing with all subjects. Fortunately for this purpose 

 we have comparable values for comparison which were calculated from 

 the respiratory exchange as determined by the respiratory-valve appa- 

 ratus. 



This computation was carried out in the usual way by using the 

 ventilation of the lungs and the carbon-dioxide production according 

 to the following formula : 



Car bon dioxide excreted per minute 

 Alveolar carboR dioxide = Total ventilation - (Respiration rateX 

 (per cent) ^^q ^^ ^^^^ space). 



Per cent CO2X barometric pressure— 47 nom. = tension in millimeters. 



This method of computing the alveolar carbon dioxide involved the 

 use of a constant dead space in the respiratory passages of 140 c. c, 

 in accordance with the method used by Loewy and Zuntz.^ 



The irregularities noted from day to day with Pea seem to be veri- 

 fied in large part by the computed values, although certain exceptions 

 appear contrary to this. Thus the low value of 39.9 mm. found by 

 the direct method on November 16 is not accompanied by a low value 

 computed by the indirect method. It should be borne in mind that the 

 computation method assumes a constant dead space for all the subjects. 

 This might introduce an error in comparisons of values for different 

 subjects, but it is hardly probable that the dead space would change 

 so profoundly from day to day as to effect a real variation in the 

 calculated alveolar carbon dioxide. Therefore the comparison of the 

 variations in the two sets of values is based on sound principles. 

 Although we had the cooperation of the subjects and the long period 

 of observation made them thoroughly familiar with the technique, 

 the fact that somewhat more regular values for the alveolar carbon- 

 dioxide tension are found by the computation method than those 

 secured by direct determination should not be lost sight of, and this 

 leads one to beheve that the calculated values in the long run prob- 

 ably have a higher degree of accuracy and the ir variations from day 



1 Loewy and Zuntz, Berl. klin. Wochenschr., 1916, 53, p. 828. 



