800 CHANGE OF COMPOSITION OF ALVEOLAR AIR, 



by eliminating the logarithms. If the values of p and t be 

 inserted into the equation for pairs of equidistant values of t, 

 equations containing only P and p may be obtained, and, from 

 these, the values of P may be determined In this way, it may 

 be calculated that, when the breath is held, the alveolar tension 

 of carbon dioxide (curve A) rises from the initial value of 38-0 

 mra.Hg towards a final value of 50-0 mm. Hg. When the air in 

 the lungs is breathed into and out of a closed bag, the alveolar 

 tension of carbon dioxide (curve C) rises from the same initial 

 value towards the value of 59-Omm.Hg. The value towards which 

 the alveolar tension of oxygen sinks when the breath is held 

 (curve B) is found by a similar calculation to be .05 mni.Hg, the 

 initial value being 1164 mm.Hg. 'J'he curvature of curve B is 

 much less than that of the two preceding curves, and the accu- 

 racy with which the value of P can be calculated is correspond- 

 ingly less. In the case of curve D, representing the variation 

 of the alveolar tension of oxygen when the air of the lungs is 

 breathed into and out of a bag, the curvature is so small, that 

 the value of the tension which would be reached eventually, if 

 the tension continued to fall in the same manner, cannot be 

 determined with any precision by the above calculation. This 

 is due to the fact that, in the calculation, the differences of 

 observed values appear. These differences become smaller as 

 the curvature decreases, and as the whole experimental error 

 falls on the differences, the uncertainty of their values soon 

 becomes so great as to render them useless for calculation. The 

 value given for P for each of the curves A, B, and C, is the mean 

 of six values calculated from six different sets of points on the 



curve. 



The values of these final tensions can be determined graphically 

 with more precision by assuming certain values for P, and 

 plotting the graphs of the corresponding equation (2). It is 

 found that the curve so obtained is a straight line, t.e., is de- 

 scribed by equation (2), only when the value chosen for P lies 

 between certain limits. 



In the following Table are given the values of log (P - p) when 

 the values assumed for the final tension, P, are 485 mm.Hg for 



