RESPIRATION 89 



during ordinary laboratory work. In regulating the temperature 

 of the bath containing the saturator, analyzing the samples of air 

 from the saturator, observing the barometric pressure, measuring 

 the sample of blood (of which about i cc. was used for each anal- 

 ysis), and determining the CO2 by means of the blood-gas ap- 

 paratus (we used Brodie's modification of the original apparatus), 

 it was impossible to avoid combined errors of I or 2 per cent of 

 the quantities to be measured, so that we could not say how exact 

 Nature's regulation of the curve is. At any rate it was so exact 

 for my blood that the most exact existing chemical methods did 

 not show any deviations from the curve, any more than they 

 could show deviations from the oxyhaemoglobin or CO-haemo- 

 globin dissociation curves. Marked temporary deviations could, 

 however, be produced by severe muscular exertion ; and probably 

 very distinct deviations may occur after meals. 



With the blood of other persons the results were only slightly 

 different. Thus the curves, so far as ascertained, for the blood of 

 Miss Christiansen and Dr. Douglas were slightly below, and 

 otherwise parallel to mine under normal conditions. The blood of 

 most persons seemed to take up about 50 volumes of CO2 per 100 

 volumes of blood at 40 millimeters pressure of CO2; but under 

 abnormal conditions, as will be shown below, there are great 

 temporary variations from this standard, corresponding to the 

 great variations observed under the unfavorable conditions in 

 experiments on animals. 



More than 50 years ago it was suspected by Ludwig that oxygen 

 may have some influence in turning out CO2 from the venous 

 blood which comes to the lungs. The experiments made to ascer- 

 tain whether oxygen helps to turn out CO2 from blood gave, how- 

 ever, only a negative result, and more recent work by Bohr, 

 Hasselbalch, and Krogh^ led to similar negative conclusions. We 

 had been making experiments to investigate the rise of alveolar 

 CO2 pressure when the breath was held, or when a small quantity 

 of air was rebreathed. One result of these experiments was to show 

 that if the alveolar oxygen pressure fell much below normal the 

 percentage of CO2 in the alveolar or rebreathed air was always, 

 without exception, lower after any definite interval of time, than 

 was the case under the same conditions but with the alveolar oxy- 

 gen percentage high. This brought us back to Ludwig's old ques- 

 tion, which with the new blood-gas method we could investigate 



* Bohr, Hasselbalch, and Krogh, Skand. Arch. f. Physiol., XVI, p. 411, X904. 



