DIVEKSE COMPONENTS 343 



The enormous change in rate of carbon dioxide output through 

 the lungs with each small change in load or tension of carbon diox- 

 ide, is the feature that led Haldane ('17) to emphasize this com- 

 ponent as the example par excellence of a regulated quantity. Its 

 constancy was evident, once alveolar air sampling and analysis 

 were perfected; indeed, qualitative tests alone are sufficient to 

 demonstrate the responses to change of pco.- By relating now the 

 rates of elimination and of production to the loads of CO2 in the 

 body, I can compare the sensitivity of this regulation (as measured 

 by net velocity quotient) with corresponding sensitivities to other 

 components (§ 136). The believed insensitivity to carbon dioxide 

 exhibited by diving mammals and very many other living units, 

 may eventually be compared by means of the same parameters. 



§ 121. Oxygen in man 



Oxygen, too, is easier to discuss in qualitative terms than quan- 

 titative. Excesses of oxygen are difficult to impose beyond the 

 lungs, but deficits occur both in deprivation and in increased oxy- 

 gen utilization. At the conclusion of a period of oxygen depriva- 

 tion, oxygen intake is measured, indicating how rapidly net oxygen 

 is added to the body in the first few seconds of recovery. Without 

 physical exercise the rate of oxygen consumption may increase ten- 

 fold, as in dinitrophenol administration to dogs (Hall et al., '33). 

 It is believed that small deficits of oxygen then prevail and induce 

 the augmented intake. 



As oxygen is consumed during recovery, the oxygen deficit or 

 debt is paid off at initial rates that are indicated in figure 172. The 

 rate of gain of oxygen is temporarily very large, while the rate of 

 recognized combustion of it is immediately smaller than during the 

 exercise. Thereby, the net oxygen content of the body is restored. 



Rate of oxygen intake is related to oxygen load, but not inde- 

 pendently of time (fig. 172). Or, deceleration of oxygen intake fol- 

 lowing exercise is correlated with time as well as with deficit or 

 debt. No guarantee exists at present that other types of oxygen 

 load are related with oxygen exchanges like the one here described. 



The oxygen content of the human body in oxygen balance is 

 variously estimated (exclusive of the lungs) at 0.7 to 1.5 liters or 

 0.01 to 0.02 liters/kg. (Irving, '34). This is based on the belief that 

 very little molecular oxygen exists outside of that combined with 

 hemoglobin. Such a quantity of oxygen is sufficient to carry on 

 usual combustions for only 3 to 6 minutes at rest. 



