THE CONTROL OF THE RESPIRATION 359 



of the respiratory center to the C H of the blood may occur after long- 

 continued exposure of the center to the changed tension of 2J yet they 

 deny .that such alteration can occur as a temporary condition. These 

 workers found that, in order to raise the pulmonic ventilation by 100 

 per cent, the increase in the alveolar C0 2 tension required was practically 

 the same (0.3 per cent) when the inspired air contained 20 per cent of 

 2 as when it contained 54 per cent. 



In the observations already referred to on the decerebrate cat, R. W. 

 Scott 20 has secured some evidence that would seem to support Haldane's 

 contention. He found that the response of the respiratory center to the 

 percentage of C0 2 in the respired air was exactly the same whether the 

 latter contained a low (13-14) or a high (30 and over) percentage of 2 . 

 The possibility that the excitability of the respiratory center is affected 

 directly by the 2 tension is to be considered as one of the most im- 

 portant problems awaiting solution. When the deficiency is marked, 

 it ultimately depresses all nerve centers, including the respiratory, so 

 that respiration becomes irregular and then ceases. This occurs in 

 the final stages of asphyxia and, no doubt, in pneumonia, and accounts 

 for the great relief to breathing afforded by oxygen inhalations. 



Much light has been thrown on the relationship of 2 to respiratory 

 activity by observing the respirations during breathing in and out of 

 rubber bags through soda lime absorption bottles of sufficient size to 

 remove the C0 2 . We have already seen that even the general results 

 of such observations (page 349) indicate clearly how much more potent 

 a respiratory stimulant is accumulation of C0 2 than deficiency of 2 . 

 More particular investigation in which the alveolar air is analyzed bears 

 out these conclusions and at the same time indicates the exact conditions 

 under which organic acids become developed. 



With a very small bag (a few liters' capacity) hyperpnea of a dis- 

 tressing type but without cyanosis supervenes in a few minutes, and the 

 alveolar air contains perhaps as low as 6 per cent 2 and 4 per cent C0 2 . 

 Of still greater interest and significance, however, is the fact that the 

 ratio between the volume of C0 2 excreted and of 2 absorbed (respira- 

 tory quotient) during the hyperpnea is raised considerably above unity, 

 indicating that an excessive excretion of C0 2 must be occurring. This 

 result is explained by assuming that the deprivation of 2 causes large 

 quantities of fixed acids to be produced, and that these expel C0 2 from 

 the blood more quickly than the 2 is absorbed. In corroboration of 

 this explanation, it has been observed that, after outside air is breathed 

 for some time following the above experiment, the respiratory quotient 

 becomes very low, so that C0 2 must now be accumulating in the blood. 



If the above experiment is repeated with a larger bag (about 200 

 liters), so that the 0, falls slowly, the breathing can be maintained for 



