THE CONTROL OF THE RESPIRATION 359 



of the respiratory center to the CH of the blood may occur after long- 

 continued exposure of the center to the changed tension of 2 , 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 

 O 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. 



Even if it may have a certain influence on the excitability of the re- 

 spiratory center, 2 deficiency per se can serve as a direct stimulus of 

 the center only when it is of extreme degree. 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) show clearly how much more potent a respiratory stimulant 

 is accumulation of C0 2 than deficiency of 2 . More particular investi- 

 gation 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 Avith a larger bag (about 200 

 liters), so that the 2 falls slowly, the breathing can be maintained for 



