368 



THE RESPIRATION 



ventilation as to demonstrate the changes produced in the sensitivity of 

 the respiratory center in pneumonia. 



Possibility that C0 2 Specifically Stimulates Center. After showing 

 that C0 2 acts as an excitant of the respiratory center, the question arises 

 as to whether the action depends on the raising of the C H of the blood, or 

 whether it may be a specific action of the CO 2 . Many attempts have 



Fig. 129. Composite curve obtained from the data on sixteen experiments, showing the re- 

 spiratory response to CO2 in the decerebrate cat. Abscissae = percentage of COs in the inspired 

 air. Ordinates = the percentile increase the tidal air per minute. (From R. W. Scott.) 



been made to decide this question experimentally, the general principle 

 of the experiments being to determine whether CH of the blood runs 

 parallel with the C0 2 content of the respired air and with the hyperpnea. 

 Using the gas-chain method (page 31), Hasselbalch and Lundsgaard 22 

 found that the hyperpnea produced in rabbits by breathing in C0 2 -rich 



