CARBON DIOXIDE TENSION. 815 



the probable tension of this gas in the blood, we may learn the tension of the 

 carbon dioxide in the blood. As above mentioned the oxygen tension can be 

 determined by the same method. 



According to this method the carbon-dioxide tension of the arterial 

 blood is on an average 2.8 per cent of an atmosphere, 1 corresponding to 

 a pressure of 20 mm. mercury (STRASSBURG) . In the blood from the 

 pulmonary alveoli NUSSBAUM found a carbon-dioxide tension of 3.81 

 per cent of an atmosphere, corresponding to a pressure of 27 mm. mer- 

 cury. STRASSBURG, who experimented in non-tracheotomized dogs 

 in which the ventilation of the lungs was less active and therefore the 

 carbon dioxide was removed from the blood with less readiness, found 

 in the venous blood of the heart, a carbon-dioxide tension of 5.4 per 

 cent of an atmosphere, corresponding to a partial pressure of 38.3 mm. 

 mercury. 



Another method, which was first used by PFLUGER and his pupils 

 WOLFFBERG and NUSSBAUM, depends upon excluding a part of the lungs 

 by means of the lung catheter. 



The principle of this method is as follows: By the introduction of a catheter, 

 of a special construction, into a branch of a bronchus the corresponding lobe of 

 the lung may be hermetically sealed, while in the other lobes of the same lung, and 

 in the other lung, the ventilation remains unchanged, so that no accumulation 

 of carbon dioxide takes place in the blood. When the cutting off lasts so long that 

 a complete equalization between the gases of the blood and the retained air of 

 the lungs is assumed, a sample of this air of the lungs is removed by means of 

 the catheter and analyzed. 



When a complete exchange between the gases of the inclosed part of 

 the lungs and the gases of the circulating venous blood has taken place, 

 the tension of the gases in this part of the lungs can be considered as a 

 measure for the gas tension in the venous blood, if we admit that the 

 gas exchange is due only to physical forces. In their experiments 

 WOLFFBERG and NUSSBAUM found only 3.6 per cent CC>2 in the air taken 

 out with the catheter. NUSSBAUM also determined the carbon-dioxide 

 tension in the blood Irom the right heart in a case simultaneous with 

 the catheterization of the lungs. He found almost identical results, 

 namely, a carbon-dioxide tension of 3.84 per cent and 3.81 per cent 

 of an atmosphere, which also shows that complete equalization between 

 the gases of the blood and lungs in the inclosed parts of the lungs had taken 

 place. The method of catheterizing the lungs is, as shown by LOEWY 

 and v. ScHROTTER, 2 also applicable to man, and they found that the 

 carbon dioxide tension of human venous blood was equal to 6 per cent 



1 Here and in the following discussion we mean by atmospheric pressure the pressure 

 in the lungs after subtracting the aqueous vapor tension (about 50 mm.), namely, 

 760 50 = 710 mm. mercury pressure. 



2 1. c., footnote 1, page 812. 



