814 CHEMISTRY OF RESPIRATION. 



air is 6 per cent less than the inspired air, it will be seen that the alveolar 

 air contains 15 per cent oxygen. As the total pressure of the air of the 

 lungs after deducting the aqueous tension of about 50 mm. can be cal- 

 culated as about 710 mm. the partial pressure of the oxygen in man 

 can be put at about 106 mm. and that of the carbon dioxide as about 

 45 mm. 



Based upon several respiration experiments upon different persons, 

 LOEWY has been able to calculate the composition of the alveolar air 

 of human beings almost at the atmospheric pressure, from the com- 

 position of the expired air and the depth of inspiration and expiration, 

 taking into consideration the air in the upper air-passages. He obtained 

 results which varied between 101 and 105 mm. Hg for the oxygen tension 

 and between 32-42 mm. for the carbon dioxide tension. 



The alveolar oxygen tension in dogs can be calculated from the car- 

 bon dioxide content of the alveolar air and is also found to be above 

 100 mm. Hg. 



If the oxygen partial pressure in the alveoli is put at about 105 

 mm. Hg, and we compare this with the highest results obtained for the 

 oxygen tension of the arterial blood as determined by tonometric means, 

 we find that the taking up of oxygen in the lungs can be simply explained 

 according to physical laws as a diffusion process. The conditions are 

 quite different if we start with the high-tension results of BOHR, 101-144 

 mm. Hg., or the still higher results of HALDANE and SMITH. The oxygen 

 tension in the blood is, in many cases, according to these latter authors, 

 always higher than the tension in the lungs, as average for various races 

 of animals. In these cases the passage of oxygen from the lungs to the 

 blood cannot be explained simply by a diffusion. We must therefore, 

 with BOHR, accept a special specific activity of the lungs, and according to 

 him a secretory activity of the lungs also exists besides diffusion. 



As opinions on the taking up of oxygen are disputed so also are those 

 on the giving up of caibon dioxide. 



The tension of the carbon dioxide in the blood has been determined 

 in different ways by PFLUGER and his pupils, WOLFFBERG, STRASSBURG, 

 and NussBAUM. 1 



According to the aerotonometric method the blood is allowed to flow directly 

 from the artery or vein through a glass tube which contains a gas mixture of a 

 known composition. If the tension of the carbon dioxide in the blood is greater 

 than the gas mixture, then the blood gives up carbon dioxide, while in the reverse 

 case it takes up carbon dioxide from the gas mixture. The analysis of the gas 

 mixture after passing the blood through it, will also decide if the tension of the 

 carbon dioxide in the blood is greater or less than in the gas mixture; and by a 

 sufficiently great number of determinations, especially when the quantity of carbon 

 dioxide of the gas mixture corresponds as closely as possible, in the beginning, to 



1 Wolffberg, Pfliiger's Arch., 6; Strassburg, ibid.; Nussbaum, ibid., 7. 



