CHANGES IN AIR AND BLOOD IN RESPIRATION. 679 



the dead space by x, a binominal equation may be expressed which 

 can be solved for either x or ij. Thus, 



A = amount of air in large expiration. 



.4i = amount of air in small expiration. 



B = percentage of CO2 in the large expiration. 



Bi = percentage of CO2 in the small expiration. 



Then AB = {A—x)y, 



Ai Bi = {Ai—x)y. 

 Solving this equation for y, we find — 



AB—Ai Bi 



y = ' A-A. 



The author reports an average value for y of 5.45 per cent. 



Loewy and von Schrotter have determined also the average 

 tension of these gases in the blood of man. Their method* con- 

 sisted in blocking off one lung or one lobe of a lung by a metal 

 catheter inserted through the trachea. After the lapse of half an 

 hour or so the gases in this occluded portion had reached an 

 equilibrium by interchange with the venous blood which repre- 

 sented the tension actually existing in the circulating venous 

 blood. A portion of this air was then withdrawn by means of a 

 suitable device and was analyzed. Their average result was that 

 in the venous blood the oxygen exists under a tension of 5.3 per 

 cent, of the alveolar atmosphere (710 X .053 = 37.6 mms. Hg.), 

 and the CO2 under a tension of 6 per cent. (42.6 mms. Hg.). The 

 physical relations of pressure between the alveolar air and the 

 gases in the venous blood may be represented as follows: 



Oxygen. Carbon Dioxid. 



Alveolar air 100 mms. 35 to 40 mms. 



Membrane J "^ 



t I 



Venous blood . . . 37.6 mms. 42.6 mms. 



Diffusion must take place, therefore, in the direction indicated 

 by the arrows. As the oxygen passes through into the blood it is 

 combined with the hemoglobin and it is estimated that the arterial 

 blood as it flows away from the lungs is nearly saturated with 

 oxygen, lacking perhaps only 1 volume per cent, of being completely 

 saturated (Pfliiger). That is, if the normal arterial blood contains 

 19 c.c. of oxygen for each 100 c.c. of blood, it is probable that one 

 more cubic centimeter might be combined by the hemoglobin if 

 exposed fully to the air or oxygen. The difference in tension 

 between the carbon dioxid on the two sides of the membrane is not 

 so great as in the case of the oxygen, but owing to the more rapid 

 difl'usion of this gas it is probable that this difference suffices to 

 explain the exchange. In this matter one must bear in mind also 



* Loewy and von Schrotter, "Zeitschrift fur experimen telle Pathologie 

 und Therapie," 1, 197, 1905. See also Loewy, "Handbuch der Biochemie," 

 IVi, 1908. 



