CHANGES IN AIR AND BLOOD IN RESPIRATION. 687 



further that the observation was made at a barometric pressure of 760 mms., 

 then the pressure of the oxygen in the alveoli would be (76046.6X0.147) 

 99+ mms. Hg. 



Actual observations made by these authors upon human beings 

 in whom the expired air was analyzed indicate that the composition 

 of the alveolar air may vary under different conditions between 

 the following limits: Oxygen between 11 and 17 per cent, of an 

 atmosphere; carbon dioxid between 3.7 and 5.5 per cent, of an 

 atmosphere. Haldane and Priestley have devised a simple 

 method by means of which the last portions of the air breathed 

 out in an expiration may be collected. The sample thus collected 

 represents practically the alveolar air, and its average composition 

 for normal quiet respirations may be given as oxygen, 14 per cent, or 

 100 mms. Hg. (76046.6X0.14); carbon dioxid, 5.5 per cent, or 

 40 mms. Hg.; nitrogen, 80 per cent, or 570 mms. Hg. Other ob- 

 servers state that the direct determination of the CO 2 in the alveolar 

 air by the method of Haldane and Priestley gives figures that are 

 too high, and that it is safer to estimate this factor indirectly. 

 Pearce* suggests the following method: The expired air from two 

 expirations of different depths is collected, measured exactly, and 

 analyzed for its CO 2 . With these factors known, and representing 

 the percentage of CO 2 in the alveolar air by y, and the volume of 

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

 can be solved for either x or y. Thus, 



A = amount of air in large expiration. 



A\ = amount of air in small expiration. 



B = percentage of CO 2 in the large expiration. 



BI = percentage of CO 2 in the small expiration. 



Then AB = (Ax)y, 



A! Bi = (A l x}y. 

 Solving this equation for y, we find 

 _ ABAi Bi 

 A At 



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 A portion of this air was then withdrawn by means of a 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



* Pearce, "American Journal of Physiology," 43, 73, 1917. 



t Loewy and von Schrotter, "Zeitschrift fur experimentelle Pathologic 

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

 IV , 1908. 



