42 



Scientific Proceedings (113). 



We have been able to avoid this difficulty by modifying the 

 principle, and basing the calculation not upon the dilution of one 

 gas, but upon the volume ratio of two gases. The subject breathes 

 to and from a bag containing oxygen, sufficient to satisfy his 

 requirements for the length of the experiment, and mixed with 

 the oxygen a known volume of hydrogen approximating the volume 

 of the nitrogen in the lungs. The CO2 is removed by a scrubber 

 of sodium hydroxide shells. After mixture is complete, the N 2 

 and H 2 in the gas are determined. Since 



initial vol. N 2 in lung air final per cent. N2 in gas mixture 

 initial vol. H 2 in bag final per cent. H 2 in gas mixture' 



, xt , tt percent. N 2 , 



vol. N 2 = vol. H 2 X ^ TT . Since the nitrogen constitutes 



per cent. H 2 * 



r 1 , r • • , , • VOL N 2 _ 



0.791 of the air, the volume of air in the lungs is . The air 



& 0.791 



volume thus determined is corrected by subtracting air present 

 in the dead space of the apparatus at the start, also any air present 

 as impurity in the oxygen or hydrogen used. Changes in volume 

 of oxygen or C0 2 in the system do not affect the results, and absorp- 

 tion of hydrogen is negligible. Without changing the respiration 

 from that normal at rest, results for residual air are obtained after 

 about 2 minutes breathing that are not altered by further breathing 

 and that agree with the results obtained by the Lundsgaard-Van 

 Slyke method in subjects capable of properly cooperating in the 

 latter. The error of the present method does not appear to exceed 

 4 per cent, of the lung volume estimated. 



For the safe use of hydrogen two precautions are essential: 

 The hydrogen, especially if made by the action of acid on a metal, 

 such as zinc, should be tested for arsine to avoid fatal poisoning; 

 and flames should be kept away from the apparatus to prevent 

 explosion. 



