40G 



PEACTICAL PHYSIOLOGY 



CHAPTER XLVL 



RESIDUAL AIR. CARBON MONOXIDE POISONING. 

 OXYGEN IN BLOOD. 



TENSION OF 



Measurement of the Residual Air. The spirometer is filled with 

 hydrogen generated in a Kipp's apparatus. Make the deepest possible 

 expiration, and then put the mouthpiece in position, open the clip on 

 the tube which connects the mouthpiece with the spirometer, and 

 breathe in and out of the spirometer two or three times, so that the gas in 

 the lungs and in the spirometer reaches the same uniform composition. 

 Clip the tube, and drive a sample of the gas in the spirometer over into 

 the Haldane gas analysis apparatus. Measure the volume of the 

 sample and the amount of 2 and C0 2 it contains. Suppose the spiro- 

 meter originally contained 4000 c.c. H, and after the experiment it was 

 found to contain 1000 c.c. of the lung-gases, i.e. O 2 and C0 2 , then in 

 the spirometer there must be 3000 c.c. H and 1000 c.c. 9 and C0 2 , 

 and in the lungs there must be 1000 c.c. H and the same proportion 

 of 2 and C0 2 , viz. 250 c.c. The residual air is therefore 1250 c.c. 

 Carbon Monoxide Poisoning. Blood retains in simple solution (0*5 



per cent, volumes 2 when ex- 

 posed to air), 2-6 per cent, when 

 exposed to an atmosphere of pure 

 oxygen, 5 -2 per cent, when ex- 

 posed to two atmospheres of pure 

 oxygen. 6-8 per cent, volumes 

 of 2 are used up in the circula- 

 tion of the blood. An animal 

 exposed to two atmospheres of 



C D 



FIG. 263. Haldane's method for the determina- 

 tion of the tension of oxygen in the blood. A.Measure 

 bottle containing CO. Water drops into this and 



drives at a measured rate a stream of CO into the 

 air current which passes through the mouse- 

 chamber B ; C, metre ; D, filter pump aspirator. 



2 has nearly this amount dis- 

 solved in the plasma. A mouse 

 just poisoned with coal gas which 

 contains CO recovers on being placed in two atmospheres of 2 in 

 the pressure apparatus (Fig. 261). CO poisoning is caused by want 

 of oxygen. The CO combines with the haemoglobin. Otherwise it 

 is, physiologically, an indifferent gas. 



Determination of the Tension of Oxygen in the Blood (Haldane's 

 Method). The maximum amount of CO capable of being absorbed by 

 the blood from air containing a given small percentage of CO depends 

 upon the relative affinities of oxygen and CO for Hb, and the relative 

 tension of the two gases in the arterial blood. 



A mouse is placed in a bottle through which a current of air 



