426 RESPIRATION 



from the tubing, which is then connected with the bag as shown in the 

 figure, and the bag filled pretty full with oxygen. Meanwhile the height 

 of the water in the cylinder is accurately read off, and the temperature 

 of the cylinder and barometric pressure noted. 



The subject of the experiment now begins to breathe from the bag, 

 oxygen being supplied as required. The water tap is now slightly 

 opened, and the tap F turned so as to let CO as well as oxygen pass. The 

 required volume of CO is in this way very gradually driven in from the 

 measuring cylinder, about 20 cc. being passed in per minute. After the 

 CO has been passed in, the water tap is turned off, and the 3-way tap 

 turned so as to shut off the CO. The CO is absorbed from the bag very 

 rapidly and completely. The oxygen supply is continued for at least ten 

 minutes, after which the subject is allowed to absorb most of the oxygen 

 in the bag. About 1 5 minutes after the last of the CO has been given, a 

 drop or two of blood is taken and diluted for analysis by the carmine 

 method described above. At the same time the oxygen capacity of the 

 blood is determined in the ordinary way by the Gowers-Haldane haemo- 

 globinometer. For further certainty it is well to make both determina- 

 tions in duplicate. 



As a little air always gets mixed with the CO, a sample of the CO in 

 the cylinder should be taken for analysis. It is usually sufficient to 

 determine the CO 2 (of which none should be present) and oxygen. From 

 the latter the proportion of air can be deduced. 



Let us suppose that 150 cc. of CO were given, the temperature 12, 

 and the barometer 765 mm. ; also that there was 0.82 per cent of oxygen 

 in the CO, corresponding to 3.9 per cent of air. 150 cc. of gas saturated 

 with moisture would correspond to 142.5 cc. of dry gas at o and 760 mm. 

 But as 3.9 per cent of this was air, only 137 cc. of CO were administered. 

 Let us also suppose that the percentage oxygen capacity of the subject's 

 blood was 18.1 (98 per cent by the haemoglobinometer), and the per- 

 centage saturation with CO was 19.5. The total oxygen capacity or CO 



capacity must have been 137 x =703 cc. ; the blood volume 703 x 



i9-5 



IOO 



=3880 cc. If the subject's weight was 60 kilos this corresponds to 



18.1 



6.5 liters of blood to 100 kilos of body weight; and this result is usually 

 expressed as a blood volume of 6.5 per cent of the body weight. 



In the original description of our method, we directed that the blood 

 sample should be taken within two or three minutes of the cessation of 

 administration of CO, as we assumed that by that time the CO would 

 be evenly distributed in the blood all over the body. The results from 

 samples taken three minutes after the first sample confirmed this as- 



