966 PHYSIOLOGY 



from an oxygen cylinder through the tube c. D is a graduated vessel containing 

 pure carbonic oxide gas. While the subject is breathing in and out of the bag 

 a given volume of carbon monoxide is admitted into the bag, being driven out 

 from the tube D by allowing water to flow through the tap E. The required 

 volume of carbon monoxide is gradually driven in from the measuring cylinder 

 at the rate of about 30 c.c. every two minutes. When the required quantity 

 has been driven in and pushed forward by the oxygen an interval of two or 

 three minutes is allowed to elapse. After this a drop of blood is taken for 

 analysis. It contains a certain amount of CO -haemoglobin. The relative 

 saturation of the blood in carbon monoxide is determined by the colorimetric 

 method. A number of narrow test-tubes of exactly equal' diameter and each 

 holding about 6 c.c. are taken, and 2 c.c. of water saturated with air measured 

 off into each. Two cubic millimetres of the blood of the subject are measured 

 off in the ordinary way by means of a hsemoglobinometer pipette into each of the 

 six tubes, the solutions being well mixed. Four cubic millimetres of this blood are 

 thoroughly saturated with coal gas and placed in another shorter tube, which is 

 filled full and tightly corked. In this tube the haemoglobin is completely saturated 

 with carbon monoxide. After the subject has breathed the carbon monoxide, a 

 sample of his blood is taken and diluted as before. The solution in this tube is, 

 of course, pinker than those in the other tubes. -A standard solution of carmine 

 is now added from a narrow burette to one of the tubes of normal blood solution 

 until its tint is the same as that of the blood taken after the inhalation. Addition 

 of the carmine is then continued until the tint is equal to that of the blood 

 solution which is entirely saturated with carbon monoxide. Supposing that 

 045 c.c. of carmine was required to produce equality of tint with that of the 

 blood taken during the experiment and 2-5 c.c. to produce equality of tint with 

 that of the saturated blood, then as 2-5 c.c. of carmine in 4-5 c.c. of liquid were 

 required to produce saturation tint, and only 045c.c. of carmine in 245 c.c. of 

 liquid to produce the tint of the blood under examination, the percentage 

 saturation of the latter could be calculated by the following sum : 



2-5 45 



4* = 245 :: 10 ' * 

 .-. x - 33-1 



Although this method requires careful execution in order to avoid 

 fallacies, it is possible to attain results, as has been shown by Douglas, 

 closely agreeing with Welcker's method. The error is probably not 

 greater than 10 per cent., which is negligible in comparison with the 

 large changes in total blood volume which have been found to occur 

 in certain cases of disease. The total record of two such observations 

 by Haldane and Lorrain Smith may be here quoted : 



NORMAL INDIVIDUAL 



