856 PHYSIOLOGY 



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 haemoglobinometer 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 0-45 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 0-45 c.c. of carmine in 2-45 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 : 



.-. 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 



In applying this method in cases of disease it is important not to give too 

 large a dose of carbonic oxide gas. In a normal individual 30 per cent, 

 of the haemoglobin may be combined with carbon monoxide before any 

 oxygen hunger is felt, and it is possible to saturate half the haemoglobin 

 with this gas, though with considerable discomfort to the individual. In 

 cases such as heart disease, where the patient is at the very margin of his 

 resources, even 30 per cent, diminution of the oxygen capacity of the blood 

 may have serious results, and the carbon monoxide inspired must be there- 

 fore kept at the lowest limit at which it is possible to carry out a reliable 



