41 8 RESPIRATION 



three-way taps are not available T tubes may be substituted. Messrs. 

 Siebe Gorman & Co., 187 Westminster Bridge Road, London S. E., 

 supply it. 



D. Colorimetric Determination of Percentage Saturation of 

 Haemoglobin with CO 



This very convenient method is used in determining the oxygen pres- 

 sure of arterial blood, the total haemoglobin in the body, or the blood vol- 

 ume, as well as for investigations as to the properties of CO haemoglobin 

 and the phenomena of CO poisoning. It depends on the fact that a dilute 

 solution of CO haemoglobin has a pink color, quite different from the 

 yellow color of similarly diluted oxyhaemoglobin. 



I originally used this color difference as an easy and delicate means 

 of recognizing the presence of CO in blood and roughly estimating the 

 saturation with CO; and I then thought that as it is impossible to 

 recognize by the difference of tint a difference of less than about 5 per 

 cent in the percentage saturation of haemoglobin with CO, the method 

 was at best a rough one. Various recent writers have fallen into the same 

 error. Further experience showed that with proper precautions the 

 method gives results of great accuracy. The following description is 

 taken almost verbatim from the account of the method given in 191 2 by 

 Douglas and myself in our paper on oxygen secretion. ^"^ 



A solution of normal human blood (or blood from the animal experi- 

 mented on) is prepared of such strength as to correspond to about 0.5 

 per cent of the proportion of haemoglobin in standard human blood of 

 100 per cent strength by the Gowers-Haldane haemoglobinometer scale. 

 Two test tubes of equal bore of about 0.6 inch are selected, and into 

 each of these 5 cc. of the blood solution are measured with a pipette. 

 From a o.i per cent solution of carmine in ammoniacal distilled water 

 (this solution being kept in the dark in a cupboard) a dilute solution of 

 carmine in distilled water with a strength of tint about equal to or rather 

 greater than that of the blood solution is then prepared in a measuring 

 cylinder. The requisite amount of dilution (about one-twentieth of the 

 o.i per cent solution if the latter has been recently prepared) can easily 

 be estimated by the eye, and can be obtained at once, when experiments 

 are made daily, by diluting to a definite extent. A burette is filled with 

 the carmine solution, and another burette with water. The blood solution 

 in one of the test tubes is then saturated with CO by allowing coal gas to 

 run through the free part of the test tube, quickly closing the tube with 

 the thumb, and shaking the blood solution with the gas for a few seconds. 



" Douglas and Haldane, Journ. of Physiol., XLIV, p. 305, 19 12. 



