414 RESPIRATION 



read off, and the flask turned up so as to let the ferricyanide flow into 

 the blood solution. Before doing this, however, the blood solution should 

 be observed to make sure that it is perfectly laked and transparent; 

 otherwise more saponin must be added. The flask is now agitated as 

 long as gas continues to come off as shown by the movements of the 

 gauge. This will take three or four minutes. The burette is again read 

 off, which gives the volume of oxygen given off. This is reduced to dry 

 volume at o and 760 mm. and per 100 cc. of blood. 



Let us suppose that the oxygen capacity of the haemoglobin in the 

 above example was 17.4 cc. per 100 cc. of blood. The percentage satura- 

 tion of the haemoglobin in the arterial blood was therefore 



17.40 .92 



100 x 94.7. 



17.40 



It is easier to determine the oxygen capacity by means of a Gowers- 

 Haldane haemoglobinometer, in which 100 per cent corresponds 

 to an oxygen capacity of 18.5. For this purpose a sample of the 

 blood drawn from the artery is used for the determination. In the above 

 example the oxygen capacity of 17.4 corresponds to 94 per cent on the 

 haemoglobinometer scale, and the range of error in carefully made 

 haemoglobinometer determinations is only about 0.5 per cent. The ac- 

 curacy of both methods is strikingly shown by the fact that in 36 determi- 

 nations by Meakins and Davies of the oxygen capacity of blood from 

 patients and healthy persons the maximum difference between the re- 

 sults by the haemoglobinometer and by the new method was under i per 

 cent of the oxygen capacity. 14 



A haemoglobinometer can, of course, be exactly standardized by the 

 method just described. If the haemoglobinometer is used, it is unneces- 

 sary to use saponin or ferricyanide in determining the percentage satura- 

 tion of the haemoglobin in the sample of blood. The total available 

 oxygen in the sample of arterial blood is the oxygen combined with 

 haemoglobin plus the dissolved oxygen. This was, in the above example, 

 16.48 +.24 =16.72 cc. per 100 cc. of blood. 



If, instead of being normal arterial blood, the sample was venous 

 blood, or arterial blood of abnormally low saturation with oxygen, the 

 calculation must be slightly modified, since less oxygen in simple solu- 

 tion is present in the sample. Thus if the blood turned out to be only 

 half saturated with oxygen the partial pressure of oxygen in the sample 

 would only be about 4 per cent of an atmosphere. Hence there would 

 only be .09 cc. of dissolved oxygen present, instead of .24 cc. This would 

 increase the correction at 15 for dissolved gas from .81 to .96 cc. a 

 difference which, however, affects the result but little. Ordinary varia- 



14 Meakins and Davies, Journ. of Pathol. and, Bacter., XXIII, p. 454, 1920. 



