W. N. M. RAMSAY 



and oxygen or carbon monoxide to justify the application of the 

 gasometric methods to the determination, or even the detection, of 

 such small proportions of ferrihaemoglobin as may reasonably be 

 expected to occur in normal blood. 



It is interesting, then, to turn to analytical methods which are based 

 on different properties of ferrihaemoglobin : the spectrophotometry 

 methods. It is true that these methods demand that the solutions 

 used for the evaluation of the original spectrophotometry constants 

 must have the requisite degree of purity, which may be difficult to 

 ensure, but as the actual analysis may not require any further chemical 

 action on the specimen, or at worst only reactions which proceed 

 rapidly to completion, the results are perhaps easier to interpret than 

 those of gasometric analyses. Several methods have been based on 

 the fact that the high extinction coefficient of ferrihaemoglobin in the 

 region of 631 m;x is changed to a very low one by the addition of 

 KCN (see, for example, K. A. Evelyn and H. T. Malloy 16 ; H. O. 

 Michel and J. S. Harris 17 ). W. D. Paul and C. R. Kemp 18 have 

 applied the method of Michel and Harris to blood samples from 20 

 blood donors, all of which appeared to contain ferrihaemoglobin, 

 although the quantities found ranged only from 0-2 per cent to 

 0-9 per cent of the total pigment present. Other analysts, such as 

 for example Q. H. Gibson and D. C. Harrison 19 have reported 

 similar results, which stand in marked contrast to those of the 

 gasometric experiments. Although it is true that contamination of 

 the original oxyhaemoglobin standard with ferrihaemoglobin would 

 lead in the end to low results, and furthermore that many of the 

 methods used have been based on constants published by one set of 

 workers 20 , 21 , 22 , so that any error in the original would be repeated 

 through all the applications, the original figures show great consistency 

 with a number of different pigment preparations. This in itself makes 

 it unlikely that the oxyhaemoglobin preparations were appreciably 

 contaminated with ferrihaemoglobin. B. L. Horecker 23 , who gives 

 similar but not identical figures, points out that different instruments 

 may have different effective widths of slit, and such differences will 

 undoubtedly be reflected in the results obtained. Sufficient attention 

 has perhaps not always been paid to this point, but the good agreement 

 of results from different laboratories suggests that in this connection, 

 at any rate, it has not been important. 



Spectrophotometric evidence of a rather different kind has been 

 given by D. L. Drabkin and C. F. Schmidt 24 , who made examina- 

 tions of arterial blood in dogs and men. They used a special cuvette 

 only 007 mm in depth, and were thus able to make spectrophoto- 

 metric observations on undiluted specimens within a few seconds of 



236 



