SPECIAL ESTIMATIONS 303 



at €54o,„;x, with a small correction for the sulfhemoglobin not con- 

 verted to this compound and having a slightly lower absorption at 

 540 mju. Hemiglobin is measured by the decrease of cessnm in phos- 

 phate buffer of pH 6.6 caused by the addition of cyanide. For 

 modifications of this method see (138,19J^7). 



In addition to methods using the visible region of the spectrum, a 

 method of determination of total hemoglobin, oxyhemoglobin, hemo- 

 globin, and carboxyhemoglobin has been published by Horecker 

 (1343), in which the absorption of these compounds in the near 

 infrared is utilized. The initial method (134^6) was designed for the 

 more elaborate type of photoelectric spectrophotometer, but a sim- 

 plified type of instrument using filters has recently been described 

 (57), suitable for use in clinical work. From the absorption spectra 

 of the compounds (Section 2.5.) it may be seen that two measure- 

 ments in the region 8000-10,000 A, one before and one after the 

 addition of cyanide, will give the concentration of hemiglobin. For 

 determination of oxy- and carboxyhemoglobin a third reading suffices. 

 In the original method this was made on the diluted solution, reading 

 at 4965 A; in the later method the compounds were converted to 

 acid hematin and the absorption read in the same infrared region as 

 before. While the method offers a comparatively simple means of 

 estimating three hemoglobin derivatives on the same blood sample, 

 it does not appear to have any advantage over reading in the visible 

 region when only oxyhemoglobin is required. 



