BLOOD. 



341 



y-band is much more diffuse than the oxyhaemoglobin bands, and its limits 

 therefore, especially in weak solutions, are not well denned; in solutions 

 of blood diluted 100 times with water, which would give a haemoglobin 

 solution of about 0.14 per cent., the absorption band lies in the part of the 

 spectrum included between the wave-lengths ^ 572 and A 542. The width 



70 65 



FIG. 90. Diagrammatic representation of the absorption spectrum of haemoglobin (reduced haemoglo- 

 bin) (after Rollett). The numerals give the wave-lengths in hundred-thousandths of a millimeter ; the 

 letters show the positions of the more prominent Fraunhofer lines of the solar spectrum. The red end 

 of the spectrum is to the left. The single diffuse absorption band lies between D and E. 



and distinctness of this band vary also with the concentration of the 

 solution. This variation is sufficiently well shown in the accompanying 

 illustration (Fig. 91), which is a companion figure to the one just given 

 for oxyhaemoglobin Fig. 89). It will be noticed that the last light to 

 be absorbed in this case is partly in the red end and partly in the blue, 

 thus explaining the purplish color 

 of haemoglobin solutions and of 

 venous blood. Oxyhaemoglobin so- 

 lutions can be converted to haemo- 

 globin solutions, with a correspond- 

 ing change in the spectrum bands, 

 by placing the former in a vacuum 

 or, more conveniently, by adding 

 reducing solutions. The solutions 

 most commonly used for this pur- 

 pose are ammonium sulphide and 

 Stokes's reagent. 1 If a solution of 

 reduced haemoglobin is shaken with 

 air, it quickly changes to oxyhaemo- 

 globin and gives two bands instead 

 of one when examined through the 



aBC 



spectroscope. Any given solution 

 may be changed in this way from 

 oxyhaemoglobin to haemoglobin, 

 and the reverse, a great number 

 of times, -thus demonstrating the 

 facility with which haemoglobin 

 takes up and surrenders oxygen. 



1 Stokes's reagent is an amraoniacal solution of a ferrous salt. It is made by dissolving 2 

 parts (by weight) of ferrous sulphate, adding 3 parts of tartaric acid, and then ammonia to dis- 

 tinct alkaline reaction. A permanent precipitate should not be obtained. 



FIG. 91. Diagram to show the variations in the ab- 

 sorption spectrum of reduced haemoglobin with vary- 

 ing concentrations of the solution (after Rollett). The 

 numbers to the right give the strength of the haemo- 

 globin solution in percentages ; the letters give the posi- 

 tions of the Fraunhofer lines. For further directions 

 as to the use of the diagram, see the description of 

 Figure 89. 



