434 



BLOOD AND LYMPH. 



Solutions of reduced hemoglobin examined with the spectroscope 

 show only one absorption band, known sometimes as the "f-band." 

 This band lies also in the portion of the spectrum included between 

 the lines D and E; its relations to these lines and the bands of 

 oxyhemoglobin are shown in Fig. 183. The f-band is much more 

 diffuse than the oxyhemoglobin bands, and its limits, therefore, 

 especially in weak solutions, are not well defined. The width and 

 distinctness of this band vary also with the concentration of the 

 solution. This variation is sufficiently well shown in the accom- 

 panying illustration (Fig. 185), which is a companion figure to the 

 one given for oxyhemoglobin (Fig. 184). It will be noticed that 



the last light to be ab- 

 sorbed in this case is 

 partly in the red end 

 and partly in the blue, 

 thus explaining the pur- 

 plish color of hemoglo- 

 bin solutions and of 

 venous blood. Oxy- 

 hemoglobin soluti o n s 

 can be converted to 

 hemoglobin solutions, 

 with a corresponding 

 change in the spectrum 

 bands, by placing the ( 

 former in a vacuum or, 

 more conveniently, by 

 adding reducing solu- 

 tions. The solutions 

 most commonly used 

 for this purpose are am- 

 monium sulphid and 

 Stokes's reagent.* If 

 a solution of reduced 

 hemoglobin is shaken 

 with air, it quickly 

 changes to oxyhemo- 

 globin and gives two 

 bands instead of one 

 when examined by the 



spectroscope. Any given solution may be changed in this way from 

 oxyhemoglobin to hemoglobin, and the reverse, a great number of 



* Stokes's reagent is an ammoniacal solution of a ferrous salt. It is made 

 by dissolving 2 parts (by weight) of ferrous sulphate, adding 3 parts of tar- 

 taric acid, and then ammonia to distinct alkaline reaction. A permanent 

 precipitate should not be obtained. 



0.4 



0,3 

 0.2 



0.1 



0, 



BC 



Fig. 184. Diagram to show the variations in the 

 absorption spectrum of oxyhemoglobin with varying 

 concentrations of the solution. (After Rollett.) The 

 numbers to the right give the strength of the oxy- 

 hemoglobin solution in percentages; the letters giye 

 the positions of the Fraunhofer lines. To ascertain 

 the amount of absorption for any given concentration 

 up to 1 per cent., draw a horizontal line across the 

 diagram at the level corresponding to the concentra- 

 tion. Where this line passes through the shaded part 

 of the diagram absorption takes place, and the width 

 of the absorption bands is seen at once. The diagram 

 shows clearly that the amount of absorption increases 

 as the solutions become more concentrated, especially 

 the absorption of the blue end of the spectrum. It 

 will be noticed that with concentrations between 0.6 

 and 0.7 per cent, the two bands between D and E fuse 

 into one. 



