GENERAL PROPERTIES". THE CORPUSCLES. 



397 



show only one absorption band, known sometimes as the u 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. 170. The r-band is much more 

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

 especially in weak solutions, are not well defined; in solutions of 

 blood diluted 100 times with water, which would give a hemoglobin 

 solution of about 0.14 

 per cent., the absorp- 

 tion band lies in the 

 part of the spectrum 

 included between the 

 wave lengths X 572 and 

 X 542. The width and 

 distinctness of this band 

 vary also with the con- 

 centration of the solu- 

 tion. This variation is 

 sufficiently well shown 

 in the accompanying 

 illustration (Fig. 172), 

 which is a companion 

 figure to the one just 

 given for oxyhemo- 

 globin (Fig. 171). 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 ex- 

 plaining the purplish 

 color of hemoglobin so- 

 lutions and of venous 

 blood. Oxyhemoglobin 

 solutions can be con- 

 verted to hemoglobin 

 solutions, with a corresponding 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 

 purpose are ammonium sulphid and Stokes's reagent.* If a solu- 

 tion of reduced hemoglobin is shaken with air, it quickly changes to 



aBC 



Fig. 171. 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 give 

 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. 



* 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. 



