THE BLOOD. 



249 



which renders the divergent rays of light parallel. These parallel rays sub- 

 sequently fall on the prism, by which they are dispersed and directed into the 

 tube, A, which is nothing more than a small telescope. On looking into it 

 at the ocular end the spectral colors are seen. If the light has been derived 

 from the sun, the spectrum will present vertical dark lines, the so-called 

 Fraunhofer's lines. They are given from A to F in Fig. no. If a colored 

 medium be held in front of the slit so that the light has to pass through it first, 

 certain dark bands will appear in the spectrum, owing to the absorption of 

 certain rays. 



Dilute solutions of arterial blood show absorption bands between the 

 Fraunhofer lines, D and E, in the green and yellow portion of the spectrum. 

 (See Fig. 1 10.) The band nearest D, frequently designated as alpha, is dark 

 in the center and sharply defined. The band which lies toward E, desig- 

 nated as beta, is broader and less sharply defined. 



aBC D 



FIG. in. GRAPHIC REPRESENTA- 

 TION OF THE ABSORPTION OF LIGHT IN 

 A SPECTRUM BY SOLUTIONS OF OXY- 



HEMOGLOBIN OF DIFFERENT STRENGTHS. 



The shading indicates the amount of 

 absorption of the spectrum, and the 

 numbers at the side the strength of the 

 solution. (Rollet.) 



aBC D 



G h 



FIG. 112. GRAPHIC REPRESENTATION 

 OF THE ABSORPTION OF LIGHT IN A SPEC- 

 TRUM BY SOLUTIONS OF REDUCED HEMO- 

 GLOBIN OF DIFFERENT STRENGTHS. The 

 thading indicates the amount of absorp- 

 sion of the spectrum, and che numbers at 

 the side rhe strength of the solution. 

 (Rollet.) 



As the amount of light absorbed varies with the concentration of the 

 solution as well as its thickness, and gives rise to absorption bands of different 

 widths and intensities, it becomes necessary, in order to obtain the character- 

 istic bands, to employ only dilute solutions. 



The absorption spectra, as seen with different strengths of solution one 

 centimeter thick, are shown graphically in Fig. in. It will be observed 

 that solutions varying in strength from o.i per cent, to 0.6 per cent, give rise 

 to the two characteristic bands, but with gradually increasing breadths. 

 With a percentage greater than 0.65 per cent, the light between D and E, 

 the yellow-green, becomes extinguished and the two bands fuse together, 

 forming a single band overlapping slightly the lines D and E. At the same 

 time there is a progressive darkening of the violet end of the spectrum. At 

 0.85 per cent., all the light is absorbed with the exception of a small amount 

 of the red. Solutions less than o.oi per cent, to 0.003 P er cen t. show but a 

 single absorption band that nearest D. 



A solution of venous blood or of reduced hemoglobin shows but a single 



