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TEXT-BOOK OF PHYSIOLOGY. 



portion of the spectrum. (See Fig. 106.) The band nearest D 

 frequently designated as alpha is dark in the center and sharp y 

 denned. The band which lies toward E is broader and less sharply 



denned. . 



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 characteristic bands, to employ only dilute solutions. 



The absorption spectra, as seen with different strengths of solu- 

 tion one centimeter thick, are shown grapically in Fig. 107. 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 



Red. Orange. 



Yellow. 



Green. 



Cyan Blue. 



Reduced 

 Hemoglobin 



FIG. 106. SPECTRA OF HEMOGLOBIN AND SOME or ITS COMPOUNDS. (Landois and 



Stirling.) 



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 cent, show but a single 

 absorption band that nearest D. 



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

 single absorption band (see Fig. 106), frequently designated as 

 gamma, broader and less marked between the lines D and E, but 

 extending slightly beyond D. Fig. 108 shows in the same graphic 



