THE RED BLOOD CORPUSCLES 



193 



the fact that different substances affect the spectrum in very specific 

 ways so that it is possible to determine their presence by the number, 

 intensity and location of the absorption bands. But, as some of these 

 bands occupy the same or very nearly the same positions, it is desira- 

 ble to possess certain landmarks in the spectrum for our guidance. 

 This purpose is served by the Fraunhofer lines. The spectrum of sun- 

 light extends between the ultra red and ultra violet colors, i.e., between 

 rays possessing, on the one hand, a wave length of 757^^/ and, on the 

 other, one of 392^i/x. The Fraunhofer lines traverse the spectrum at 

 definite distances from one another. Thus, the B-Yme, transects the 

 red end with a wave length of 686.8/x/x, the D-line the golden yellow 

 with a length of SSQ/x/x, and the ^-line the green with a length of vibra- 

 tion of 527 jjLfj.. 



Fig. 107. — Diagram of Spectroscope. 



The spectrum of oxyhemoglobin is a very characteristic one. Two absorption 

 bands are visible at the border of yellow and green, between the Fraunhofer D- and 

 £'-lines (Fig. 108). The left band is narrow but dark and sharp and is generally 

 designated as the "a-band." The one on the right, which is broad and less 

 clearly outlined, is referred to as the "jS-band." But as the absorption of the 

 light is dependent upon the thickness and the concentration of the solution, these 

 bands are not always equally distinct. Thus, if the percentage of oxyhemoglobin is 

 greater than 0.65, the bands coalesce and the yellow-green color between them 

 disappears. Greater concentrations eventually give rise to one dark band which 

 overlaps the D- and £'-lines and causes a darkening of the violet end of the spectrum. 

 Quite similarly, very dilute solutions (0.01-0.003 per cent.) produce only a single 

 band, namely, the one nearest the Z>-line. It is essential, therefore, to employ 

 solely solutions in strengths of from 0.1 to 0.6 per cent., while the layer of the 

 solution should be 1 cm. in thickness. These bands may also be obtained from 

 circulating arterial blood. A good object for this purpose is the ear of the rabbit, 

 a hand spectroscope being applied directly to its surface. 



Reduced hemoglobin gives only one absorption band which is commonly 

 spoken of as the "y- band. " It is situated between the D- and ^-lines, extending 

 farther toward the red end of the spectrum and slightly beyond the D-line. It 

 exhibits a considerable width and rather poorly defined margins, but its character- 

 istics vary somewhat with the strength of the solution. 



The spectrum of hemoglobin and its oxygen combination is invariably made use 

 of in the detection of blood, the suspected substance, smear or stain being first 

 extracted with a definite quantity of normal saline solution. In these examinations 



^ liJLfx = 1 millionth of a millimeter. 



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