CH. VI] MICRO-SPECTROSCOPE AND POLARISCOPE 147 



and the color will change to the bright red of fresh blood. Examine 

 it again with the spectroscope and the two bands will be visible. After 

 five or ten minutes another examination will show but a single band. 

 Incline the bottle so that a thin stratum may be examined. Note 

 that the stratum of liquid must be considerably thicker to show the 

 absorption band than was necessary to show the two bands in the first 

 experiment. Furthermore, while the single band may be made quite 

 black on thickening the stratum, it will not separate into two bands 

 with a thinner stratum. In this experiment it is very instructive to 

 have a second vial of fresh diluted blood, say that from the watch- 

 glass, before the opening of the comparison prism. The two banded 

 spectrum will then be in position to be compared with the spectrum of 

 the blood treated with the ammonium sulphide. 



The two banded spectrum is that oi oxy-hemoglobin, or arterial blood, 

 the single banded spectrum of hemoglobin (sometimes called reduced 

 hemoglobin) or venous blood, that is, the respiratory oxygen is present 

 in the two banded spectrum but absent from the single banded spectrum. 

 When the bottle was shaken the hemoglobin took up oxygen from the 

 air and became oxy-hemoglobin, as occurs in the lungs, but soon the 

 ammonium sulphide took away the respiratory oxygen, thus reducing 

 the oxy-hemoglobin to hemoglobin. This may be repeated many 

 times (Fig. 122). 



§ 211. Met-Hemoglobin. — The absorption spectrum of met- 

 hemoglobin is characterized by a considerable darkening of the blue 

 end of the spectrum and of four absorption bands, one in the red near 

 the line C and two between D and E, nearly in the place of the two 

 bands of oxy-hemoglobin ; finally there is a somewhat faint, wide 

 band near F. Such a met-hemoglobin spectrum is best obtained by 

 making a solution of blood in water of such a concentration that the 

 two oxy-hemoglobin bands run together (§ 210), and then adding 

 three or four drops of a jo P er cent, aqueous solution of permanganate 

 of potash. Soon the bright red will change to a brownish color, when 

 it may be examined (Fig. 121). Instead of the permanganate one 

 may use hydrogen dioxide (H 2 2 ). 



§ 212. Carbon Monoxide Hemoglobin (CO-Hemoglobin). — 

 To obtain this, kill an animal in illuminating gas, or one may allow 

 illuminating gas to bubble through some blood already taken from the 

 body. The gas should bubble through a minute or two. The oxygen 

 will be displaced by carbon monoxide. This forms quite a stable com- 

 pound with hemoglobin, and is of a bright cherry-red color. Its 



