OXYGEN-COMBINATIONS OF HEMOGLOBIN. 55 



observer. In this way the observer can see the spectrum and in or over it the 

 scale. To exclude extraneous, disturbing light, the prism and the inner extremities 

 of these tubes are enclosed within a metallic capsule whose interior is colored 

 black. 



Absorption-spectra. If a colored medium, as, for instance, a solution of blood, 

 be placed between the slit of the spectroscope and a source of light, the interposed 

 solution does not permit the passage of all of the rays of white light, but some 

 of these are absorbed. Therefore, that portion of the spectrum whose rays are 

 not permitted to pass appears dark to the observer. 



FIG. 12. Diagrammatic Representation of the Spectroscope for Study of the Absorption-spectra of the Blood. 



Flame-spectra. If combustible substances are permitted to burn before the 

 slit in a non-luminous (gas) flame at the extremity of a platinum wire the elements 

 of the ash yield bands of a special color occupying a definite position. Thus, 

 sodium gives rise to a yellow, potassium to a red and a violet line, which are found 

 on combustion of the ash of almost all organs. If sunlight alone is permitted 

 to pass through the slit the spectrum exhibits a large number of lines (Fraun- 

 hofer's lines) occupying definite positions within the colors and according to which 

 different parts of the spectrum can be localized. These are designated A, B, C,|D, 

 etc., a, b, c, etc. (Fig. 15). 



OXYGEN -COMBINATIONS OF HEMOGLOBIN: OXYHEMOGLOBIN AND 



METHEMOGLOBIN. 



Oxygen-hemoglobin or Oxyhemoglobin abbreviated to O-Hb is read- 

 ily developed when hemoglobin comes in contact with oxygen or with air 

 (details on p. 78). Oxyhemoglobin is somewhat less readily soluble 

 than hemoglobin. On spectroscopic analysis it exhibits two dark 

 absorption-bands in the yellow and the green, whose position and 

 width in an 0.18 per cent, solution are shown in Fig. 15 (2). 



Oxyhemoglobin is contained within the erythrocytes in the circu- 

 lating blood of the arteries and capillaries, as may be demonstrated by 

 spectroscopic examination of the ear of the rabbit and of the thin layers 

 of skin between two fingers placed in apposition. It is an exceedingly 

 unstable chemical combination, yielding its oxygen even through the 

 influence of such agents as release absorbed gases, as, for instance, setting 

 free of gas through the action of an air-pump or the passage of other 



