930 PHYSIOLOGY 



tissues of the oxygen which is normally carried to them by the red 

 corpuscles.^ 



Haemoglobin and its derivatives give well-marked absorption 

 spectra. Thus dilute solutions of oxyhaemoglobin placed in front 

 of the slit of a spectroscope show two well-marked absorption bands 

 between Fraunhofer's lines D and E. The centre of the band nearest 

 to D corresponds to X 579, and is often spoken of as the band a, 



FIG. 357. The spectra of oxy haemoglobin in different grades of concentration, 

 of (reduced) haemoglobin, and of carbonic oxide haemoglobin. (After 

 PREYER and GAMGEE.) 



1 to 4. Solution of oxy haemoglobin containing (1) less than '01 per 

 cent., (2) -09 per cent., (3) -37 per cent., (4) -8 per cent. 5. Solution of 

 (reduced) haemoglobin containing about '2 per cent. 6. Solution of 

 carbonic oxide haemoglobin. In each of the six cases the layer brought 

 before the spectroscope was 1 cm. in thickness. The letters (A, a, &c.) in- 

 dicate Fraunhofer's lines and the figures wave-lengths expressed in TTnjVw 

 millimetre. 



while the second band, the one next to E, which can be called the 

 band fi, is broader, has less sharply defined edges, and its centre 

 corresponds approximately to X 554. On concentrating the solution 

 or using thicker layers a point is reached at which the two bands fuse 

 into one, and with a still stronger solution it will be found that the 

 whole of the spectrum is absorbed with the exception of the red end. 



The above figure shows the spectrum of oxyhsemoglobin in vary- 

 ing concentrations, a stratum one centimetre thick being examined. 

 If a reducing agent be added to the solution of oxyhaemoglobin 

 the two bands disappear and their place is taken by a more 

 diffuse band lying midway between the two (Fig. 357, 5), its 

 centre corresponding to X 555. This is the absorption spectrum of 

 haemoglobin or reduced haemoglobin. The spectrum of carboxy- 



