866 



PHYSIOLOGY 



NO. We have therefore a series of three compounds which can be arranged 



in order of stability, thus : 



NO-hoemoglobin. 

 CO-hsemoglobin. 

 O 2 -h8emoglobin. 



The poisonous properties of carbon monoxide are due to its power of turning 

 out the oxygen from the oxyhaemoglobin, thus depriving the tissues of the 

 oxygen which is normally carried to them by the red corpuscles. 



Hsemoglobin and its derivatives give well-marked absorption spectra. 

 Thus dilute solutions of oxyhsemoglobin placed in front of the slit of a 

 spectroscope show two well-marked absorption bands between Fraunhofer's 



FIG. 372. The spectra of oxyhaemoglobin in different grades of concentration, 

 of (reduced) haemoglobin, and of carbon monoxide haemoglobin. (After 

 PREYER and GAMGEE.) 



1 to 4. Solution of oxyhsemoglobin 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 carbon monoxide 

 haemoglobin. In each of the six cases the layer brought before the spectroscope 

 was 1 cm. in thickness. The letters (^4, a, etc.) indicate Fraunhofer's Hues and 

 the figures wave-lengths expressed in unfrmr millimetre. 



lines D and E. The centre of the band nearest to D corresponds to A 579, 

 and is often spoken of as the band a, while the second band, the one next 

 to E, which can be called the band /?, is broader, has less sharply defined 

 edges, and its centre corresponds approximately to A 544. 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 oxyhaemoglobin in varying 

 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. 372, 5), its centre corresponding to A 555. This is the 



