248 PRACTICAL PHYSIOLOGY 



two bands of oxyhaemoglobin have disappeared, and are replaced 

 by one band, the centre of which is between the two bands of 

 oxy haemoglobin. The band is a broad one, shading off more 

 gradually on the red side, and the darkest part corresponds in 

 wave-length to X 550 (Spectrum 4 in Chart). 



3. The Visible Spectrum of Carbon-Monoxide Haemoglobin. If a 



stream of carbon monoxide, or even of coal-gas, be passed through 

 some diluted defibrinated blood, the scarlet tint is changed to a 

 carmine or cherry colour. The oxygen is replaced by carbon mon- 

 oxide. Examined spectroscopically the blood shows two bands 

 differing from those of oxyhaemoglobin in being slightly shifted 

 towards the blue end. The two bands have centres corresponding 

 in wave-length to A 575 and A 540 approximately (Spectrum .5). 



The proportion of red and blue unabsorbed at the ends of the 

 spectrum is different in oxyhsemoglobin and CO-hsemoglobin, there 

 being more blue unabsorbed in CO-hsemoglobin than in the former. 

 Hence, comparing dilute solutions of similar strength in test tubes 

 of the same diameter, the CO -haemoglobin has a distinct bluish tinge, 

 contrasting markedly with the yellowish-red of the oxyhsemoglobin. 

 This difference of end- absorption can be best shown as follows : 

 Take a fairly dilute solution of oxyhsemoglobin showing the two 

 characteristic bands clearly, but not strong enough to produce any 

 intermediate shading. Note as carefully as possible where the red 

 and blue are first visible. Pass a stream of coal gas or carbon 

 monoxide through the solution by means of a fine nozzle for two 

 or three minutes. Note the change in colour produced, and again 

 examine the spectrum. It will now be found that rather more of 

 the blue is visible, whilst the red is unaltered or slightly more 

 absorbed. 



An important difference between oxyhsemoglobin and CO- 

 hsemoglobin is seen in the effect of reducing reagents. If CO- 

 hsemoglobin be treated with Stokes' fluid or ammonium sulphide, 

 it is unchanged. 



4. The Visible Spectrum of Methsemoglobin. To a solution of oxy- 

 hsemoglobin, in which the two bands are so wide as to partially 

 overlap, add a few drops of a strong solution of potassium ferri- 

 cyanide. The colour changes to a chocolate tint. If this be 

 spectroscopically examined, a distinct band is seen on the red side 

 of the D-line, the wave-length of its centre being about A 635 

 (Spectrum 12). On diluting the solution down, other bands may 

 be seen one just on the blue side of the D-line (A 581), another 

 still further towards the blue (A 540), and a fourth may be made 

 out on the bluish-green (A 500) (Spectra 13 and 14). The two 

 middle bands are probably not due to any traces of oxyhsemoglobin, 

 but are characteristic of methsemoglobin. 



If such a solution of methsemoglobin be treated with ammonium 

 sulphide, a transient spectrum of oxyhsemoglobin may be seen, 

 succeeded by a permanent spectrum of reduced haemoglobin. 



