96 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



spectrum 2). There are two distinct absorption bands between the 

 D and E Hnes ; the one nearest to D (the o band) is narrower, 

 darker, and has better defined edges than the other (the ft band). 

 As will be seen on looking at fig. 36, a solution of oxyhaemoglobin of 

 concentration greater than 0*65 per cent, and less than 0'85 per cent, 

 (examined in a cell of the usual thickness of 1 centimetre) gives one 

 thick band overlapping both D and E, and a stronger solution only 

 lets the red light through between C and D. A solution which gives 

 the two characteristic bands must therefore be a very dilute one. 

 The one band (y band) of haemoglobin (fig. 37, spectrum 3) is not so 



Fig. 37.— 1, Solar spectrum ; 2, spectrum of oxyliEemoglobin (0-37 per cent, solution") : 3, spectrum of 

 haemoglobin ; 4, spectrum of CO-hsemoglobin ; 5, spectrum of methremoglobin (concentrated 

 solution). 



well defined as the a or ^ bands. On dilution it fades rapidly, so 

 that in a solution of such strength that both bands of oxyhaemoglobin 

 would be quite distinct the single band of haemoglobin has dis- 

 appeared from view. The oxyhaemoglobin bands can be distinguished 

 in a solution which contains only one part of the pigment to 10,000 

 of water, and even in more dilute solutions which seem to be colourless 

 the a band is still visible. 



Methsemoglobin. — This may be produced artificially by adding 

 such reagents as potassium ferricyanide or amyl nitrite to a solution 

 of oxyhaemoglobin ; it may also occur in certain diseased conditions in 

 the urine ; it is therefore of considerable practical importance. It 

 can be crystallised, and is found to contain the same amount of 



