TTTE BLOOD 



119 



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. 



Methaemoglobin. 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 

 oxygen as oxyhaemoglobin, only combined differently. The oxygen 

 is not removable by the air-pump, nor by a stream of a neutral gas 

 C D E6 F G 



FIG. 37. 1, Solar spectrum ; 2, spectrum of oxyhaemoglobin (0'37 per cent, solution) ; 3, spectrum of 

 haemoglobin ; 4, spectrum of CO-haemoglobin ; 5, spectrum of methfernoglobin (concentrated 

 solution). 



like hydrogen. It can, however, by reducing agents like ammonium 

 sulphide, be made to yield haemoglobin. Methaemoglobin is of a 

 brownish-red colour, and gives a characteristic absorption band in 

 the red between the C and D lines (fig. 37, spectrum 5). 



The ferricyanide of potassium or sodium not only causes the 

 conversion of oxyhaemoglobin into methaemoglobin, but if the reagent 

 is added to blood which has been previously laked by the addition of 

 twice its volume of water there is an evolution of oxygen. If a small 

 amount of sodium carbonate or ammonia is added as well to prevent 

 the evolution of any carbonic acid, and the oxygen is collected and 

 measured, it is found that all the oxygen previously combined in 

 oxyhaemoglobin is discharged. This is at first sight puzzling, because, 



