THE INDIVIDUAL GROUPS OF PROTEINS 479 



this band becomes resolved into two, the one lying nearer D being 

 narrower than the other. It is immediately to the right of the sodium 

 or D line, as can be seen by introducing a little sodium chloride into the 

 flame when examined by gaslight. At the same time light will pass 

 through the violet region. 



It should be noted at what dilution of the blood these two bands 

 are first clearly visible, so that this dilution can be used for the ex- 

 amination of the derivatives. 



(a) Oxyhaemoglobin. HbO 2 . 



The two bands as seen above are characteristic of oxyhaemoglobin. 



Very dilute solutions of oxyhaemoglobin, yellowish-red in colour to 

 the naked eye, still show the two characteristic bands. 



(V) (Reduced) Haemoglobin. Hb. 



The most remarkable property of haemoglobin is its power of ab- 

 sorbing a molecule of oxygen and its power of giving it up again. 

 Oxyhaemoglobin and haemoglobin exist side by side in circulating 

 blood ; oxyhaemoglobin preponderates in amount in arterial blood, 

 haemoglobin usually in venous blood ; the difference in the red shade 

 of two kinds of blood shows which preponderates ; the bright red 

 colour is that of oxyhaemoglobin, the dull red colour is that of haemo- 

 globin. Blood kept in the absence of oxygen becomes dull red and 

 will contain haemoglobin. Haemoglobin is characterised by a single 

 absorption band. 



Solutions of haemoglobin can be artificially prepared by the 

 action of reducing agents upon blood, such as alkaline solutions of 

 ferrous salts (Stokes' reagent), ammonium sulphide, sodium thio- 

 sulphate, hydrazine ; thus 



(i) A few drops of ammonium sulphide are added to a solution of 

 oxyhaemoglobin and the solution is gently warmed to about 50. The 

 colour becomes darker and on examination with a spectroscope a 

 single broad absorption band will be seen between D and E. 



(ii) Two or three drops of Stokes' reagent 1 are added to a solution 

 of oxyhaemoglobin. It acts more rapidly than ammonium sulphide and 

 need not be warmed. The single absorption band of haemoglobin is 

 seen with a spectroscope. 



Conversion of Hemoglobin into Oxyhcernoglobin. 



On shaking up the solution of haemoglobin with air, it is converted 

 into oxyhaemoglobin and two bands become visible. If excess of re- 

 ducing agent has been added the two bands will disappear and the 

 solution will show the single band of haemoglobin. 



1 Stokes' reagent consists of ferrous sulphate, tartaric acid and ammonia. It is pre- 

 pared by dissolving 3 gm. ferrous sulphate in cold water, adding a cold solution of 2 gm. 

 tartaric acid and then making the mixture up to 100 c.c. Strong ammonia is then added 

 till the precipitate first formed is redissolved. The solution rapidly absorbs oxygen and 

 must therefore be freshly prepared. The solution of ferrous sulphate and tartaric acid can 

 fee kept for some time ; the ammonia is therefore added when the reagent is required for use. 



