THE RED BLOOD-CORPUSCLES 929 



cent, sulphur. All specimens are alike in containing a constant pro- 

 portion of iron, as is shown in the following Table : 



Oxyhaemoglobin of Fe per cent. Authority 



Dog. . . 0-336 .. Jaquet. 



Horse . . . 0-335 . . Zinoffsky. 



Ox . . 0-336 .. Hufner. 



Hen . 0-336 .. Jaquet. 



On the assumption that each molecule of oxyhaemoglobin contains 

 one atom of iron, its molecular weight would be 16,660, and this 

 result is borne out by the volume of oxygen or carbonic oxide which 

 can enter into combination with haemoglobin. It has been suggested 

 by Bunge that the enormous size of the haemoglobin molecule finds a 

 teleological explanation ; if we consider that iron is eight times as 

 heavy as water, a compound which would float easily along with the 

 blood- current through the vessels could only be secured by the iron 

 being taken up by so large an organic molecule. Oxy haemoglobin is 

 a compound in definite proportions of oxygen and haemoglobin or 

 reduced haemoglobin. It can be easily dissociated and is split up by 

 such simple means as exposure to a vacuum. If for instance, some 

 arterial blood or solution of oxyhaemoglobin be introduced into a 

 Torricellian vacuum, the fluid is seen to give off bubbles of gas, and 

 the colour changes from a brilliant scarlet to a dull bluish red. In 

 this process each gramme of .oxyhaemoglobin gives off 1-34 c.c. of oxygen. 

 The same change can be effected by treating a solution of oxyhaemo- 

 globin with reducing agents such as an alkaline solution of ferrous 

 tartrate (Stokes's fluid) or ammonium sulphide ; in the latter case 

 reduction is aided by gently warming the solution. Another reagent 

 of value for effecting the reduction of oxyhaemoglobin is a solution of 

 hydrazine. The oxygen in oxyhaemoglobin can be replaced by equiva- 

 lent quantities of other gases. Thus if carbon monoxide gas be led 

 through a solution of oxyhaemoglobin, oxygen is given off and its 

 place is taken by an equal volume of carbon monoxide with the forma- 

 tion of a more stable compound, carbonic oxide haemoglobin. This 

 body is only dissociated with extreme slowness and is unaffected by 

 the addition of reducing agents. By using special precautions to' 

 prevent oxidation of the gas the carbon monoxide can be replaced in 

 this compound by nitric oxide, NO. We have therefore a series of 

 three compounds which can be arranged in order of stability, thus : 



NO -haemoglobin. 



CO -haemoglobin. 



2 -haemoglobin. 



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

 turning out the oxygen from the oxyhaemoglobin, thus depriving the 



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