HAEMOGLOBIN. 201 



amount per c. c. that water can dissolve under like conditions. 

 For example, let us imagine human blood to be water. It would 

 carry then only 1/40 of the volume of oxygen that it does, and 

 the body would need the vascular system of an elephant or the 

 tissues of a rabbit in order to obtain as much oxygen as normally 

 is supplied by the blood. Therefore it is obvious that the laws 

 for simple solutions can apply only in a slight degree to the 

 gases in the blood. They would account at the most for only 0.7 

 per cent of the total oxygen and 2 per cent of the carbon dioxide 

 found in the blood. 



Haemoglobin. The extraordinary ability of the blood to 

 carry oxygen and carbon dioxide lies in the presence of sub- 

 stances capable of chemically uniting and thus storing up large 

 amounts of the gases. The iron containing protein substance 

 called haemoglobin, found in the red blood cells carries the oxygen, 

 and the alkalies and proteins of the blood carry most of the car- 

 bon dioxide. Analysis of samples of arterial and venous blood 

 gives the following average figures, which represent the volumes 

 of the gas found in one hundred volumes of blood. 



Oxygen CO., Nitrogen 



100 vol. arterial blood contains 20 40 1-2 



100 vol. venous blood contains 10-12 45-50 1-2 



The small amount of nitrogen present in the blood in spite of 

 the large percentage found in the atmosphere (4/5 of the baro- 

 metric pressure being due to nitrogen) is due to the absence of 

 any chemical body within the blood plasma which will unite with 

 nitrogen. Of the 20 volumes per cent of oxygen found in arterial 

 blood only 0.7 per cent is in solution in the plasma. 



RELATION OF OXYGEN TO HEMOGLOBIN. In order to under- 

 stand the affinity of oxygen for haemoglobin, we must investigate 

 the various conditions which favor the union of haemoglobin with 

 oxygen and the break-down of the resulting oxygen compound, 

 oxyhasmoglobin, into oxygen and haemoglobin. Equal quantities 

 of pure Jicemoglobin solution are placed in a series of glass ves- 

 sels containing variable quantities of oxygen mixed with nitrogen ' 



