CHAPTER XI 



BLOOD: THE BLOOD CELL 



(Contributed by R. G. PEARCE) 



THE RED BLOOD CORPUSCLES, OR ERYTHROCYTES 



The most prominent function of the blood is to carry oxygen to the 

 tissues. It owes this property chiefly to the red blood cells which are 

 present in large numbers (5,000,000 per c.mm. of blood). These cells 

 are biconcave discs, having a diameter of about 7.7 ju. They are con- 

 structed out of a framework composed largely of lipoid material, in 

 the meshes of which is deposited a substance called hemoglobin, to 

 which the remarkable oxygen-carrying power of the blood is due. Nei- 

 ther the manner by which the red cell carries its hemoglobin nor the 

 intimate structure of the cell itself is accurately known. It is com- 

 monly believed that the hemoglobin is held enmeshed in a framework 

 or stroma, or encased in the cell membrane. One thing is certain, how- 

 ever, that the union of hemoglobin with the stroma of the red cell is 

 a fairly strong one, since mere fragmentation of the corpuscle fails to 

 liberate the hemoglobin. The fact that the framework contains a large 

 amount of lipoid substances enables the corpuscles to maintain their shape 

 and is responsible for their characteristic permeability. 



Hemoglobin is a very complex substance belonging to the group of 

 conjugated proteins. By chemical means it can be broken up into a 

 simple globulin and a pigment hematin, containing iron. When com- 

 pletely saturated, oxygen is present in hemoglobin in the proportion 

 of two atoms of oxygen to one atom of iron (Peters); or 401 c.c. of 

 oxygen can 'be carried by hemoglobin containing one gram of iron, the 

 molecular weight of the molecule being about 16.669, or some multiple 

 thereof (Barcroft and Peters) (see also page 392). At this figure the 

 iron in the molecule would represent 0.34 per cent of the total weight 

 of the molecule. The corpuscular surface area has been estimated to 

 be 3200 square meters. There is therefore a very large surface avail- 

 able for the absorption of oxygen from the alveolar air, as the blood 

 corpuscles pass in single file through the capillaries of the lungs. 



Since the amount of oxygen which the blood can carry depends upon 

 its hemoglobin content, it is of some importance clinically to have 



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