THE CORPUSCLES 313 



The young corpuscle is called an erythrohJost and has a nucleus. It 

 may live and die in its place of origin. In that case the valuable 

 constituent of the pigment, the iron, is retained by the marrow 

 and used in the construction of other cells. Most of the cells, 

 however, do not remain in the bone marrow. Their nuclei undergo 

 pyknosis and the enucleated corpuscles pass into the blood stream 

 on their way to the liver and spleen, where they are alleged to be 

 destroyed after 10 to 40 days. Those which die by the way are 

 taken out of the circulation by the spleen. Economical Nature in 

 this way makes use of the dying erythrocyte as a beast of burden. 

 In the next chapter we will consider the function of the red cells 

 in the transport of the respiratory gases, and later will give con- 

 sideration to the part they play in the preservation of a constant 

 pH in the blood. There are one or two interesting physical 

 problems in connection with the shape, structure and composition 

 of the red cell which must first be considered. Why should the 

 mammal (except camelidae) have circular biconcave discoids ? 



Shape, Volume, etc., of Red Cells. 



The 5,000,000 (± 1,000,000) of these cells found on the average 

 in every cubic millimetre of healthy human blood vary in diameter 

 and in thickness with variations in the composition of the plasma 

 in which they are suspended. Variations in size and shape are 

 also introduced whenever these cells are measured away from their 

 natural environment. Let us consider these artificial variations 

 first. 



The usual methods of examination entail one or other of the 

 following manipulations : drying in air, dehydrating by alcohol, 

 washing free from plasma, staining, mounting on a glass slide, etc. 

 All of these introduce errors. For example, drying in air, by 

 reducing the water content from about 60 per cent, to almost 

 nothing, is bound to cause shrinking and distortion of the membrane, 

 alteration in the pH of the colloidal matter of the corpuscle due 

 to loss of CO2, etc. Fixation, even by such a rapid fixative as 

 osmic acid, produces peculiar bell-shaped forms. Nevertheless, 

 drying, fixing and staining methods are universally employed, and 

 the results obtained by them appear in most text-books as stan- 

 dard. The best that one can say of methods which take such 

 liberties with a delicate colloidal structure is that they are rapid, 

 and if applied in a standardised way, that they will give compara- 

 tive results. 



The cell and its environment, the erythrocyte and its plasma, 

 must be considered together. Measured in this way, at a constant 

 tension of CO,, the human red cells are 8-8/x in mean diameter as 



