THE RED CORPUSCLES. 233 



at the diagram, Fig. 99, in which the corpuscles are drawn to 

 scale, will give an idea of their relative sizes in examples of the 

 different classes of animals, and will make the following points 

 more rapidly obvious than any description. 



The size of the animal has no general relation to the size of the 

 corpuscles. The human red disks are of a fair average size when 

 compared with those of other mammals, and therefore man's blood 

 cannot be distinguished from that of the other mammalia. 



The mammalian corpuscles are, on the whole, small when com- 

 pared with those of the other vertebrates. The batrachians are 

 distinguished by the great size of the corpuscles. Those of the 

 Amphiuma Tridactylum are visible to the naked eye. 



The following measurements are given by Welcker for the 

 human disks 



Diameter, 0.0077 of a millimetre = ^TF f an inch. 



Thickness, 0.0019 of a millimetre = T1 ^ of an inch. 



Volume, . . . 0.000,000,077 of a cubic millimetre. 

 Surface, .... . 0.000,128 of a square millimetre. 



The last measurement would give about 2816 square metres for 

 the entire blood of an adult. A surface of 11 square metres is 

 exposed every second in the lungs for the absorption of oxygen. 



When circulating in the vessels, or immediately after removal, 

 the red corpuscles are very soft and elastic, being bent and altered 

 in shape by the slightest pressure, and easily stretched to twice 

 their diameter. But the moment pressure or traction is removed, 

 they return to their normal biconcave, disk shape if the medium 

 in which they lie continue of the normal density. (See Fig. 97, 

 p. 227.) 



Changes take place in the blood shortly after it is removed 

 from the body, which seem to be associated with the loss of func- 

 tion (death) of the red disks, as shown by their rapid destruction 

 if reintroduced into the circulation. 



These changes are checked by cold and facilitated by heat, a 

 temperature above that of the body causing them to take place 

 almost immediately. Associated with the loss of function of the 

 disks is observed a change accompanied by an apparent increase 

 of adhesiveness, which causes them to stick together, commonly 

 20 



