88 



HUMAN TISSUES 



Blood corpuscles. The red corpuscles are circular, biconcave 

 disks lacking nuclei. There are- approximately five million in a 

 cubic millimeter of normal human blood. They have a yellowish 

 red tinge when viewed singly, but in great numbers appear red. 

 This color is due to an iron-bearing compound, haemoglobin, 

 which is in the cytoplasm. This haemoglobin readily unites 

 with oxygen and just as readily gives it up when oxygen is scarce. 

 The red corpuscles, in spite of their extremely minute size, can 

 carry large quantities of oxygen. Human tissue cells are not in 

 direct contact with the oxygen of the air. Therefore, they de- 

 pend upon the specialized red corpuscles for their supply of oxygen. 

 The white corpuscles are irregular masses of cytoplasm con- 

 taining one nucleus or several nuclei. Normally, they number 

 between eight thousand and nine thousand to a cubic millimeter. 

 They move and feed in a manner similar to that of amoebas. 

 They send out projections of protoplasm which engulf and digest 



foreign materials. They are 

 sometimes called the scaven- 

 gers of the body because they 

 rid the body of germs and 

 other foreign material. Un- 

 like other body cells, they 

 have the power of independent 

 motion and can move in a di- 

 rection opposite to the blood 

 current. They can even make 

 their way out of blood vessels 

 and get into the surrounding 



Part of a drop of blood that has been magnified tisSUCS to destroy germs. 



Specialization of human 

 tissues. It is evident from 

 the preceding chapters that the different tissues of the body are 

 adapted to perform particular functions. Epithelial tissue is 



2500 diameters and then enlarged. The cell 

 shown in the center with a large nucleus is a 

 polynuclear white corpuscle. 



