172 ANATOMY AND PHYSIOLOGY 



as that of a flattened sphere (Fig. 116). (They are oxygen- 

 carriers.) 



Note. The illustration presents the appearance under the microscope 

 of blood which has been removed for a time from the vessels and cooled. 

 Careful studies under other conditions indicate that the living cells are 

 slightly bell-shaped. In the early stage of formation they contain a nucleus. 



The red cells are composed largely of hemoglobin held in a net- 

 work or stroma of protoplasm. This itself is amber colored, but 

 when a great number of cells are together as in a drop of blood, 



FIG. 117. WHITE CORPUSCLES PENETRATING CAPILLARY WALLS. 

 (Landois and Stirling.} 



it gives the red hue to the fluid. The color varies with the 

 quantity of oxygen in the cell, from bright scarlet with much 

 oxygen to bluish red with little. Hemoglobin is a protein substance 

 whose most important property is its power to combine with 

 oxygen forming oxy-hemoglobin, and to give it up. It contains 

 a minute quantity of iron in combination (hematin) which is neces- 

 sary to life processes. 



The origin of the red cells is in the red marrow of cancellous 

 bone. 



The white cells or leucocytes are of different sizes (the average 

 size, about ^ 00 of an inch in diameter). They move more slowly 

 in the plasma and are far less numerous, numbering only about 

 7500 in a cubic centimeter. 



They are nucleated, flexible and elastic. Their shape is spher- 

 ical (often irregular) , and they consist of a transparent material 

 containing one or several nuclei and many fine granules of protein 

 substances of several kinds. They also contain glycogen and 

 enzymes. 



