CIRCULATION 



395 



a liquid (serum) which carries the food and waste products, and a 

 proteid substance (fibrinogen), which when exposed to air aids in 

 forming a clot to stop bleeding. The corpuscles are of two sorts, 

 red and white; the former much more numerous, thus giving 

 the red color to the blood. 



The red corpuscles are minute, disc-shaped, blood cells, so small 

 that ten million can be spread on a square inch, yet so numerous 



FIG. 128. Blood corpuscles. A , magnified about 400 diameters. The red 

 corpuscles have arranged themselves in rouleaux; a, a, colorless corpuscles; 

 B, red corpuscles more magnified and seen in focus; , a red corpuscle slightly 

 out of focus. Near the right hand top corner is a red corpuscle seen in three- 

 quarter face, and at C one seen edgewise. F, G, H, I, white corpuscles highly 

 magnified. From Martin-Fitz. 



that there are enough in the average body to form a row four times 

 around the equator. Their red color is due to a complex iron com- 

 pound (haemoglobin) which carries oxygen from the lungs to the 

 tissues. When laden with oxygen it is a bright red, but becomes 

 darker when the oxygen is removed, causing the difference in color 

 of the blood on going to and coming from the tissues. 

 The white corpuscles are really almost colorless and can change 



