136 THE BLOOD-CORPUSCLES. 



Hence they are called the red corpuscles, (B, C, D). In 

 blood, the corpuscles are so closely packed that there 

 are more than five millions in a single drop. It is this 

 which makes the blood so red; if you dilute a drop of 

 blood with a teaspoonful of water, or spread it out very 

 thin on a piece of glass, it appears yellow. 



7. The Shape of the Red Corpuscles is that of thin circu- 

 lar disks, a little hollowed out on each of their larger 

 surfaces. If you made a piece of dough into a round 

 cake, an inch across and a quarter of an inch thick, and 

 then pressed it between thumb and finger so as to make 

 a slight hollow on each side, you would have a very good 

 model of a red blood-corpuscle. It would, however, be 

 thirty-two hundred times broader and thicker than the 

 real corpuscle. Put in another way, we may say that 

 three thousand two hundred red corpuscles placed in a 

 line, and touching one another by their edges, would 

 make a row one inch in length; and twelve thousand 

 eight hundred, piled one on another, would make a col- 

 umn an inch in height. 



8. The Red Corpuscles of other Animals. The red cor- 

 puscles of most mammalia (p. 9) resemble those of man 



in being circular pale 

 yellow disks slightly 

 hollowed on each side; 

 those of camels and 

 dromedaries, however, 



FIG. 36. Red corpuscles of the frog. are Oval. The blood- 



corpuscles of dogs are so like those of man in size that 



7. Shape of the red corpuscles ? Illustrate. What is said of their 

 size? 



8. How do the red corpuscles of most mammalia resemble man's ? 



