HUMAN STRUCTURE AND LIFE-ACTIVITIES 483 



About 90 per cent of the plasma consists of water, which has 

 been absorbed from the digestive organs, and more than 9 per 

 cent consists of absorbed foods. There is also a small amount 

 of excretions which have been absorbed from cells and are 

 on their way to being eliminated by the excretory organs. 



There are two 

 kinds of corpus- 

 cles or cells visible 

 with the micro- 

 scope; namely, 

 the red and the 

 white. The red 

 ones are bi-con- 

 cave discs, about 

 -g-^Vff of an inch in 

 diameter. They 

 are often seen in 

 rolls like piles of 

 coins. The num- 

 ber of them is as- 

 tounding, for 

 there are about 

 five millions in a 

 cubic millimeter 

 of blood. (A mil- 

 limeter is approx- 

 imately ^V of an 

 inch long ; com- 

 pute how many red corpuscles in a cubic inch of blood.) 

 In the diseased condition known as anaemia, which is char- 

 acterized by the whiteness of the skin, the number of red 

 corpuscles is greatly reduced. 



The red color of these blood-cells is due to a substance 

 called hcemoglobin, which is most important in the blood's 

 work of carrying oxygen to the cells of the body. 



1^0. Human blood-cells. A, rolls of red cells 

 with two white cells a. B, C, D, E, various views of 

 red cel i s . Ft white ce ii magnified same as D. H, I, 

 re d ce ^ s covered with little knobs (abnormal, due 

 to changes after blood is placed on object-slide). 



(From * uxley , } 



