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BIOLOGY FOR BEGINNERS 



their shape much like the amoeba. There are probably several 

 kinds and their functions differ, but seem to be concerned in aiding 

 the absorption of fats and in destroying disease germs in the blood. 

 They are formed in the lymph glands. They have the power to 

 penetrate the capillary walls and wander through the lymph spaces; 

 they collect at wounds and points of infection and oppose the at- 

 tack of disease germs. 



Healing a Wound. In the healing of a cut there are several proc- 

 esses set at work by the blood. First, as the blood oozes out, 

 fibrinogen is exposed to the air, hardens to fibrin, entangles the 

 corpuscles, and the clot or scab forms. Then the blood supply is 

 automatically increased to bring extra white corpuscles on guard 

 to oppose infection; this causes the redness (inflammation). As 

 the fibrin forms, it contracts, causing the puckering of a scar and 

 as fast as new tissue is built, the clot or scab is shed. A slight 

 scratch or blister often lets only the plasma through, while a 

 " black and blue " bruise is in part due to breakage of capillary 

 walls and consequent clotting of blood under the skin. 



Changes in Composition of Blood. The composition of the blood 

 is constantly changing as it receives and distributes its various 

 burdens. This is shown in the following table. 



CHANGES IN COMPOSITION OF BLOOD 



