REPAIR OF INJURIES 403 



5. The changes which take place about an injured part 



cause it to become red, painful, swollen, and warmer 

 than usual. 



6. If wounds and all other injuries were protected against 



bacteria, they would heal at once without discharg- 

 ing pus or other matter. 



7. In injuries to mucous membranes, the white blood cells 



and plasma pass through the thin tissues to the sur- 

 face and are discharged at once. 



8. Taking cold means an injury due to bacteria. 



9. The matter discharged from an abscess or from a 



"cold" is composed of the best cells of the body 

 which have died in its defense. 



DEMONSTRATIONS 



175. Scratch the skin upon the lower part of the arm. Notice that a 

 red line develops in a moment. Explain that the scratch injured the 

 cells and partly paralyzed the blood vessels, and that the redness is due 

 to more blood in the part, which has come to repair the damage and to 

 protect the rest of the body. 



176. A pimple upon the face will illustrate the different stages of 

 inflammation . Explain that a pimple may be caused by a prick too small 

 to be noticed, but which has introduced some bacteria beneath the skin. 

 Explain that the redness is due to the blood which has come to repair 

 the damage. Explain that the white spot upon the top of the pimple is 

 the softened area through which bacteria and dead cells will finally pass 

 out, and that the pus is composed of white blood cells which have died 

 fighting to protect the body against the bacteria. 



177. Place a tiny drop of matter pressed from a pimple or a cut or a 

 scratch upon a microscope slide and examine it with a power of 400 

 diameters. Notice that it is composed of white blood cells, containing 

 nuclei. Examine also a drop of mucus from the nose and notice that it 

 consists largely of the same kind of cells. 



178. Obtain a prepared microscopic specimen from a wound in the 

 process of healing. Show that the newly formed tissue consists of 



