LECTURE XVII 

 WOUNDS 



A -wound is a sudden break in the continuity of a tissue, 

 caused by external violence. 



Healing. — All wounds heal by the production of new cells and 

 new intercellular substance formed from preexisting tissue 

 cells. The embryonic cells change later into mature cells like 

 those of the adjacent tissue. Complete union implies a restora- 

 tion of circulation and nutrition. This again implies new blood 

 vessels for the new tissue. 



Union by primary intention. — The essential features of this 

 mode are rapid union and the absence of germs and pus. All 

 wounds which heal without suppuration heal in this way. There 

 is always some new tissue formed, although it may not be visible. 



By granulation. — This is observed in the healing of open 

 wounds and consists of the formation of new tissue by the 

 multiplication of preexisting cells. This new tissue fills the 

 space between the wound margins and replaces the tissue that 

 was destroyed. 



Newly formed tissue in open wounds is composed of capil- 

 laries, embryonic connective tissue cells, and leucocytes. If the 

 wound is free from harmful bacteria and the surfaces are kept 

 at rest and close together, healing is very rapid and but little 

 new tissue is needed. Where there is loss of much tissue, how- 

 ever, it may be impossible to bring the surfaces together and a 

 great deal of new tissue is needed. Connective tissue cells de- 

 velop from preexisting connective tissue cells, and epithelial 

 from epithelial, bone from bone, etc. 



When wounds are covered with granulations, each little eleva- 

 tion contains a loop or network of new blood vessels. The 

 white blood corpuscles emigrate through the new blood vessels 

 and form part of the pus, when pus is present. Healthy granu- 

 lations are small, firm, pink in color, and the surface is slightly 

 moistened with a colorless fluid. In this ease the wound heals 

 rapidly and usually leaves a small scar. 



