LECTURE XVI. 

 WOUNDS. 



Definition. — A sudden break in the continuity of a tissue, 

 caused by external violence. Wounds are usually open, some- 

 times subcutaneous. 



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

 and new intercellular substance formed from preexisting tissue 

 cells. These constitute granulation tissue. The embryonic cells 

 change later into mature cells like those of the adjacent tissue. 

 Complete union implies a restoration of circulation and nutri- 

 tion. This again implies new blood vessels for the new tissue. 



Union by primary intention. — The essentials of this mode 

 are rapid union and absence of pus. All wounds which heal with- 

 out suppuration heal in this way. There is always some new 

 tissue, although it may not be visible. 



By granulation. — The new cells are formed by the division 

 of preexisting cells. All wounds heal only after the develop- 

 ment of more or less granulation tissue between the divided sur- 

 faces. If the wound is free from germs and the surfaces are 

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

 new tissue needed. Where there is loss of much tissue, it m-iy 

 be impossible to bring the surfaces together and a great deal 

 of new tissue is needed. Connective tissue cells only develop 

 from preexisting connective tissue cells, epithelial from epithelial, 

 bony from bony, etc. 



When wounds are covered with granulations, each little ele- 

 vation 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 this is present. Healthy gran- 

 ulations are small, firm, jiink in color, and the surface around 

 them is slightly moistened with a colorless fluid. In this case 

 the wound heals rapidly and usually leaves a small scar. 



Proud flesh is merely a mass of profuse granulations, and 



