458 



Again, a clean-cut wound wliicli lias not been exposed to the air, and 

 which'lodges no foreign body and no septic nor infecting germ, will 

 heal readily by simple adhesion, whereas those that have been exposed 

 and contain matter foreign to the tissues will have healing delayed 

 or prevented by the disturbing action of such bodies. 



Healing in wounds may be said to take place by these modes: 



(1) By primary adhesion, in which case the spherical {enibryonic) 

 cells, and the stellate connective tissue cells (placoids) thrown out on 

 the surface of the wound, rapidly multiply and form a bond of union 

 between the divided lips. Union by this means may be affected 

 within twenty-four hours after the wound has been inflicted. Of all 

 domestic animals, however, the horse is the least prone to such union, 

 being more disposed to the formation of pus. 



(2) By granulation, which is the common form of healing in raw, 

 exposed\sores, in those containing foreign bodies and septic and infect- 

 ing ferments; also in torn and contused wounds. In this form the 

 wound becomes covered with a layer of embryonic and placoid cells, 

 of which the superficial ones degenerate into pus cells, and thus the 

 surface is kept moist by a layer of whitish, creamy pus. In the deeper 

 layer of cells minute loops of capillary blood vessels start up, causing 

 the small rounded elevations known as granulations. In this way the 

 deeper layer of cells receiving a blood supply is transformed into con- 

 nective tissue, and from its surface new loops of blood vessels start 

 into the layer above, and thus layer after layer of new tissue is formed, 

 and the breach caused by the wound is gradually filled up. The 

 new tissue as formed undergoes a steady contraction, drawing in the 

 adjacent skin over the wound, and hence large wounds healed in this 

 way have the skin more or less puckered around them. 



(3) By secondary adhesion, in which two granulating lips of a wound 

 having been brought together and kept in apposition, union takes 

 place through the medium of the cells, as in primary adhesion. 



(4) By scabbing, in which the exudation on the surface of the wound 

 dries up into a firm scab, under Avhich the process of repair goes on 

 by the development of tissue from the deeper cells, as in adhesion. 



In treating clean, incised wounds, attempts should be made to secure 

 healing by primary adhesion, even in the horse. Bleeding should 

 first be arrested, or nearly so, by applying a cold or hot sponge, or 

 by tying bleeding vessels, and the lips of the wound should then be 

 closed accurately, without any twisting or overlapping. ^ In small 

 wounds pieces of sticking plaster may be used, the lips of the wound 

 having fii-st been smootlily shaved, so that they may adhere firmly. 

 In larger wounds the wound may be sewed with a curved surgical 

 needle\nd a silk thread dipped in a solution of carbolic acid. The 

 stitches may be continued from end to end of the wound and the 

 thread prevented from slipping and loosening by a knot at each end; 

 or the stitches may bo independent, the two ends being tied together 

 across the wound. In such cases they may be one-quarter to one- 

 third inch apart; or the lips of the wound may be pinned together, the 



