382 BIOLOGY: GENERAL AND MEDICAL 



are absent. The type of epithelium in the new covering 

 conforms to that originally present, squamous cells 

 being formed where squamous cells pre-existed, columnar 

 cells, where columnar cells pre-existed. 



2. The FibriUar Connective Tissues. When the injury 

 or disease has involved a greater depth of tissue, the 

 fibrillar connective tissue manifests activity and soon 

 shows itself to be the most important factor engaged 

 in the process of repair. Its cells multiply, pass through 

 stages analogous to those seen in the formation of the 

 areolar tissue of the embryo, and eventually produce 

 fibres of collagen and fibroglia, by which the wound is at 

 first more or less completely closed and subsequently 

 drawn together. Newly formed tissue of this kind is 

 known as cicatricial tissue and constitutes the "scar." 

 It at first appears in excess, but subsequently contracts 

 more and more, loses its cellular character, and becomes 

 more and more densely fibrous until the separated edges 

 of the wound are more or less closely approximated and 

 strongly bound together. In freshly repaired wounds 

 one sees through the delicate newly formed epiderm, 

 a mass of pink scar tissue which becomes whiter and less 

 conspicuous as time elapses. 



3. The Blood Vessels. As growing tissues, such as 

 form the new scars, require to be nourished during the 

 period of active growth, new capillaries, arterioles, and 

 venules are formed to meet this requirement. Capil- 

 laries are formed as filamentous offshoots from pre-exist- 

 ing capillaries. These increase in size and gradually 

 come to consist of several endothelial cells which become 

 channeled. Arterioles and venules are formed by en- 

 largement of capillaries whose walls become supported 

 by fibrillar and muscular tissues that extend over them 

 from the larger vessels. Such new vessels may be per- 

 manent or may be of temporary use only and sub- 

 sequently disappear through the pressure exerted upon 

 them by the contracting fibrillar tissue as the repair 

 becomes more and more perfect. 



