412 BIOLOGY: GENERAL AND MEDICAL 



1. Epithelial Tissues. Whenever the covering epithe- 

 lium is removed by accident or destroyed by disease, 

 repair soon begins through the proliferation of cells at 

 the periphery of the denudation. The multiplying cells 

 extend more and more until, if the denuded area is not 

 so great as to occasion the death of the individual, or so 

 infected as to destroy the cells as they form, a new cover- 

 ing is produced. This new integument usually lacks the 

 appendages with which the original structure may have 

 been provided. Thus in repair of the skin, the hair 

 follicles, sweat and sebaceous glands are usually absent 

 or very few, and in the mucous membranes the glands 

 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 Fibriltar 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 



