CHAPTER VII. 

 PROGRESSIVE TISSUE CHANGES. 



REGENERATION. 



DEFINITION. 



EXTENT — Depends upon aqe and tissue involved 

 Blood. 



Connective tissue. 

 Fibrous 

 While. 

 Yellozv. 

 Cartilage — Rarely regenerated perfectly. 

 Bone. 

 Epithelium. 



Surface — Complete and perfect. 

 Glandular — Irregular and inciniplete. 

 Muscle — Perfect regeneration rare. 

 Nerve — Cells do not regenerate, fibres do. 



Regeneration is the process by means of which destroyed 

 tissues are replaced. Tissue destruction is the result of necro- 

 sis, primarily, and inflammation and degeneration, secondarily. 

 Regeneration is accomplished by multiplication of pre-existing 

 adjacent cells or by invasion and multiplication of wandering 

 connective tissue cells. The proliferating cells assume the charac' 

 teristics of embryonal cells, that is, their reproductive property 

 is over-developed and their other vital functions depressed. The 

 power of regeneration of a tissue is inversely proportional to its 

 specialization. Regeneration of the tissues of the less complex 

 animals is more nearly perfect than that of the tissues of highly 

 organized animals ; thus invertebrates regenerate entire organs 

 or parts. Spallanzani cut off the legs and tail of a salamande 

 and observed in the course of three months six crops of these 

 members. In the entire three months 687 perfect bones were re- 

 produced and the regeneration was perfect regardless of the 

 point of amputation. The tissues of young growing animals are 

 more easily regenerated than those of mature animals. Single 

 cells or small areas of tissue are more perfectly regenerated than 

 larc^e areas. In some cases destroyed tissues are not regenerated 

 but are replaced by fibrous tissue. The functions of some de- 

 stroyed tissues and organs may be performed by other struc- 

 tures. Thus, if the tibia of a dog is destroyed, the fibula in- 

 creases in size and assumes its function. Destruction of one 

 kidney is succeeded by a compensatory hypertrophy of the other 



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