Reasons for Regeneration. 233 



The causes, or better, the reasons why, after tissue injuries and 

 losses, regenerative growth occurs, are complex. Normal increase 

 of cells depends upon inherent peculiarities of the cells themselves. 

 The capacity for multiplication is characteristic of all cells for a 

 certain time after they are formed; it is most active during em- 

 bryonic life and in youth, diminishing and, within certain limits, 

 ceasing after the full development of the body, as determined by 

 the relative tension of the tissues and the inherited characteristics 

 (phylogenetic). From those influences exerted by the tissues upon 

 each other and by which mutual restraint is maintained so that 

 an overgrowth of one cannot take place at the expense of the rest, 

 the normal inter-resistance of tissues, the so-called tissue tension,'^'- 

 takes its significance. (However, as ^larchand has suggested, 

 mechanical resistance to growth does not alone explain tissue 

 equilibrium ; there are other participating influences, as nutrition. 

 The constancy of the shape and size of the organs and the cells is 

 a fundamental peculiarity of the species.) 



\\'e mav see in many cases where removal of normal tissue 

 resistance has taken place (where, for example, the tissue tension 

 has been released by the formation of cavities) the parts bordering 

 on such situations assume active growth. This is very strikingly 

 apparent where there is a cleft in the diaphragm next to the liver, 

 as the result of which the liver tissue invariably grows through the 

 round or oval diaphragmatic opening into the chest cavity (as a 

 button goes through a buttonhole), the otherwise uniform opposi- 

 tion which the diaphragm exerts upon the anterior surface of the 

 liver being interrupted at this position and lost. In any defect 

 produced by trauma or analogous loss of continuity of the tissues 

 the normal resistance is more or less lowered and the adjacent cells 

 are able to penetrate into the vacant space and fill it (vacuum 

 growth). As a result of the displacement of the cells thus pene- 

 trating the vacant area from their original station, space is afforded 

 in the latter position as well, thus giving opportunity for further 

 proliferation of the elements persisting there (Ribbert). According 

 to Ribbert the displacement of cells even from distant positions 

 may be explained by such a release of tension ; thus in the regenera- 

 tion of blood, leucocytes pass into the circulation and spaces are 

 left in the bone marrow, which are filled by newly forming cells. 

 and with the passage of these the process repeats itself indefi- 



* Ribbert means by tissue tension not only pj-essure conditions, but all the 

 opposing influences of the various tissues upon each other. 



