234 Regeneration. 



nitely. Anything, even hypersemia, which tends to separate the 

 tissues, has in Ribbert's opinion the same effect to decrease tension 

 and produce space. Although objection may be made that the dis- 

 tending cause must also have a pressure effect which should inter- 

 fere with growth, it must be granted that the vessels distended 

 and engorged in hypersemic conditions separate from each other 

 the closely packed cells, and that similarly the filling up of the 

 lymph spaces with exuded material forces the cells apart and in 

 this sense has an influence to relieve tension. The release of 

 mechanical tension is, however, not invariably the only cause of 

 tissue growth ; there are other factors which are operative to di- 

 rectly stimulate cellular proliferation. There can be no doubt that 

 increase of nutrition, provided the cells are in condition to 

 assimilate it, must necessarily favor multiplication. Especially in 

 inflammatory regeneration it may be appreciated that there is such 

 a rich nutritive supply possible for the cells at the periphery of 

 the inflammatory focus from the albuminous fluid exudates, fibrin 

 and products of disintegration of leucocytes and blood coagula. 

 that there cannot but coexist a condition of extra nutrition of 

 these elements along with relaxation of and space formation in 

 the tissue. The multiplication of tissue in chronic inflammations, 

 protracted hyperemias and lym])li congestions may also be partly 

 explained by this idea. 



In addition it is possible that the elevation of temperature 

 attending inflammatory processes may play a part, as it 

 is well known that warmth is an important stimulus to cellular 

 activity and therefore to cellulai" proliferation. Chemical agents 

 should also be included among the important factors of stimulation 

 of cell multiplication. Just as the mobile leucocytes are attracted 

 by nutritive substances and other materials and assume a phagocytic 

 activity, the fixed cells respond to the chemotactic stimulus of 

 nutrient matter. They do not merely manifest evidence of phago- 

 cytic action which underlies their hypernutrition and consequent 

 cell division, but there may be distinctly recognized, as in the 

 regeneration of nerves, that there exists some special substance 

 exerting attraction, which determines the direction of growth of 

 the proliferating cells. Fibrin especially seems to exert this two- 

 fold influence ; in most cases where a layer of fibrin overlies the 

 tissue, the latter is apt to soon proliferate into the fibrin 

 (Marchand). The substances set free by the destruction of leu- 

 cocytes are apparently capable of exerting a chemical stimulus 



