244 



anatomy poxr proves that cell division and gro\rfch do not gt all 

 represent inseparably linked processes and that the total re- 

 sult of separate processes, which in the nornal course of de- 

 velopment are constantly repeated in the same v?ay, is cspahle 

 ^^4.Z^^l different modification. V/e can cause cells to divide 

 without previous growth, which under normal conditions, would 

 nave been enlarged and then have divided, and conversely can 

 cause their growth without any -division taking place. The first 

 experiment is successful, when we taJ^e away from the cells the 

 S™iJ^°*f presupposed by growth. Therefore, with previous" 

 growtn, those factors may also become effective in the cell, 

 wniQii incite division. In experiments of the second kind, we 

 m?.ko the cell incapable of reacting normally to these very 

 lactors, or we do not allow any of the conditions and substances 

 tp appear which incite division. Ko matter how we may wish to 

 interpret the state of affairs here described, it teaches at 

 any rate that factors leading to division in the cell can also 

 pe produced witjjout any previous growth and that conversely 

 division should not be understood to be a physically necessary 

 (oari\ It^^ °"^ growth which has already taken place, - ±n other words, 

 [dUi)} that the phenomenon of cell growth and that of cell-division 

 can occur independently of one another, according to the con- 

 ditions, which are already effective on the cell and in the cell. 



This same "independence" occurs in all other processes of 

 division, the sum pi which malres up the development of an or- 



fg,nism. In g^rowing root hairs etc., an increase in cell volume 

 eeps pace with the new formation of cell walls. We may arrest 

 the grovrth and still find that the cellular products continue 

 their course. Cell division and nuclear division are indeed 

 independtot of one another. Even in plants, which under normal 

 conditions consist of only unicellular units, multicellular 

 elements are produced under certain circumstances, if for any 

 reason the conditions Necessary frjr the formation of cross- 

 walls are not filled. On the other hand, nuclear division can 

 be "arrested". Just as "independent" as the processes of di- 

 vision Just named, are also those which give the cells their 

 characteristic "inner foim" and signif^r all differentiations 

 of cells and tissues. The processes of tissue differentiation, 

 taking place normally after a certain number of cell divisions, 

 can also occur abnormally early, before the normal number of 

 cells is present, or can be lacking even when the usual number 

 has been reached, or indeed exceeded, and the like. 



According to the number of processes of division tkking 

 part in the formation of various abnormal tissues, we can con- 

 struct a list beginning with the simplest hypertrophies and 

 ending with the most coriplicated hyperjilasias. G rowth of the 

 cells alone was observed in the production of nmny hyperhydric 

 tissues (kata|2lastic hypertrophic) , growth toget&er v/ith in - 

 crease of cytOTjlasm . for instance, in the gall hypertrophies,- 

 growthj cytoplasmic increase and nuclear division lead to the 

 formation of multinuclear giant cells; the same processes to- 

 gether with cross-wall forr.iation may be found taking place in 

 almost all hyperplasias. In the preceding chapter in the dis- 

 cussion of pros ©plasmatic gacDLls, it v/as shov/n, how diverse are 

 the combinations in which the different kinds of differentiation 

 processes can be united with other processes, the production of 

 which is made possible by a hyperplastic tissue outgrov;th, with- 

 out its being connected v/ith them. We find that lignification 

 takes place in many abnormal tissues after repeated cell divi- 

 sion. - The same process is enacted in other cases, however, 



