HYPERTROPHY, HYPERPLASIA, METAPLASIA, REGENERATION. 97 



of the resting intranuclear network (Fig. 30, 7). The achromatic fibrils 

 disappear from the new cell, while the centrosome may also disappear or 

 may take its place in the cytoplasm beside the new nucleus. 



There are countless variations and details in the minute processes of 

 mitotic cell division and much interesting conjecture as to the meaning of 

 the various changes in mitosis, which the scope of this work does not 

 permit us to consider. But the facts already at hand are of extreme sig- 

 nificance to the biologist and point toward large fields of research in 

 pathology when the normal processes shall have been more clearly and 

 exhaustively determined. 



Abnormal Phases of Mitosis are not infrequent. Thus the mitotic fig- 

 ures may be asymmetrical, so that the distribution of chromatiu sub- 

 stance to the daughter cells may be unequal (Fig. 31). There may be 

 multipolar mitosis, so that instead of two, several nuclei may form. Or, 

 the new-formed chromosome 

 masses may fail to share in the .,,- 

 formation of the new nuclei. f>* 



Such abnormal mitoses are ^ 



frequent in certain tumors, and ^ .Sf 31 



they may be experimentally in- ^^ ^-^ 



duced by the application of vari- 



OUS Chemical substances to living FI0 ^ ABKOMIAI PHASES OF MITOSIS. 



cells. Too little is known about In ^ ^ the mltosis ls Mynuiie&tau , and in the cell 

 the conditions under which ab- totheiefttripoiar. 



normal mitoses occur, and too 



little about the nature of the impulse to cell division in general, to 

 justify to-day far-reaching conclusions as to the significance of these 

 interesting abnormalities in the life of the cell. 



The Significance of Mitosis. The term mitosis or Mryomitosis is applied 

 to this indirect mode of cell division, on account of the involvement of 

 the nuclear threads. It is also sometimes designated as Jcaryokinesis, from 

 the form changes which these threads undergo. Aside from its intrinsic 

 biological interest, a knowledge of mitosis in proliferatiug-cells is of im- 

 portance in pathology, because the recognition of mitotic figures often 

 enables us to decide with certainty what particular cells or cell groivps 

 are involved in the formation of new tissue. The most significant feat- 

 ure, however, of the whole process of mitosis, with all its intricate 

 variations, appears to be that the chromosomes, during their separation 

 into two or more clusters to form the basis of new cells, undergo an exact 

 longitudinal division. So that, under normal conditions, no matter how 

 unequal the division of the cytoplasm may be, all of the new nuclei share 

 alike in the chromatin substance of the parent nucleus. This fact ap- 

 pears to be of extreme importance in the recognition of a physical basis 

 of inheritance. ' 



1 See reference to summary by Wilson, pp. 272 and 273. 



