98 HYPERTROPHY, HYPERPLASIA, METAPLASIA, REGENERATION. 



DIRECT (AMITOTIC) CELL DIVISION. 



In this, which although relatively rare appears to be the most simple 

 mode of ceil division, without those preliminary changes in the nucleus 

 which are seen in mitotic cell division, the nucleus with its membrane 

 becomes constricted and finally divides into two or more parts which be- 

 come new nuclei. At the same time or following this simple nuclear 

 division the cell body divides, and thus two or more cells may form in 

 the place of one. Sometimes the nuclear division is not followed by a 

 division of the cell body, and thus multinuclear cells, or "giant cells" 

 may be formed. 



The signifiance of the difference between the amitotic and the mitotic 

 cell division is that, while in the former there is an exactly even division 

 of chromatin to the daughter nuclei, the division in the latter is of the 

 unclear mass as a whole. 



Amitotic, as well as mitotic, division occurs in leucocytes, in some 

 forms of epithelium, and in pathological new formations. While the na- 

 ture of the process is little understood, there appears to be much reason 

 for the belief that, in general, amitotic division is "characteristic of highly 

 specialized or degenerating cells in which development is approaching its 

 end." 1 



GENERAL CHARACTERS AND LIMITATIONS OF CELL 

 REGENERATION. 



It should be borne in mind, in studying the regeneration of various 

 kinds of cells and tissues, that the acquirement by certain cells of special 

 functional powers as the result of the physiological division of labor has 

 involved the impairment of some of their more primitive general capac- 

 ities, among these that of reproduction. Thus it is that we find in the 

 ganglion cells an almost total lack of reproductive capacity ; while in 

 many of the gland cells this is slight, in others considerable. In some of 

 the less highly differentiated cells of the body, on the other hand, as in 

 certain forms of epithelium, in blood cells, and, in the cells of the con- 

 nective tissue, this primitive capacity of protoplasm to form new simi- 

 lar cells by division is maintained, and may be evoked by the changed 

 conditions which injury or loss involves. 



Although the occurrence of mitosis is the mark by which we espe- 

 cially recognize the regenerative process in cells, it should be remembered 

 that mitosis or some of its phases may occur in cells, without being fol- 

 lowed by those further changes which lead to new cells or new tissues. 2 



We may also often recognize new-formed cells and tissues by differ- 



1 For a comprehensive summary of facts and theories concerning the cell, both in 

 higher and lower forms of life, consult Wilson's masterly work, "The Cell in Develop- 

 ment and Inheritance," 1900. 



4 One is often disappointed in seeking for mitotic figures to find so few of them even 

 in rapidly growing tissues. This is due to the faet that cell division even when active 

 is not continuous, and periods of rest may follow the act of division. See 2'homa's 

 "Text-book of General Pathology," English Tr., vol. i., p. 481. 



