BINUCLEATE CELLS IN TLSSUE CULTURES. 97 



The twin nucleus is, then, to be regarded as potentially a single nucleus, in 

 which the nuclear material is separated into two or more sacs. This nuclear material 

 is not to be considered as in any way equally divided between the nuclear portions, 

 which are by no means daughter nuclei. This view is strengthened by the fact 

 that the centrosome, as has been observed, is single in binucleate cells. Before the 

 cell containing such a single twin nucleus can divide, it seems to ho (>ssential, judging 

 from the observations, that the nuclear material should recombine and a spireme 

 be formed from the chromatin material in its entirety. 



It may be asked whether nuclear fusion, in these binucleate cells, ever occurs 

 without an accompanying mitosis. I have seen no evidence of such recombination, 

 either in living or fixed preparations, and regard it as improbable, because (among 

 other reasons) the i)arts increase in size following their division and the single 

 nucleus, which would result from their reunion, would be unusually large. 



Nothing was brought to light, in the material examined, which would in any 

 way sui^port the assumjition that there are two distinct types of cell division, 

 amitosis and mitosis, for the type of amitosis which 1 have descriljed involves only 

 the nucleus, and mitosis was the only process which resulted in the formation of two 

 separate cells. 



These observations upon nuclear amitosis do not point to its being an evidence 

 of cell degeneration, for the cells in which it is found are not highly specialized and 

 do not show any more tendency to degenerate than the other cells of the culture. 

 It is generally assumed that mitosis takes place only in normal cells, so that the 

 occurrence of mitosis in amitotically divided nuclei hardly allows them to be con- 

 sidered as degenerate. 80, too, the occurrence of amitosis and mitosis in the same 

 preparation (as in the culture from which figure 2 was drawn), where tlie conditions 

 under which the cells are growing are apparently identical, militates against the 

 view that the environment is not favorable, for the two processes are going on side 

 by side, and mitosis demands suitable conditions. Th(> statements of Wieman 

 (1910, p. 174), "amitosis occurs usually under abnormal metabolic conditions which 

 are unfavorable to normal metaboUc processes" and "it can occur under circum- 

 stances that make mitosis impossible, " are out of harmony with his finding of both 

 direct and indirect division side by side in the same field, as shown in his figure 

 13. This coincident occurrence of mitosis and amitosis has been noted by other 

 investigators. 



The conception of amitosis which I have advanced thus differs radically from 

 that of Flemming (1892 and 1893), vom Rath (1891 and 1895), Ziegler (1891), and 

 Ziegler u. vom Rath (1891). They believed that amitosis occm-red in cells which 

 were of a transient character and in those which were very highly specialized or on 

 the way to degeneration; and that in cells of amitotic origin the process of mitosis 

 was not believed to take place. In their scheme the condition w hich I shall speak 

 of as nuclear fragnnnitation seems to have a place. 



According to this conception, then, amitosis constitutes simply a cliange in 

 form of the nucleus without increase in its reproductive capacity, and not an actual 

 cell division; and division of such an amitotic cell occurs only by karyokinesis in 

 which there is a recombination of the nuclear material. If this view be correct, 



