100 lUXrCLEATE CELLS IX TISSUE CrLTrUES. 



grown in oxygen-poor media showed division of the nucleus without cleavage of the 

 cell protoplasm, and \Meman (1910) expresses the view that lack of oxygen may be 

 a cause of a similar nuclear fragmentation in the material which he examined. 

 Again, Holmes (1914) noted such a fragmentation in tissue cultures kept a week or 

 more without changing the medium; when, however, the medium was changed 

 frecjuently there was no indication of such nuclear change. Fragmentation was 

 accompanied by other evidences of degeneration. Here, too, lack of oxygen may 

 be the underlying cause, and the increased nuclear surface due to the change in 

 form and multiple division of the nucleus may represent the effort, on the ])art of 

 the cell, to secure an increased respiratory area. 



The mechanics of nuclear fragmentation is no less comjilicatod than that of true 

 nuclear amitosis; indeed, it is probable that new and obscure factors l)ring about 

 a change in nuclear outline and division of its substance. The activity of the centro- 

 sphere and mitochondria may be regarded as similar to that found in the true form 

 of nuclear amitosis, since their relation to the nucleus is the same. 



Nuclear forms somewhat resembling those just described, but simpler in 

 character, are occasionally seen in ai)i)arently normal tissue cultures; c. g., those 

 shown in figures 11, 12, and 13. Similar forms have been described in embryonic 

 tissue developing normally, as figures 76, 8 a and c of Child (1904) and some of tli(^ 

 figures of INIaximow (1908). They appear to be exami)les of spoi'adic and simple 

 fragmentation. The fate of these buds is obsciu'e, but is prol)ably degeneration. 



SUMMARY. 



The following general conclusions, based ui)oi^ the results of the fort^goiiig 

 investigations, have been reached: 



BINUCLEATE CELL. 



Incidence: In 20 preparations the binucleate cells made up 0.9 j^er cent of the 

 total cells appearing in the new growth. They were more abundant in membranes 

 growing from the heart than in growths from any other tissue, and in cultures of 

 hearts of 5 days of age than in those from older cardiac tissue. They were also 

 more abundant in new growths from cultures of the second day than in those of the 

 first; this suggests that some, at least, of these cells have arisen in the new growth 

 rather than in the original piece, with subsequent migration into the new growth. 



The proi)ortion of cells containing amitotic (constricted) nuclei to the total 

 number of cells was 1 to 835; that of amitotic nuclei to bipartite nuclei was 1 to 7.5, 

 and that of amitotic to mitotic nuclei was 1 to 3.4. 



Origin: The paired nuclei of binucleate cells in tissue cultures arise by direct 

 division of the nucleus, or nuclear amitosis, without division of the cytoplasm. This 

 occurred in perfectly normal cells. 



Constriction of the nuclear membrane, from one or both sides, which seems to 

 be associated with a karyoplasmic streaming away from the nuclear ('((uator, was 

 the onh' mechanism observed in direct nuclear fission, and in this process an activitj' 

 of the centrosjihere and mitochondria, combined with elongation of the nucleus, 

 appeared to be the principal factors. The centrosphere does not di\-ide, nor do the 

 centrosomes separate. 



