AMITOSIS IN CELLS GROWING IN VITRO. 451 



changed. Variation in the nucleoli is noted, there being now three in one nuclear 

 sac and four in the other. The outline of the cell body is now quadrilateral, and 

 this shifting of form has perhaps accounted for the rearrangement in relative posi- 

 tion and relationship of the nuclear parts. These, at 2.30, were again in contact, 

 but subsequently repeated the process of moving apart and coming together three 

 times during the observation, which ended at 11.15 p.m. During this time (nj^ 

 hours) the cell was observed continuously, and underwent constant minor changes, 

 such as that of the outline, shifting about of cytoplasmic structures, and breaking 

 up, recombination and variation in size and shape of the nucleolar fragments. After 

 almost twelve hours the cytoplasm showed no indication of dividing. 



These observations brought out the fact that what might be 

 mistaken for a single nucleus divided by a membrane across its 

 equator is really two nuclear sacs pressed close together, the equal 

 tension in the two bodies resulting in a flat membrane between 

 them, made up of the surfaces of contact. Child (191 1) describes 

 a type of amitosis which is characterized apparently by the growth 

 through the nucleus of a membrane or plate, the subsequent 

 splitting of which leads to the production of two nuclear sacs 

 quite separate one from the other. Nuclear fission of this type 

 was not found, and appearances suggesting a process of this 

 kind probably result from the close relationship of separate 

 nuclear parts, similar to the condition found in the cells of 

 tissue cultures. Partitions within the nucleus ave also simu- 

 lated, in these flattened cells, by long nucleoli, mitochondria 

 or folds in the nuclear membrane. 



These observations also illustrate the characteristic behavior 

 of the nucleolar bodies, which undergo constant changes in size, 

 shape, number and position. These bodies stain well with gentian 

 violet when applied to the living culture. They appear as dark 

 masses after iron hematoxylin, but if differentiation with iron alum 

 is carried too far what was before a homogeneous mass becomes a 

 collection of granules (Fig. 27). The nucleolus appears to be a 

 concentrated gel of varying density, the granules representing 

 the denser areas. 



Similar observations upon other living cells were carried out, 

 and in no case did any direct fission of the cytoplasm occur; this 

 finding was supported by the study of fixed preparations. On 

 the contrary the history of these binucleate cells was the same 

 as that of mononucleate cells of the same type. It was even 

 found that mitosis occurred in these cells, for, during the obser- 



