78 BINUCLEATE CELLS IN TISSITE CULTirRES. 



linin stretched across a luiclcus with chromatin granules upon it often gives the 

 ai^pearance of a membrane dividingthe nucleus aniitotically(endogenous division?)." 

 Ho also states that he has found no evidence of the "endogenous" division of 

 Child (1907a, p. 95); nor have I seen anything of this kind in tissue cultures. 

 Optical appearances similar to Child's (1911) figure 6 have been seen in living cells 

 and interprct(Hl as indentations and infoldings of the nuclear membrane. All these 

 conditions can be made clear by the use of a dye like gentian violet upon the living 

 culture, or by proper fixation and staining. In no case has a bona Jidr intranuclear 

 membranous partition been found in any kind of i)rei)aration. 



I may also state here that my ()l)servations upon fixed and stained cells in 

 tissue cultures have not disclosed cases where one nuclear half was more darkly 

 stain(>(l than the other, such as those mentioned by Child (1904, p. 549; 190(5, ]). 595; 

 1907c, p. 171 ; and other i)laces) and which he believes to indicate "a certain degree 

 of physiological independence before separation of the parts." In the living condi- 

 tion, too, the nuclear jiortions present no evident difference in cytoplasm. The 

 contents of the nuclear ])arts are in every way similar to those of the single nuclei. 

 The nucleoplasm ;i])i)ears homogeneous during life and when fixed with osmic-acid 

 vapor is finely granular. This method of fixation {)reserves most accurately the 

 details of the living cell (Lewis and Lewis, 1915). 



There is usually at least one nucleolus or karyosome in each nuclear portion, 

 and more often two (figs. 7 and 9) or even more. The nucleoli of the connective- 

 tissue type of cell are irregular in shape, often elongated, and vary greatly in size 

 (fig. 8). In the living cell they are highly refractive. They continuously undergo 

 changes in shape, size, and number during the life of the cell (figs. 24 to 35, and 

 plate iv), as can be seen by watching the living nucleus. It is then apparent that 

 their outline is "ragged," as Lewis and Lewis (1915) describe it. The bodies even 

 appear to break up from time to time, and afterward to recombine (figs. 24 to 35). 

 At times the nucleolus comes to lie ver.y close to the nuclear membrane (fig. 29) 

 and it may even appear to be attached to it. These bodies take the gentian violet 

 dye very well and stain darkly with hematoxylin. If overdifTerentiated with iron 

 alum the nucleolus appears as an agglomeration of small granules of about equal 

 size (fig. 10); it is jirobably to be regarded as a gel of varying density, the densest 

 portions being represented by these darkly staining granules. 



During mitosis the nucleolus disappears with the formation of the s]nreme, and 

 the daughter nucleoli reappear in the reorganizing daughter miclei. The nuclear 

 l)ortions may be separated by an interval (fig. 9), or simply touching one another 

 (fig. 7), or may be pressed so close together that their adjacent surfaces are flattened, 

 similar to the condition in the early cleavages of Moniezia, as mentioned by Harman 

 (1913, p. 221). They tend to remain close to one another, and do not migrate far 

 apart, as nuclei in a .syncytium. When separated, the nuclear portions show mito- 

 chondria betw'cen them (fig. 9) and usually the centrosphere is situated either in the 

 interval between the nuclear portions, or opposite this interval, as in figures 7 and 59. 



In the living condition the centrosphere or "central body" of Lewis and Lewis 

 (1915) appears as an area of .slightly greater refractivity situated at one side of the 

 nucleus in mononucleate cells; this side is frequently concave, with the centro- 



