94 BIXl'CLEATE CEI.I.S IN TISSUE Cl'LTURES. 



and clatisificatioii of cells, was made of tlic 20 preparations from oliick heart men- 

 tioned before. In tliese estimates only the pro])hases were counted, since it is 

 imjiossihle to say of the cells in the later staf^es of mitosis wheth(M- th(\v arose from 

 a monopartite or bijjartite nucleus. Degenerate ci'lls were omitted, anil al.so the 

 area close to the original piece was not counted, since the cells here were usually too 

 small and clo.sely ])acked to l)e seen clearly. Nuclei with more than two i)arts of 

 equal size were rare: such w(>re groujud with the ))iiuicleate cells in this estimation. 



It was found that there was a total of 41,100 mononucleate' cells (excluding 

 the later mitotic and amitotic forms); of these 47 were in the proi)hase of mitosis, 

 or 0.1 14 per cent of the total. In the same series there was a total of 375 binucleate 

 cells, 2 of which were in the prophase, or 0.53 per cent. 



In si^ite of the rarity of occurrence of binucleate cells in prophase (there being 

 only 2 in a total of 41 ,725 cells) it will be .seen from this result that mitosis occurred 

 even more freciuently among the binucleate cells than among the mononucleate — 

 in fact, 4.65 times as frequently. Thus, while it can not be stated definitely that 

 mitosis with recombination of the nucleus always follows amitotic nuclear division, 

 or, indeed, that it freciuently does, it may nevertheless be affirmed with confidence, 

 even allowing for the limited extent of the ob.servation, that the incidence of mito.sis 

 ill the l)inucleate cells is at least as high as tliat among the mononucleate. 



If, in addition to this division by mitosis which these binucleate cells show, 

 they be considered as also ])roliferating by direct division of the cytoplasm, it will 

 be readily seen that their rate of proliferation wouKl then be very much greater than 

 that of the mononucleate cells. Tlic improbability of this excessive multi])lication 

 strengthens the negative evidence to be put forward later that there is, in these 

 Itiiiucleate cells, no division of the cyto]ilasm following direct division of the nucleus. 



We have seen that a single mitotic hgure can be formed from two nuclear 

 l)ortions, jireviously separate, but contained within the same cell. It has also been 

 found that the spireme may form in a bent nucleus of a shape similar to tho.se under- 

 going direct division. Figure 20 represents an early sjjireme in such a nucleus. 

 There is apparently but a single centrosphere, situated in the cleft. Figure 21 

 shows a somewhat more advanced spireme. The nuclear membrane has dis- 

 appeared and thi> chromosomes are more definite. One centrosphere is situated 

 above, in the cleft, and there is an indistinct trace of a second in the clear area below. 



We can thus construct a series, from cells taken from fixed sjiecimens, illus- 

 trating ])roi)hases in single nuclei, in double nuclei, and in the intermediate forms 

 connecting these. Figures 14 and 19 show .spiremes in single nuclei. In the last 

 are two well-marked centrospheres, indicating that a spindle is about to be formed. 

 Figures 20 and 21 show the process in intermediate forms, and figures 22 and 23 

 show it in the double nucleus. 



In figures 20 and 21 it is reasonable to sujipose that the amitotic process has 

 ceased, since the nuclear membrane has almost or ciuite disappeared, and for the 

 same reason the process of karyokinesis, which is .so obviously taking jilace in these cells 

 and in those represented in figures 22 and 23, must in all of th(»se cases be considered 

 as starting up under circumstances where amitosis of the nucleus was under way, or 

 was completed, rather than as having the process of amitosis superpo.sed upon it. 



