Spindle and Cytoplasm 97 



Among the first experiments at Brussels, 21 hours was considered 

 a reco\er\ time in manmials, and at 48 horns -'^- ''^' "■' normally divid- 

 ing cells were in abundance. Many cells degenerated before 24 hours. 

 Residts with Siredon and Xcn<)j)us ha\e been discussed in Chapter 2. 



Generally, 5 to 10 hours represented the duration of arrested mam- 

 malian mitoses, while in cold-blooded vertebrates mitoses may remain 

 arrested for several da)s. 



Clertain trends are seen not only in the recovery figures with Tn- 

 turus xiiridcscens,'^ but also in the recovery frequencies in corneal 

 tissues.i*^' 5" A cornea is treated and then allowed to recover. The 

 maxinuuii arrested metaphases obser\ed at the first fixation (8 hours) 

 arc an unoriented type (92 per cent) which means that both con- 

 tinuotis and chromosomal fibers are inactivated. Only 5 per cent of 

 the figines are stars and 2 per cent bipolar mitoses. The next fixa- 

 tion shows a drop in unoriented metaphases and an increase in stars, 

 69 per cent and 20 per cent, respectively. Bipolar mitoses increase 

 to 8 per cent. Finally at 72 hours, only 5 per cent of the figures are 

 unoriented while the stars maintain their niunbers up to 16 per cent, 

 and most remarkable is the increase in bipolar mitoses to 80 per cent. 

 The picture at 72 hours is a reversal compared to the 8-h()ur fixation. 



Diploid, tetraploid, and octoploid mitoses definitely show that 

 animal cells can be made to double the number of chromosomes.'^-*' 

 -^- - A fcAv airaphase bridges, fragments, as well as chromosomes were 

 found outside the nucleus."^ As late as 168 hours, some bimetaphases, 

 or the "distributed" c-mitoses, were found in Tn turns, also some tri- 

 metaphases that present a multipolar picture. ■••* 



Conclusions drawn from studies of the recovery pattern are that 

 (1) chromosomal fibers recover first — otherwise stars ^votdd not be 

 first to rise and fall; (2) the continuous fibers follow the chromo- 

 somal in recovery; (3) the interaction between two kinds of spindle 

 fibers and the centromeres determines the metaphasic type to be ex- 

 pected; and (4) ;infnial cells may de\elop into polyploid cells ca- 

 pable of dividing upon recovery. 



The nuclear figures were followed during recovery in rats ha\ing 

 recei\ed single injections following jjartial hepatectomy.^'' The re- 

 generating liver offered special ad\antages for the tracing ol these 

 stages; a definite series was noticed."' 



At 12 hours, there were t\vo changes; (1) the chromosomes thick- 

 ened and shortened, while (2) a gradual clumjjing was seen. At 18 

 hours, the cells were fidl of miniatiue nuclei, the micronuclei. Some 

 swelling accompanied the clumping. 



Between 18 and 48 hours, some amoeboid patterns emerged. These 

 were obviously a residt of fusing micronuclei.^^' ^^' i*' Perhaps the re- 

 lated and progressive stages were the binuclear and trinuclear stages. 



