Spindle and Cytoplasm 89 



the spindle may determine the course of cytokinesis. These data 

 have been limited mostly to eggs, where the principles of cytokinesis 

 in relation to the mitotic mechanism are better observed than among 

 other animal cells. Further data on the action of colchicine on eggs 

 are to be found later (cf. Chapter 8) . 



In those cases where a lowered \iscosity is related to mitosis, it is 

 assumed that the gelation-solation phases are influenced.^ If solation 

 conditions destroy spindles, then lowered viscosity acts accord- 

 ingly. Sj)indles arc inhibited because colchicine acts upon a mechanism 

 that changes the solation conditions. But viscosity changes ma\ be 

 secondary efl^ects \\hile other mechanisms operate before cytoj)lasmic 

 changes take place. ••" 



Birefringence tests show that the normal \ariations of the cortical 

 layer of eggs of the sea urchin, Psammecbinus tniliaris, presumably 

 s^'chronized ^\ith sjiindle and monaster expansion, are entirely inde- 

 pendent.'" The sjjindle and \iscosity changes in the cortical la\ers 

 may go on simultaneously, yet remain independent. Rhythmical 

 surface changes of eggs of Tubifex were not modified by arrest with 

 colchicine. This further substantiates the premise that c\ tojjlasmic 

 processes are not entirely controlled ^\hen the mitosis is controlled. 



In the neuroblastic cell, lowering of c\ toj:)lasmic \iscosity was 

 visible through the increased activity of mitochondria.-^'-' Brownian 

 movements were used to indicate the changes. Chromosomes settled 

 to the lower half of the cell when spindles were completely destroyed. 

 Disappearance of the spindle and a more rapid Brownian movement 

 •were correlated. The notable decrease in \iscosit} was suggested as a 

 consequence of a decrease in the content of ribonucleic acid and 

 phosjjhorus at the time colchicine acts upon mitosis. •^•* 



3-y~-- Cell plate foffiidtion i)! phnit.s. The continuous fibers form 

 the spindle of c\tokinesis upon which the cell jjlate forms. Between 

 the spindle and cell wall a phragmoplast completes the fibrous struc- 

 ture and the cell jjlate across the cell."- ■*■' Since colchicine destroys 

 or prevents continuous fibers, there is no spindle of cytokinesis or 

 phragmoplast. 



During recovery and regeneration of the sj:)indle, \ arious abnormali- 

 ties may be seen, but these processes are characteristic only in rela- 

 tion to recovery and rc\ersible effects of ^vhi(h the cells are capalile 

 after colchicine. 



By the special technic|ues for apphing colchicine at certain stages, 

 the phragmoplast has been tested specificalh with regard to the role of 

 the drug acting u]jon such structures already formed. ■'•'* If the 

 phragmo]jlast is in formation, colchicine can reverse the process, 

 changing the fibers hack to a fluid stage, a kind of cytoplasmatization. 

 E\en rudimentary cell plates and the beginnings of septa from each 



