Spindle and Cytoplasm 69 



Similarly lor Tradcscnntia, fibers do not develop at projihasc 

 A\ith concentrations ol 0.05 per cent or 0.1 per cent colchicine.-''' 1 here 

 arc other cases, bnt these two are enough to prove that the first stage 

 ol sj)indle inhibition sets in at j^rophase. 



Full strength solutions applied at prophase cause total inhibition: 

 no \estige of the mitotic spindle can be observed. Partial inactiva- 

 tions are only foimd at the threshold le\'els.""' The continuous fibers 

 and astral rays rather than chromosomal fibers are then the ones in- 

 hibited during a partial inactivation. That is, enough colchicine is 

 present to inhibit the exterior spindle, but the interior spindle devel- 

 ops. Such partial inactivation leads to a star metaphase. 



Sj)indle material may be con\erted into such bodies as hyaline 

 glob ides,'-'' (Fig. oAD) , the lakelike substance in Arbacia'' (Fig. 3.5), 

 achromatic sphere of AJUiim-^-"' (Fig. 3.6), or the deformed atracto- 

 plasm among Tradesanitid.'^'' All these structures are closely associated 

 to karyolymph; consequently, the inhibiting process of a normal 

 spindle fiber is in reality transformation to another form of substrate. 



Electron microscojjic anahsis of colchicinc-treated polar cap stages 

 in Allium indicated a "solubilization"' and "fragmentation" ol fibrous 

 strands. These changes are interpreted as spindle fiber transforma- 

 tions. Submicroscopic interpretations are difficult, l>ut the evidence 

 is consistent with other microscopic data."^- 



A jjrimary effect of colchicine is the inhibiton of a mitotic spindle." 

 Secondary eftects stemming from this action are colchicine pairs, 

 chromosomal changes, desynchroni/ation of mitotic processes, delayed 

 separation of chromosomes, and restitution nuclei instead of daughter 

 nuclei.^ 



Originally the term cGlchicinc-tnitosis designated an "effect of 

 colchicine on the course of mitosis" that is entirely specific."'"' Addi- 

 tionally, in a colchicine-mitosis the spindle aj:)paratus is totally in- 

 activated, and this causes completion of a "chromosome mitosis with- 

 out nuclear or cellidar mitosis." ''''' 



3.3: Destruction of the Spindle Fibers 



That colchicine inhibits the spindle at late prophase is well estab- 

 lished. Less familiar are the facts about colchicine when applied to a 

 mitotic spindle that has developed as far as anaphase (Fig. ?).2s-v) . 



Ao establish these facts, special technicpies had to be developed. 

 Individual cells nuist be observed at the critical stage, anaphase, and 

 the chemical nuist be ajjjjlied at a precise moment when the mitosis 

 has reached a certain stage. Fortiniatelv, several excellent methods 

 for i)lants and animals^'- ^^- ^^- *'■'• •''' have been develojjcd, and we may 

 now learn what ha|)ijens when the drug is added to a cell after a 

 spindle has foriiud. 



