36 Colchicine 



ing exj^hiiKilions: (1) The metaphasic arrest arises when the spindle 

 fiber mechanisms are partially or totally destroyed.^-- ^^- -•''• -^' ^' ^'^' ^^' 

 77, 75, 39 ^2) Chromosomes lose their metaphasic orientation when the 

 spindle fibers become disengaged from the chromosomes. •^^' ^^' ^^' ^^' 

 7, 2G, 22 ^3^ The spindle mechanisms are inhibited by colchicine; 

 therefore, nuclear mitoses are arrested at metaphase.-"'' ''• •'■^' ^-^^ ^"' !• "•^- -^^ 

 While three similar cases are presented, each thesis leads to the same 

 general conclusion: the metaphasic arrest. That is why agreement in 

 the final analysis is so excellent considering the many different bio- 

 logical specimens studied. Universally every one's attention is di- 

 rected first to the chromosomal pattern at metaphase arrested by 

 colchicine (Fig. 2.1(7, 2.4/;, and 2.8/1) that is quite different from 

 the normal metaphasic orientation (Fig. 2AA) . Spindle mechanisms 

 enter the discussion only after the first impressions of chromosomal 

 patterns have been obtained. Accordingly, our discussion is first di- 

 rected to the chromosomal patterns of arrested metaphase. After 

 these have been compared, it would appear consistent to discuss and 

 analyze the spindle mechanisms that must operate in the production 

 of c-mitosis. The spindle mechanism will be considered in Chapter 3. 



2.4-1: Types of arrested meta phases. The regular metaphasic fig- 

 ures and equatorial plate orientations are replaced by different 

 chromosomal patterns (Figs. 2.1A, 2.SA, and 2.40). Such distribu- 

 tions are induced by colchicine, and these arrangements are not 

 wholly random ones.^' ''•• Characteristic stages repeat often enough 

 that a classification (Fig. 2.5) is possible. ^ If we disregard spindle 

 action lor the moment, the arrested metaphases may be grouped into 

 two major categories: (1) the oriented metaphase (Fig. 2.5, above), 

 (2) the unoriented metai)hase (Fig. 2.5, beloiv) . There are subtypes 

 for each group which will be considered under the special headings 

 that follow. 



Analysis of the pattern will be made on the basis of interacting 

 factors that create the special type of arrested metaphase, while direct 

 reference to spindle mechanisms will be deferred for the moment. 

 The classification shown in Figure 2.5 was made from stained cells 

 by cytological methods not thoroughly reliable in differentiating the 

 fibers.i For this reason, criticism"'' has been made regarding assump- 

 tions involving spindle mechanisms, specifically with reference to 

 the distorted star metaphase. Even though this classification was de- 

 veloped by a chromosomal pattern, an insight into c-mitosis and the 

 arrested metaphasic types can be gained by such comparisons. 



Colchicine penetrates the cell very rapidly. Effects may be noticed 

 within seconds after the drug contacts the nucleus. C-mitosis in 

 AUiuiii ck\elops permanently and completely within fifteen minutes.^'^ 

 Rate of jjenetration, as well as concentration, is very important. The 



