82 Colchicine 



somal fibers (Fig. 3.1) . Sometimes these two are called the exterior 

 and interior spindles, ^ or the centrosomic and centromeric spindles. '^'^ 



The birefringence ]jattern for a metaphasic sjiindle^' in Chae- 

 toptenis egg, disappearance due to the action of colchicine, registers 

 the fading of continuous fibers and astral rays first, while the chromo- 

 somal fibers are the last to disappear. Action uj^on astral ravs before 

 the interior jiortions has been demonstrated with other material. •** 

 Hence, data on the Ii\ ing cell and f)n fixed tissue are in accord as to 

 the action upon the several parts of the total spindle. 



Acenaphthene is 1000 times slower in action upon a spindle than 

 colchicine. ■'"'•'' This slower activity jjermits a better analysis, because 

 the exterior spindle is destroyed before the interior. Colchicine acts 

 so totally and abruptly that this delicate difference is frequently o\er- 

 looked. Until the threshold concentrations are employed, a partial 

 action showed that colchicine in dilute solution, like acenaphthene, 

 destroyed the exterior spindle before the interior. That is, continuous 

 fibers are first to be affected. This exjicrience is like dissecting an 

 organism into its essential parts. •^''' 



Certain concentrations of colchicine applied to the metaphasic 

 spindle in neuroblasts cause star formations (Fig. 3.1). The con- 

 tinuous fibers are inactivated, but chromosomal fibers remain intact. 

 The centromeric ]>ortions of chromosomes are drawn to one focal point 

 (Fig. 3.1). Ihere, however, is another way to j^roduce a star meta- 

 phase in neuroblastic cells. To obtain the correct concentration for 

 prophasic treatment, enough colchicine is used to inhibit the con- 

 tinuous fiber in its development, bin such a concentration does not 

 act in the same manner on the chromosomal fiber. These interactions 

 lead to a star metaphasc. 



Now a final explanation for Triton- and Tnturus"^ appears to be 

 at hand. Tritoii cells removed from colchicine show star metaphases 

 at 3 hours, build up to a jjeak within 12 hours, and are succeeded by 

 unoriented metaphases. Colchicine acts progressively more strongly 

 as the peak is being built. During the action, continuous fibers were 

 destroyed before chromosomal fibers, tjivina^ cause for stars in Triton 

 cells. Finally, the whole spindle was inactivated when colchicine 

 reached full effect and unoriented types took precedence (cf. Chapter 

 2) . Inspection of data from Tri turns"'* leads to another observation. 

 The stars appear later, and after the peak is reached, the bipolar 

 mitoses occujjy the prominent position among dividing cells. As re- 

 covery was taking place, the colchicine was becoming more dilute. At 

 a certain point the continuous fibers were inhibited but not the 

 chromosomal fibers. Then at last, Ijoth continuous and chomosomal 

 fibers developed, and bijjolar mitosis predominated among the divid- 

 ing cells. Among cells of Triton the stars appear as the effect of col- 



