Spindle and Cytoplasm 75 



sources has been effectively concluded. Therefore, colchicine acts 

 either by an inhibition before mitosis or by destruction after spindles 

 ha\e been formed. 



^.3-4: The pulayizalion micruscope. Submicroscopic structures 

 were followed with an improved polarization microscope adapted for 

 specific biological purposes. The birefringence pattern is clear because 



Fig. 3.3 — Effects of colchicine upon first cleavage in Arbacia punctulato. The area where 

 colchicine causes spindle destruction is a "lakelike' body. Compare A, the control, with 

 B, a treated metaphase. A. Spindle fibers of untreated egg at metaphase. B. Colchicine 

 applied when egg was at metaphase, both polar areas laked and chromosomes are 

 clumped. 0.0002 molar concentration of colchicine in sea water applied 10 minutes 

 after fertilization, temperature 22 to 24.4 C. C. Prophase when treated causing lique- 

 faction of spindle and asters at one side. D. Spindle destroyed, chromosomes separated, 

 but no cleavage furrows. E. Three groups of chromosomes. F. Four groups of chromo- 

 somes with laked areas around each group. (Drawings adapted from photomicro- 

 graphs by Beams and Evans, 1940) 



spindle fibers are optically anisotropic. The fibers, therefore, shine 

 l>rightly, as compared with a dark grey for the chromosomes. 



The disappearance of the spindle was correlated with the disappear- 

 ance of the l)irefringcnce pattern. Therefore, as colchicine acted upon 

 the spindle, a reduction was noticed by a definite fading out of the 

 light pattern. Obviously the fibers changed their form under an attack 

 by the chemical. This general procedure made it possible to pci foi ni 

 some critical experiments.*" 



Ihe first matuiation di\ision of the egg, the metaphasic sjjindle 

 of a marine annelid ^vorm, Chaeloplerus pergamcutnct'us. was cho.sen 



