Spindle and Cytoplasm 77 



Several other similar observations were made at the same time 

 spindle disappearance was studied. The continuous fibers are the first 

 to disappear along ^vith the astral rays. These observations confirmed 

 previous Avork. Accordingly, the last fibers to lose their birefringence 

 were the chromosomal fibers. 1 liese data also fit other results. The 

 order in which the component spindles disappear is important to an 

 explanation for the star metaphase. Acti\e chromosomal fibers and 

 supi^ressed continuous fibers create the star figure. 



A\'hile stronger solutions cause the most rapid disappearance of the 

 spindle, the shortening of the spindle during its disapjjearance is not 

 the same for each strength. Rapid destruction showed very little 

 shortening, whereas weak solutions. Avhich rec^uire a long time, showed 

 much shortening during destruction. The shortening process carried 

 the chromosomes up to the periphery of a cell. While this reduction 

 in length of spindle occurred, the chromosomes were always main- 

 tained at a midway point between two poles. At the same time 

 chromosomes retained their metaphase position on the equator. 



Another important detail was noticed just before the final dis- 

 appearance of the metaphasic spindle. The chromosomal fibers Avere 

 the last to disappear, and as soon as the last vestige of spindle faded 

 out, the chromosomes scattered. Tlieir position in the equatorial 

 plate exidently was maintained 1j\ chromosomal fibers. Thus chromo- 

 somal fibers are responsible for equatorial orientation. Chromosomal 

 fibers once destroyed caused a scattering of the chromosomes and a 

 typical exploded metaphase. 



Spindle retardation, measured in millimicrons, showed that changes 

 in spindle measured against time, and plotted accordingly, showed a 

 rapid decrease at first then a sloA\ing doAvn of this process (Fig. 3.5) . 

 An exponential decay curve Avas obtained for this activity. 



Confirmation of an action of colchicine along similar lines Avas 

 obtained by a phase contrast microscope in Avliich no spindle fibers 

 were detected 24 iiours after treating testis cells of Melanoplus difjer- 

 entialis Avith colchicine.'^" By other methods and Avith different chemi- 

 cals, the spindle fibers Avere studied as bodies that operated during 

 a mitosis. These could be destroyed, or transformed into other 

 structures. The net result was c-mitosis.^'' 



Fibers that appeared anisotropicallv acti\c. liiiearlv differentiated 

 Avith iiiicelhu- particles arranged end to end, changed in their 

 structural pattern. Birefringence sho\\ed that colchicine destroyed 

 the fil^rous arrangement progrcssivclv, step by stej). First the con- 

 tinuous fibers and asters disappeared, then the chromosomal fibers. 

 These critical tests w iih a polarization microscope deal a solid bloAV to 

 the argument that spindle fibers are (\ tological artefacts. Not only can 

 the spindle fibers be demonstrated bv a light pattern but their changes 



