THE EFFECT OF ULTRACENTRIFUGING UPON CHICK EMBRYONIC CELLS, WITH SPECIAL REFERENCE TO THE "RESTING" NUCLEUS AND THE MITOTIC SPINDLE

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Abstract
Chick embryonic cells, both "resting" and in stages of division, were centrifuged at ca. 150,000 X gravity for 10 min. The elements of the "resting" nucleus were stratified in the order of their decreasing specific gravity as follows: (a) nucleoli; (b) chromatin and "reticulum"; (c) nuclear "sap." Evidence is presented to support the view that fixed preparations of the "resting" nucleus give as characteristic a representation of the elements during life as do fixed preparations of prophase nuclei and meta-phase chromosomes. The metaphase spindle has been distorted, its chromosomes displaced, its fibers separated, and, in some cases, it has been completely disintegrated by centrifuging. These results support the claim that spindle fibers and centrioles as seen in fixed preparations have a morphological basis in the living spindle.