The viability and the average desoxypentosenucleic acid content of micronuclei-containing cells produced by colchicine treatment in the Ehrlich ascites tumor.

The appearance, after colchicine treatment, of cells containing large numbers of micronuclei also called chromosome-vesicles, idiomeres, karyo meres—has been observed by several authors in different biological materials. Brues and Jackson ( @) foundtheminregenerating rat liverandinter preted their formation to be due to the swelling of the individual chromosomes after mitosis has been arrested by the drug. All intermediate stages be tween the increase in the size of the chromosomes and the fully developed micronuclei were found. With the use of animal cells, similar findings have been reported by Ries (18) in axolotl epidermis, by Tennant and Liebow (@4) in tissue cultures of mammary cancer, by Schairer (19) and confirma tively by Dittmar and Maas (4) in the Ehrlich ascites tumor. Lettré (14) failed to produce large numbers of micronuclei-containing cells after col chicine treatment in the Ehrlich ascites tumor, but obtained them with great regularity and in high frequency after injections of N-methyl-colchica mide. In this experiment he observed that, while arrested metaphases reached a maximal frequency 16—@20 hours after treatment, multinucleate cells started to appear later and were at maximum @4—@5 hours after the injection of the drug. He, as all other authors quoted, interpreted the formation of micronuclei similarly to Brues and Jackson as a reconstruction of resting nuclei from individual dispersed chromosomes or small groups of chromo somes. In plant cells, micronuclei-containing cells and the eventually reconstructed resting nuclei have been shown to become polyploid (16). For animal cells, two different opinions were expressed as to the probable number of chromosome sets con tamed by the micronuclei-filled cells. Ries, in axolotl epidermis, found that the micronuclei gradually fuse into a single resting nucleus. This resting nucleus was of the same size as nuclei in the