various nuclear and chromosomal aberrations such as , fragmentation of the chromosomes , extreme clumping and unequal groupings of the chromosomes , vacuolization of nuclei and nucleoli , and irregular anaphase chromatid breaks , were observed in the materials treated with 500 and 750 micrograms/ml streptomycin , and 250 and 500 micrograms/ml tetracycline , and which , however , were not seen with any of the concentrations of penicillin employed .
C0007610
nuclei
C0007609
nucleoli