Description:
<jats:p>The effects of ethidium bromide (EB) at 0.13 m<jats:italic>M</jats:italic> and of chloramphenicol (CAP) at 46 m<jats:italic>M</jats:italic> on the mitochondria and mitochondrial nucleoids in <jats:italic>Euglena gracilis</jats:italic>. Z strain, were examined by fluorescence microscopy and by electron microscopy. Ethidium bromide stopped the multiplication of cells and decreased their respiratory activity by 55% after treatment for 10 days. Most of the mitochondria became slender with few cristae and some became cup‐shaped with stacked cristac. Mitochondrial nucleoids decreased markedly in number after treatment with EB for more than 2 days. After treatment for 3 days with EB, mitochondrial nucleoids could not be detected in about half of all cells examined. Treatment with CAP for 10 days reduced the respiratory activity by 47%. Chloramphenicol did not decrease the number of mitochondrial nucleoids but it increased the number of cristae and the volume of mitochondria.</jats:p>