EFFECT OF CERTAIN BACTERIA ON THE OCCURRENCE OF ENDOMIXIS IN PARAMECIUM AURELIA

¹ From the Zoölogical Laboratory, Johns Hopkins University

1. In the long-lived stock of Woodruff, cultivated in a standard medium containing a normal concentration of Flavobacterium brunneum, endomixis occurred only at very long intervals, of 75 to 109 days, or more. Increase in the quantity of Flavobacterium to 100 times the normal concentration made the conditions very unfavorable, but hardly increased the incidence of endomixis.

2. Substitution of Bacillus niger for Flavobacterium, in the same proportions, brought on endomixis and increased its frequency, although it did not make the conditions unfavorable. Increasing by 100-fold the concentration of B. niger caused a further increase in the frequency of endomixis, but still without making the medium unfavorable.

3. Bacillus cereus was not appreciably unfavorable in its action on Paramecium, yet like B. niger it increased the frequency of endomixis. Its tendency to induce endomixis appears to be slightly less than that of B. niger. Increasing the concentration of B. cereus 100-fold made conditions very unfavorable, but did not increase the tendency to endomixis.

4. Bacillus prodigiosus is slightly unfavorable as compared with Flavobacterium, but it does not increase the frequency of endomixis.

5. Bacillus coli is unfavorable as compared with Flavobacterium. It produces a tendency to fragmentation of the macronucleus, usually not followed by complete endomixis.

6. Thus in these experiments there is no correlation between the unfavorable effect of certain bacteria and their tendency to produce endomixis. Certain species (Bacillus niger and B. cereus) are not unfavorable to Paramecium aurelia yet (in this stock at least) they much increase the frequency of endomixis. Certain other conditions that are unfavorable (particularly high concentrations of Flavobacterium) do not increase the frequency of endomixis.