Quite recently Calkins has carried out a somewhat similar series of experiments, which have an important bearing on the interpretation of Maupas’ results. The experiment of isolating an individual and tracing the career of its descendants was repeated with the following results: two series were started, the original forms coming from different localities. Of their eight descendants four of each were isolated. The remaining four of each set were kept together as stock material. The rate of division was taken as the measure of vitality. The animals divided more or less regularly from February to July. After each division (or sometimes after two divisions) the individuals were separated. About the 30th of July the paramœcia began to die “at an alarming rate, indicating that a period of depression had apparently set in, or degeneration in Maupas’ sense.” Up to this time the animals had been living in hay infusion, renewed every few days, from which they obtained the bacteria on which they feed. Calkins tried the effect of putting the weakened paramœcia into a new environment. Infusion of vegetables gave no good results, but meat infusions proved successful. “The first experiment with the latter was with teased liver, which was added to the usual hay infusion. The result was very gratifying, for the organisms began immediately to grow and to divide, the rate of division rising from five to nine divisions in successive ten-day periods.” This beneficial effect was not lasting, however, and after ten days the paramœcia began to die off faster than before, and the renewed application of the liver extract failed to revive them. A number of other extracts were then tried without effect. Finally they were transferred to the clear extract of lean beef in tap water. The effect of this medium was interesting, for, although it restored the weakened vitality, there was no rapid increase in the rate of division, as when first treated with the teased liver. The infusoria were, however, now large and vigorous, and did not die unless transferred from the beef medium to the usual hay infusion. “When this was attempted, they would become abnormally active and would finally die. The division rate gradually increased during the month of August until, in the last ten days, they averaged six generations. Finally, in September, the attempts to get them back on the old diet of hay infusion were successful, and then the division rate went up at once to twelve times in ten days, and a month later they were dividing at the rate of fifty times a month.”