Note 15 — LECTURE XVI

Since the above was written Calkins has made a series of new experiments, the results of which differed in several respects from those yielded by Maupas' experiments. When his infusorian-cultures began to grow weaker, as happened frequently and at irregular intervals, he was always able to restore them to more vigorous life by a change of diet, and especially by substituting grated meat, liver, and the like for infusions of hay. Certain salts, too, had the same effect: the animals became perfectly vigorous again. Calkins believes that chemical agents, and especially salts, must be supplied to the protoplasm from time to time. He reared 620 generations of Paramœcium without conjugation. But the 620th was weakly and without energy. The addition of an extract of sheep's brains made them perfectly fresh and vigorous again. Further experiments in this direction are to be desired, but, according to those of Calkins, it is probable that Infusorians can continue to live for an unlimited time even without conjugation.