Page:Popular Science Monthly Volume 80.djvu/570

566 raised above all doubt. Yet this statement, though it seemed to rest on irrefragable evidence, and agreed with everything else that was known, was quite false, and in Maupas's time had been completely abandoned. Perhaps this was a type of the fate to be met by many other supposed demonstrations as to the function of conjugation, including that of Maupas—and not impossibly the one here presented.

Before leaving the work of Maupas, we must mention certain other observations that he made which are of great importance for understanding the matter. In his experiments, after degeneration had begun, many specimens within the same series (all derived from the same parent) conjugated together. But this did not rejuvenate them. On the contrary they died all the sooner after conjugating with close relatives. This happened in many cases.

So Maupas concluded (1) that conjugation with close relatives does not rejuvenate; (2) that conjugation with related individuals is not merely useless, but destructive; as soon as they do this, says Maupas, their doom is sealed; (3) that rejuvenation is due to conjugation with unrelated individuals.

This work of Maupas had of course tremendous influence; it seemed to be definitive. There appeared to be no escape from his conclusions, and for many years they were hardly seriously questioned.

But in very recent times have come a series of investigations that have shaken the conclusions of Maupas and given the entire matter a new aspect. It appears to me that the time is ripe for a revision of judgment on the whole general problem of age, death and conjugation in these lower organisms. I shall attempt to give briefly the grounds for such a revision, and the direction which the final judgment must apparently take.

1. The credit for seriously opening the question anew, as well as for getting some of the most important evidence leading to what seem to me the correct conclusions, is due to Calkins in his investigations extending from 1901 to 1904. After cultivating Paramecium for about 200 generations (three months) without conjugation, Calkins found that they become depressed; the division rate decreases; many die. As you remember, he found that by changing the diet at these periods, by transferring from hay infusion to beef extract, to pancreas or brain extract—the animals could be revived, and their life and propagation continued. In this way he kept them for 742 generations (23 months), but at the end of that period they finally died, in spite of any changes that were made in their food. This showed that the infusoria could be kept alive without conjugation a much longer time than Maupas had observed. Calkins kept his animals for more than twice as many generations as did Maupas.