Thus from these experiments, repeated many times, on an extensive scale, there is no evidence that conjugation causes rejuvenescence. On the contrary, it appears to be a dangerous ordeal, which sets back the rate of reproduction; and results for many individuals in abnormalities and death. What conjugation seems to do positively is to produce a great number of varying combinations, some of which die out, while others continue to exist.
Before attempting to draw more fully the conclusions from these experiments, let us follow the investigations a little farther. In conducting an investigation it is necessary not only to satisfy one's self as to the correctness of a result, but also to meet the objections of those that are firmly of the opposed view. Now, to the results thus far set forth the following objections might be made. Conjugation, it could be said, may indeed be of no use, and even disadvantageous, when organisms are in a strong, healthy condition; they would doubtless do as well without it. Probably they conjugate many times when there is no necessity for it. Yet, it might be urged, if you did not allow them to conjugate at all for many times the usual period, then possibly the need of conjugation might show itself. If you had a race that was in a depressed, degenerate condition, from whatever cause, possibly you might find that conjugation would restore them.
I therefore next carried out experiments to determine whether this objection holds. A certain race of Paramecium conjugates as a rule every month or two. A culture of this race was divided into two parts. One part was allowed to conjugate every month, while the other was cultivated on slides and not permitted to conjugate. In this way the one set was allowed to conjugate four times in succession, in the course of a number of months, while the other set did not conjugate at all. "We have thus a set that had missed four normal conjugations.
Now, as a matter of fact, the set that had missed the conjugations did become depressed; it multiplied slowly and irregularly, and many died. This may have been due, not to lack of conjugation, but to long-continued cultivation on slides; such cultivation does, of itself, produce an unhealthy condition. But in any case, we have now a depressed race and we can test the effect of conjugation upon it. Will conjugation end the depression, rejuvenate the organisms?
The experiment is performed by putting the members of this depressed race under the conditions that induce conjugation. Then, as conjugation begins, we permit one set to complete the process, while another lot is isolated without conjugation. The two sets are then cultivated under identical conditions. We have now an opportunity to determine the effects of conjugation on a depressed race, not complicated by any other differing factors.
The results were striking, and to a certain degree unexpected. All those that had not conjugated continued to be weak and sickly, and they