572 THE POPULAR SCIENCE MONTHLY 



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 con- 

 ducting 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 oj^iDosed 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 conjuga- 

 tion end the depression, rejuvenate the organisms? 



The experiment is performed by putting the members of this de- 

 pressed 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 cul- 

 tivated 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 



