EFFECT OF CONJUGATION 325 



conclusion is e\ddent that the reason why the conjugants (K) are 

 more vigorous than the non-conjugants (Z>) of the shde series, 

 is because the latter were cultivated for a month longer on slides. 

 For the non-conjugants (H), cultivated throughout in the same 

 way as the conjugants, are still more vigorous than the latter. 



To this the only objections that could be raised in favor of 

 the view that conjugation has caused rejuvenescence would be 

 as follows: (1) It might be held that it is not possible to be 

 certain, in taking free specimens from a watch glass containing 

 conjugants, that one is not taking specimens that have already 

 conjugated. I believe that there is no ground for this objection 

 in the present case, since the cultures in question were watched 

 with the utmost care in order to detect conjugation at its begin- 

 ning. Further, Experiments 11a and 116 show that there was an 

 actual difference between conjugants and non-conjugants, of the same 

 sort as that found in all our other experiments, the non-conjugants 

 being the more vigorous. It is clear therefore that in this case 

 we were actually dealing with non-conjugants. (2) It might be 

 said that it would be difficult to be certain that in the period that 

 had elapsed since June 3 there had not been conjugation in the 

 vessels of 'non-conjugants.' It may be admitted that this diffi- 

 culty exists, though in this case the organisms were inspected 

 daily, and I believe that no conjugations occurred. But this 

 objection is in fact negated by the experimental results themselves. 

 The greater vigor of the non-conjugants seen in Experiment 11 ^, 

 of July 16, is of just the same character as that seen immediately 

 after conjugation (Experiments 11a and 116) and as that charac- 

 teristic of the non-conjugants in all our other experiments, to 

 which the present objection is not applicable. 



But is the explanation given above — ^the fact that the non- 

 conjugants of one set (D) were cultivated a month longer than 

 the other {H) on shdes — a credible one? I believe that everyone 

 who has had extensive experience with experiments of this sort 

 will agree with me that long continued cultivation on slides does 

 produce a depressed condition. There are some stocks that will 

 not stand it at all, though they live perfectly in mass culture. 

 x\nd in fact, my experimental records show that in this partic- 



