AGE, DEATH AND CONJUGATION 567 



The results of Calkins's experiments can evidently be interpreted 

 in two ways : 



1. It may be held that the depression was due to a too great uni- 

 formity in the food, or to the fact that the food and other conditions 

 were not fully adapted to the animals : what the organisms needed was 

 a change of diet. With frequent changes in diet, perhaps, there would 

 be no degeneration at all. The final death would, on this interpreta- 

 tion, be due to the fact that the injury produced by uniform diet had 

 gone too deep to be remedied by the means which Calkins tried. 



2. But Calkins inclined, in view of the evidence then at his com- 

 mand, to another interpretation. This work came shortly after the first 

 portions of Loeb's brilliant investigations on artificial parthenogenesis. 

 Calkins interpreted his results in the light of those experiments. He 

 held that the infusoria were really in senile degeneration, ready to die 

 of old age. What he had done was essentially to induce artificial par- 

 thenogenesis ; he had replaced conjugation by chemical means. The 

 final death, he held, was due to the fact that conjugation could not be 

 indefinitely thus replaced; old age finally asserted its power, and in 

 the absence of conjugation produced death. 



Now I think it will be apparent at this point that there are two 

 independent questions involved in the investigations; to understand 

 later work it is needful to distinguish them clearly. 



1. Does multiplication without conjugation result in degeneration, 

 senility and death ? What is the actual cause of the degeneration that 

 has been observed? 



2. Does conjugation remedy this degeneration? An affirmative 

 answer to this second question has been generally assumed. If animals 

 degenerate and die without conjugation, then evidently conjugation 

 must be what prevents and remedies this result ; such has been the rea- 

 soning. But if this is true it must be possible to observe this effect of 

 conjugation ; we shall do well to follow the example of Maupas, and not 

 rest till a plausible hypothesis has been transformed into an observed 

 fact. 



These two questions then suggest two lines for further work, and 

 both of these lines have been followed. 



Enriques and Woodruff have followed up the question : What is the 

 cause of the degeneration that has been observed? I myself have pur- 

 sued mainly the second question, as to the actual effects of conjugation. 

 The results of all these investigations seem to me harmonious and to 

 lead to definite conclusions. 



Enriques, in 1903 to 1908, carried out cultural investigations which 

 led him to the following results and conclusions: 



1. If he did not take pains to keep his cultures free from the prod- 

 ucts of bacterial action, the animals degenerated in time, just as ob- 

 served by Maupas and Calkins. 



