33^ LIFE AND DEATH. 



as the temporary pairing of two individuals, which 

 are otherwise very much alike, and which cannot be 

 distinguished as male and female. They become 

 closely united on one of their faces; they reciprocally 

 exchange a semi-nucleus which passes into the con- 

 joint individual; and then they separate. But 

 infusoria can be prevented from this conjunction by 

 regularly isolating them immediately after their birth. 

 Then they grow, and are constrained after a lapse of 

 time to divide according to the first method. 



Maupas has shown that the infusoria could not 

 accommodate themselves to this regime indefinitely ; 

 they couIS not go on dividing for ever. After a 

 certain number of divisions they show signs of 

 degeneration and of evident decay. The size 

 diminishes, the nuclear organs become atrophied, 

 all the activities fail, and the infusorian perishes. 

 It succumbs to this kind of senile atrophy unless it 

 is given an opportunity of conjugation with another 

 infusorian in the same plight. In this act it then 

 derives new strength, it grows larger, attains its 

 proper size, and builds up its organs once more. 

 Conjugation gives it life, youth, and immortality. 



A limentary Rejuvenescence. Recent observations 

 due to Mr. G. N. Calkins, an American biologist, 

 and confirmed by other investigators, have shown 

 that this method of rejuvenescence is not the only 

 one, and is not even the most efficacious. Conju- 

 gation has no mysterious, specific virtue. The 

 infusoria need not be married in order to be 

 rejuvenated. It is sufficient to improve their food. 

 In the case of the " tailed " paramecium we may 

 substitute beef broth and phosphates for conjuga- 

 tion. Calkins observed 665 consecutive generations 



