Conjugation 89 



take better care of the animals ; to give them proper food, 

 and to vary their food, the organisms were found to live 

 longer and longer without conjugation, and to give less 

 indication of old age. Calkins (1904) kept the infusorian 

 Paramecium caudatum for 742 generations without conjuga- 

 tion, but they finally weakened and died. Enriques (1903) 

 kept Glaucoma scintillans for 683 generations without con- 

 jugation and with no sign of harmful effects; and he has 

 recently (1916) kept Glaucoma pyriformis for 2701 genera- 

 tions with no sign of degeneration. And finally Woodruff 

 (1917) has kept Paramecium aurelia for more than 6000 

 generations without conjugation; the stock at last accounts 

 was still flourishing, with no sign of aging, of degeneration. 



Now the fact that one can by proper methods of culture 

 keep these creatures healthy for more than 6000 generations 

 without conjugation, shows that the degeneration which 

 came, under other methods of culture, in a few hundred 

 generations, was not evidence that conjugation is required, 

 but only that the culture methods were not good. It has 

 been found that some species of infusoria cannot stand, save 

 for a short time, the method of culture necessary if the 

 separate generations are to be accurately counted; others 

 can exist under these conditions for a greater number of 

 generations; other indefinitely; and that without conjuga- 

 tion. 



Thus the result of the work so far done has been to con- 

 firm the view that the infusoria may live indefinitely without 

 mating. I believe that we may look upon this as one of 

 the secure results of science. There are many of the uni- 

 cellular creatures, particularly the bacteria, in which 

 nothing like mating is known. It is sometimes held that 

 such processes must yet be found in these creatures. But 

 the fact that infusoria, which do mate, may nevertheless live 



