Endomixis 83 



The question becomes of extreme interest whether such a 

 process as this is of general occurrence ; whether it is neces- 

 sary in order that aging and death shall not occur. Many 

 investigations are therefore at this time directed upon 

 endomixis. Certain questions must occur to everyone ; some 

 of these have already been answered. 



First, is this replacement perhaps merely something 

 brought about by unfavorable conditions of the environment, 

 and not necessary if all conditions continue good? Jollos 

 (1916), Young (1917), and Woodruff (1917) find that 

 under unfavorable conditions the replacement of the active 

 nucleus from the reserve is brought about more quickly than 

 would otherwise occur. But under the most favorable con- 

 ditions the process does not cease, and under uniform con- 

 ditions it takes place at uniform intervals. Woodruff found 

 that whenever the process of replacement ceases entirely, the 

 race dies out. This evidence therefore indicates that the 

 process is a necessity for continued life. 



Enriques (1916) attempted to test the matter by studying 

 an organism in which there were no periods of slow fission, 

 such as are found while the replacement is occurring. He 

 found such an infusorian in Glaucoma pyriformis, which 

 under the conditions he used may produce 10 to 13 genera- 

 tions a day, and continue this without interruption. He 

 kept this organism for 2701 generations, or for more than 

 8 months, during which there were not less than 9 genera- 

 tions every single day. The culture was still in progress 

 at last accounts; there was no sign of degeneration, and 

 no periods of slow fission. Enriques therefore holds that 

 endomixis has not occurred. He concludes that endomixis 

 is not necessary to continued life, just as conjugation is not. 



It is evident however that this conclusion is insecure; it 

 is not impossible that endomixis occurred without interrupt- 



