144 On the Genetics of the Ciliate Protozoa 



32. Popoff (1907) has obtained results which he interprets in a. 

 similar manner. He cultivated a lino of Stylonychia mytilus for 

 3^ months. During this time he observed "depression periods" — like 

 those of Calkins (§ 28) — which became deeper and deeper until the 

 culture finally died out. In depressed individuals he found the mega- 

 nucleus abnormally large (§§ 29, 31 ), and often fragmented or of irregular 

 shape : the micronuclci frequently multiplied, and the whole organism 

 was smaller (§ 21). No conjugations were observed', though depre.ssed 

 animals were "inclined to conjugate." They recovered from depression 

 by resorption of the excess of chromatin in the meganucleus (?) — thus 

 restoring the karyoplasmic ratio to normal (§ 31). Similar dejiression 

 periods were caused in Paramecium by overfeeding. Recovery occurred 

 as a result of conjugation. The morphological changes observed were 

 similar to those seen in Stylonychia; and PopotT sees "a complete 

 parallel " in the nuclear behaviour during depression with that seen 

 during conjugation. " Everything goes to show that the cause of 

 depression is not to be sought in accidental changes in environment 

 (such as food, water, etc.), but that it lies in the organism itself." 



33. In a series of papers, Enriques (1903-1910) has maintained 

 that the " depression " or " senescence " seen in cultures of ciliates is 

 not due to "old age" or any internal cause, but is merely the result of 

 adverse environmental conditions — the most important being overgrowth 

 of bacteria. " Depression " is due to prolonged poisoning with bacterial 

 toxins. If these are not allowed to accumulate, and the culture medium 

 is frequently renewed, no depression occurs, and the animals are capable 

 of multiplying asexually ad infinitum. The chief evidence advanced by 

 Enriques in support of the last proposition is the statement that he has 

 kept Glaucoma, in cultures for 683 generations, without it conjugating 

 or showing an}- signs of " depre.ssion " or " .senile decay " (1905). Other 

 organisms kept for shorter periods gave similar results — e.g. Oxytricha, 

 Stylonychia, Vorticella (1903, 1905 a, 1910, etc.). "Agamic reproduction 

 can be continued as long as one likes, if the technique is good and 

 bacteria are not too numerous. No change of food is necessary" (1909rt). 

 Enriques strongly criticizes the work of Calkins (§ 28) and Popoff 

 (§ 32). 



34. In his later papers Popotf (1909 a, 1909 i) has shown that 

 "depression" such as he observed in his cultures (§ 32) may be brought 

 about by treating the animals with certain chemicals. He cultivated 



' Possibly because the animals were all descended from the same ancestor? (§ 20). 



