CONDITIONS FOR CONJUGATION 351 



of solid hay being added to each to prevent starvation of the 

 infusoria. These seven dormant cultures were renewed with 

 hay infusion and distilled water on March 3, 1920, changed on 

 March 6th and March 8th. On March 9th conjugants were 

 found in one of these renewed cultures, 2a, to the extent of 

 about 5 per cent; on March 12th in culture 4-4o^, 5 to 10 per cent; 

 and on March 17th in culture 57a, about 5 per cent. The animals 

 in 44(^ continued to conjugate in increasing numbers after the 

 12th, reaching a maximum of 30 to 50 per cent on the 15th. 

 A similar, but less extensive, epidemic manifested itself in 57a 

 during a period of many days, attaining a maximum of about 

 10 per cent. Experiments with various salt solutions were 

 started on March 9th, and repeated on March 12th. In the 

 first set of experiments, in which FeCls and AICI3 were used in 

 the optimal concentrations recommended by Zweibaum, negative 

 results were obtained (March 10th). In the second attempt,' 

 AICI3 and NaNOs were used, the first one in two concentrations, 

 and this time also essentially negative results were obtained, 

 for although conjugation was already in progress in the culture 

 44(1, the relative number of conjugants in the experimental 

 cultures was not appreciably altered as a result of the treatment 

 with salts. 



If these seven cultures be compared with the continuous cul- 

 tures of the same races from which they were derived originally, 

 it will be seen that the conditions in one set tend to parallel 

 those in the other; that is, conjugation tends to occur in two 

 distinct cultures of the same race even after they have been 

 subjected to quite diverse conditions. For in the continuous 

 culture 44(1 (after the dormant culture had been derived from 

 it on November 14th) conjugation took the form of an extensive 

 epidemic between November 16th and December 15th, and in 

 the continuous culture 2a conjugation occurred on November 

 8th (5 per cent), and again, in small numbers, on January 11, 

 and 12, 1920. No conjugation was observed to occur in the 

 continuous culture 57a, but in a subculture of this race, which 

 had been set aside on October 31st with abundant nutriment, 

 and allowed to undergo evaporation (method of Hance, '17), 



