CONDITIONS FOE CONJUGATION 363 



Cultures lib, lie, lid, and llf. These were derived from cor- 

 responding exconjugants of 11a isolated on March 20th. A well- 

 marked epidemic of conjugation, involving about three-fourths 

 of the culture, occurred in lie on April 4th. The process was 

 repeated on April 14th (about 5 per cent), and continued until 

 April 18th (casual). In culture llf conjugation appeared first 

 on April 15th (casual), and on the day following, to the extent 

 of about 60 per cent. On April 17th about 10 per cent were in 

 union. No conjugants were observed in lib and lid, examined 

 daily until April 18th, and casually thereafter. 



Exconjugant strains oi lie were started from ten pairs isolated 

 April 4th, and of llf, from six pairs, on April 17th. The twenty 

 exconjugant cultures of lie, designated as races llg (1 to 20), 

 were grown under very uniform conditions, in hay infusion made 

 up with distilled water, and renewed each week. Under the 

 favorable conditions thus imposed, no conjugation was observed 

 in any of the cultures for over two months. Similar negative 

 results were obtained with the twelve strains derived from llf 

 exconjugants, designated as llh (1 to 12), subjected to daily 

 observation for six weeks and examined casually afterward. 



On the 6th of July an individual of llg (from a culture which 

 had lain dormant for about a month) was isolated in a watch- 

 glass, in hay infusion containing 0.003 N NaNOs. On July 10th 

 conjugation occurred among the numerous progeny to the extent 

 of 15 per cent. From the exconjugants two daughter strains 

 were started (Hi and llj). No conjugation was noted in these 

 cultures prior to July 24th, when they were left unobserved and 

 unaltered. 



In each of these conjugation was again obtained in small 

 numbers during September by renewing the dormant cultures 

 with hay infusion containing NaNOs (table 6). No conjugation 

 occurred, however, in those cultures which were renewed with 

 hay infusion alone. 



The study of 11a and its descendants reveals a condition 

 which is prevalent in various other races of this species (e.g., 

 3a and 23a), as well as in caudatum. Conjugation was found 

 to occur very readily in cultures of the race during the first 



