60 GEORGE ALFRED BAITSELL 



been noted previously by other investigators. Other experiments 

 would have been tried in an endeavor to restore the non-conjuga- 

 ing animals to a normal condition had it not been for the fact that 

 the number of animals in the culture became so reduced that none 

 were available for additional experimental work. 



The June epidemic of conjugation occurred in the stock of the 

 second culture kept on the beef medium (Sbhb) from June 14, to 

 July 5, 1911 (diagram 3 point marked X). This epidemic differed 

 from the previous one in that the number of animals on any one 

 slide was very much less than in the previous case, due to the less 

 rapid division rate of this culture. In comparison with the Sb 

 culture this one never attained a high rate of division and, at the 

 time when conjugation appeared in the stock, the main lines were 

 averaging a little less than one division per day. However, dur- 

 ing the month previous to the appearance of conjugation there had 

 been a gradual increase in the division rate from about one-half 

 division to nearly one division per day. Because the animals di- 

 vided so slowly a stock slide of a few days standing would rarely 

 contain more than fifty animals and, in general, the number was 

 considerably less than that. Nevertheless an epidemic of conju- 

 gation occurred and numerous pairs were observed on some slides 

 which had as few as twenty-five animals present. As has been 

 noted in the former epidemic, all the animals of the culture ap- 

 peared to be in the same physiological condition and some slides 

 were seen on which practically every animal was united in conju- 

 gation. Also there began in this culture, coincident with the ap- 

 pearance of conjugation in the stock, a marked and rapid decline 

 in the fission rate of the main lines of the cultures and this decline 

 ended in the death of the culture twenty days later. The appear- 

 ance of the animals, the degenerative processes through which 

 they passed and the entirely negative results obtained from en- 

 deavors to stimulate them by artificial means, all gave proof that, 

 as in the first epidemic, some fundamental change had taken place 

 in the animals of the culture. This change was of such a character 

 as to produce conjugation whenever a sufficient number of animals 

 were present on a slide. If the phenomenon was prevented the 

 non-con jugants degenerated and died. 



