The Life-History of Hypotrichous Infusoria. 593 



vitiated the culture, and I immediately examined the stock of the 

 line — some of which had not been touched for a number of days. 

 I found that this also had started dividing at the same rapid rate, 

 and as there was apparently no way in which all the preparations 

 could have become contaminated simultaneously, I was convinced 

 that the increase in rate was due to some change in the culture 

 itself — a conviction which was substantiated by a study of the 

 cytological changes in the permanent preparations; but to leave 

 no chance for error I removed the rapid line (A-i) to another 

 moist-chamber and thus isolated it from all the rest. This con- 

 dition of affairs — A-i dividing about three times each day and 

 the other lines once in two days — continued for just a month 

 when the three other lines sprang into activity. This at once, of 

 course, brought up the average of the four lines as is seen in the 

 twenty-ninth period (Diagram I) when the average rate of multi- 

 plication reached over three and one-half divisions per day. 

 This twenty-ninth period was the high record for the division- 

 rate of this culture. During the next ten days the rate fell to 

 three divisions per day; then occurred a slight rise above this for 

 twenty days, and then another drop to about two and three- 

 quarters divisions per day for the thirty-third period. This rising 

 and falling of the division-rate continued to the very end of the 

 life of the culture, or from August, 1902, to July, 1903, nearly a 

 year. 



At the fifty-third period it was clear that the culture was again 

 approaching extinction and, accordingly, two lines, A-i and A-2, 

 were transferred for a day to beef-extract, leaving A-3 and A-4 

 in the normal hay-infusion. This had no visible effect on the 

 lines treated and both died out at different times, and their places 

 were supplied by individuals from the other two lines. 



During period 54 the culture medium for all lines was changed 

 from hay-infusion to an infusion made with fresh grass in order to 

 see what effect a change in medium would have on the behavior of 

 the culture. The very slight rise in the division-rate which followed 

 for the next three periods may be due to this change, but I think 

 it is more probable that it is due to a decided rise in temperature 

 which took place at this time {cf. Diagram VII). During the 

 next two periods no attempt was made to revive the culture, and 

 as the fission-rate remained quite uniform I postponed all experi- 

 ments in order to see what would take place if the culture was 



