410 Louise Hoyt Gregory 



with the exception of the 26th period. Finally, in the 35th period, 

 there was a second period during which the vitality suffered, 

 when all save the two lines were lost. Fortunately the stock 

 material was in better condition than in July, and the cultures 

 were renewed. At this time, a third beef culture was started and 

 carried along with the newly stimulated K2HPO4 culture. The 

 entire set was again treated on October 21, 31, and November 

 14. Both cultures seemed to respond to the jfirst stimulus only, 

 and from the 36th period showed a gradual weakening in the vital- 

 ity. Abnormalities appeared, the division plane not always pass- 

 ing entirely through, or sometimes unevenly through the encysted 

 organsim. Calcium and potassium nitrate were used as stimu- 

 lants (one drop of a #- solution being added to 10 drops of medium ), 

 but nothing seemed effective, and gradually the lines died out, 

 sometimes bv the formation of abnormalities, more often by the 

 formation of permanent cysts. Attempts were made with dilute 

 HCL to dissolve this cyst membrane. This was unsuccessful, 

 and the last individual formed its permanent cyst on December 

 16, the culture having passed through 546 generations in 13 

 months. 



No attempt was made to keep permanent cysts alive after they 

 had been formed for more than ten days. Possibly if some indi- 

 viduals had been kept for longer periods, they might have event- 

 ually resumed their normal condition. 



During the ten-day periods 26, 27, a few experiments were made 

 to compare the effects of an initial, daily and weekly treatment 

 with one drop of yV tV solution KjHPO^. From the few experi- 

 ments, the results seem to indicate that a repeated treatment 

 increases the vitality to a greater extent than an initial treatment. 

 If, however, the treatment is too frequent, the accelerating effect 

 is lessened, and is finally lost. Woodruff found that in comparison 

 with the control culture, an initial treatment (30 minutes) of a 

 solution of y|o K2HPO4 causes a slowing of the division rate, while 

 a daily causes a marked inhibition. The results are practically 

 the same in both series of experiments, though the response of 

 Tillina to the treatment was very slight in comparison with that 

 of Oxytricha. 



