62 ENCYSTMENT AND EXCYSTATION OF AMtEBA 



Cysts from the same stock were placed into 

 each of these solutions, and each sample examined 

 daily with special reference to excystation in re- 

 lation to abundance of bacterial growth. See 

 Table I., p. 61. 



In sample No. 3, although there was no apparent 

 bacterial multiplication at the end of four days, 

 excystation had taken place, and the culture also 

 contained a number of minute, very active amce- 

 bulae (diam. about 0'5 /*,). Two days later similar 

 small amoebae appeared in No. 4. These pre- 

 parations were observed for a fortnight, the 

 small forms persisting in this condition, possibly 

 through lack of food. The tendency of amoebae 

 to remain in the free state in the absence of bac- 

 terial products was very noticeable. There were 

 at least six amoebae to every cyst at the end of 

 the fourteen days, under ordinary circumstances 

 the ratio being at least in the opposite direction. 

 In samples 1 and 2, with obvious bacterial growth, 

 encystment began after four or five days, and 

 at the end of a week there were more cysts than 

 amoebae. The cysts in the stronger alkali solutions 

 appeared to be uninjured, and those from sample 6 

 excysted on a fresh medium. 



From these results it is clear that it is not the 

 alkalinity of the medium which initiates the 

 excystation, because, if so, one would then expect 

 increasing strengths of alkali to hasten the process, 

 whereas the converse is the case. Also cysts will 

 excyst on an acid medium (citric or hydrochloric 

 acid). It is probably some extract of the bodies 

 of the bacteria (which were added to the solution 

 along with the cysts) which is the effective agent, 



