68 ENCYSTMENT AND EXCYSTATION OF AMCEBA 



it was seen that the amoebae did not appear to 

 multiply, in fact they gradually died out. This 

 invariably happens when their only food supply 

 consists of dead bacteria killed by hydrochloric 

 acid. It is interesting to note that encystment 

 did not take place in the absence of injurious 

 bacterial products. The amoebae therefore have in 

 fact been made to excyst by artificial means, i.e. 

 by the chloroformed extract of bacteria, but they 

 are unable to encyst again to avoid death by 

 starvation, a fact which confirms our previous 

 experiments. A similar result was obtained by 

 incorporating the chloroformed solution in the jelly 

 medium (1 cc. in 5 cc.), the mixing being done 

 at 40 C. in order that the enzymes might be 

 unaffected. The amoebae excysted in three hours, 

 lived precariously on the dead bodies of the 

 bacteria, and then gradually died. 



The chloroformed solution was then boiled, and 

 found to be ineffective in hastening excystation 

 either in solution or when mixed in a jelly, 



The amoebae excysting in the absence of living 

 bacteria are all characterised by a transparent, 

 faintly granular appearance ; their karyosome is 

 small, movement is sluggish, growth in size is 

 slow, and multiplication appears to be absent. 

 The food vacuoles under these conditions were 

 almost entirely absent. 



Suspecting >the action of a ferment from the fact 

 that boiled extract was of no use, we then tried 

 pepsin (0-4 per cent.) and HC1 (0*2 per cent.) in 

 the jelly, and inadvertently boiled the pepsin to 

 sterilise it. No excystation occurred. Unboiled 

 pepsin was, however, effective, excystatipn taking 



