54- ENCYSTMENT AND EXCYSTATION OF AMCEBA 



a mixture of creatine and choline 0'2 per cent, 

 (equal volumes). This is then replaced by the 

 pure choline or cadaverine 0'2 per cent, for 24 

 hours, then 0*4 per cent, for 12 hours, and then 

 0-8 per cent., when some will encyst, and many 

 are preparing to do so. A 1-per-cent. solution is 

 finally employed, and in from 12 to 24 hours all 

 amoeba? will encyst. As a general rule, if amoebae 

 are placed directly into 1-per-cent. cadaverine or 

 choline they are poisoned too quickly to encyst. 

 From these experiments we conclude that the 

 process of encystment is to protect the amoebae 

 from bacterial products in excess, and that limited 

 cell-death occurs at the periphery, and the pro- 

 ducts of this protoplasmic degeneration form a 

 cyst wall. 



Summary and Conclusions. From the results of 

 these experiments it will be seen that an amoeba 

 is able to protect itself against poisoning and death 

 brought about by certain bacterial products in its 

 environment. The nature of two of these products 

 is known, namely, choline and cadaverine. These 

 substances have been shown in the first chapter 

 of this volume to be capable of accelerating the 

 multiplication of the amoebae. We have thus an 

 example of totally different effects (viz. repro- 

 duction and poisoning leading to self-protection) 

 being brought about by the same substance accord- 

 ing to the dose in which it is employed. We think 

 an analogy may be drawn between the action of 

 a kinetic such as choline on an isolated cell such 

 as an amoeba, and the effect of the chemical 

 substances which are liberated during "chronic 

 irritation" of the tissues of the higher animals. 



