58 ENCYSTMENT AND EXCYSTATION OF AMOEBA 



wall. It will be shown later that these substances 

 are probably of the nature of ferments, and that 

 their action is increased by the presence of kinetics 

 which are also produced by the bacterial growth. 



As regards the two main processes which have 

 hitherto been suggested by others to be responsible 

 for the phenomenon in question, namely, the action 

 of an internal ferment and the influence of altera- 

 tions of osmotic pressure, we have no proof that 

 either of these plays any part ; but we think that, if 

 they have any influence, it is only a secondary one, 

 and that they are unable to act on the cyst without 

 the assistance of other factors. 



Rate of excystation dependent on the concen- 

 tration of dissolved substances in the surrounding 

 medium. The first indication of this fact was the 

 observation that excystation invariably takes place 

 sooner on a jelly surface than in a solution. In 

 the former case the immediate surroundings of the 

 cysts are more constant than in a solution in which 

 physical processes are continually at work removing 

 the bacterial products. For the same reason, ex- 

 cystation is more rapid if the jelly is merely 

 saturated with moisture than if it is covered with 

 a layer of liquid. Again, salts, which have been 

 shown to delay the diffusion of soluble substances 

 into living cells, have a similar effect in delaying 

 excystation, although their effect is not marked. 

 For example, cysts selected from the same stock, 

 so that their age and resistance could be regarded 

 as uniform, were found to discharge their contents 

 in tap water quicker than in solutions of sodium 

 chloride or sodium citrate. The complexity of the 

 factors involved in the process, such as the nature 



