64 ENCYSTMENT AND EXCYSTATION OF AMCEBA 



In (3) a large number have excysted, and vast 

 numbers of amcebulae have appeared, resembling 

 the forms derived from conjugation. 



Excystation induced by products of bacterial 

 growth. The next steps were carried out with 

 cysts which had been freed from living bacteria. 

 Before we could prove the action of bacterial pro- 

 ducts on the cysts, it was obviously necessary to 

 obtain a culture of cysts which were free from 

 organisms. Then, having accomplished this, it 

 only remained to add various forms of bacteria 

 deliberately to the cysts and watch the results. In 

 order to free the cysts from bacteria, in the first 

 place a large quantity of cysts from an impure 

 culture was exposed to formalin (3 per cent.) for 

 a week, the reagent being subsequently thoroughly 

 washed away. After many failures for various 

 reasons cysts were obtained apparently free from 

 all living bacteria (fig. 24), no growth of the latter 

 taking place when plated on a sterile nutrient 

 jelly. No excy station of the cysts, however, 

 occurred on plain 2-per-cent. agar jellies, but when 

 transferred from these to live slides with tap water 

 and bacteria the amcebae were set free again on 

 the third day. A culture of Staphyloccus albus 

 was then made in 1-per-cent. peptone water con- 

 taining 0'5-per-cent. sodium chloride, and after a 

 week's growth the solution was passed through a 

 Chamberland filter. A 2-per-cent. plain agar slope 

 was smeared thickly over with the sterile peptone 

 culture, and the formalised cysts as prepared above 

 planted on it. After two days the tube was 

 examined, and many free amoebae had escaped, 

 there being no sign of bacterial growth. The 



