EXCYSTATION 67 



solution containing the products of growth of 

 B.fluorescens liq. in nutrient gelatin, the bacteria 

 having been killed by means of chloroform. 1 In 

 twenty-four hours the majority had excysted, but 

 it was observed that they did not multiply appreci- 

 ably, and gradually died out through lack of 

 nourishment. They did not encyst again. These 

 experiments were carried out with a jelly on the 

 slide, and in A and B no living bacteria were at 

 any time visible, and only appeared in C after 

 three days. We think the experiment is conclu- 

 sive that excystation will not take place in pure 

 water or in water in which the soluble products of 

 bacteria are diluted to such an extent as to be 

 negligible. Organically pure ammonia-free water 

 was used in these experiments. 



Excystation brought about by bacterial extracts 



and ferments. The next experiment was to try the 



" chloroformed solution " of the products of growth 



of B. Jluorescens liq. on cysts which had been freed 



from living bacteria by hydrochloric acid in the 



usual way. This time it was smeared over the 



surface of a plain 2-per-cent. agar slope, a control 



tube being made with distilled water. Examined 



in the course of twenty-four to forty-eight hours, 



the control showed a few scattered amoebae in 



those areas thick with dead bacteria, while in the 



tube with the bacterial extract the jelly was 



covered with living forms. Watching this culture, 



1 A nutrient gelatin stab of the selected bacillus is made, and after 

 a few days the liquefied mass is treated with pure chloroform shaken 

 well and allowed to stand. The upper layer consists of an aqueous 

 solution of the bacterial products, and can be easily removed and 

 filtered through a Chamberland filter. For convenience we shall 

 subsequently refer to this solution as the " chloroformed solution." 



