72 ENCYSTMENT AND EXC YSTATION OF AMCEBA 



such as an ordinary nutrient agar jelly, our experi- 

 ence leads us to believe that this is not possible. 

 It is our intention to make further investigations 

 as to whether amcebse can live on sterile liquid food, 

 which has not been boiled, and, as a preliminary 

 test, a few experiments have been carried out with 

 normal sterile horse serum. This was selected for 

 two reasons, viz., firstly, because it contains 

 ferments, which, we thought, might be capable of 

 causing excystation ; and secondly, because it con- 

 tains proteins in a soluble (colloidal) form, which 

 might possibly be utilised as food by the amcebae. 



The effect of tyrosin and choline on reproduction 

 of amcebce in pure culture. Six test-tubes were ob- 

 tained, each containing 5 cc. of 2-per-cent. agar jelly. 

 Each of these was then prepared in a particular 

 way (vide Table II., p. 74), by adding an auxetic 

 or a kinetic or both to the jelly, and the tubes were 

 labelled A to F. These were then sterilised and 

 sloped. Dead bacteria (B. fluorescens liquefaciens, 

 which had been killed by boiling) were smeared 

 over the surface of each of the slopes and a few 

 drops of horse serum were placed on those labelled 

 A D. Cysts * (free from living bacteria) were 

 then placed on each slope. The tubes were 

 examined at intervals of every few hours to see if 

 excystation had taken place, and they were subse- 

 quently inspected every day for a week to find out 

 if there was any multiplication of those amcebae 

 which had escaped from the cysts. The results of 

 these observations are tabulated under the respec- 



1 The cysts were selected from the cultures on choline jellies, in 

 which encystment had occurred after a fortnight's growth in the 

 absence of living bacteria. 



