DIFFICULTIES IN PICKING OFF CYSTS 89 



tube, while, if the surface is wet, the introduction 

 of the tube sets up a disturbance which is likely to 

 attract bacteria from a distance as the tube is 

 withdrawn. The most practical plan is to use a 

 dry jelly, and touch the neighbourhood of the cyst 

 with the fine, wet end of the tube, and then move 

 it about gently. If the far end of the tube is then 

 lowered sufficiently, the cyst may rush in by the 

 action of gravity, the whole proceeding being 

 carried out under a low power of the microscope. 

 This principle is of use in the separation of cysts 

 from moulds, flagellates, etc., or for removing a 

 clump of cysts as the first stage in the purification 

 of cultures, but may be simplified, as it is only 

 necessary to touch the jelly surface with the fine, 

 wet point of a glass tube, when many cysts will 

 adhere, and can be transferred to a fresh medium. 

 We have failed to isolate cysts with bristles coated 

 with vaseline, etc., and we have had no experience 

 with the Barber pipette. We have not been able 

 to pick off a single free living amoeba and re- 

 cover it from the tube into which it was drawn. 



(2) Methods depending on migration of amoebae 

 from the site of inoculation. In some cultures 

 where the amount of water present is limited, 

 amcebas may wander away apparently free from all 

 bacteria ; but we have not succeeded in removing 

 them without contamination, although thin slices 

 have been taken off the jelly and portions have 

 been cut out with a tube attached to the objective. 

 A method has been described, based on this 

 principle, in which a series of walls consisting of 

 a pure strain of bacteria were drawn around the 

 site of inoculation, so that wandering amoebas 



