Many workers in the field of protozoology have observed the occasional occurrence of encystment in cultures of Endamoeba histolytica. This is particularly true when the culture medium used contains starch granules. However, as far as the author is aware, no one has been able to so influence cultures of E. histolytica as to cause such encystment consistently. During the past six months encystment of cultures of E. histolytica has been produced daily by use of the following technique:

• 1.  Cultures of E. histolytica, free from Blastocystis hominis, are carried routinely in Boeck-Drbohlav medium made as follows:
  • (1)  Eggs.
  • (2)  Sterile Ringer's solution (autoclave at 15 pounds pressure for thirty minutes and then allow to cool).
    
    Sodium chloride 8.0 grams
    
    Potassium chloride 0.2 gram
    
    Calcium chloride 0.2 gram
    
    Distilled water 1,000.0 cc.
  • (3)  Sterile horse serum (must not contain tricresol or other preservative).
    
    Four whole eggs are washed in 70 per cent ethyl alcohol and then broken and emulsified in 50 cc. of the sterile Ringer's solution.