Occurrence and Nature of an Amœba Excystment Factor produced by Aerobacter sp.

Abstract

ALTHOUGH an excystment factor potentiating the emergence of trophozoites from their resting cysts in Protozoa has long been postulated, there has so far been no convincing experimental evidence of its existence. A critical appraisal of previous work^1–4 has revealed that the factor has variously been attributed to hypo- and hyper-tonicity of the medium, low oxygen tension, change of pH, reducing agents, presence of enriched nutrient media, change of temperature, etc. Earlier workers in this field do not appear to have adequately recognized the risk of extraneous infection inherent to such experiments, particularly when nutritionally rich and highly susceptible media, such as ‘Difco’ yeast extract, are examined for the presence of this factor⁵. Unless absolutely aseptic conditions are maintained in the course of experiments, the results will remain open to doubt.