Chemical stimulation of Schistosoma mansoni miracidial activity.

The movements of S. mansoni miracidia immersed in various solutions of organic chemicals were recorded by dark ground photography. Reduction of miracidial speed was recorded for miracidia in solutions of fatty acids and ammonia. The speed reduction was concentration dependant and pH dependant, indicating in both cases that the un-ionized molecule was responsible. Ammonia at concentrations between 0.4 mM and 0.8 mM elicited an increased "rate of change of direction" by miracidia. No changes in miracidial movements were recorded for miracidia immersed in aqueous solutions of amino acids, sugars or of molluscan nitrogenous excretion products other than ammonia. A possible role for chemo-klinokinetic behaviour patterns in miracidial host location was formulated.