Stimulation of the activity of Schistosoma mansoni miracidia by snail-conditioned water.

A dark-ground photographic technique was used to analyse the reactions of Schistosoma mansoni miracidia to homogeneous solutions of snail-conditioned water (SCW). The most significant effect of this water was to increase miracidial turning. This effect was maintained under both acid and alkaline conditions, after passage of the SCW through a mixed bed resin and after chelation of either calcium or both calcium and magnesium ions. The stimulant in the water was unaffected by trypsin but was protease-sensitive, suggesting its possible identity as a peptide. The importance of 'active spaces' rather than concentration gradients in miracidial host-location was emphasized.