[Reinfection of molluscs by protostrongylids : phenomena of limitation and facilitation].

Land-snails (Otala lactea, Theba pisana, Cochlicella ventricosa and C. conoidea) previously infected experimentally by protostrongylids were reinfected at different time-lags, from one day to 126 days. The efficacy of daily reinfections was nil. The susceptibility of all species of snails was lowered for reinfection at short time-lags (up to 15 days) and enhanced for long time lags (over 21 days). The former phenomenon was called limitation and the latter, facilitation. It is suggested that limitation is related to the survival of penetrated first-stage larvae and that facilitation is induced by a better penetration of first-stage larvae.