In three experiments, children's reliance on other people's testimony as compared to their own, first-hand experience was assessed in the domain of ontology. Children ranging from 4 to 8 years were asked to judge whether five different types of entity exist: real entities (e.g. cats, trees) whose existence is evident to everyone; scientific entities (e.g. germs, oxygen) that are normally invisible but whose existence is generally presupposed in everyday discourse; endorsed beings (e.g. the Tooth Fairy, Santa Claus) whose existence is typically endorsed in discourse with young children; equivocal beings (e.g. monsters, witches) whose existence is not typically endorsed in discourse with young children; and impossible entities (e.g. flying pigs, barking cats) that nobody believes in. Children make a broad dichotomy between entities and beings that they claim to exist (real entities; scientific entities; and endorsed beings) and those whose existence they deny (equivocal beings and impossible entities). They also make a more fine-grained distinction among the invisible entities that they claim to exist. Thus, they assert the existence of scientific entities such as germs with more confidence than that of endorsed beings such as Santa Claus. The findings confirm that children's ontological claims extend beyond their first-hand encounters with instances of a given category. Children readily believe in entities that they cannot see for themselves but have been told about. Their confidence in the existence of those entities appears to vary with the pattern of testimony that they receive.

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Imagination et témoignage dans la construction de la réalité de l’enfant. Bien que les enfants apprennent beaucoup sur la réalité grâce à l’observation directe, ils apprennent également à partir du témoignage des autres. Par exemple, ils prennent connaissance de différentes entités et êtres invisibles, non pas du par leur expérience personnelle mais par la communication avec les autres personnes. Quatre différents types d’expériences montrent que les enfants sont plein d'assurance quant à l''existence de deux catégories importantes d'entités invisibles auxquelles ils ont eu accès par le biais du témoignage : les entités scientifiques -les germes et l’oxygène, et des êtres spéciaux -le Père Noël ou Dieu. Toutefois, les enfants expriment une plus grande confiance dans celles-là que dans celles-ci. Deux explications possibles de ce phénomène sont envisagées.

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Hydroxyapatite (HA) discs were treated for 1 min with fluoride solutions of varying concentrations and pH. The calcium fluoride and fluoridated hydroxyapatite (FHA) formed were analysed independently of each other following their separation in molar potassium hydroxide. Only the more intimately associated FHA was found to affect the rate of acid dissolution of HA and its level of formation and the reduction in acid dissolution rate of HA were both found to be linearly related to the logarithm of the ionic fluoride level in the treatment solution following 1 min. pretreatment. The benefit of using acidulated fluoride treatment of enamel is questioned as neutral fluoride treatments of enamel mineral resulted in equivalent protection.

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