Seneca nevertheless has occasion to repeat some tall stories, such as that the river Alpheus of Greece reappears as the Arethusa in Sicily and there every four years casts up filth from its depths on the very days when victims are slaughtered at the Olympic games.[478] He also affirms that living beings are generated in fire; he believes in such effects of lightning as removing the venom from snakes which it strikes; and he recounts the old stories of floating islands and of waters with the virtue of turning white sheep black.[479] On the other hand, he qualifies by the phrases, “it is believed” and “they say,” the assertions that certain waters produce foul skin-diseases and that dew in particular, if collected in any quantity, has this evil property; and he doubts whether bathing in the Nile would enable a woman to bear more children.[480] He ridicules the custom of the city which had public watchmen appointed to warn the inhabitants of the approach of hail-storms, so that they might avert the danger by timely sacrifice or simply by pricking their own fingers so that they bled a trifle. He adds that some suggest that blood may possess some occult property of repelling storm-clouds, but he does not see how there can be such force in a drop or two and thinks it simpler to regard the whole thing as false. In the same chapter he states that uncivilized antiquity used to believe that rain could be brought on or driven off by incantations, but that now-a-days no one needs a philosopher to teach him that this is impossible.[481] [Sidenote: Belief in natural divination and astrology.]