There is an old story that the legend of vampires came from observing people with a rare genetic defect they can't make hemoglobin. The disease is Porphyria - named after the ring that makes the center of the hemoglobin molecule- porpheryn. In the middle ages, people didn't understand or recognize it was a disease and so stories circulated about people drinking blood (usually animals not humans), etc. Them assuming animal forms like bats was an embellishment of the real symptoms. And of course religion had to be thrown in the stories to support "The Church" so we got the fear of the Cross and Holy water BS !! I don't know where the stake through the heart came from ... maybe Vlad the Impaler ! crazy

BUT lacking hemoglobin they were very pale skinned, could NOT come out during the day (sunburned very easily) = were nocturnal , and some had facial distortions exposing the canines (fangs)... and in addition exposure to garlic worsened their condition. So some was fact but a lot was fiction. wink . . And of course Dracula was fashioned from Vlad the Impaler...
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David (OFI)