Everything you wanted to know about bloodletting (which to be fair may not be very much) https://www.youtube.com/watch?v=j_Pk2k70KqY&t=2s
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@estherschindler
There's a scene in Treasure Island where the doctor takes quite a bit of blood out of an old pirate having a stroke, and it's clear they were using it to try to treat malignant hypertension. It probably worked occasionally enough to get people to keep trying it.