@naillit
Good question.
via Baldric's link, I found: -
"What Does the Bible Say About Blood Transfusions?
According to the Bible, God gave the command to ‘abstain from blood.’ "
In the first century context, surely "abstain from blood" meant don't eat it (eg haggis) and don't drink it (drinking the blood of a camel without causing its death, as practised by desert peoples, when water was unavailable, would not have been unknown to Levant people)?
I would challenge anyone to find the word "transfusion" in the bible although it is facetious to say so, because everyone knows it is a technical term, created at the time this medical practice was first invented. (qv.)
Someone has -interpreted- a word in the bible as meaning transfusion whereas I think the imaginations of that time would have been limited to concepts like ingestion.
As an aside, it is worth mentioning that ingestion results in complete destruction of all blood cell structures, since only small molecules - single amino acids, nucleotides, sugars, lipids - can pass through the cell membranes of the gut. There is no mechanism to absorb genetic information from anything you eat (waves to anti-GMO crowd).
The outwardly visible deleterious effects of eating pork (tapeworm) would have been long-known, in biblical times, so it would not have required forensic, or medical, skills to work out the true cause of illnesses, merely the adoption of a ban at the cultural level. Similarly, any observable correlation between blood eating/drinking and disease would lead to its prohibition.
Colloquial knowledge may have been extended by cultures in the wider world who practice the "blood brothers" ritual: skin cutting and intermingling of bloods. As most of us know, mixing incompatible blood groups leads to coagulation and early attempts at blood transfusion had a "Russian roulette" quality to them, until it was learned that blood groups even exist.
If Victorian doctors didn't, there is no reason to believe ancient civilisations did. Or, perhaps, they tried but failed often enough to, as with foods, justify the banning the mixing of blood between persons.
If the early, problematic, era of blood transfusions coincided with the invention of the Jehovah's Witnesses, I would find that intruiging.