system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't we take blood from dead people?
gpt
Blood taken from dead people is actually very usable.  The first experiments were done by taking blood from a dead dog and putting that blood into a living one -- if it were done within ~6 hours, the living dog suffered no ill effects.

Taking blood from cadavers was done in the Soviet Union, but it didn't catch on in America because of the general public's feelings toward it.  It also raises the question of consent -- would a patient be okay with blood from a dead person?  Would the deceased's family consent?

It's just a sticky situation with current mentalities -- similar to the issues that plague cadaver research.

Source:  This was all taken from the book *Stiff* by Mary Roach.  It's a generally well-regarded nonfiction.