There was an old belief in the 17th and 18th centuries that life was sustained by a vital fluid. This fluid could be extracted, refined, purified and transferred, or so the philosophers and alchemists believed. All life had this vital fluid; that’s why we eat living things to stay alive, they believed. As time went by, this attitude receded into the mists of time as a footnote in the history of science. Curiously, it found new currency in science fiction.
Mary Wolstonecraft Godwin’s “Frankenstein” (she wasn’t married when it was first published) took the refined concept of vital fluid, which had morphed into animal electricity, and used it to animate the monster. Since then, there has been a stock cliché in sci-fi and space opera of creatures, machines, etc. that drain life force, transfer it, etc.
When sci-fi hit television, the cliché didn’t go away. We’ve seen variations of it in Star Trek (The original series), X-Files, The X-Men and Babylon 5. Now I, personally, believe in a soul/spirit, but I don’t buy the idea there is a life essence that can be transferred between people. Yet shows that are purportedly about science continue to use this anachronism.