Just heard that phrase somewhere recently.
In Torah our souls is said to be in our blood, or be our blood.
10. And any man of the House of Israel or of the strangers that sojourn among them, who eats any blood, I will set My attention upon the soul who eats the blood, and I will cut him off from among his people.
11. For the soul of the flesh is in the blood, and I have therefore given it to you [to be placed] upon the altar, to atone for your souls. For it is the blood that atones for the soul.
12. Therefore, I said to the children of Israel: None of you shall eat blood, and the stranger who sojourns among you shall not eat blood.
- Leviticus 17
Hate to disagree, but we can transfuse every drop of our blood without changing anything about a person. If we have a soul it's gotta be in our brains. Can transplant anything else without effecting who someone is.