The  origin of Blood Brothers is said to be Middle English during 1350-1400.  Depending on where in the World this oath was and is taken to this day, depends on how the ritual is preformed. It is the intertwining of one another’s blood as to make a connection, spiritually. I am wondering if  blood type reactions were noted if the “oath” was null. For instance, rh incompatibly…would this “oath” sensitize a rhesus negative individual? Would there be an immune response? Would there be visual agglutination of the blood? Was the “Blood Brother” ritual meant to find a common connection related to blood type?

Definition: blood brother