As a bit of medical trivia, blood formation requires a very tiny amount of copper. So tiny that
when research was being done on copper requirments over sixty years ago, the researchers
were baffled as to difficulty in producing copper deficiency in rabbits. After many months, someone
noticed rabbit liking brass wire holding tag on cage, and realized they were getting tiny but
adequate amounts of copper from the brass.
Tinier still is the amoount of cobalt necessary in Vitamin B 12