woah so what is causing the observed rejuvenating effects? just eliminating some of the endogenous blood from the circulatory system? no, i see, perhaps it is that the body must generate new plasma factors.

but i though it determined that putting old mouse blood into young mice caused them to show signs of senescence. or did i just imagine that?

ok here it is:

significant dilution of autoregulatory proteins that crosstalk to multiple signaling pathways (with their own feedback loops) would, through changes in gene expression, have long-lasting molecular and functional effects that are consistent with our observations

so wait a minute. the medieval bloodletters were actually onto something. just not what they thought.