The technique of parabiosis is very uncontrolled, so ultimately un-satisfyin
g to a molecular biologist, BUT it does help to point out events that are
cell-intrinsic and others that vary with the internal environment. Obviousl
y this is not much use unless further experiments are done to define WHAT in
the cell or the serum/lymph, etc are actually responsible. Transplantations
to young orgs of old cells/tissues are often used for a similar purpose,
cf some expts of David Harrison on mouse hematopoetic cells. Laura Hoopes
