Erasistratus, again, by his favourite principle of
_horror vacui_ could never explain the secretion of
urine by the kidneys. While, however, he acknowledged
that the kidneys do secrete urine, he makes no attempt
to explain this; he ignores, but does not attempt to
refute, the Hippocratic doctrine of specific
_attraction_. "Servile" position taken up by Asclepiades
and Erasistratus in regard to this function of urinary
secretion.