= Ezio Merler
{c}
\b[Ezio Merler] coauthored the 1971 study of angiogenic activity isolated from <tumours>, alongside <Judah Folkman>, <Charles Abernathy> and <Gretchen Williams>.<Isolation of a Tumor Factor Responsible for Angiogenesis by Judah Folkman and others>[Byline and Abstract]{ref} The investigators coupled biochemical separation with a biological response, asking whether separated material could induce new <capillaries>.
This is the logic of <bioassay-guided fractionation>: a fraction is interesting because a reproducible biological effect follows it through the separation procedure. An active fraction need not be a single pure molecule. The historical preparation should therefore not be identified retrospectively with <vascular endothelial growth factor> merely because both concern <angiogenesis>.
An original example distinguishes recovery from enrichment. Suppose a starting extract contains 100 arbitrary units of angiogenic activity in 20 milligrams of <protein>. Its activity per milligram is $100/20=5$. A later fraction contains 40 units in 2 milligrams, giving $40/2=20$ units per milligram. The process has achieved fourfold enrichment with 40 percent activity recovery. Neither number establishes chemical purity. Here the activity units are assumed additive for illustration; an ordinal visual score cannot automatically be treated as an additive biochemical quantity.
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