 Ezio Merler

Ezio Merler coauthored the 1971 study of angiogenic activity isolated from tumours, alongside Judah Folkman, Charles Abernathy and Gretchen Williams.^[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.