Fib₄₂₀ versus total fibrinogen: Fib₄₂₀ levels in the adult but not fetal population remain constant. Values plotted are taken from Table 1. Total immunoreactive plasma fibrinogen as determined by rocket immunoelectrophoresis is plotted along the abscissa. Plasma Fib₄₂₀ concentration (ordinate) was derived from the latter using the molar proportion of Fib₄₂₀ as determined by quantitative Western blot assay. First-order linear regression analyses are shown. Adult plasma (•); fetal plasma (○).