  Molecular Communication (MC) architectures suffer from molecular build-up in
the channel if they do not have appropriate reuptake mechanisms. The molecular
build-up either leads to intersymbol interference (ISI) or reduces the
transmission rate. To measure the molecular build-up, we derive analytic
expressions for the incidence rate and absorption rate for one-dimensional MC
channels where molecular dispersion obeys the Brownian Motion. We verify each
of our key results with Monte Carlo simulations. Our results contribute to the
development of more complicated models and analytic expressions to measure the
molecular build-up and the impact of ISI in MC.
