The growth (decay) of bacteria colonies can be modeled using
exponential functions. For example, one type of bacteria commonly
used in research is *Escherichia coli* (also known as *
E. coli*), a bacteria residing in the human digestive system. During
the growth phase, approximately 12 hours, of *E. coli* the colony
grows exponentially. For practicality, bacteria colonies are measured
by mass rather than the number of cells present. The equation used to
represent growth is

where is the initial mass of the bacteria population, *r* is the
growth rate and *M* is the mass of the population after time *t*.

Tue Sep 24 13:59:38 EDT 1996