  Recent work on solutions to the Born-Infeld theory used to describe D-branes
suggests that fundamental strings can be viewed, in a certain limit, as
D-branes whose worldvolumes have collapsed to string-like configurations. Here
we address the possibility of undoing this collapse, by inducing the string to
tunnel to an extended brane configuration. Using semiclassical methods we argue
that, by putting one of these Born-Infeld strings in the background of a
uniform 4-form RR field strength, the string can nucleate a spheroidal bulge of
D2-brane, or, if the string is wrapped around a small enough circle, it can
tunnel to a toroidal D2-brane. This process can also be interpreted in terms of
the M2-brane. We also address the extension to other D$p$-branes, and discuss
the range of validity of the approximations involved.
