  We analyze the temporal structure of long ((T_{90}>2sec)) and short
((T_{90}<2sec)) BATSE bursts. We find that: (i) In many short bursts (\delta
t_{min}/T\ll 1) (where (\delta t_{min}) is the shortest pulse). This indicates
that short bursts arise, like long ones, in internal shocks. (ii) In long
bursts there is an excess of long intervals between pulses (relative to a
lognormal distribution). This excess can be explained by the existence of
\emph{quiescent times}, long periods with no signal above the background that
arise, most likely, from periods with no source activity. The lognormal
distribution of the intervals (excluding the \emph{quiescent times}) is similar
and correlated with the distribution of the pulses width, in agreement with the
predictions of the internal shock model.
