my $name = "file000";
open STDOUT, ">>file000" or die "cannot append to file000: $!";
while (<>) {
  if (/Experiment/) {
    open STDOUT, ">>".(++$name) or die "Cannot append to $name: $!";
  }
  print;
  if (/Reagent Lot/) {
    open STDOUT, ">>file000" or die "Cannot re-append to file000: $!";
  }
}