The Lost Jungle is a 1934 Republic serial. This version is is edited together to form a feature-length film.
Clyde Beatty, an animal trainer, leads a rescue party to search for his girlfriend Ruth and her father who have been lost on an expedition searching for a mysterious island. Clyde takes a drigible to search for her but it crashes. Fortunately, it crashes on the same island that Ruth is stranded on.
Clearly designed to cash in on the previous year's King Kong, The Lost Jungle contains many similarities: the mysterious island, wild animals...there's even a dangerous trip over a chasm across a fallen tree trunk.
Clyde Beatty is played by none other than Clyde Beatty, a world-famous lion tamer and animal trainer. Beatty was famous for his "fighting act", in which he entered the cage with wild animals with a whip and a pistol strapped to his side. He act included lions, tigers, cougars, and hyenas, sometimes brought together all at once in a single cage, a potentially nasty situation. Some reports suggest that Beatty was the first lion tamer to use a chair in his act.
A large part of this film is really just Beatty's animal act. Not that that's a bad thing -- he's in a cage with live lions, tigers and bears (although the filmakers cheat a couple of times as Beatty stares down a lion that's actually a rear-projection lion... in reality the lion isn't really there), but for the most part it's the real deal, and the animal act scenes are well-integrated into the movie. The animal footage is crudely shot by today's standards, but it's excitng and pretty amazing to watch.