Differences/Similarit ies?

What are the main differences/similarities between Mamoulian's adaptation and Stevenson's novella?

I have not yet seen the film in question but I notice it seems to introduce a romantic element through the characters of Muriel and Ivy which is not present in the original novel. Are there any other additions to the plot?

Or are certain events omitted, due to the way in which time constraints force film to suggest pictorially things that a novel can explore in more depth?

Not only in terms of plot, which obviously differs between versions in the endings and introduction of certain characters, does the film adaptation actually gain something over the novel?