The Movie Whitewashed the Novel
As I suspected, the movie was a Hollywood-censored version of the story told in the novel. If you want to know more, I refer you to Tim Dirks's online review: http://www.filmsite.org/kingr.html. Dirks says this:
"The Hays Code of 1934 required that much of the questionable, unfilmable content of the novel be modified - eliminating or seriously muting subjects such as illicit premarital sex, homosexuality, a sadistic and vengeful surgeon, and father-daughter incest leading to a murder-suicide."
Presumably the homosexuality was between Parris & Drake, hinted at in the scene in which Parris lovingly embraces the bed-bound Drake, at which point Randy leaves the room & invokes the Virgin Mary.
Dirks also says:
"Dr. Tower murders Cassie because of her insanity, but really because she has become pregnant, and because of her sexual relationship with Parris. Then, the doctor kills himself in an act of suicide. [In the novel, Cassie was afflicted with nymphomania, not insanity. Dr. Tower's diary revealed that the warped doctor had eliminated his wife and then committed incest with his daughter in order to study its psychological effects. He then killed Cassie when she threatened to leave him and go to Parris.]"