THE INVISIBLE RAY (1936)
The power of radioactive elements isn't generally a subject for films in this period, at a time when science fiction stories were less common. Things would of course be very different some years later in the true atomic age. Instead this is a kind of prototype for later features, many of which still cast classic horror stars. As a result it's a strange mixture of ideas in which new discoveries are seen as miracle cures, as well as fuelling deadly weapons. The narrative itself is often a mixed bag but it's a fairly compelling one, despite the lack of actual medical accuracy. But it makes a change from mad scientists studying biology as their subject. Instead it's about starlight and rocks from outer space.