Scientific Films of the 1920s - 1930s - continued...
A common theme of such instructional films was that of movement and its disorders. Robert Janker's x-ray films of the movement of head and neck, or of normal and pathological breathing, illustrate this genre and its claim to heightened objectivity and transparency. More self-reflexively, the incorporation of sound into his film on the physiology of speech is marked by a moment wherein the voice of the man depicted speaking informs us that increasing the film speed from 12 to 24 frames per second "heightens the scientific possibilities" of the medium. [Röntgentonfilm der Sprache ("X-Ray Film of Speech")]. Given the still primitive state of sound technology, however, increasing the speed still further to 48 frames per second, as we are subsequently informed, results in the loss of sound.
Excerpt from the movie: Röntgentonfilm der Sprache (00.30 min.)
Reference: Killen, Andreas. 2009. Scientific and Medical Films in the 1920s-1930s. The Virtual Laboratory (ISSN 1866-4784), https://vlp.mpiwg-berlin.mpg.de/references?id=art74&page=p0002