Between July 1898 and 1902 Romanian neurologist Gheorghe Marinescu (Georges Marinesco) made the world's first documentary films in his clinic in Bucharest. "Marinescu perfected the use of cinematography as a research method in neurosciences and published five articles based on cinematographic documents. He focused his studies particularly on organic gait disorders, locomotor ataxia, and hysteria. He adapted Charcot’s method of lining up several patients with the same disorder and showing them together to permit appreciation of archetypes and formes frustes. He decomposed the moving pictures into sequential tracings for publication. He documented treatment results with cases filmed before and after therapy.” (Barboi A.C., Goetz C.G. & Musetoiu R., "The origins of scientific cinematography and early medical applications," Historical Neurology, 2004, 62, 2082-2086). The films were (with titles in English translation):

"The walking troubles of organic hemiplegy (1898), The walking troubles of organic paraplegies (1899), A case of hysteric hemiplegy healed through hypnosis (1899), The walking troubles of progressive locomotion ataxy (1900) and Illnesses of the muscles (1901). All these short subjects have been preserved. The professor called his works "studies with the help of the cinematograph", and published the results, along with[drawings of] several consecutive frames, in issues of La Semaine Médicale magazine from Paris between 1899 and 1902.^[3]  In 1924 Auguste Lumiere recognized the priority of professor Marinescu concerning the first science films: "I've seen your scientific reports about the usage of cinematograph in studies of nervous illnesses, when I was still receiving La Semaine Médicale, but back then I had other concerns, which left me no spare time to begin biological studies. I must say I forgot those works and I am thankful to you that you reminded them to me. Unfortunately, not many scientists have followed your way "(Wikipedia article on Gheorghe Marinescu, accessed 11-2019)

Also in 1899 Marinescu published "Un cas d'hémiplegie hystérique guéri par la suggestion hypnotique et étudié à l'aide de la chronophotographie," Semaine méd, 19, 421.  Marinescu illustrated his articles with still images taken from his documentary films.