Das Versuchskaninchen (1916)

Jesta’s mischievous and playful manner is driving her father and his new lady friend mad. Finally they have had enough, and Jesta is sent away to a girls’ school, bundled onto the first train available. However, a mix-up occurs at the train station. A professor in dire financial straits, who has finally gotten a young, mentally challenged sent to him for treatment, mistakenly takes Jesta home with him to his clinic – a move he will soon regret … (stumfilm.dk)