John Nesbitt
— Narrator (voice)
Shepperd Strudwick
— Dr. Semmelweis
Rudolph Anders
— Doctor (uncredited)
King Baggot
— Passerby (uncredited)
William Bailey
— Passerby (uncredited)
Barbara Bedford
— Nun Reading Book (uncredited)
Ralph Brooks
— Medical Student at Lecture (uncredited)
Mary Howard
— Young Stricken Mother (uncredited)
Leonard Penn
— Semmelweis' Assistant (uncredited)
Beatrice Roberts
— Passerby (uncredited)
Edward Van Sloan
— Hospital Chief of Staff (uncredited)
E. Alyn Warren
— Professor (uncredited)