A true story about Louis Pasteur, who revolutionized medicine by proving that much disease is caused by microbes, that sanitation is paramount and that at least some diseases can be cured by vaccinations.
| Actor | Role |
|---|---|
 Paul MuniLouis Pasteur | Louis Pasteur |
 Josephine HutchinsonMarie Pasteur | Marie Pasteur |
 Anita LouiseAnnette Pasteur | Annette Pasteur |
 Donald WoodsDr. Jean Martel | Dr. Jean Martel |
 Fritz LeiberDr. Charbonnet | Dr. Charbonnet |
 Henry O'NeillDr. Emile Roux | Dr. Emile Roux |
 Porter HallDr. Rossignol | Dr. Rossignol |
| RRaymond BrownDr. Radisse | Dr. Radisse |
 Akim TamiroffDr. Zaranoff | Dr. Zaranoff |
 Halliwell HobbesDr. Lister | Dr. Lister |
 Frank ReicherDr. Pfeiffer | Dr. Pfeiffer |
 Dickie MooreJoseph Meister | Joseph Meister |
| RRuth RobinsonMrs. Meister | Mrs. Meister |
 Walter KingsfordNapoleon III | Napoleon III |
 Iphigenie CastiglioniEmpress Eugénie | Empress Eugénie |
| HHerbert CorthellLouis Adolphe Thiers, 1st President, Republic of France | Louis Adolphe Thiers, 1st President, Republic of France |