At a city health department laboratory, Ted Jones visits his bacteriologist brother, Frank, and learns to focus a microscope on bacteria associated with spoiled food. Their lesson explains that bacteria occur in air, water, and soil and emphasizes their useful roles in enriching soil, making cheese, breaking down dead matter, and producing antibiotics, while noting that some cause spoilage and disease. Microscopic views, diagrams, and staged examples show how scientists observe and study these organisms.
A historical section credits Anton van Leeuwenhoek with early observations of microorganisms and describes work by Louis Pasteur and Robert Koch on fermentation, germ theory, nutrient media, and bacterial cultures. Frank organizes bacteria by their food sources as parasites, saprophytes, or autotrophs, then by shape as round cocci, rod-shaped bacilli, spiral spirilla, or filamentous forms. The film also identifies bacteria as non-green plants, reflecting the scientific classification used in the production.
Diagrams and microscope images explain that bacteria absorb soluble food through their cell walls and reproduce by cell division when food and temperature are favorable. Some bacteria form resistant spores under adverse conditions, while others move through liquids by means of flagella. The closing laboratory scenes show researchers growing and testing cultures to identify bacteria, control harmful kinds, and make use of beneficial ones.
