John Tyndall (TIN-duhl) (1820–1893) was an English physicist who explained the need for prolonged heating to destroy microbial life in broth. He discovered that bacteria existed in heat-stable and heat-sensitive forms. Prolonged or intermittent heating was needed to destroy the heat-stable form. Intermittent heating, now called tyndallization, killed both forms. Almost simultaneously, German botanist Ferdinand Cohn (1828–1898) described the heat-stable forms as endospores, which are formed during the life cycle of certain bacteria (see Chapter 21).

Joseph Lister (1827–1912) was an English surgeon who recognized the role of airborne microorganisms in postsurgical infection. By applying carbolic acid to dressings and using an aerosol of carbolic acid during surgery, he lowered the risk of infection after surgery.

Robert Koch (1843–1910) was a German physician who provided the techniques and discipline necessary to guide future microbiologists. He developed a two-part dish that was used for growing bacteria and a technique used for isolating pure colonies of bacteria (Fig. 18-1). The two-part dishes were named Petri plates after Julius Petri (1852–1921), a German bacteriologist. Petri plates are still used in microbiology laboratories today.

To prove that a specific microorganism caused a particular disease, Koch applied guidelines that are still in use today.

Louis Pasteur (1822–1895) was the famous French chemist who disproved the theory of spontaneous generation of life and associated living microorganisms with disease. Pasteur designed flasks shaped like swan necks (S-shaped) for heating broths. The curved pathway caused by bends in the glass prevented dust particles, which contained microorganisms from the air, from entering the heated broth. Instead, the dust particles settled in the bends of the long-necked flasks, even over an extended period. When the top of a flask was removed, microorganisms once again appeared in the liquid. Pasteur’s experiments put an end to the theory of spontaneous generation of life.

Pasteur’s ongoing contributions to the emerging germ theory of disease earned him the title “Father of Microbiology.” At the request of Napoleon III in 1863, Pasteur saved the French wine industry by showing that vats of spoiled wine contained acid-producing bacteria. Contaminants could be destroyed in a short time at temperatures of 50° to 60° F. The process of heating grape juice to reduce microorganisms became known as pasteurization. Today, pathogens in milk are destroyed through pasteurization.

Pasteur prepared the first vaccine for the fatal animal disease rabies. Although he never isolated the actual rabies virus, he infected rabbits by inoculating them with a preparation from the medulla (a portion of the brain stem and spinal cord) of rabid dogs. The virus migrated to the spinal cord and the brain of rabbits. Pasteur maintained the organism through successive inoculations in rabbits (Fig. 18-2). He inoculated dogs with dried, powdered rabbit medulla, suspended in broth, to prevent rabies.

The French government built the Pasteur Institute in 1888 to honor Pasteur, whose last words reportedly were, “There is still a great deal to do” (Fig. 18-3).