By Brian UzombaGirolamo Francastro He suggest that invisible organisms may cause disease. Robert Hooke publishes his discovery of cells and sees he first microorganism. Antony Leewenhoek observed the first bacteria. He was observing the lake water and found these organisms. This sparked a start to microbiology. Edward Jenner introduced the vaccination of smallpox. Mathias Schleiden and Theodor Schwann propose that all organisms are composed of cells. J. Henle Proposes the germs are the cause of diseases. John Snow demonstrates the epidemic spread of cholera through a contaminated water supply. Louis Pasteur develops pasteurization to destroy organisms in wine. Robert Koch demonstrates that a bacterium causes anthrax. Robert Koch introduces pure culture techniques in the laboratory. Walter an Franny Hesse introduce the agar plate as a solidifying gel for the culturing medium. Christian Gram describes the Gram stain. Elie Methnikoff discovers phagocytic cells which engulf bacteria. Frederick Griffith discovers genetic transformation in bacteria. Alexander Fleming discovers first antibiotic, penicillin. Avery, MacLeod, and McCarty demostrate that Griffith's Transforming principle is DNA. Watson, Crick, and Franklin determine the structure of DNA being a double helix structure. Theodor Diener demonstrates fundamental differences between viroids and viruses. Boyer and Cohen Clone DNACarl Woese classifies all organisms into three domains. The first complete nucleotide sequence of a bacterial chromosome is reported.