13 The Role ofM walls of the cuved necks.If the necks were broke growth com by161 but shown how to ke English physicist John Tyn 893)deal 187 During the lly heat-resistar forms of ba cteria.Working independe tence ofat-resant 1.Describe the field of microbiology in terms of the size of its 1.3 The Role of Microorganisms in Disease Indirect evidence that micro ns were agents of humar sed with Pasteur's studies on the involvement of micro Recognition of the Relationship ments were heat sterilized and phenol was used o between Microorganisms and Disease Although Fracastoro and a few others had sugg ested that invisi. Lister published his findings in867.It also provideds indi und inf se because The first direct demonstration of the ole of bac ia in caus accepte the criteria proposed by his former teacher.J ob Henk He nany diseases were due to microbial infe mice.h ated a pice spleen containing th by the French gov pores.When the ere injected into mice he study of fermentation.Pasteur was askec nthrax d ped.His criteria or proving t e causal re ggs proPrescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 walls of the curved necks. If the necks were broken, growth com￾menced immediately. Pasteur had not only resolved the controversy by 1861 but also had shown how to keep solutions sterile. The English physicist John Tyndall (1820–1893) dealt a final blow to spontaneous generation in 1877 by demonstrating that dust did indeed carry germs and that if dust was absent, broth re￾mained sterile even if directly exposed to air. During the course of his studies, Tyndall provided evidence for the existence of excep￾tionally heat-resistant forms of bacteria. Working independently, the German botanist Ferdinand Cohn (1828–1898) discovered the existence of heat-resistant bacterial endospores (see chapter 3). 1. Describe the field of microbiology in terms of the size of its subject material and the nature of its techniques. 2. How did Pasteur and Tyndall finally settle the spontaneous generation controversy? 1.3 The Role of Microorganisms in Disease The importance of microorganisms in disease was not immedi￾ately obvious to people, and it took many years for scientists to establish the connection between microorganisms and illness. Recognition of the role of microorganisms depended greatly upon the development of new techniques for their study. Once it became clear that disease could be caused by microbial infec￾tions, microbiologists began to examine the way in which hosts defended themselves against microorganisms and to ask how dis￾ease might be prevented. The field of immunology was born. Recognition of the Relationship between Microorganisms and Disease Although Fracastoro and a few others had suggested that invisi￾ble organisms produced disease, most believed that disease was due to causes such as supernatural forces, poisonous vapors called miasmas, and imbalances between the four humors thought to be present in the body. The idea that an imbalance be￾tween the four humors (blood, phlegm, yellow bile [choler], and black bile [melancholy]) led to disease had been widely accepted since the time of the Greek physician Galen (129–199). Support for the germ theory of disease began to accumulate in the early nineteenth century. Agostino Bassi (1773–1856) first showed a microorganism could cause disease when he demonstrated in 1835 that a silkworm disease was due to a fungal infection. He also suggested that many diseases were due to microbial infec￾tions. In 1845 M. J. Berkeley proved that the great Potato Blight of Ireland was caused by a fungus. Following his successes with the study of fermentation, Pasteur was asked by the French gov￾ernment to investigate the pébrine disease of silkworms that was disrupting the silk industry. After several years of work, he showed that the disease was due to a protozoan parasite. The dis￾ease was controlled by raising caterpillars from eggs produced by healthy moths. Indirect evidence that microorganisms were agents of human disease came from the work of the English surgeon Joseph Lister (1827–1912) on the prevention of wound infections. Lister im￾pressed with Pasteur’s studies on the involvement of microorgan￾isms in fermentation and putrefaction, developed a system of anti￾septic surgery designed to prevent microorganisms from entering wounds. Instruments were heat sterilized, and phenol was used on surgical dressings and at times sprayed over the surgical area. The approach was remarkably successful and transformed surgery after Lister published his findings in 1867. It also provided strong indi￾rect evidence for the role of microorganisms in disease because phenol, which killed bacteria, also prevented wound infections. The first direct demonstration of the role of bacteria in caus￾ing disease came from the study of anthrax (see chapter 39) by the German physician Robert Koch (1843–1910). Koch (figure 1.4) used the criteria proposed by his former teacher, Jacob Henle (1809–1885), to establish the relationship between Bacillus an￾thracis and anthrax, and published his findings in 1876 (Box 1.1 briefly discusses the scientific method). Koch injected healthy mice with material from diseased animals, and the mice became ill. After transferring anthrax by inoculation through a series of 20 mice, he incubated a piece of spleen containing the anthrax bacil￾lus in beef serum. The bacilli grew, reproduced, and produced spores. When the isolated bacilli or spores were injected into mice, anthrax developed. His criteria for proving the causal relationship between a microorganism and a specific disease are known as Koch’s postulates and can be summarized as follows: 1. The microorganism must be present in every case of the disease but absent from healthy organisms. 1.3 The Role of Microorganisms in Disease 7 Figure 1.4 Robert Koch. Koch (1843–1910) examining a specimen in his laboratory