Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 33

The 19th century was a period of revolution in scientific thought, particularly in ideas about the origins of living things. The publication of Charles Darwin’s The Origin of Species in 1859 crystallized startling (and, to many people, shocking) new ideas about the origin of diversity in plants and animals, until then generally attributed directly to the hand of God. These insights permanently undermined the perception that humans were somehow set apart from all other members of the animal kingdom. From the point of view of the science of virology, the most important changes were in ideas about the causes of disease.

The diversity of macroscopic organisms has been appreciated and cataloged since the dawn of recorded human history. However, a vast new world of organisms too small to be visible to the naked eye was revealed through the microscopes of Antony van Leeuwenhoek (1632–1723). Van Leeuwenhoek’s vivid and exciting descriptions of living microorganisms, the “wee animalcules” present in such ordinary materials as rain or seawater, included examples of protozoa, algae, and bacteria. By the early 19th century, the scientific community had accepted the existence of microorganisms and turned to the question of their origin, a topic of fierce debate. Some believed that microorganisms arose spontaneously, for example, in decomposing matter, where they were especially abundant. Others held the view that all were generated by their reproduction, as are macroscopic organisms. The death knell of the spontaneous-generation hypothesis was sounded with the famous experiments of Pasteur. He demonstrated that boiled (i.e., sterilized) medium remained free of microorganisms as long as it was maintained in special flasks with curved, narrow necks designed to prevent entry of airborne microbes (Fig. 1.6). Pasteur also established that distinct microorganisms were associated with specific processes, such as fermentation, an idea that was crucial in the development of modern explanations for the causes of disease.

From the earliest times, poisonous air (miasma) was generally invoked to account for epidemics of contagious diseases, and there was little recognition of the differences among causative agents. The association of particular microorganisms, initially bacteria, with specific diseases can be attributed to the ideas of the German physician Robert Koch. He developed and applied a set of criteria for identification of the agent responsible for a specific disease (a pathogen), articulated in an 1890 presentation in Berlin. These criteria, Koch’s postulates, can be summarized as follows.