The paradigm shifts from humoral theory to germ theory

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2024

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Faculty of Science, University of Kelaniya Sri Lanka

Abstract

This study examined the historical and intellectual transformation from humoral theory to germ theory on diseases, marking a significant shift in medical thought. Utilizing qualitative methodology, the research examined primary and secondary sources under historic method and content analysis to illuminate the decline of humoral theory and the subsequent ascendancy of germ theory. Humoral theory, rooted in ancient Greek medicine (5th Century BCE), posited that human health depended on a delicate equilibrium of four bodily fluids: blood, yellow bile, black bile, and phlegm. Dominating medical practice for millennia, this paradigm influenced diagnosis, treatment, and social perceptions of health. However, its limitations in explaining the etiology and progression of diverse diseases created an intellectual void, especially in explaining the cause of infectious diseases, the existence of which was not known in early days of history. Concurrently, the Renaissance ushered in a renewed emphasis on observation and experimentation, and it challenged, among many other thoughts, the theoretical underpinnings of humoral medicine. The invention of the microscope opened a new frontier, revealing a previously unseen microbial world. Although the first microscopists Antonie van Leeuwenhoek observed the first microorganisms and subsequent microscopy revealed more about them, their relevance to diseases remained unknown. Then, in the 19th century, the world witnessed a watershed moment in terms of the emergence of germ theory. Louis Pasteur’s groundbreaking work on infectious diseases, coupled with the procedure Robert Koch formulated to confirm the link between a disease and the pathogen that causes it, a procedure came to be known as the Koch's postulates, provided irrefutable evidence for the microbial causation of the relevant diseases. Unsurprisingly, this paradigm shift in medicine was met with resistance from traditional medical practitioners entrenched in humoral theory. Intellectual debates ensued regarding the nature of contagion, the role of the environment, and the implications of the new theory on public health eventually leading to the acceptance of germ theory on infectious diseases, and acceptance which brought in had profound consequences. It transformed science of medicine, birthing the novel disciplines medical microbiology and immunology. Public health measures, such as sanitation, and vaccination, and procedures including disinfection, sterilization and aseptic techniques, were predicated on germ theory. However, the legacy of humoral theory persists, and the importance of regulated body biochemistry in non-infectious diseases remains undeniable. It is still seen influencing concepts like balance, temperament, and the mind-body connection in contemporary medicine and alternative healing practices. This study underscored the dynamic nature of medical knowledge, shaped by a complex interplay of historical, scientific, and social factors. The transition from humoral theory to germ theory exemplifies a paradigm shift in the field of medicine, highlighting the importance of empirical observation, experimental rigor, and intellectual openness in medical understanding.

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Keywords

Humoral theory, Germ theory, History of medicine, Scientific methodology

Citation

Randiwela R. M. D. S.; Subasinghe A. W. K. W. (2024), The paradigm shifts from humoral theory to germ theory, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2024-Kelaniya) Volume 4, Faculty of Science, University of Kelaniya Sri Lanka. Page 213

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