‘Febris non est morbus, sed bellum contra morbum’. A Study of Seventeenth-Century Theories of Fever,

This paper offers a survey of the 17th-century debate on fevers, trying to elucidate the practical and the theoretical issues involved in the investigation of fevers. Galen’s view of fevers provided the foundation to most 16th and early 17th century understanding of fevers. Galen’s doctrines became matter of debate in the Renaissance and were attacked by Paracelsus and Pereira. Paracelsus claimed that heat was not the cause of fever, but was only a sign of the disease. For Pereira, the cause of fevers was not preternatural heat, but by the effort of the organism to expel the disease. Paracelsus and Pereira gave impulse to investigations of fevers that relied on spirits and fermentation. Campanella and van Helmont adopted Pereira’s thesis, ruled out the humoral pathology and explained fevers as an irritation of the vital principle, namely spiritus and Archeus. Both Willis and Borelli resorted to the corpuscular theory of matter and to the circulation physiology. Willis (De febribus, 1659) espoused the chemical doctrine of principles (which he interpreted in corpuscular terms) and explained fevers as the outcome of anomalous fermentation. Borelli’s tract on malignant fevers (1649) adopted Campanella’s definition of fevers and resorted to the vix medicatrix naturae to account for the body’s response to the external morbid agent. In De motu animalium (1680-81) Borelli criticised Willis’ theories on the basis of experimental and anatomical evidence. Borelli maintained that blood was not the proximate cause of fevers, which he explained by resorting to the composition and motion of the nervous juice.