Linnaeus, smut disease and living contagion

Abstract

This paper examines the rise and fall of Carl Linnaeus's ideas on living contagion, focusing on his work with plant smut diseases. Early in his career, Linnaeus named a plant altered by anther-smut disease as a separate species, but then, probably realizing it was a diseased specimen, demoted it to a variety. He later drew direct parallels between minute insects attacking plants and infectious diseases in humans, but did not yet draw an analogy to smut diseases. After Otto von Münchhausen had sent Linnaeus the first instalment of his book Der Hausvater (1764) , Linnaeus realized smuts were contagious. He carried out his own investigations that appeared to confirm Münchhausen's conclusion that smut spores germinated to produce living and mobile animalcules. This cemented Linnaeus's view that animalcules caused contagion in human diseases, a view which he expressed forcefully, urging further studies. However, his results were questioned and discounted by others, especially John Ellis. An analysis of correspondence between Linnaeus and other microscopists shows that it is likely Linnaeus did actually see “animalcules” emerging from cereal grains. He was unaware that smut-like symptoms in wheat could also be caused by seed-gall nematodes in the genus Anguina. Linnaeus himself came to doubt the connection between fungi and contagion, and did not pursue these studies further. The presumption that Linnaeus was fanciful in his observations of animalcules may partly explain why his views had only a tangential impact on the germ-theory of disease, and why his insights remain unappreciated to this day.