1840

Jacob Henle, Koch’s teacher, publishes “ “Of miasmas and contagions and of miasmic-contagious diseases,” which propounded an idea of contagion far ahead of its time.  “Henle believed that disease was caused by seeds or germs, which were living animate beings.  These entered the system through mucous membranes, the alimentary canal, and broken skin.  Inside the body they increased rapidly, a fact verified by the period of incubation after exposure to the disease.  Henle thought the germs were probably plant parasites or fungi, of which different varieties produce different disease” (Allen, 501-02; P. Kazanjian, Intro). In late 1840s, textbooks by George B. Wood and Alfred Stillé, both of University of Pennsylvania, contained the animalcular hypothesis of disease, presenting it to readers as a possible explanation of disease (Allen, 509-10).  John K. Mitchell (also of Phila) propounded an influential animalcular theory that diseases were caused by fungi in 1849 (Cryptogamous Origins of Fevers) (511-12).