An argument for a mathematics program that is more compatible with the nature of the learner is therefore an argument for a greater degree of involvement with manipulative materials and exploitation of appropriate mathematical applications.
The Germ theory of disease, developed in the 1860s and 1870s by Louis Pasteur, states that tiny living beings are the cause of infectious diseases. The theory was developed to explain puerperal fever, or Child bed fever.
Prior to germ theory, it was widely believed that disease was spread by noxious odors. As disease-spreading conditions-rotting meat, open sewage, and such things-was often highly odorous, the smell and disease were associated.