Here comes Pasteur's great work.

Before him Egyptian darkness; with his advent a light that brightens more and more as the years give us ever fuller knowledge.

The facts that fevers were catching, that epidemics spread, that infection could remain attached to articles of clothing, etc., all gave support to the view that the actual cause was something alive, a contagium vivum.
It was really a very old view, the germs of which may be found in the Fathers, but which was first clearly expressed--so far as I know--by Fracastorius, the Veronese physician, in the sixteenth century, who spoke of the seeds of contagion passing from one person to another;( 12) and he first drew a parallel between the processes of contagion and the fermentation of wine.

This was more than one hundred years before Kircher, Leeuwenhoek and others began to use the microscope and to see animalcula, etc., in water, and so give a basis for the "infinitely little" view of the nature of disease germs.

And it was a study of the processes of fermentation that led Pasteur to the sure ground on which we now stand.
(12) Varro, in De Re Rustica, Bk.