[by Dean Smith] Bacteria wasn’t discovered until 1676, when using a single-lens microscope he had built, Anton van Leeuwenhoek saw the world of microscopic creatures.
At the time, some wondered if these invisible creatures could be responsible for disease transmission. This theory was not fully developed until Italian Agostino Bassi conducted a series of tests between 1808 and 1813 that showed these invisible creatures or bacteria were directly responsible for disease.
However, centuries earlier when you look at the Old Testament we see an understanding of Leeuwenhoek’s discovery in practice through clean and unclean.
There were a number of rituals involved due to contamination caused by contact with unclean objects. These could range from isolation when a person touched a dead body to washings for lesser forms of uncleanness.
An object could be made unclean by contact with a carcass of any kind and as well unclean animals such as rats, mice or even carrion eating creatures such as vultures. Because of this, the Jews were keen on ridding their property of vermin such as rats which were responsible for the bubonic plague during the middle ages.
In Leviticus 11, we have an interesting discussion on uncleanness. If any object, clothing or wood, came in contact with something unclean, it could be cleansed by washing it with water (verses 24-28). After that happened, the uncleanness washed off the object and into the water making it unsuitable for drinking. The water was declared unclean and thrown out.
Unclean pots treated differently
This applied to all objects except earthenware or clay pots (v 33). If a pot became unclean because of contact with an unclean animal or carcass, i.e. a mouse got into it, the pot had to be broken. It could not be cleansed by water.
At that time, clay pots were porous and bacteria could easily seep into the clay and water would not be able to wash it out. Since pots were used to store food or drink, they could potentially contaminate anything put in them later. But the Israelis would not have known that, they were just obeying the law.
An interesting exemption for grain
Now if grain came in contact with something unclean, such as rats (v 29), it could be cleansed by washing it with water making the grain suitable for consumption. When that happened the Bible specifically notes again that the water is “unclean to you” (vss 37-38) — meaning they couldn’t drink it.
But then we notice an interesting exception. If rats got into grain that was to be used for planting instead of consumption, then it was safe for planting (v 37).
So the grains’ usage determined if it was unclean or dangerous to humans.
For the Jews, the law provided a basic understanding of bacteria and disease transmission without Israelis even being aware of their existence.
Some might call The Law, Divine revelation.