Microorganisms、too embarrassed to ask others about！（Part 5）

6. where are the microorganisms?

Microorganisms are everywhere, unless the environment is controlled. There are microbes in the air, in the water, in the sea, in the soil, on the deep-sea floor, in the stratosphere, in desert sand, and of course in our bodies. We are surrounded by microorganisms. The only places in nature where microorganisms do not exist are in very limited environments, such as in fire or in the lava of a crater.

There are over 100 trillion microorganisms in our bodies. Most of them are found on our skin, in our oral cavity, and in our digestive tract. Human skin is said to contain tens of thousands of microorganisms per square kilogram. A gram of stool contains 10 to 100 billion intestinal bacteria.

The number of cells that make up the human body is said to be about 37 trillion, which means that we live with about three times as many microorganisms as the number of cells that make up the human body. Most of them live in symbiotic relationships with humans and usually do not cause any harm to the body.

However, if we look at the situation from a slightly different perspective, we can see the exact opposite.

It is true that we are surrounded by microorganisms. But in fact, our bodies are nearly sterile. The surface of our body is covered with skin and mucous membrane. There are many microorganisms on the skin and mucous membranes. The digestive tract is also home to a large number of microorganisms. What about the blood? What about the muscles and brain? In a healthy person, there are no microorganisms in them. In other words, they are sterile. In this way, the inside of the skin and mucous membranes is virtually sterile.

From a more macroscopic perspective, the fact that life exists only in a very small area on the Earth's surface and beyond raises the question, "Is there life in the universe outside of the Earth? And, moreover, is there life in the universe other than on Earth?  In this way, it is rather normal for life to be sterile, and the existence of life, including microorganisms, may be more special.