The animal expert came in.

Bacteria can be divided into beneficial bacteria and pathogenic bacteria. There are innate beneficial bacteria in the intestines of mice. Pathogens are mainly obtained in dirty environment. Of course, if the mother mouse has a pathogen, it can also be transmitted to the fetal mouse through the umbilical cord, and it is a pathogen from birth. If healthy mice are born, there will be no pathogenic bacteria in the body.

Experimental mice used in experiments are generally healthy, and experiments cannot be carried out without health. But healthy mice don't mean they have no germs in their bodies. Because bacteria need to reach a certain number in the body to cause disease.

The toxin of puffer fish is produced by its poison glands, but it can only be produced after the poison glands develop to a certain extent. The mechanism of producing poison glands is innate, which means that this mechanism can be passed down from generation to generation.