What is the missing number?

Little Johnny watched the science teacher start the experiment with the worms. Four worms were placed into four separate jars.
The first worm was put into a jar of alcohol
The second worm was put into a jar of cigarette smoke.
The third worm was put into a jar of sperm.
The fourth worm was put into a jar of soil.
After one day, these were the results:
The first worm in alcohol - dead.
Second worm in cigarette smoke - dead.
Third worm in sperm - dead.
Fourth worm in soil - alive.
So the Science teacher asked the class - "What can you learn from this experiment."
Little Johnny quickly raised his hand and said - "As long as you drink, smoke and have sex, you won't have worms."