Body system that fights disease. Crossword

The study of how and why diseases occur.
The process or act of imitation or acting out.
To imitate how something happens in a real-world situation by acting it out using a model.
A person who begins the spread of disease in a group.
A disease that spreads very readily from person to person.
A disease that cannot be passed on by the person who is sick to other people.
The thing you change in an experiment.
What you're trying to measure in an experiment
The thing that stays the same in an experiment. They keep the experiment fair.
The study of microorganisms.
Wiped out.
A type of medicine that kills microbes or prevents them from growing.
The most common form of one-celled organisms.
A substance that protects a person from a disease; from the Latin vacca, for cow.
Body system that fights disease.