The immune system is a remarkably adaptive defence system that has evolved in vertebrates to protect them from invading pathogenic microorganisms and cancer. Immunology is the science that studies the immune system, how it works, and the way in which we can stimulate the system to protect against disease. Virology Virology is the study of viruses. Viruses are unable to multiply unless they are within a living cell, as they do not possess any of the machinery necessary for multiplication. Viruses are infectious agents so small that they can only be seen at magnifications provided by the electron microscope.
Viruses are incapable of independent growth.
They can only grow in animal or plant cells, or in microorganisms. They reproduce in these cells via a process in which many copies of the virus are made and then released from the cell.