If they decide to change to suite their <span>
environment </span> or not.
Interferon's are the answer.
Interferon's are a group of proteins produced by virus infected cells that help other cells resist viral infection. <span />
The Nervous System is the power source of your body. Using electrical impulses, your nervous system helps control your muscle movements. The two main functions are the Sensory(afferent) division- which brings information to your brain. Then your Motor(efferent) division- which sends signals out.
A leech is an example of a parasite
