Why are human experiments called Guinea Pigs?

Ever thought of that, when someone says hes treating you like a guinea pig..Where did that saying came from, I am sure you did. People who went into experiments, were usually people in need of money. So they would often be paid for their guinea pig attitude. They would receive one guinea, guinea was minted from West African Gold, more specifically the country of Guinea. But the pig part is an error. People mixed up the guinea pig who lived in Guyana(South America), they thought it lived in Guinea(Africa) so they named it after it.

On a another note, Guyana is the only country to be in the common wealth in the continent of South America. A beautiful country, with the northern parts of the tropical forest embedded in it.