Which kind of tumor grows slowly and is surrounded by membranes that prevent it from spreading from the original site?

The answer is benign tumor.

A tumor is abnormal growth of the cells and it could be a benign or a malignant tumor. The benign tumor is non-cancerous growth in the body. It must be distinguished from the malignant tumor. They are surrounded by membranes and cannot spread to the other parts of the body unlike the malignant tumor which has ability to spread through the body (to metastasize). 

Telling them to either contract or relax