We live on earth in different types of surroundings. This surrounding is our environment. We eat, breathe, clothe ourselves, reproduce and then die. The next generation comes and the cycle goes on; and the human race flourishes on earth. The physical environment on the earth provides favorable conditions for the existence and growth of different life forms, including man. These living beings constitute the biological environment. Both the physical and biological environments are in a close interaction with each other and form a stable self perpetuating system. In prehistoric days man lived in harmony with nature but in the course of his evolution man has developed a new type of environment, the man-made environment.