CONSIDER THE ENVIRONMENTAL FACTORS. - Keeping a clean environment, of course,  is extremely important. Toxic working and home environments should be avoided. The use of anything toxic  in the house, garden and work place  such as fly sprays, herbicides, fungicides and other chemicals should  never be used. Many things which people use about the house and garden are used in good faith that they won't hurt the user. Rat poison  is a good example. This is extremely toxic and contaminates the area in which it is laid even if it is not physically spread about. But rats and mice will spread ...