Read the text and answer the question!

    Although science has made enormous steps in making food more fit to eat, it has, at the same time, made many foods unfit to eat. Some research has shown that perhaps eighty percent of all human illnesses are related to diet and forty percent of cancer is related to the diet as well, especially cancer of the colon. People of different cultures are more prone to contract certain illnesses because of the characteristic foods they consume.

    That food is related to illness is not a new discovery. In 1945, government researches realized that nitrates and nitrites (commonly used to preserve color in meats) as well as other food additives caused cancer. Yet, these carcinogenic additives remain in our food, and it becomes more difficult all the time to know which ingredients on the packaging labels of processed food are helpful or harmful.

    The additives that we eat are not all so direct. Farmers often give penicillin to cattle and poultry, and 10 because of this, penicillin has been found in the milk of treated cows. Sometimes similar drugs are administered to animals not for medicinal purposes, but for financial reasons. The farmers are simply trying to fatten the animals in order to obtain a higher price on the market. Although the Food and Drug Administration has tried repeatedly to control these procedures, the practices continue.

    A healthy diet is directly related to good health. Often we are unaware of detrimental substances we 15 ingest. Sometimes well-meaning farmers or others who do not realize the consequences add these substances to food without our knowledge.

Based on the passage, penicillin is used for ....