Toxicology may be defined as the science of poisons, their effects, antidotes, and detection. In the modern-day world with our constant exposure to foreign chemicals in the form of food additives, pesticides, fertilizers, cosmetics, therapeutic drugs, and air pollutants, it is important to have some knowledge of toxicology. Basic to the science of toxicology is the fact that chemical compounds vary in their hazard to man, domestic animals, and other living members of the environment. Thus, while practically all materials can be toxic under the proper conditions, there is a classification of materials of high toxicity and high hazard under normal conditions of use and encounter in small quantities which are called poisons. The final section of this book discusses the toxic qualities of a large number of commonly-encountered chemical materials. See also Section 1. In addition, the dosage or amount of the chemical required to produce harm is important. The numbers used to express the toxic level constitute the quantitative aspect of toxicology.