A toxic substance shows its harmful effect by entering a reaction with the living organism; this effect is called
. As a result of toxication, some symptoms appear in the biological system such as convulsion, tremor, nausea and aches in several parts of the body. Also, some breakdowns at the macromolecular level occur, which can lead to liver degenerations, leukemia, methemoglobinemia, etc. In toxication, a toxic substance passes through the following phases in showing its toxic effects (Figure 3.1).