Final answer:
Emetics are used to induce vomiting in poisoned patients who have ingested egg whites or milk to prevent absorption of toxic heavy metals throughout the digestive system. Egg whites and milk can form complexes with these metals, immobilizing them temporarily, and vomiting helps to expel these potentially harmful complexes beforehand.
Step-by-step explanation:
Poisoned patients might be advised to use emetics after ingesting substances like egg whites or milk due to their potential interaction with toxic compounds. For instance, certain heavy metal ions like Pb²⁺ and Hg²⁺ can form harmful complexes within the body, particularly through reactions with -SH groups to form salt bridges. Egg whites or milk can act as antidotes in cases of heavy metal poisoning because they contain proteins that can bind with the metal ions, effectively precipitating them within the stomach.
Inducing vomiting through the use of emetics is done to prevent the toxic metal complexes from being absorbed further down the digestive tract where they could cause more harm. This is especially important as the precipitates could dissolve later in the digestive system, releasing the potentially toxic metals again. The concept of proteins binding to heavy metals relies on the reaction mechanisms similar to those that underlie the denaturing and coagulating of proteins by organic solvents like alcohol.