An antihistamine is a type of pharmaceutical drug that opposes the activity of histamine receptors in the body.Antihistamines are subclassified according to the histamine receptor that they act upon: the two largest classes of antihistamines are H1-antihistamines and H2-antihistamines.n H3-antihistamine is a classification of drugs used to inhibit the action of histamine at the H3 receptor. H 3 receptors are primarily found in the brain and are inhibitory autoreceptors located on histaminergic nerve terminals, which modulate the release of histamine.
U.S. Secret Service. U.S. Secret Service, federal law-enforcement agency within the United States Department of Homeland Security tasked with the criminal investigation of counterfeiting and other financial crimes. After the assassination of Pres.
President Lincoln created the Secret Service to investigate and prevent the practice of counterfeiting. Read this introduction to an informative essay about the Secret Service. Part of the executive branch, the Secret Service was created by President Abraham Lincoln in April 1865. At the time, it belonged to the Department of Treasury and protected US currency. Since then, the role of the Secret Service has grown and changed. Now part of the US Department of Homeland Security, the Secret Service protects government leaders as well as the nation's currency.