Cigarette testing. Cigarettes being tested at a government laboratory to check that the nicotine and tar content shown on the packaging is correct. The cigarettes are held horizontally in tubes and air is drawn through them. The air will be analysed for its tar and nicotine content. Nicotine acts as a stimulant on the central nervous system and is the chemical which causes cigarette addiction. Tar is one of the numerous toxic by-products released by the burning of the cigarette.