Alcohol is an anesthetic, just as all the old western movies show. By modern standards, it is not a very good one: the dose required to produce anesthesia is very close to the lethal amount. When the vital centers have been depressed enough by alcohol to produce unconsciousness, it only takes a wee bit more to put someone permanently to sleep. Sadly, a couple of times a year almost any newspaper obituary column documents a death from alcohol. Usually it involves chugging a fifth of liquor on a dare, or as a prank, which very quickly yields a lethal dose of alcohol.

Despite biological differences between people, each and every human body reacts to alcohol in basically the same way, al amount or concentration dissolved in the blood. Exactly the same thing happens with alcohol. The breathalyzer measures the concentration of alcohol in the exhaled air; from this the exact concentration of alcohol in the blood can be determined.

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