Ethyl alcohol is a Central Nervous System Depressant, and as such it deadens nerve endings, and even in small concentrations alcohol reduces inhibitions and can impact the delicate systems of the brain. As blood alcohol concentration increases, a person's response to stimuli slows and becomes less precise, speech becomes slurred, motor skills are adversely affected, the person becomes unsteady and has trouble walking. When the blood alcohol concentration (BAC) is extremely high (0.35 or more) - a person can become comatose and die. However, none of this will occur until the ethanol reaches the central nervous system - the brain, brain stem and spinal cord – and ethanol gets to the brain via the blood. Therefore, the important piece of information is the quantity of ethanol in the brain – and since ethanol gets to the brain via the blood, for DUI / DWI enforcement we seek to measure the amount of alcohol in a person’s blood.