How to cause damage on collision?

I want it so that when my character walks into a certain object he loses health. Right now when he walks into the object the debug log says hit player, but no health is taken away. Need help fast please.
This is the script.

#pragma strict
public var damage = 10;
public var health = 100;
var healthnow;

function Start () {

}

function Update () {



}
function OnCollisionEnter (cool : Collider) {
if (cool.gameObject.name == "AttackThreshhold") {
		health = health - damage;
		Debug.Log("Hit player");
		
		
}
if (health < 0) {
Application.LoadLevel("Close");
}
}

function OnGUI () {
	if (GUI.Button (Rect (10,10,150,100), "Your Health is " + health)) {
		
	}
}

Yep so like your message says, OnCollisionEnter has to have an argument of type Collision: Unity - Scripting API: Collider.OnCollisionEnter(Collision)

That collision contains the collider object you need