Any idea why my int wont display on GUI

 using UnityEngine;
 using System.Collections;
 
 public class player_health : MonoBehaviour {
 
     public int health = 100;                // setup player health and default value
     
     
     // Update is called once per frame
     void FixedUpdate () {
         Debug.Log ("PLayer Health : " + health);        // display player health (for debugging)
         if (health==0)
         Application.LoadLevel("Death Screen");
     }
     
     
     
     public void Increase_Health (int amount)        // a function that takes an integer as a parameter and adds this amount from player health
     {
         health = health + amount;
     }
     
     
     
     public void Decrease_Health (int amount)     // a function that takes an integer as a parameter and subtracts this amount from player health
     {
         health = health - amount;  // This is the function that damage_player is using, giving damage to as 'amount'
     }
     
 
     void onGUI()
     {
         GUI.Label (new Rect (400, 25, 500, 125), string.Format("{0}", "Health =" + health));    //This displays the health value on the screen.
     }
 }

I am unsure why the int 'health' will not be displayed, I have tried many different methods of displaying it with OnGUI, none have worked, so there must be something I am missing, so I would appreciate a fresh pair of eyes to help me out finding my problem.