function on(pic)
{ m = document.images[pic] .src.lastIndexOf("O")
   document.images[pic] .src=document.images[pic].src.substr(0,m) + "On.gif"
}

function off(pic)
{ m = document.images[pic] .src.lastIndexOf("O")
   document.images[pic] .src=document.images[pic].src.substr(0,m) + "Off.gif"
}