if (document.images) {
var a_off = new Image();
a_off.src = "../_i/structure/a_off.png";
var a_on = new Image();
a_on.src = "../_i/structure/a_on.png";
var b_off = new Image();
b_off.src = "../_i/structure/b_off.png";
var b_on = new Image();
b_on.src = "../_i/structure/b_on.png";
var c_off = new Image();
c_off.src = "../_i/structure/c_off.png";
var c_on = new Image();
c_on.src = "../_i/structure/c_on.png";
var d_off = new Image();
d_off.src = "../_i/structure/d_off.png";
var d_on = new Image();
d_on.src = "../_i/structure/d_on.png";
var spe_off = new Image();
spe_off.src = "../_i/structure/spe_off.png";
var spe_on = new Image();
spe_on.src = "../_i/structure/spe_on.png";
}

function act(imgName) {
  if (document.images) 
    document[imgName].src = eval(imgName + "_on.src");
}

function inact(imgName) {
  if (document.images)
    document[imgName].src = eval(imgName + "_off.src");
}