crtArt = new Array(24)
for(i = 1; i < 25; i++) {
    crtArt[i] = new Image()
        crtArt[i].src = "art/crt"+i+".gif"
 }

function imag_on(loc,img) {
    loc.src=crtArt[img].src;
 }

function imag_off(loc,img)  {
    loc.src=crtArt[img].src;
 }