if (document.images){
	previous_off=new Image
	previous_on=new Image
	next_off=new Image
	next_on=new Image
	home_off=new Image
	home_on=new Image
	introduction_off=new Image
	introduction_on=new Image
	themes_off=new Image
	themes_on=new Image
	tour_off=new Image
	tour_on=new Image
	checklist_off=new Image
	checklist_on=new Image
	colophon_off=new Image
	colophon_on=new Image
	returnarrow_off=new Image
	returnarrow_on=new Image
		
	previous_off.src="images/previous_off.gif"
	previous_on.src="images/previous_on.gif"
	next_off.src="images/next_off.gif"
	next_on.src="images/next_on.gif"
	home_off.src="images/home_off.gif"
	home_on.src="images/home_on.gif"
	introduction_off.src="images/introduction_off.gif"
	introduction_on.src="images/introduction_on.gif"
	themes_off.src="images/themes_off.gif"
	themes_on.src="images/themes_on.gif"
	tour_off.src="images/tour_off.gif"
	tour_on.src="images/tour_on.gif"
	checklist_off.src="images/checklist_off.gif"
	checklist_on.src="images/checklist_on.gif"
	colophon_off.src="images/colophon_off.gif"
	colophon_on.src="images/colophon_on.gif"
	returnarrow_off.src="images/returnarrow_off.gif"
	returnarrow_on.src="images/returnarrow_on.gif"
	
}

function chgImg(imgField,newImg){
	if (document.images){
		document[imgField].src=eval(newImg+".src")
	}
	
}