function fill_products(form_name, pclass, selection) {
  document.forms[form_name].ID_Category.options.length = 0;
  if (product_categories[pclass].length != 0) {
    i = 0;
    arr_product_categories = product_categories[pclass];
    for (category in arr_product_categories) {
      document.forms[form_name].ID_Category.options[i] = new Option(arr_product_categories[category], category, false, false);
      if (category==selection) document.forms[form_name].ID_Category.options[i].selected = true;
      i++; 
    }
  }
}