Bring the vinegar, water and sugar to boil in a 1 to 1- half quart enameled or stainless-steed saucepan, stirring constantly until the sugar completely dissolves. Then remove the pan from the heat and let the pickling liquid cool to room temperature. Meanwhile, wash the herring in cold running water and cut them into 3 cm thick pices. Arrange a thin layer of onions in a 1 litre glass jar (a Mason jar, if possible) equipped with a tightly fitting cover. Top with a few slices of herring, carrots, giner root and horse-radish and scatter with allspice, mustard seeds and bay leaf. Repeat until all of the ingredients have been used, making 3 or 4 layers. Pour the cool pickling liquid into the jar; it should just cover the contents. Close the jar securely and refrigerate it for 2 or 3 days. Serve as an appetizer or as part of the sm�rg�sbord.