Ingredients not generally available may be found at health food stores. Dissolve yeast in 1/4 c warm water. Add chicken stock and pour into dry ingredients. Knead for 3 minutes, working into a stiff dough. Roll dough into a 1/4 in. thick sheet and cut with cookie cutters (cutters shaped like dog biscuits are available). Bake in 300 degree oven for 45 minutes, then turn oven off and leave biscuits in oven overnight. In the morning the biscuits will be bone hard.Note: This dough is extremely stiff to work with, but the end product is excellent. From the Chester County, PA ASPCA