These animal or digestive enzymes and fat decomposing substances originate, in-so-far as they are not of vegetable origin, for the most part in the upper portions of the digestive tract. The use of these substances effects an imitation of the purely enzymatic and fat decomposing processes that go on in the upper part of the intestines, but omits the processes--not less important for digestion and the formation of excrement--occurring in the large intestine and the adjoining portions of the digestive tract. Here the bacteria and the vegetable enzymes secreted thereby, play the chief part. They decompose not only the food constituents--partly by putrefaction--but also the albuminoid digestive secretions and the gall, so that only small quantities thereof are left. Hence when applied to the puering process, the use of bacteria, together with their specific enzymes and metabolic products, is equivalent to a restriction of the immoderate digestive action of the pancreatic and digestive juices, i.e. of the animal enzymes. Digestion therefore, with the resulting formation of excrement, is carried on with the accompaniment of a mutual control, excitation and restriction on the part of the digestive secretions and the bacterial phenomena. These latter form the real basis of the puering of hides in dung preparations. This is also evident from the purely practical experience that dog dung puer, e.g. for glove leather, is essentially improved by leaving the dung to ferment for several weeks or rather months. During this process an increase occurs in the micro-organisms present, and also in their metabolic products and enzymes, but not in the digestive juices originating in the organs of the animal body--the term “digestive juices” being restricted to indicate only such juices as are produced in the course of the digestive tract by the organs and cells of the animal body, in contradistinction to the juices produced by bacteria. According to the present invention, the bacterial cultures, together with their metabolic products or products of digestion and enzymes, are used in combination with one or more of the substances that are excreted in the digestive tract by the animal body itself in order that not only each of these substances may exert its special action on the skin, but also that the aforesaid mutual influencing, and more particularly regulating of the action may take place.