The examination of the dog, pigeon and poultry dung in bacteriological respect, and of the industrial applicability of all the different results obtained, shows in the first instance that, even after removal of all other ingredients, which, according to the hitherto ruling views, enter into reaction, the result of the treatment remains the same as it had been before the removal. The continued research led to the second result that a great number of micro-organisms play a role in the lye, partially an advantageous, and partially a detrimental one. Generally speaking, the non-peptonizing bacteria act advantageously, while the peptonizing ones generally have a detrimental effect. In connexion herewith two methods of utilizing these discoveries have been found. One can either, according to the methods of bacteriology (plate process), remove all the detrimental or even the less useful bacteria, and effect the treatment of the hide or skins by applying a pure culture of one or at least a mixture of the different most effective bacteria; or one can, without employing such a refined process, but still utilizing the said discoveries, apply the dog dung, and in particular the white descriptions which are most effective, or, for certain kinds of leather, the pigeon or poultry dung, subjecting the said dungs to a certain treatment, which, by the use of a suitable cultivating bed, will develop the useful bacteria, while on the other hand, the increase of detrimental bacteria may be prevented or retarded by the addition of materials hindering the development of the latter. In every case the employment of the process secures greater rapidity of execution, and more reliable and better results than the process heretofore applied. The leathers obtained are tough and yet softer, and in any case any discolouring, such as is often unavoidable with dog dung, is avoided. An advantage not to be underrated with the use of germ cultures, is that liquors or cakes having a definite percentage of really effective substance can be prepared, whereas it was heretofore necessary to proceed by way of trials, the result being subject to great uncertainty. In addition, the dung liquors are subject to changes overnight under the influence of atmospheric changes (thunder-storms) in a most unaccountable manner, owing, as has now been discovered by my correspondents, to the growth of detrimental bacteria which are mixed with the effective ones, and which gain the upper hand over the latter under the change of atmospheric conditions. The features of the newly discovered useful bacteria are fully described in the following, and experiments have shown that the particular kinds designed with 3, 7 and 12 in the table of bacteria, set forth in the Specification to German Patent No. 86,335 and hereinafter fully described, are those which are of value for the purpose in question; in particular No. 12 is the most effective, and 3 the least effective of these three descriptions.