Moulds and Putrefaction.—In view of the fact that moulds are of frequent occurrence on dog dung, a brief mention of them is necessary. So far as our present knowledge goes the researches of Van Tieghem, De Bary, Rankin, Marshall Ward, V. H. Blackman and others indicate that their action on the essential bating constituents of the dung is a destructive one. They grow usually on acid media, and in so doing break down the acids present into simple inorganic bodies, such as CO2 and water, utilizing the carbon and nitrogen for their own growth. Although these fungi secrete almost all varieties of enzymes (Bourquelot), yet we have no evidence that any of the enzymes contained in dog dung are from this source. In the usual case of dung preserved in pits or casks, the upper surface only becomes mouldy, since moulds require a free supply of oxygen. The mycelium penetrates but a very little way into the body of the dung, and cannot therefore effect any decomposition, except of the surface layer. The dung exposed to the action of the mould is generally a bad colour, and is rejected as unsuitable for puering.
The following species have been noted and classified as growing on dog dung, though probably not all of them are specific.
1. Pilaira dimidiata (Grove).
2. Mucor caninus (a variety of Mucor mucedo).
3. Circinella simplex (Van Tieghem).
4. Pilobolus crystallinus (also on cow-dung).
Certain myxobacteria are found on dung, among these Chondromyces, described as long ago as 1857 by Berkeley, and at that time included among the Hyphomycetes. It was rediscovered in 1892 by Thaxton, and owing to his researches the whole class of myxomycetes is now generally considered as a division of Bacteria. Another myxomycete, Polyangium primigenum (Quehl), forming a red fructification on dog dung, is figured in the Encyclopædia Britannica, XI. edition, vol. 3, p. 163.
The following abstract gives some account of putrefaction, and may be of use in conjunction with the account of the bacteriology of the bate which has been given. Since it was written Dr. G. Abt (see Bibliography [51]) has also given a very full description of putrefactive processes as affecting leather manufacture. The subject is still occupying the attention of a large number of bacteriologists, and we may expect more light to be thrown on the whole question during the next few years.
Abstract of Paper on Recent Advances in the Bacteriology of Putrefaction. Read before the Nottingham section of the Society of Chemical Industry, January 24, 1906.[91]
To those who have to do with the manufacture of leather, the changes which take place in the skin from the time it leaves the animal are of the utmost interest. The most important of these changes is the natural process of decomposition known as putrefaction.
Putrefaction may be defined as the decomposition of nitrogenous organic matter by living organisms, accompanied by the evolution of malodorous gases. The study of it may be divided into two parts—(1) the biological, (2) the chemical. The first concerns the organisms which break down the proteid molecule either directly or by means of enzymes; the second that of the different products of the action of these organisms. It is extremely difficult to separate these two studies.
Dr. Sims Woodhead ([59]) gives a concise account of the earliest researches on the organisms causing putrefaction by Leeuwenhoek (1692), Plenciz of Vienna, Müller of Copenhagen (1786), Needham (1749), Spallanzani (1769), Schwann (1837), Schroeder and Van Dusch (1854), Tyndall (1870), Lister (1878). These names show that the history of putrefaction proceeds parallel with the evolution of the microscope and the development of the comparatively recent science of bacteriology. I propose to-night briefly to carry it up to the present day.
I need scarcely say that putrefaction is not a specific fermentation like alcoholic or acetic fermentation, but that it is extremely complex. In any putrefying matter, such as gelatin or albumin, a large number of different species of bacteria may be observed as well as monads and infusoria, and in some cases moulds, all of which take part in the process. The first stage is a process of oxidation in the presence of air, in which ærobic bacteria use up the oxygen present and only simple inorganic compounds are formed, carbon dioxide, nitrates and sulphates; this part of the process is generally without odour. The second stage, or true putrefaction, takes place in the absence of oxygen by anærobic bacteria, and is a process of reduction. It has been shown that there are no bacteria in healthy tissues, and if a muscle or any organ is taken from an animal under antiseptic conditions it may be preserved indefinitely in a sterile vessel to which filtered air has free access. Solid matter is usually liquefied by organisms like B. liquefaciens magnus, which are invariably present in the air, and which prepare the way for more specifically putrefactive bacteria, such as Proteus vulgaris and B. putrificus, but if one observes a number of putrefactions of the same kind of matter under natural conditions, scarcely any two follow the same course. The modern study of putrefaction dates from Hauser ([58]), who, in 1885, isolated from putrefying flesh the three organisms—Proteus vulgaris, P. mirabilis, and P. zenkeri. He studied the action of these in pure cultures, and came to the following conclusions:—