Joseph Turney Wood

“ The list of enzymes grows longer almost daily, as some new one is separated having a specific action, until one is almost led to believe that the mechanism of life itself, as manifested in the cell, is due to enzymes.
It has been found that enzymes act very much in the same way as inorganic catalysers. As an example, the velocity of the reaction of invertase (the enzyme of yeast which hydrolyses cane sugar to grape sugar) has been compared with the same hydrolysis brought about by heating a solution of cane sugar with a mineral acid. ”

“ The only way to save the skins from destruction is to add salt to the drench; this reduces the swelling and, in fact, pickles the skin. I have pointed out elsewhere that this is really the origin of the modern pickling process, which is still known by the name of “rising.” A very acid drench will swell the skins almost the same as dilute sulphuric acid, and if they are then placed in a salt solution, or salt is added to the sour liquor, it is absorbed by the skins, and they are preserved almost as effectually as by the use of mineral acids. ”

“ I have now discovered that the bating action of a dung bate is due to the combined action of enzymes, or unorganized ferments, and certain chemical compounds, which compounds consist principally of amines—i.e. ammonia in which one or more atoms of hydrogen has or have been replaced by alcohol radicles—in combination with organic acids usually found in dung, and of the compounds so formed the lactates and acetates are the most important. ”

“ Just as in the spontaneous souring of milk numerous bacteria have free access to it, yet the lactic ferment is generally so pure that it may be, and is, used as a pure culture on a large scale in the manufacture of lactic acid.
Coming to the action of the bacteria on the skin fibres, from the work of Abt and Stiasny,88 we may conclude that the substance of the conjunctive fibres is less profoundly decomposed by bacterial fermentation than by the action of lime. The latter dissolves about 2 per cent. of skin substance from a fresh skin, whereas a puer acting normally dissolves about 1 per cent. ”

“ The intensity of the osmotic action of puer upon skin must depend upon the quantity of substances contained in it, to which skin substance acts as an impermeable membrane, and which on that account induces an osmotic pressure between the outer puer solution and the solutions held in the skin fibre. The effect of puering does not necessarily imply the actual expulsion of water from the skin—in fact, well puered skin may quite possibly contain as much water as it did in the swelled condition. ”

“ A well-puered sheep-skin, on the other hand, shows no resilience at all, i.e. on releasing the pressure the whole of the compression persists. In the case of an ox-hide subjected to a bate of hen-dung, a slight recovery takes place on releasing the pressure. This accords with the fact that it will never be possible to puer a thick ox-hide so effectively as a thin sheep-skin. A piece of india-rubber, on the other hand, is completely resilient, i.e. it wholly recovers its thickness on releasing the pressure. ”

“ So far as is at present known the unorganised ferments in the dung, besides those which are secreted by the bacteria, are mostly digestive ferments114 —pepsin, pancreatin, and trypsin—certain quantities of which pass out of the animal’s body in an unchanged condition. Of these, pepsin only acts in an acid solution, and, although fresh bate liquor is faintly acid to litmus, it quickly becomes neutralised by the lime in the skins, so that the action of this ferment can only be limited in extent. ”

“ 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. ”

“ From observations extending over several years it is evident that a similar cycle occurs in dog dung. When quite fresh it contains comparatively few bacteria; then certain groups of species take possession, causing decompositions in the dung; these in their turn give place to other species, which decompose the products formed by the first, so that no one species produces or can produce the complex chemical and physiological changes which take place, or the bodies necessary for the bating of skin, as has been supposed by some observers. ”

“ I have isolated in plate cultivations several species which liquefy the gelatin.
If skins are allowed to lie in the bate, zoogloæ of these bacteria collect in the folds and attack the fine “grain,” so that the leather is covered with lines and markings, or “flaked.” Thus the operation is a very critical one, requiring careful watching; under certain atmospheric conditions and at a temperature of 35°–40° C. the skin, if only left a short time too long, will completely melt away. The more skin substance is dissolved in the liquid, the more rapid and pronounced the bacterial action becomes. ”

“ I have shown128 that simple cultures of bacteria in certain nutrient media, in the absence of amines and other bodies, have an imperfect bating action on skin. This was the case, whether the cultures were pure or mixed, but the mixed cultures have a better action than the pure cultures of any of the organisms I have hitherto used. Bacteriological processes in nature are usually carried on by a mixture of species of bacteria ”

“ 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. ”

“ These are examples of what I may call the selective influence of the nutrient medium. The nutrient medium used in my former experiments was a solution of gelatin and mineral salts, such as is used in general bacteriological work, modified in various ways. On careful consideration, this did not appear to be a medium at all corresponding to the natural bate. The albuminoids in the process of digestion are peptonised, and dung contains only those bodies which the animal is incapable of assimilating. It is from these bodies that the necessary enzymes are produced by bacteria. ”

“ Experiments in the laboratory and in practice have shown that it is not the dissolving action on the skin substance in the narrow sense which is desired in bating the derm with dogs’ dung, but in order to prepare the hide for the manufacture of a soft and elastic leather, the albuminous intercellular substances and more particularly the layers of fat lying at the roots of the hair, in the corium and in many cases also on the epidermis, must be dissolved and thereby the fibrils of the skin loosened. ”

“ Lipase was one of the first enzymes in which the reversibility of the reaction was shown, i.e. it is not only capable of hydrolysing a fat, but also of causing the formation of one by the combination of the fatty acid and glycerin.107 This explains why the reaction of such an enzyme is never complete. An equilibrium is reached just as with ordinary reversible chemical reactions like the precipitation of magnesium hydroxide by ammonia. ”

“ Efforts have been made for years to replace dogs’ excrement used in many cases in tanning as a bate, by other simpler products and methods which in particular shall have the advantage of greater uniformity and thereby act with greater certainty.
Now it has been ascertained that substances which are only solvents of lime, such as acids of inorganic or organic nature and their salts, form an incomplete substitute. It has been shown by Eitner, Wood and others that there are enzymes and bacteria to which dogs’ dung owes its specific or bating properties. ”

“ The fibres, in-so-far as they are accessible at all to the action of the colloidal enzymes, are removed from outside without the fibrils being loosened and straightened. Hence they are weakened by the digestive puer to such an extent that the hides seem to be gradually pulled down; but the skin will by that time have lost too much substance, so that, inter alia, even the grain appears to have been corroded. In this way the leather is rendered thinner and lighter than that from the dung or bacterial puer—a defect manifest to every expert. ”

“ Popp and Becker have also pointed out that peptonising bacteria do not exert a favourable reducing action on skin. It is impracticable to grow these non-peptonising organisms on a large scale in a solid medium, and it occurred to me that gelatin, previously peptonised by chemical means, would be a favourable medium. Experiments with hydrochloric and sulphuric acids gave hopeful results. The acid was neutralised with ammonia after the chemical action was complete, and the bacteria cultivated in this solution. ”

“ The action, therefore, of the acids is a reducing one, inasmuch as skin is dissolved, but as the fibres hold a certain amount of acid, the skin appears to be plumped. Where the acid is a mineral one the skin tans plump, but with a brittle and inelastic fibre, weak organic acids make a plump, soft leather with a moderately elastic fibre, giving to the skin a somewhat india-rubber feel. We thus see that weak acids alone do not produce a similar result to a dung bate, which causes the skin to fall and produces a flat soft leather with a stretch in it, which will not spring back. ”

“ For many years Metchnikoff, in Paris, has been studying the bacterial flora of the human intestines. His theory is, that old age is caused by the poisonous products of these intestinal bacteria, and he proposes to counteract the effects of these poisonous organisms, by introducing into the system large quantities of lactic acid bacteria, either in the form of tabloids, or in the form of sour milk cultures.
78 For the demonstration of flagellæ, the material is taken from a culture on solid media—a young agar culture is best. ”

“ An important role in the process of manufacture of many kinds of leather is played by the dung liquor or lye, which in particular for calf skins and skivers constitutes one of the necessary preparatory operations for the subsequent actual tanning process, and which has for its purpose to bring the skins or hides, which have been previously swelled by the liming process, into a condition which allows the easy and thorough removal of the lime and lime soap as well as the remaining hairs by the subsequent mechanical treatment, and to obtain a uniform shrinking of the swelled hides. ”

“ The acids neutralize any lime which has not been neutralized in the bate, and they do this in a very gradual and mild way, being produced by bacterial fermentation exactly as required, in a similar manner to fermentations taking place in presence of calcium carbonate. The gases evolved bring the skins to the surface of the drench, and distend the fibres; the workman attending to the drenches puts the skins down under the liquor with a pole, but a better way is to have the drench vat fitted with a wooden paddle, which may be pulled round by hand when necessary ”

“ In actual working we found from 1·07 to 2·34 grm. total acids per 1000 c.c., while in artificial cultures, with addition of calcium carbonate, inoculated with pure cultures of bacteria, obtained from drenches, we obtained from 4·53 to 11·44 grm. total acids per 1000 c.c. Now traces of lime in the skins act in just the same way as the calcium carbonate; they neutralize a portion of the acid produced by the bacteria, and so allow a greater amount of acid to be produced than if it accumulated in the liquid. ”

“ In the putrefaction of vegetable matter the cellulose is attacked by specific organisms, which have been thoroughly investigated by Omeliansky (75) . He has shown that the fermentation of cellulose is an anærobic process, caused by two species of bacteria belonging to the class of butyric ferments. Morphologically the organisms closely resemble one another, but one of them decomposes the cellulose with evolution of hydrogen, the other with evolution of methane; in both cases considerable amounts of acetic acid and normal butyric acid are produced. ”

“ If, for instance, specially hard goat skins are to be pulled down strongly by puering, it is advisable to add to the nutrient medium of the bacteria a little papayotin or papain, either—according as rendered necessary by the local conditions—in the preparation of the bacterial puering liquor, or during the propagation of the bacteria. If the fells are less hard so that less pulling down is required, the hides are first treated with a weak solution of the digestive ferments, and then with the bacterial liquor. ”