Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/108

 98 F E R F E R of a multiplicity of chemical reactions. A comparatively simple case is the putrefaction of urine, which substantially consists in this that the urea, by assimilating water, passes into carbonate of ammonia, just as it does when heated by itself with pure water to high temperatures. In the case of animal tissues, which, broadly speaking, may be said to consist of fats and albuminoids, the latter always give way first. Their decomposition is a most complex set of successive reactions, Icucine, tyrosine, fatty acids, and many other things appearing as primary products, ammonia, compound ammonias, sulphuretted hydrogen, hydrogen, and nitrogen as second ary ones. Less rapidly, but none the less constantly, the fats are changed, being decomposed, in the first instance, into fatty acids and glycerine, which latter undergoes further transmutations, while the former survive for a considerable time. The &quot;adipocere&quot; which is so well known as one of the constant ultimate products of the decay of dead bodies that have been kept from the air, and which consists of palmitateand stearate of lime (Hoppe-Seyler), well illustrates the high stability of fatty acids. Regarding the causes of putrefaction, we can scarcely do more than refer to what we have quoted from the researches of Schwann and his followers. From these researches two things are clear, namely, (1) that putrefaction is not pos sible under conditions precluding the development of life, or, in other words, that there is no putrefaction where there is not at least potential life ; and (2) that in 999 out of a thousand cases this potential life assumes the actual form of bacteria and vibriones. 1 Putrefactions going on in presence of air are always accompanied bj processes of oxidation, the effects of M 7 hich are difficult to dif ferentiate absolutely from those of putrefaction pure and simple. C. Cases of Oxidation. 1. Acetous Fermentation is the best known of these. Every body knows that weak fermented liquors, when exposed to the air, soon turn sour and ultimately become vinegar. The chemical re action involved consists of two stages. In the first the alcohol in the. liquor absorbs oxygen from the air, with formation of alde hyde and water, according to the equation C 2 H 6 + O = C a H 4 *- H 2 0. Alcohol. Aldehyde. AVater. This aldehyde, however, in ordinary acetous fermentation never actually appears, being at once oxidized by the direct action of the air into acetic acid, thus : C,H 4 + = C,H 4 2 Aldehyde. Acetic acid. These two reactions can be realized in all their chemical simpli city, not, it is true, by oxygen-gas pure and simple, but easily by oxygen as condensed on platinum-black ; and as the deoxi dized platinum-black readily reabsorbs oxygen from the air, a small quantity of this reagent suffices to oxidize large quantities of alcohol into acetic acid by means of atmospheric oxygen. Upon this observation of Dobereiner s Schiitzenbach based a rapid and practical method of vinegar-making, which consists in this, that the dilute alcohol is made to trickle through a tower of beech-wood shavings, packed into a tall barrel, constructed so as to draw in an ascending current of air. When a temperature of 20 C. is main tained in the room, and the spirit introduced having a temperature of 26, the temperature within the barrel is found to rise to 38-40 :&amp;gt; , the heat being produced by the rapid oxidation of the alcohol into acetic acid. What, in the old method of vinegar-making, required weeks or months is thus accomplished in a day or even less. It is difficult to avoid the conclusion that in Schutzenbach s process the wood-shavings, besides serving to spread the alcohol over an immense surface, act exactly as the platinum-black does in Dbber- einer s experiment, condensing oxygen in their pores in order to hand it over to the alcohol. And, supposing this theory to be correct, the old process, which consists in exposing the wine to the air in half-filled tubs or casks, would appear to rest on the same principle, the wood of the cask acting as the shavings do in Schutzenbach s process, only far more slowly. But then it is an old experience of vinegar-makers that the old process at least always involves the formation of two organized products, namely, that of a kind of mould which appears on the surface as a membrane, and goes by the name of &quot;flowers of vinegar, &quot;and that of a mucilaginous mass within the liquid, called &quot;mother of vinegar;&quot; and it has always been admitted that the presence of these substances ma terially accelerates the process of oxidation. This, however, is no contradiction to the theory ; it would only prove that the mould- membrane and the mucilaginous mass are more effective carriers of 1 Bacteria are microscopic organisms, composed of two elongated cells united end to end, possessed of varied powers of motion, and almost without exception &quot;rather in themselves reproductive organs &quot; (Lister) than beings possessed of powers of reproduction. The vibriones are seemingly nothing more than polymerized bacteria with intensified powers of locomotion. With regard to their position in the world of life present evidence leaves it uncertain whether they are plants or animals. oxygen than the wood of the tub. Besides, in Schutzenbach s pro cess, the shavings, according to experience, work the better the freer they are of from organized deposits. Hence, one might say, with Liebig, that the efficacy of these substances is a function only of their physical and chemical condition, the presence of life in the mould plant being purely accidental and immaterial to the process. According to Pasteur this view is a mistake. With him it is the membranous mould on the surface of the fermenting liquid which hands the oxygen to the alcohol, and it does so only when it consists of living specimens of a certain species of mould-plant which he calls Mycoderma accti. Other moulds or dead Mycoderma accti do not work. Mother of vinegar, according to Pasteur, is the &quot;non-aero- biotic &quot; form of the mycoderma. Only the aerobiotic form acts. To keep it alive we must take care that the liquid contains the phos phates and the albuminoids or ammonia, which it needs as food. But, if it is to produce vinegar, it must not be fed too liberally, because, when in a vigorous state of health, it oxidizes the alcohol into carbonic acid and water. If the oxidation is to stop at acetic acid, the mycoderma must be in a peculiar abnormal condition, which may be ensured by the presence in the liquid of a certain limit percentage of alcohol. In the case of Schutzenbach s process, Pasteur maintains (in spite of apparently contrary experience) that it is the very same Mycoderma accti which enables the wood shavings to act. One of his arguments is the acknowledged fact that Schiitzcn- bach s towers require to be started with ordinary vinegar, although they can be worked with distilled spirits. A more powerful argu ment he derives from the following experiment. A very sloAv current of dilute alcohol was caused to trickle down a long string suspended in a room kept at the most favourable temperature to acetous fermentation. The alcohol failed to assume an acid reaction. But the slightest coating of Mycoderma accti attached to the string caused it to act exactly as the shavings do in the Schiitzenbach casks. After all, however, it is a little difficult to believe that the many pounds of alcohol which, in the course of a day, pass through a Schiitzenbach tower and come out below as acetic acid, have all been under the direct influence of the few grains of Mycoderma accti which a microscopist might hunt tip amongst the Avood shavings. It appears far more rational to assume that the mycoderma acts only indirectly, perhaps by converting a small portion of the alcohol into aldehyde, which diffuses itself through the Avhole mass of the alcohol, and, through its inherent attraction for oxygen atoms, which is assisted by a similar tendency in the porous wood, reduces the stability in a far larger number of oxygen molecules than it needs itself, to such an extent that these so to say half-liberated oxygen atoms become available for the oxidation of alcohol, the more readily as the reaction itself involves a considerable liberation of energy. 2. Ercmacausis. Animal and vegetable matters, besides being liable to putrefy, are known, on exposure to air and water, to undergo a slow process of oxidation which ultimately converts them into products of simpler atomic constitution. Speaking quite generally, the process, in the case of wood and vegetable tissues generally, con sists in this, that the hydrogen is eliminated more and more eom- pletely : most of it in the form of water, a small portion in the form of marsh gas (CH 4 ), the rest of the carbon passing gradually into substances more and more closely allied to charcoal. In the case of albuminoids eremacausis is always preceded and accompanied by putrefaction, the most general effect of the former being that the ammonia produced by the latter is turned into nitrogen and water, or, in the presence of basic substances, such as lime, carbonate of lime, carbonates of alkalies, &c., is oxidized into nitrites and nitrates successively. This process of &quot;nitrification&quot; is going on in all porous soils and waters contaminated Avith nitrogenous organic matter, and, under favourable circumstances, progresses at a great rate. When sewage is filtered through a bed of porous soil, the drainage waters are generally found almost free from ammonia, the whole of the nitrogen having been oxidized into nitrites and nitrates. Accord ing to recent researches by Schlb sing and Miintz (which were con firmed by Warrington) nitrification, like acetous fermentation, is determined by the presence in the soil of organized ferments, the chief arguments being that a purely inorganic soil does not act, and secondly, that nitrification in a soil is stopped, or at least very effectually checked, by antiseptic vapours such as those of bisul phide of carbon, chloroform, and carbolic acid. ( W. D. ) FERMO, the ancient Firmum Picenum, an archiepisco- pal city of central Italy, and the chief town of a circle in the province of Ascoli Piceno, 34 miles S. by E. of Ancona. From its situation on a rocky height it commands a splen did prospect of the surrounding country, including a fine vieAV of the Adriatic Sea. It is surrounded by old walls, and besides the cathedral possesses numerous churches and convents, a university, and two fine collections of statuary and paintings. The ruins of the ancient Roman town, which was destroyed in the 5th century, are still to be seen.