Chapter II., but it will be seen from what has been said in the present

chapter that the chemistry and bacteriology of the puer overlap, and that it is difficult, if not impossible, to separate them entirely. The bacteria are continually manufacturing chemical compounds, and decomposing others.

In this respect it is interesting and instructive to note that Nencki, in his classical work “The Chemical Mechanism of Putrefaction,”[85] considers the processes by which the putrefaction of proteids is brought about by bacteria, to be analogous to those taking place by melting the bodies with potash, and he holds the view that in the hydration processes brought about by bacteria, the water plays the same part as the potash.

[85] Journ. f. Prakt. Chem., Bd. xvii., 1878; see also Stoklasa, Cent. Bl. f. Bakt. vi., p. 526.

---+-------------+--------------+---------------------+---------------- No.| Fermenting | Cause of | Fermentation | Authors. | Substance. |Fermentation. | Product. | ---+-------------+--------------+---------------------+---------------- 1 |Calcium |Bacteria from |_Calcium carbonate, |Hoppe-Seyler, |formate |sewer slime. |CO_{2} and H_ |Archiv f. d. g. | | | |Physiol. xii. | | | | 2 |Calcium | " " |_Calcium carbonate, | " " |acetate | |CO_{2} and CH_(4)_ | | | | | 3 |Calcium |Thin bacillus |1. _Propionic acid_, |Fitz, nine |lactate | |and, as by-products, |papers in |Undergoes | |_acetic acid_, |the “Berichte |four | |_succinic acid_ and |der Deutsch. |different | |_alcohol_. |Chem. |fermentations| | |Gesellschaft,” | |Other species |2. _Propionic acid_ |1876–1884. | |of bacteria: |and _valerianic | | |short aerobic,|acid_. | | |butyric | | | |bacteria |3. _Butyric acid_ and| | |(Fitz). |_propionic acid_. | | | | | | | |4. _Butyric acid_, | | | |according to Pasteur | | | |(Comptes rend. 1861) | | | | | 4 |Calcium |Bacteria |1. Chief product, |Schützenberger, |malate |(not |_propionic acid_; |“Fermentation,” | |described). |and, as by-product, |1876. | |Thin bacilli. |_acetic acid_. | | | | | | | |2. Chief product, | | | |_succinic acid_; | | | |and, as by-product, | | | |some _acetic acid_. | | | | | | | |3. _Butyric acid_ | | | |and _H_. | | | | | | |Bacteria |4. _Lactic acid_ | | | |and _CO_{2}_. | | | | | 5 |Calcium |Different |1. Chief product, | " " |tartrate |species of |_propionic acid_; | | |bacteria. |by-product, _acetic | | | |acid_. | | | | | | | |2. _Butyric acid_. | | | | | | | |3. Chief product, | | | |_calcium acetate_; | | | |by-products, _ethyl | | | |alcohol_, _butyric_ | | | |and _succinic acids_.| | | | | 6 |Calcium |Small, thin |_Acetic acid_ in |Fitz. |citrate |bacilli |large quantities, | | | |along with small | | | |quantities of _ethyl | | | |alcohol_ and | | | |_succinic acid_. | | | | | 7 |Calcium |Micrococci |1. _Calcium acetate_,| " " |glycerate | |along with small | | | |quantities of | | | |_succinic acid_ | | | |and _ethyl alcohol_. | | | | | | |Medium-sized |2. _Formic acid_, | | |bacilli |with some _methyl | | | |alcohol_ and _acetic | | | |acid_. | ---+-------------+--------------+-------------------+----------------

Nencki explains, for example, the metamorphosis of leucin by putrefaction in this way: The bacteria decompose the water into hydrogen and hydroxyl, which act upon the leucin as follows:--

CH_{3} \ OH CH - CH_{2} - CH - COOH + H = NH_{3} / | CH_{3} | Leucin NH_{2}

+ OH - CH_{2} (CH_{2})_{4} COOH (oxycaproic acid)

The resulting oxycaproic acid is then split up by the second water molecule into methylenglycol and valerianic acid:--

OH | CH_{2} OH | + H = CH_{2} (OH)_{2} + CH_{3} (CH_{2})_{3} COOH (CH_{2})_{4} | COOH

The methylenglycol, which changes into formaldehyde and water, is now split up into CO_{2} and hydrogen, as it would be by melting with caustic alkali.

OH H H.OH / C O + = CO + 2H_{2} H H.OH \ OH

As we shall see in the chapter on the action of enzymes, the phenomena are of a catalytic nature. Any urea present is decomposed, by the direct action of micrococcus ureæ, into ammonium carbonate and ammonium carbamate, so that it does not play any part in the bating process as usually carried out with dung which has been kept for some time, but the ammonia produced plays an important part in the chemical action of the bate, as we have already seen.

If, however, dung containing the urinary products be used in a fresh condition, the urea has indirectly a very important influence on the bating, as it favours the permeability of the skin fibre. (See p. 72.)

The fermentation of the cellulose in the dung has not been studied from the bating standpoint, but it is well known that it is fermented by various species of bacteria, which have been grouped together under the generic name of Amylobacter.

Deherain and Gayon first showed that the solution and fermentation of cellulose in the form of dead vegetable matter, which had previously been observed, also took place in dung. Van Tieghem, in 1879, showed that the solution of cellulose is caused by bacteria, whose properties correspond with those described by him as Amylobacter. Tappeiner was able to ferment cellulose by mixed cultures of bacteria from the intestines of oxen--in neutral solution, CO_{2}, methane, H_{2}S, aldehyde, butyric acid, and acetic acid, were all recognized. In alkaline solutions, the principal products were CO_{2} and hydrogen, together with the same by-products as before.

From the researches of Van Sennis, in 1890, it seems pretty certain that the fermentation of cellulose is due to the symbiotic action of at least two different organisms The decomposition of the cellulose may be explained by considering that first a sugar-like carbohydrate is formed by hydrolysis, and that this is then split up into equal volumes of CO_{2} and CH_{4}. It may be noted that the fermentation is anaerobic, and no doubt, so far as bating is concerned, the chief products are the organic acids produced, principally butyric and acetic acids. Van Sennis nearly always found Clostridium butyricum associated with this fermentation.[86]

[86] Proc. Roy. Soc., lxvii., 1900.

Another group of organisms which have some influence in the bating process, are the class called by Beijerinck, Granulobacter. They produce butyric acid, and this acid, combining with the ammonia compounds of the dung, forms salts which undoubtedly exert an effect on the lime in the skins, though its action on the fibre is, perhaps, not so great as the compounds of lactic and propionic acids.

The most common butyric ferment is the old Clostridium butyricum, now known as B. butyricus, (Prazmowsky), which is anaerobic. It forms spindle-shaped spores, hence the name Clostridium (from _κλωστηρ_κλωστηρ, a spindle). Another species (Fig. 23), found in milk by Hueppe (1884), is aerobic, and ferments lactic acid and its salts to butyric acid, CO_{2}, and hydrogen; it appears to correspond with Granulobacter polymyxa of Beijerinck.

Oxalic acid is known to be produced by some bacteria and the moulds Penicillium and Sclerotinia, and in the white rot of the turnip it is produced by Pseudomonas; it is also produced by some saccharomycetes, such as B. Hansenii.[87] There is reason to believe that its production plays a part in the bate, as we have already mentioned in