Vegetable corruption invariably presupposes fermentation.
Fermentation is a state of vegetable matter, the component parts of which have acquired sufficient force to produce an intestinal motion, by which the earthy saline, the oily and aqueous particles therein contained, exert their several peculiar attractive and repulsive powers, forming new combinations, which at first change, and at length altogether destroy the texture of the substance they formerly composed.
There are two things essential towards creating and supporting the intestinal motion, namely, heat and humidity; for without heat, the air, which is supposed to be the cohesive principle of all bodies, cannot be so rarefied as to resume its elasticity; and without humidity there can be no intestinal motion.
According to Baron Liebig, the decay of wood takes place in the three following modes:—First, oxygen in the atmosphere combines with the hydrogen in the fibre, and the oxygen unites with the portion of carbon of the fibre, and evaporates as carbonic acid: this process is called decomposition. Second, we have to notice the actual decay of wood which takes place when it is brought in contact with rotting substances; and the third process is called putrefaction. This is stated by Liebig to arise from the inner decomposition of the wood in itself: it loses its carbon, forms carbonic acid gas, and the fibre, under the influence of the latter, is changed into white dust.
The fungus occasioning the dry rot is of various appearances, which differ according to the situation in which it exists. In the earth, it is fibrous and perfectly white, ramifying in the form of roots; passing through substances from the external surface, it somewhat differs from that form; here it separates into innumerable small branches.
Mr. McWilliam observes, “If the fungi proceed from the slime in the fissures of the earth, they are generally very ramous, having round fibres shooting in every direction. If they arise from the roots of trees, their first appearance is something like hoar frost; but they soon assume the mushroom shape.”
Hence it appears that we frequently build on spots of ground which contain the fundamental principle of the disease, and thus we are sometimes foiled in our endeavours to destroy the fungus by the admission of air. In this case the disease may be encouraged by the application of air as a remedy. When workmen are employed in buildings which contain dry rot, and when they are working on ground which contains the symptoms of this disease, their health is often affected. A London builder informs us, that a few years since, while building some houses at Hampstead his men were never well: he afterwards ascertained that the ground was affected with rot, and that within one year after the house was erected, all the basement floor was in a state of premature decay. Sir Robert Smirke, architect, remarked in 1835, that he had noticed “there are certain situations in which dry rot prevails remarkably.”
The fungus protruded in a very damp situation is fibrous, of moderate thickness, feels fleshy. From the spot whence it arises it extends equally around, wholly covering the area of a circle. This form would possibly continue in whatever situation it might vegetate, if the air had no motion, and every part of the substance on which it grew were equally supplied with a matter proper to encourage the expansion. The surface of this fungus is pursed, and of various colours, the centre is of a dusky brown, mixed with green, graduated into a red, which degenerates into yellow, and terminates in white.
One of the most formidable of the tribe of fungi is the Merulius lachrymans (often called the Dry Rot) of which the following description is given by Dr. Greville: “Whole plant generally resupinate, soft, tender, at first very light, cottony, and white. When the veins appear, they are of a fine yellow, orange, or reddish brown, forming irregular folds, most frequently so arranged as to have the appearance of pores, but never anything like tubes, and distilling, when perfect, drops of water.” Hence the term lachrymans, from lacrymo, Lat., I weep: the Merulius lachrymans is often dripping with moisture, as if weeping in regret for the havoc it has made. In the genus Merulius, the texture is soft and waxy, and the hymenium is disposed in porous or wavy toothed folds. Berkeley, in his ‘Fungology,’ gives the following description, which is similar to Dr. Greville’s: “Large, fleshy but spongy, moist, ferruginous yellow, arachnoid and velvety beneath; margin tomentose, white; folds ample, porous, and gyroso-dentate.” The Merulius is found in cellars and hollow trees, sometimes several feet in width, and is the main cause of dry rot.
Another formidable fungi, which attacks oak in ships, is the Polyporus hybridus (the dry rot of our oak-built vessels). It is thus described by Berkeley: “White, mycelium thick, forming a dense membrane, or creeping branched strings, hymenium breaking up into areæ, pores long, slender, minute.”