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158 wood by excreting soluble ferments which dissolve the substance of their walls, and feed on the products of solution. Hence they damage the timber in two ways—they riddle it through and through by myriads of minute apertures, and thus ruin its structure, and they



reduce its substance by dissolving it and converting it to their own uses. The wood, therefore, loses in strength and in weight, and becomes "rotten." There are differences in detail as to the mode of destroying the elements of the wood, but the final result is much the same in all