508 FERMENTATION. 



even develop very luxuriantly there. The principal genera whose species cause 

 fermentation are Mucor, Aspergillus, Penicillium, Botrytis, and Ewrotiwm. 



Finally, in addition to bacteria, yeasts, and moulds, the mycelia of those fungi, 

 which are called Basidiomycetes (in reference to their characteristic reproduction, 

 which will be described in the next volume), can induce fennentation. The 

 thread-like cell-chains of these mycelia look like mould-structures; they grow 

 through and permeate the dead bodies of plants and animals, dung and refuse, 

 and black meadow-soil, the humus of the forest, and especially the trunks of 

 dead trees. But living plants also, especially the wood of living trees, may be 

 penetrated by these mycelia, and the tree ultimately killed in consequence. When 

 the mycelial threads penetrate into the wood of a living or dead tree (see fig. 32 ^), 

 they are not satisfied with merely piercing the cell-walls, and destroying those 

 places only with which they come immediately into contact, and absorbing the 

 results I if the destruction as food; on the contrary, we have an extensive decom- 

 position, with which is associated a liberation of carbon dioxide, water, and various 

 volatile materials, not well known, which give rise to a peculiar musty smell. The 

 wood loses weight, becomes rotten, and wholly transformed into a mass which 

 on drying crumbles to powder, or into a fibrous asbestos-like substance. Finally, 

 it disintegrates into dust. In popular language this fermentation produced by 

 the mycelium is called " rotting ". By many basidiomycetous mycelia the wood 

 is not only changed into a powdery, Imt even into a liquid mass, as, for example, 

 by the mycelium of the detested Dry-rot, or Wine-cask Fungus. 



All these fermentations, whether caused by the mycelia of Basidiomycetes, the 

 bud-forms of mould, by yeast, or by bacteria, have one thing in common, that they 

 have been set up by ferment-causing cells, i.e. by the active living protoplasm 

 within them without the excretion of any special chemically-active materials 

 which would come directly into contact with their surroundings. The living 

 protoplasm of the mycelia named, of bacteria, yeast, and mould, itself remains 

 chemically unaltered; it acts most energetically in the immediate neighbourhood, 

 less vigorously further oft', and its efiect diminishes with increasing distance. The 

 effect proceeding from the ferment-cells might be compared with the concentric 

 waves produced on the surface of water into which a stone has been thrown. 

 A hypothesis has been formulated, according to which the groups of atoms in the 

 ferment-protoplasm are supposed to be oscillating as long as it is alive, and it is 

 imagined that these oscillations are propagated and convej^ed to the environment 

 after the manner of a wave-motion. Alterations in the construction of the shaken 

 molecules, displacement of the atoms, and decomposition of the compounds in 

 question, would tlius result from the shaking so produced. It has even been 

 estimated that the vibrations which proceed from the living protoplasm of, e.g. 

 Yeast cells, ai"e propagated to a distance of 5'^ mm. from the surface of the cells, 

 and that they shake and alter the arrangement of the molecules of sugar even at 

 this distance. The shaking would of course vary according to the specific consti- 

 tution of the protoplasm. It may be assumed that vibrations differing in quality 



