506 FERMENTATION. 



volume. Here it is sufficieut to I'emark that bacteria appear as spherical, o\al, or 

 rod-like cells, which develop by repeated transverse division into chain-like or 

 filamentous structures, very much resembling hyphal threads. These chains of 

 cells break up, however, sooner or later, into their individual members, and then 

 look as if they had been split into fragments, tins appearance accounting for their 

 name of " Fission-Fungi ". In this way arise colonies of irregularly accumulated 

 cells which are frequently embedded in a mucilaginous matrix. Many bacteria 

 can live and multiply without taking free oxygen from the air. They obtain the 

 materials necessary for this by setting up a fermentation in tlieir immediate 

 neighbourhood, i.e. a splitting up of carbohydrates and nitrogenous compounds. 

 Fermentation gives rise to very different products, and makes itself evident in very 

 different ways, according to the composition of the bodj' attacked by the bacteria, 

 and according to the species to which the bacteria, which are commencing their 

 destructive activity, belong. In many instances pigments are produced, in conse- 

 quence of the decomposition, which colour the attacked body yellow, red, violet, or 

 blue; at another time, as, for example, in the souring of milk, a molecule of milk- 

 sugar is decomposed into two molecules of lactic aciil; or, by the fei-ment action 

 of the Bacterium aceti, acetic acid is produced from alcohol; again in another 

 instance, sugar is split up into dextrin, mannite, and carbonic acid, by a species 

 of Bacterium, in the so-called viscous fermentations. One of the commonest fer- 

 mentations is that to which albuminous compounds succumb, known as initre- 

 faction. The albumens are decomposed by the action of one or perhaps several 

 different species of bacteria into tyrosin, leuciu, various amines, volatile fatty 

 acids, ammonia, carbon dioxide, sulphuretted hydrogen, hydrogen, and water; 

 and some of these make themselves evident by their offensive odour in a most 

 unpleasant manner. To this class, too, belong the most notorious of all bacteria, 

 which give rise to a decomposition of the liquids in living human and animal 

 bodies, which deprive the blood of oxygen and bring aboiit in it various other 

 decompositions of organic compounds, and which are regarded as the cause of 

 epidemic and endemic diseases. Contagions and miasmas are indeed for the greater 

 part, if not wholly, bacterial, and the species which produce splenic fever in rumi- 

 nants, diphtlieria, small-pox, and cholera in man, ai'e of such great interest that a 

 whole section will be dedicated to them in the next volume. 



The various species of yeast, which are called Saccharomyces, consist of 

 spherical or ellipsoidal cells, which are much larger tlian the cells of bacteria, 

 and also multiply in quite another way. They increase by sprouting, i.e. knob- 

 like outgrowths arise on the surface of the multiplying-ceUs which rapidlj' enlarge, 

 so that each outgrowth in a very short time is equal in size to the cell from which 

 it originated. The daughter-cell thus formed is detached from the parent-cell, 

 and may now itself produce daughter-cells by sprouting. Occasionally several 

 successive buddings remain joined together, and then form colonies which some- 

 what resemble the pricklj- pears or opuntias in miniature. Yeast produces 

 alcoholic fermentation. It causes gi'ape-sugar to split up into alcohol and carbon 



