The abnormal and in general inflated shapes assumed by many bacteria when they have to exist for a long time in unfavourable environments are usually known as involution forms. These may take up the most varied shapes.

II

III

FIG. 140.-Bacterium Pasteurianum, Hansen.

Transformation of the thread

form into swellings and chains by cultivation in "double" beer at 34° C. I. after four, II. after five, III. after seven hours from the beginning of the experiment. 1909. (After Hansen.)

Some, e.g., the acetic acid bacteria (Fig. 141), the diphtheria bacillus, tubercle bacillus, etc., sometimes assume a mycelium-like, branched appearance, and it has been

attempted, without grounds, however, to make use of this fact in order to identify the parent forms of bacteria among the hyphomycetes. They are, however, as stated, only abnormal formations. A bacterium has never been grown and developed into a hyphomyces, and vice versa.

FIG. 141.-Bacterium aceti (Kützing), Hansen.

Unusual cell forms after several

days' cultivation in wort and "double" beer at 39° to 41° C. 1920. (After Hansen.)

All communications which have hitherto appeared on the development of bacteria from higher fungi are without proof.

With many species an enfeeblement takes place during continued culture, so that, for instance, the fermentative

activity becomes lost (as distinguished from the saccharomycetes, in which this has never been observed). Bacteria, which cause diseases in man and animals, can lose their virulence (pathogenic properties) by means of a special treatment. A change of another kind has been likewise observed in the splenitis bacillus, which, during its temporary change of form, can lose the power of spore formation; this change of form displays itself in the production of rudimentary spores.

With regard to variation among vinegar bacteria, Hansen has further shown that the mucilage of his two species, Bact. Pasteurianum and Bact. Kützingianum, which is stained blue by iodine, loses this property under certain conditions. Whether developed on the surface of a liquid or solid medium, a time arrives when they no longer give the blue reaction. In some beer cultures he found that this point was reached in three to four months at the ordinary temperature of the room; in others, on the contrary, it was not even attained after seven to nine months. These abnormal cultures usually return quickly to the normal state.

4. DISEASE BACTERIA IN THE ALCOHOLIC FERMENTATION

INDUSTRIES.

The harmful influence of bacteria in the fermentation industries is by no means small; there are, however, only relatively few species which do an appreciable amount of damage. The majority, in fact, do not thrive, or do so but indifferently, in acid liquids; beer and wine contain free acid, and are thus protected to a great extent. By the introduction of the pure culture system this injurious action of bacteria has been very much lessened in bottom and top fermentation breweries, as well as in the manufacture of wine.

The decomposition products of bacteria are of many kinds. They can develop acetic acid, lactic acid, butyric acid, various alcohols, etc. A large number liquefy nutrient gelatine through the possession of peptonising power.

Pasteur had discovered in the year 1861 that butyric acid bacteria are anaerobic, that is, they can only grow in the absence of oxygen. The majority of species, however,

thrive best with free access of air. The acetic acid bacteria are typical examples of aërobic forms.

Pasteur (1876) was also the first to point out the injurious part played by bacteria in the fermentation industry. The disease phenomena brought about by bacteria in fermented liquids are mucilage formation, decolorisation, turbidity, acid formation, disagreeable smell and taste.

Pasteur gives some information on mucilage formation in beer and wine; he mentions a Micrococcus which makes the liquids mentioned ropy. Kramer isolated from thick wines a Bacillus with which he could induce the same disease in sound white wine. From ropy Belgian beers, van Laer isolated bacilli which were the cause of the disease. L. Vandam also found in English beer a Bacillus that makes it thick. At the same time this species only attacks the beer when present in large number at the beginning of the primary fermentation. Brown and Morris describe a Coccus, likewise causing ropiness in English beer. The disease attacked the beer when it was six weeks to two months old. The source of infection appeared to be a slaughterhouse for pigs in the neighbourhood of the brewery. A Pediococcus was found by Lindner in ropy "Weissbier".

The disease known as the turning of wine consists in red wine assuming a brown colour, while white wine becomes turbid and discoloured and frequently develops a dark colouration. The tartar occurring in wine is changed by this disease into potassium carbonate, which causes the

change of colour.

from turned wines.

Kramer isolated two Micrococcus sci

The bacteria of lactic acid, butyric acid and acetic aci may be mentioned as acid producers in fermented liqui In breweries the first are especially active in the mashing stage. According to van Laer a species, Sacchar bac Pastorianus, causes the turning of beer; the beer thereby loses its brilliancy, becomes disagreeable in smell and taste and forms a sediment; the latter consists partly of nitrogenous products which separate as a result of lactic acid production, and partly of the bacteria themselves. Bacillus acidi lactici, according to Kramer, causes the "Zicken werden" (see p. 343) of wine. Butyric acid bacteria are responsible for a very unpleasant smell and taste in beer. They are especially injurious in the mashes in distilleries.

Acetic acid bacteria are found particularly in wine manufacture, where they occasion the tartness of the wine. When once the wine has been strongly attacked by them, and is in consequence vinegar sour, it is valueless; there is then no means of removing the evil. In brewing they are of most danger in top fermentation breweries, where the conditions for their development are more favourable than in bottom fermentation breweries. Hansen experimented in practice with Bacterium aceti and Bact. Pasteurianum in the presence of Carlsberg bottom yeasts No. 2 and No. 1. He came to the conclusion that the bacteria in question were indeed present in the finished lager beer if the infection took place at the beginning as well as at the end of the primary fermentation, but that this infection appeared neither in the fermentation cellar nor in the lager cellar. The bacteria can propagate themselves only after the lagered beer is drawn off; the beer, however, did not become vinegar sour if care was taken that the transport vessels and bottles were well closed and well filled. The same holds good