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again and to assume the chain form (Fig. 140). By Nageli and others such swollen forms were regarded as not belonging to normal development, but as an indication that the cells are about to die. It is shown by Hansen's above-mentioned
Fig. 138.-- Bacterium Pasteurianum, Hansen. The thread form after twenty-four
hours in "double" beer at 40° to 404° C. 1909. (After Hansen.)
acid bacteria, only few and incomplete contributions to this subject are as yet to be found. Macfadyen and Blaxall found that some thermophilic bacteria investigated by them also formed long threads at high temperatures (approaching 70° C.).
It is generally known that among organisms different conditions can produce identical or nearly corresponding
Fig. 139.-Bacterium Pasteurianum, Hansen. Development of the thread form
by cultivation on “double" beer agar-agar in a Böttcher's chamber at about 404° C. O, A chain consisting of 8 members ; a', the same after 6; a", after 10; a", after 20 hours. b, A five-membered chain; b', after 5; ", after 9 hours. c, Development after 10;d, after 21 hours. The times are reckoned from the beginning of the experiment. 1999, (After Hansen.)
forms of development. It is therefore not remarkable that various authors have stated that the change of shape referred to can also be obtained as the result of the influence of factors other than temperature; H. Buchner has found, in regard to Bacillus subtilis, that the chemical composition of the culture medium was responsible for similar changes of shape.
. 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.
Fig. 140.-Bacterium Pasteurianum, Hansen. Transformation of the thread
form into swellings and chains by cultivation in "double” beer at 34° C. 1. after four, II. after five, III. after seven hours from the beginning of the
experiment. 1949. (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 ttempted, without grounds, however, to make use of this act in order to identify the parent forms of bacteria mong 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 (Kutzing), Hansen. Unusual cell forms after several
days' cultivation in wort and “double" beer at 39° to 41° C. 1999. (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 forin 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.