The film cells are usually

34° C. after twenty-four hours. hour-glass shaped rod bacteria arranged in chains (Fig. 143); long rods and threads with or without swellings are only exceptionally found. At 40° to 40° C. long thin threads develop. The mucilage is not stained by a solution of iodine or by a solution of iodine in potassium iodide. After four days at 25° C. it develops colonies on wort gelatine which are grey, waxy, round, usually arched and with unbroken edges, seldom star-shaped, and which consist chiefly of free, small rod bacteria; the chain form is repressed here. The maximum temperature of growth in "double" beer is about 42° C., the minimum 4° to 5° C.

FIG. 144.-Bacterium Pasteurianum, Hansen. Young film formation on "double" beer at 34° C. 1999. (After Hansen.)

The species is found both in top fermentation and in bottom fermentation beers; Hansen observed it frequently in the dust of the air and Holm now and then in his analyses of water.

Bacterium Pasteurianum, Hansen (Figs. 133, 138, 139, 140 and 144). This bacterium forms on " double" beer at 34° C. after twenty-four hours a dry film which very soon assumes a wrinkled and folded appearance, and rises but little from the surface of the liquid along the sides of the flask. Like those of the foregoing species, the cells are arranged in long chains, but are altogether larger and especially thicker

(Fig. 144). The thread form (Figs. 138, 139 and 140) is also somewhat thicker at 40° to 40° C. than with Bact. aceti. The mucilage is stained blue with a solution of iodine or of iodine in potassium iodide. Plate culture colonies on wort gelatine after four days at 25° C. are usually smaller than those of Bact. aceti, otherwise they are the same as with this species. They consist chiefly of typical chains. After about three weeks the surface of the colonies is folded. On wort gelatine and on lager beer gelatine, with and without 10 per cent. of saccharose, the growth is, at 25° C., solid, dry, waxy and yellowish. The maximum temperature for growth on "double" beer is 42° C., the minimum, 5° to 6° C.

Hansen found this species in the same places as the previous one, but more frequently in top fermentation than in bottom fermentation.breweries. W. Seifert found it in vinegar-tainted wine.

The thread

Bacterium Kützingianum, Hansen (Fig. 145).-The film formed on "double" beer after twenty-four hours at 34° C. differs from that of Bact. Pasteurianum by growing high above the liquid along the sides of the flask. It consists of small rod bacteria which are, as a rule, free, or at most joined in pairs; they form long chains rarely. form at 40° to 40° C. contains relatively more short threads than Bact. Pasteurianum. The microscopical appearance differs distinctly from that of the latter; on the other hand, both species are alike in that the mucilage is stained blue by a solution of iodine or of iodine in potassium iodide. In plate cultures on wort gelatine this species develops colonies after four days at 25° C., which consist almost exclusively of small, free, rod bacteria; long chains are found only very seldom. The surface of the colonies after three weeks is smooth, not folded. The growths at 25° C., both on lager beer gelatine and wort gelatine, with and

without 10 per cent. of saccharose, are shiny, slimy anl bluish-grey. The maximum temperature of growth is about 42° C. in "double" beer, the minimum, 6° to 7° C.

Hansen found this bacterium in "double" beer; it i probably diffused to the same extent as Bact. Pasteuri

anum.

In addition to the above-cited differentiation between Bact. Pasteurianum and Bact. Kützingianum furnished by Hansen, Henneberg and Seifert have given an extensive series of physiological characteristics, among which, for example, are the following: Bact. Pasteurianum forms a most half as much acetic acid as Bact. Kützingianum in lager beer with added alcohol. Thus the former, in lager

FIG. 145.-Bacterium Kützingianum, Hansen. Young film formation on "double" beer at 34° C. 1999. (After Hansen.)

beer, with 8 per cent. of alcohol, produces 3-23 per cent. of acetic acid in twelve days, while the latter forms 6:56 per cent.; the formation of acid by Bact. Pasteurianum is likewise only half as great as that by Bact. Kützingianum when the cultivation takes place in a 2 per cent. glycol solution. When yeast water with 3 per cent. of dextrose is used as the nutrient solution, the growth of Bact. Pasteurianum at 26° to 30° C. consists of long chains, that of Bact. Kützingianum, on the contrary, of single cells, or pairs connected together. The same microscopical differences are thus found here as between the growths of both species on beer and wort gelatine.

Of the many species of acetic acid bacteria which have.

been described in the last few years we will mention here among others ::

Bacterium oxydans, Henneberg (Bact. aceti, Zopf).—This species is distinguished from Bact. aceti of Hansen described above, by having, as shown by Zopf and Henneberg, a swarming state; it was isolated from a bottom fermented beer from Halle.

Further, Beijerinck mentions a species which he calls Bact. aceti, and which he states to be the active species in quick vinegar manufacture. It is distinguished by forming a film on artificial nutrient liquids; this property, held in common with other species, is, however, not permanent in this species, and may be lost after a previous cultivation on solid nutrient media. All gradations of film development are presented here. Further, it liquefies beer gelatine containing cane sugar, this being due, according to Beijerinck, to the inversion of the sugar.

To what extent Beijerinck's Bact. aceti is the acetic bacterium of quick vinegar manufacture is, however, not established. Rothenbach found that the active bacteria of the process named are not in a condition to form a film. The loss of this power of film formation rests, in his opinion, on the circumstance that they are never allowed the opportunity of film formation in practice, because the mash is in continual motion. According to Rothenbach the quick vinegar bacteria are acclimatised forms. Some of them closely resemble Bact. aceti, Hansen, and can furnish vinegar containing a high percentage of acetic acid from a mash containing little nutrient substance and a high percentage of alcohol, in the Schützenbach acetifiers.

Of other acetic acid bacteria the following may be mentioned :— Bacterium Xylinum, A. J. Brown.-The gelatinous substance is cartilaginous, and furnishes the cellulose reaction with iodine and sulphuric acid, i.e., a blue colour. This species also occurs in the acetifiers of the quick vinegar process. Further, the following is described by Henneberg :—

Bacterium acetigenum, which was isolated from the vinegar of a quick vinegar manufactory. It yields a cellulose reaction under certain conditions, and has especially intense power of swarming; Bacterium industrium also has a swarming state.

Several species have likewise been described under the generic name Termobacterium, as for example:

Termobacterium aceti, Zeidler, which is illustrated in Fig. 135 and which possesses a long flagellum; further Termobacterium lutescens, Lindner, which renders beer turbid and gives rise to a celery odour in it.

We will mention still a few more Bacterium species:

Bacterium vermiforme, Marshall Ward, forms cells which measure 0.5 to 50 μ long and 0.5 μ broad. The gelatinisation of the cell wall with this species consists in the loosening of the strongly swollen outer layer of the cell membrane whereby the cells are enclosed as in a capsule. Together with the Saccharomyces pyriformis mentioned on p. 261 it forms the so-called ginger beer plant.

Bacterium termo, Cohn, is a collective expression for motile bacteria occurring in decomposing substances. According to Cohn's description it is a feebly fluorescent, strongly motile, short, ovate rod; but which of the numerous putrefactive bacteria is thus indicated cannot be determined.

Windisch considers that the cause of the so-called cellar flavour, by which is understood usually a raw, musty, damp taste in the beer, is undoubtedly to be looked for in the contamination of the wort during cooling, as the beer sometimes remains too long in the coolers during the warm summer months, and is, in consequence, infected by one of the bacteria belonging to the Bact. termo group.

They thrive well in hopped wort, but cannot live associated with yeast.

Most of the species included in the genus Bacillus, Cohn, form endospores. They can be classified in various groups

according to their physiological activity.

Slime-forming Species.

Bacillus viscosus I, and II., van Laer, were isolated from ropy beers. Both form rods with a length of 16 to 2-4 μ and a breadth of 0.8 μ; they are usually isolated, not infrequently, however, in pairs. I. forms on the surface of wort slimy, yellowish islands which appear to branch downwards. They give rise, in consequence, to a slimy covering containing bubbles, which result from the evolution of carbonic acid. II. does not form a slimy covering. The carbonic acid production and viscosity are less. The wort becomes darkbrown and a peculiar odour is evolved. A solution of 3 grams of saccharose and 1 gram of peptone in 100 c.c. of