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logical and developmental characteristics are, in the first place, applied as far as possible, e.g., the shape of the cell, the presence of flagella and their arrangement, the mode of germination of the endospores, etc. Further, the forms which the growth assumes on various nutrient media, e.g., on culture gelatine, in which case it is also observed to what extent the species liquefies gelatine, if at all. The products resulting from growth are also of importance. The cultures are prepared either as streak or stab cultures, the former on the surface of the gelatine, the latter by stabbing in a thick layer of gelatine (see p. 98). Drop seeding on the surface of the gelatine is also employed. The behaviour of bacteria species with various staining methods takes a large place, especially in medical bacteriology.

The bacteria considered here can be divided into two chief groups, viz., spherical bacteria (Coccacea) and rod bacteria (Bacteriacea), by which means, on practical grounds, we retain the old classification, in which shape was the criterion, and also the older names which are generally known. The author, however, is, on this point, neither for nor against this arrangement. The classification of bacteria is at present very uncertain, and is still subject to change, since no fixed, systematic, distinctive lines can be laid down. That the shape, moreover, is in several respects of little value as a systematic distinguishing feature follows, among other things, from what has been said in the foregoing on the polymorphism of bacteria.

I.-FAMILY: SPHERICAL BACTERIA (COCCACEÆ).

In the isolated state the cells are spherical. Fission takes place along one, two or three planes.

1. Genus : Micrococcus, Cohn. The cells are joined together irregularly. Included in this genus are several forms which, like Sarcina, divide along three planes, but the cells quickly separate from one another and do not remain united as in Sarcina. Such species ought rightly to be classified in the genus named.

Micrococcus viscosus is, according to Pasteur, the cause of the ropiness of beer.

Micrococcus saprogenes vini I, and II., Kramer, has been obtained by Kramer in pure cultures from turned wines from Styria and Croatia.

Diplococcus I. and II., Aderhold, makes wine ropy.

2. Genus : Pediococcus, Francke. . The cells are arranged in flat colonies ; they divide along two planes.

Pediococcus cerevisiæ, Francke, was first prepared as a pure culture by P. Lindner. The cells are 0-9 to 1:5 u in diameter. They occur either as coccus or diplococcus or in tetrads, and are to be found in large quantities in beers with the so-called sarcina turbidity.

Pediococcus viscosus, Lindner, has been isolated by P. Lindner from thick “Weissbier."

Pediococcus sarcinæformis, Reichard, causes disease in beer, according to Reichard.

Pediococcus acidi lactici, Lindner. The cells are 0·6 to 1:0 u in diameter. This species excites lactic acid fermentation in malt mashes. The optimum temperature for its growth is 40° C., whilst it dies at 62° C. It does not thrive in hopped wort nor in beer.

3. Genus : Sarcina, Goods. The cells are arranged in packet-formed octads (Fig. 136, A, 5); they are divided by three fission planes. To thi

genus belong species which form white, yellow, red or brown colonies.

Sarcina maxima, Lindner, is found in malt mashes. The cells are 3 to 4 u in diameter.

Sarcina aurantiaca, Lindner, has been isolated from Berlin “ Weissbier". This species, as also S. flara and S. alba, is said to give rise to diseases in American beer.

The species belonging to the two foregoing genera are very common in nature, and occur, among others, also in water. Jorgensen and Lindner, for example, found these forms in their water analyses. Their occurrence in breweries has been mentioned above.

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II.---FAMILY: Rod BACTERIA (BACTERIACEA).

The cells are of various lengths, cylindrical and straight never spiral. Fission takes place only in one direction, viz., transversely, and after previous elongation of the rod.

Genus 1 and 2: Bacterium and Bacillus.

The older systematists, Cohn for example, called all short rods Bacteria, all long rods Bacilli. At present it is impossible to separate the two genera completely from one another by this means. For the species appear sometimes as short, sometimes as long rods. The author, however, retains both these generic names on practical grounds, the species being hence represented with their old names ; so that, for example, the generic names Granulobacter, Clostridium, etc., are retained in what follows. For distinguishing purposes the spore formation and the flagella have been

ggested; but these characteristics also have proved to be sufficient.

Acetic Acid Bacteria.

Kützing (1837) first described an acetic acid bacterium, rhilst Hansen was the first to show that various species f acetic bacteria exist, and to give at the same time he outlines of their life history (1879). The investigations of A. J. Brown, Henneberg, Zeidler and Zopf show that

few of these species have a swarming state under certain conditions. One of these acetic acid bacteria with flagella is shown in Fig. 135. In this case the flagella are of particular importance in characterising the species. With some species the mucilage which is formed by the cells gives a blue reaction with iodine (Hansen), that of others yields the cellulose reaction (a blue stain with iodine and sulphuric acid; A. J. Brown).

Hansen has given information on the vitality of these bacteria in different nutrient media and also in the dry state. He found that Bacterium aceti lived in “double” beer more than six years, in some cases, however, not five years ; further, that after nine years in lager beer and after about two years in a saccharose solution it was still alive ; Bacterium Pasteurianum was alive after six years (in one case it was dead after two and a quarter years) in “double” beer, after more than ten years (in one case death occurred after one to two years) in lager beer, and after one year and a quarter in a saccharose solution ; but in the latter it was dead after one year and a half; lastly, Bacterium Kützingianum was alive after about six years in “double” beer (in some cases it was dead after five years), and after about seven years in lager beer (in some cases after five years only). In the dry state on small pieces of platinum wire in Freudenreich flasks the life limit of the cells of the three species named was about five months. When the abovementioned dry preparations were introduced into glass tubes, and these closed by fusing, and preserved at the ordinary room temperature and at 2° C., it appeared that the lifetime at the former named temperature was about five months, and more than a year at the latter. When the cells were introduced into the tubes in a moist state they very soon died.

The formation of acetic acid induced by these organisms is brought about by the alcohol being converted into acetic acid in the presence of a plentiful air supply. As Pasteur showed (1864), and A. J. Brown confirmed later, the combustion can proceed still further, so that the acetic acid already formed is oxidised to carbonic acid and water.

F. Lafar studied the influence of temperature on Bact. aceti and Bact. Pasteurianum with regard to their power of forming acetic acid. He found that the former species at as low a temperature as 4° to 5° C., the limit of its growth, can set up a strong acetic fermentation, but that Bact. Pasteurianum, on the other hand, formed no acetic acid at 4° to 4.!°C. With the last-named species he found, further, that the maximum acid formation is reached at 33° to 34° C. after seven days, when 3:3 per cent. by weight is produced. W. Seifert came likewise to the conclusion that morphologically different species of acetic acid bacteria also exhibit substantial differences in regard to their chemical behaviour. In his experiments he employed Bact. Pasteurianum and Bact. Kützingianum. He draws the conclusion, “ that the fermentative power of acetic acid bacteria in the presence of the monatomic primary alcohols decreases as the proportion of carbon in the latter increases; that, further, Bact. Pasteurianum has the feeblest fermentative power in the presence of the polyatomic alcohols and dextrose". Henneberg carried out investigations similar to Seifert's, but with

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