Part 4

The condition termed “Zooglœa,” which reminds us of _Nostoc_, is produced by the cells becoming strongly mucilaginous. A number of individuals in active division are found embedded in a mass of mucilage, which either contains only one, or sometimes more, of the above-named forms. The individuals may eventually swarm out and continue their development in an isolated condition. Such mucilaginous masses occur especially upon moist vegetables (potatoes, etc.), on the surface of fluids with decaying raw or cooked materials, etc. The mucilaginous envelope is thrown into folds when the Bacteria, with their mucilaginous cell-walls, multiply so rapidly that there is no more room on the surface of the fluid.

The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in _Sarcina_, _Leuconostoc_; also in a Vinegar-bacterium, _Bacterium xylinum_); a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (_e.g. Bacillus virens_) contain chlorophyll; others are coloured red (purple sulphur Bacteria); the majority are colourless. _Bacillus amylobacter_ shows a reaction of a starch-like material when treated with iodine before the spore-formation. Some Bacteria contain sulphur (see p. 37). The body, which has been described as a _cell-nucleus_, is still of a doubtful nature.

Artificial colourings with aniline dyes (especially methyl-violet, gentian-violet, methylene-blue, fuchsin, Bismarck-brown and Vesuvin) play an important part in the investigations of Bacteria.

MOVEMENT. Many Bacteria are self-motile; the long filaments of _Beggiatoa_ exhibit movements resembling those of _Oscillaria_. In many motile forms the presence of cilia or flagella has been proved by the use of stains; many forms have one, others several cilia attached at one or both ends (Fig. 23) or distributed irregularly over the whole body; the cilia are apparently elongations of the mucilaginous covering and not, as in the other Algæ of the protoplasm. In _Spirochæte_ the movement is produced by the flexibility of the cell itself. Generally speaking, the motion resembles that of swarm-cells (_i.e._ rotation round the long axis and movement in irregular paths); but either end has an equal power of proceeding forwards.

The swarming motion must not be confounded with the hopping motion of the very minute particles under the microscope (Brownian movement).

VEGETATIVE REPRODUCTION takes place by continued transverse division; hence the name “Fission-Fungi” or “Fission-Algæ,” has been applied to the Bacteria.

SPORES. The spores are probably developed in two ways. In the ENDOSPOROUS species (Figs. 28, 29), the spore arises as a new cell inside the mother-cell. The spores are strongly refractile, smaller than the mother-cell, and may be compared to the aplanospores of other Algæ. In addition to these there are the ARTHROSPOROUS species in which the cells, just as in _Nostoc_ and other Blue-green Algæ, assume the properties of spores without previously undergoing an endogenous new construction, and are able to germinate and form new vegetative generations (Fig. 27). The formation of spores very often commences when the vegetative development begins to be restricted.

The spores germinate as in _Nostoc_ by the bursting of the external layer of the cell-wall, either by a transverse or longitudinal cleft, but always in the same way, in the same species (Fig. 28, example of transverse cleft).

DISTRIBUTION. Bacteria and their germs capable of development, are found everywhere, in the air (dust), in surface water, and in the superficial layers of the soil. The number varies very much in accordance with the nature of the place, season, etc. They enter, together with air and food, into healthy animals and occur always in their alimentary tract.

GROWTH AND REPRODUCTION depend upon the conditions of temperature. There is a certain minimum, optimum and maximum for each species; for instance (in degrees Centigrade)--

Minim. Opt. Maxim. _Bacillus subtilis_ + 6 c. 30 + 50 _B. anthracis_ 15 20–25 43 _Spirillum choleræ asiaticæ_ 8 37 40 (but grows only feebly if under 16°). _Bacterium tuberculosis_ 28 37–38 42

The functions of life cease on a slight excess of the maximum or minimum temperature, numbness setting in when either of these limits is passed. _Crenothrix_-threads provided with mucilaginous envelopes may, according to Zopf, sustain a temperature of-10°. Some Bacteria are said to be able to resist the exposure to as low a temperature as-110° for a short time. It is not known at what degree of cold the death of the Bacteria occurs: the greatest degree of heat which the vegetative cells can withstand is about the same as that for other vegetative plant-cells, namely, about 50–60° C. Certain Bacteria, _e.g. B. thermophilus_, grow and thrive vigorously at 70° C. Many spores, on the contrary, are able to bear far higher temperatures (in several species a temperature for some duration of above 100°, those of _Bacillus subtilis_, for instance, can withstand for hours a temperature of 100° in nutrient solutions; the spores remain capable of development after exposure to a dry heat of 123° C.).

The _Desiccation_ of the air, if prolonged, kills many forms when in the vegetative condition. The spores however can bear a much longer period of dryness, some even several years.

OXYGEN. Some species cannot live without a supply of free oxygen (_Aerobic_), _e.g._ the Vinegar-bacteria, the Hay-bacilli, the Anthrax-bacilli, the Cholera-_Microspira_. Other species again thrive vigorously without supply of free oxygen, and are even checked in their development by the admission of air (_Anaerobic_), _e.g._ the butyric acid Bacterium (_Clostridium butyricium_ = _Bacillus amylobacter_). A distinction may be drawn between obligate and facultative aerobics and obligate and facultative anaerobics. Several Bacteria, producing fermentation, may grow without the aid of oxygen when they are living in a solution in which they can produce fermentation; but, if this is not the case, they can only grow when a supply of oxygen is available. A great number of the pathogenic Bacteria belong to the facultative anaerobics.

A luminous Bacterium (_Bacillus phosphorescens_) which in the presence of a supply of oxygen gives a bluish-white light, has been found in sea-water. Phosphorescent Bacteria have frequently been observed upon decaying sea-fish, as well as on the flesh of other animals; by transferring the Bacteria from cod fish to beef, etc., the latter may be made luminous.

_Organic carbon compounds_ are indispensable for all Bacteria, (except, as it appears, for the nitrifying organisms), as they can only obtain the necessary supplies of _carbon_ from this source. The supplies of _nitrogen_, which also they cannot do without, can be obtained equally as well from organic compounds as from inorganic salts, such as saltpetre or ammonia-compounds. The various “ash-constituents” are also essential for their nourishment.

While Moulds and Yeast-Fungi grow best in an acid substratum, the _Bacteria_, on the other hand, generally thrive _best_ in a _neutral_ or slightly _alkaline_ one.

In _sterilization_, _disinfection_, and _antisepsis_, means are employed by which the Bacteria are killed, or checked in their development, for instance, by heat (ignition, cooking, hot vapours, hot air, etc.), or poisons (acids, corrosive sublimate). The process of preserving articles of food, in which they are boiled and then hermetically sealed, aims at destroying the Bacteria, or the spores of those which already may be present in them, and excluding all others.

As the Bacteria are unable to assimilate carbon from the carbonic acid of the air, but must obtain it from the carbon-compounds already in existence in the organic world, they are either _saprophytes_ or _parasites_. Some are exclusively either the one or the other, _obligate_ saprophytes or parasites. But there are transitional forms among them, some of which are at ordinary times saprophytes, but may, when occasion offers, complete their development wholly or partly as parasites--_facultative parasites_; others are generally parasitic, but may also pass certain stages of development as saprophytes--_facultative saprophytes_.

All chlorophyll-free organisms act in a transforming and disturbing manner on the organic compounds from which they obtain their nourishment, and while they themselves grow and multiply, they produce, each after its kind, compounds of a less degree of complexity, _i.e._ they produce _fermentation_, _putrefaction_, sometimes the formation of _poisons_, and in living beings often _disease_.

Those organisms which produce fermentation are called _ferments_; this word, however, is also employed for similar transformations in purely chemical materials (inorganic ferments or enzymes). Many organic (“living”) ferments, among which are Yeast-cells and Bacteria, give off during their development certain inorganic and soluble ferments (enzymes) which may produce other transformations without themselves being changed. Different organisms may produce in the same substratum different kinds of transformation; alcoholic fermentation may for instance be produced by different species of Fungi, but in different proportions, and the same species produces in different substrata, different transformations (_e.g._ the Vinegar-bacteria oxydize diluted alcohol to vinegar, and eventually to carbonic acid and water).

In the study of Bacteria it is absolutely necessary to sterilize the vessels employed in cultivation, the apparatus, and nutrient solutions, _i.e._ to free them from Bacteria germs and also to preserve the cultures from the intrusion of any foreign germs (“pure-cultures”). A firm, transparent, nutritive medium is frequently employed. This may be prepared by adding to the nutrient solutions (broth) either gelatine, or--when the Bacteria are to be cultivated at blood-heat--serum of sheep’s or calf’s blood, agar-agar or carragen; serum alone may in itself serve as a nutrient medium. The so-called “plate-cultures” are frequently employed, _i.e._ the germs are isolated by shaking them with the melted liquid nutrient gelatine, which is then spread on a glass plate and allowed to coagulate; when later on the individual germs grow into colonies, these remain separate in the solid substratum and it is easy to pursue their further development. Similar plate-cultures may also be cultivated in test-tubes and on microscopic slides. The slides and glass plates must be placed in “moist chambers” free from Bacteria. By sowing a few cells (if possible one) using a fine platinum wire, pure cultures for further investigation may be obtained.

In order to prove the relationship between pathogenic Bacteria and certain diseases, the experimental production of pathogenic Bacteria by the inoculation of Bacteria from pure cultures into healthy animals, is very important.

It has not so far been possible to establish a _classification_ of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form.

The following Bacteria are =Saprophytes=:--

_Cladothrix dichotoma_ is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, _Leptothrix ochracea_ is one of the forms of this species which, in water containing ferrous iron (_e.g._ as FeCO_{3}), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. _Leptothrix ochracea_ and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria.

Those forms which, according to Zopf’s views, represent the forms of development of _Cladothrix dichotoma_ are placed together in Fig. 30. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small _Leptothrix_-like forms. _B_ shows the manner of branching and an incipient _Coccus_-formation. _C_ a _Coccus_-mass whose exit from the sheath has been observed. _D_ the same mass as _C_ after the course of a day, the Cocci having turned into _rods_. _E_ a group of Cocci in which some have developed into shorter or longer rods. _F_ one of these rods before and after treatment with picric acid, which causes the chain-like structure to become apparent. _G_ a portion of a plant with conspicuous sheath, two lateral branches are being formed. _H_ part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. _Leptothrix_-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. _K_ part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and _Leptothrix_-filaments. _L_ a portion of a branched _Cladothrix_, which divides into motile _Bacillus_-forms; the rays at the free ends indicate the currents which the cilia produce in the water. _M_ a spirally-twisted, swarming filament, before and after division into halves. _N_ part of a tree-like zooglœa with Cocci and short rods.--All of these spirilla, zooglœa, etc., which Zopf has connected with _Clad. dichotoma_, are according to Winogradsky, independent organisms.

_Micrococcus ureæ_ produces _urinal fermentation_ (transformation of urinal matter into ammonium carbonate); aerobic; round cells generally united to form bent chains or a zooglœa.--Several other kinds of Bacteria have the same action as this one: in damp soil containing ammonia-compounds, _saltpetre-formations_ are produced by _M. nitrificans_ and several different kinds of Bacteria.

_Micrococcus prodigiosus_ is found on articles of food containing starch; “bleeding bread” is caused by this Bacterium, which has the power of forming a red pigment; it also occurs in milk, and produces lactic acid.

_Leuconostoc mesenterioides_ is the frog-spawn Bacterium (Fig. 27) which is found in sugar manufactories, and has the power of producing a viscous fermentation in saccharine solutions which have been derived from plants, _e.g._ in beetroot-sugar manufactories, where large accumulations of mucilage are formed at the expense of the sugar, with an evolution of carbonic acid. The cell-rows, resembling somewhat a pearl necklace, have thick mucilaginous cell-walls, and form white “Nostoc”-lumps. The mucilage eventually deliquesces and the cells separate from each other; arthrospores?--Similar viscous deteriorations occur in beer and wine, which may then be drawn out into long, string like filaments--“ropiness.”

_Bacterium aceti_, the Vinegar-bacterium, oxidizes alcohol into acetic acid (acetous-fermentation) and forms a greyish covering of Bacteria (“Vinegar-mother”) on the surface of the liquid; the acetic acid formed, becomes by continued oxidization by _B. aceti_, again transformed into carbonic acid and water. Aerobic; short cylindrical cells, often united into chains, or to form a zooglœa; sometimes also rod-and spindle-shaped. The Vinegar-bacteria and other kinds with ball- or rod-forms sometimes become swollen, spindle-shaped, or oval links; they are supposed to be diseased forms[8] (“Involution-forms”).

_Bacillus lacticus_ (_Bacterium acidi lactici_, Zopf) is always found in milk which has stood for some time, and in sour foods (cabbage, cucumbers, etc.); it turns the milk sour by producing lactic acid fermentation in the sugar contained in the milk; the lactic acid formed, eventually causes the coagulation of the casein. It resembles the Vinegar-bacteria, occurring as small cylindrical cells, rarely in short rows; not self-motile.--Several other Bacteria appear to act in the same way, some occurring in the mouth of human beings; some of these Bacteria give to butter its taste and flavour.

The _kefir-grains_ which are added to milk for the preparation of kefir, contain in large numbers a Bacterium (_Dispora caucasica_) in the zooglœa-form, a Yeast-fungus, and _Bacillus lacticus_. Kefir is a somewhat alcoholic sour milk, rich in carbonic acid; it is a beverage manufactured by the inhabitants of the Caucasus, from the milk of cows, goats, or sheep, and is sometimes used as a medicine. In the production of kefir, lactic acid fermentation takes place in one part of the sugar contained in the milk, and alcoholic fermentation in another part, and the casein which had become curdled is partially liquefied (peptonised) by an enzyme of a Zooglœa-bacterium.

_Bacillus amylobacter_ (_Bacillus butyricus_), the Butyric-acid-bacterium (Fig. 29), is a very common anaerobic which produces fermentation in sugar and lactic-acid salts, and whose principal product is _butyric acid_. It destroys articles of food and (together with other species) plays a part in the butyric acid fermentation which is necessary in the making of cheese; it is very active wherever portions of plants are decaying, in destroying the cellulose in the cell-walls of herbaceous plants, and is thus useful in the preparation of flax and hemp. The cells are self-motile, generally cylindrical, sometimes united into short rows; endosporous; the spore-forming cells swell, assume very different forms, and show granulose reaction. The germ-tube grows out in the direction of the long axis of the spore.

_Bacillus subtilis_, the Hay-bacillus, is developed in all decoctions of hay; a slender, aerobic, self-motile Bacillus; endosporous (aplanospores); the spore-wall ruptures transversely on germination.

_Crenothrix kuehniana_ occurs in the springs of many baths, in wells, in water or drain-pipes.

_Beggiatoa_ (parallel with the Blue-green Alga _Oscillaria_). Long filaments formed of cylindrical cells which are attached by one of the ends, but which are nearly always free when observed. The filaments, like those of _Oscillaria_, describe conical figures in their revolutions, the free filaments slide upwards and parallel with one another; sheaths are wanting; strongly refractive sulphur drops are found in the interior. The Beggiatoas are the most prevalent _Sulphur-bacteria_. They occur, very commonly in large numbers, wherever plant or animal remains are decaying in water in which sulphuretted hydrogen is being formed; thus, for example, _B. alba_ (Fig. 31) occurs frequently as a white covering or slimy film on mud containing organic remains. ~_B. mirabilis_ is remarkable for its size and its strong peristaltic movements.~ The Sulphur-bacteria oxidize the sulphuretted hydrogen, and accumulate sulphur in the shape of small granules of soft amorphic sulphur, which in the living cell never passes over into the crystalline state. They next oxidize this sulphur into sulphuric acid, which is immediately rendered neutral by absorbed salts of calcium, and is given off in the form of a sulphate, thus CaCO_{3} is principally changed into CaSO_{4}. In the absence of sulphur the nutritive processes are suspended, and consequently death occurs either sooner or later. The Sulphur-bacteria may exist and multiply in a fluid which only contains traces of organic matter, in which organisms devoid of chlorophyll are not able to exist. The Beggiatoas very frequently form white, bulky masses in sulphur wells and in salt water, the traces of organic material which the sulphur water contains proving sufficient for them. ~The cellulose-fermentation, to which the sulphur wells in all probability owe their origin, mainly procures them suitable conditions for existence. The CaCO_{3} and H_{2}S, formed during the cellulose fermentation by the reduction of CaSO_{4} is again changed into CaSO_{4} and CO_{2} by the Sulphur-bacteria (Winogradsky, 1887).--Other Sulphur-bacteria, the so-called purple Sulphur-bacteria, _e.g._ _B. roseo-persicina_, _Spirillum sanguineum_ (Fig. 23), _Bacterium sulfuratum_, etc., have their protoplasm mixed with a red colouring matter (bacterio-purpurin) which, like chlorophyll, has the power, in the presence of light, of giving off oxygen (as proved by T. W. Englemann, 1888, in oxygen-sensitive Bacteria). The three purple Sulphur-bacteria mentioned, are, according to Winogradsky, not pleomorphic kinds but embrace numerous species.~

Many _Spirilli_ (_Spirillum tenue_, _S. undula_, _S. plicatile_, and others) are found prevalent in decaying liquids.

Bacteria (especially Bacilli) are the cause of many substances emitting a foul odour, and of various changes in milk.