_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.
[Illustration: FIG. 30.--_Cladothrix dichotoma._]
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.
[Illustration: FIG. 31.--_Beggiatoa alba_: _a_ from a fluid
containing abundance of sulphuretted hydrogen; _b_ after lying 24
hours in a solution devoid of sulphuretted hydrogen; _c_ after
lying an additional 48 hours in a solution devoid of sulphuretted
hydrogen, by this means the transverse walls and vacuoles have
become visible.]
_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.
=Parasitic Bacteria= live in other living organisms; but the relation
between “host” and parasite may vary in considerable degree. Some
parasites do no injury to their host, others produce dangerous
contagious diseases; some choose only a special kind as host, others
again live equally well in many different ones. There are further
specific and individual differences with regard to the _predisposition_
of the host, and every individual has not the same receptivity at all
times.
THE HARMLESS PARASITES OF HUMAN BEINGS. Several of the above mentioned
saprophytes may also occur in the alimentary canal of human beings;
_e.g._, the Hay-bacillus, the Butyric-acid-bacillus, etc.; but the
gastric juice prevents the development of others, at all events in
their vegetative condition. _Sarcina ventriculi_, “packet-bacterium,”
is only known to occur in the stomach and intestines of human beings,
and makes its appearance in certain diseases of the stomach (dilation
of the stomach, etc.) in great numbers, without, however, being the
cause of the disease. It occurs in somewhat cubical masses of roundish
cells (Fig. 25).
LESS DANGEROUS PARASITES. In the mouth, especially between and on
the teeth, a great many Bacteria are to be found (more than fifty
species are known), _e.g. Leptothrix buccalis_ (long, brittle,
very thin filaments which are united into bundles), Micrococci in
large lumps, _Spirochæte cohnii_, etc. Some of them are known to be
injurious, as they contribute in various ways to the decay of the
teeth (_caries dentium_); a _Micrococcus_, for instance, forms lactic
acid in materials containing sugar and starch, and the acid dissolves
the lime salts in the external layers of the teeth: those parts of
the teeth thus deprived of lime are attacked by other Bacteria, and
become dissolved. Inflammation in the tissues at the root of a tooth,
is probably produced by septic materials which have been formed by
Bacteria in the root-canal.
DANGEROUS PARASITES. In a large number of the infectious diseases of
human beings and animals, it has been possible to prove that parasitic
Bacteria have been the cause of the disease. Various pathogenic
Bacteria of this nature, belonging to the coccus, rod, and spiral
Bacteria groups, are mentioned in the following:--
=Pathogenic Micrococci.= _Staphylococcus pyogenes aureus_ produces
abscesses of various natures (boils, suppurative processes in internal
organs). The same effects are produced by--
_Streptococcus pyogenes_, which is the most frequent cause of malignant
puerperal fever; it is perhaps identical with--
_Streptococcus erysipelatis_, which is the cause of erysipelas in human
beings.
_Diplococcus pneumoniæ_ (A. Fränkel) is the cause of pneumonia, and of
the epidemic cerebro-spinal meningitis.
_Gonococcus_ (Neisser) is the cause of gonorrhea and inflammation of
the eyes.
=Pathogenic Rod-Bacteria.= _Bacterium choleræ gallinarum_, an aerobic,
facultative parasite which produces fowl-cholera among poultry; it is
easily cultivated on various substrata as a saprophyte. The disease
may be conveyed both through wounds and by food, and may also be
communicated to mammals.
_Bacillus anthracis_, the _Anthrax bacillus_ (Fig. 32), chiefly attacks
mammals, especially herbivorous animals (house mice, guinea-pigs,
rabbits, sheep, cattle), in a less degree omnivorous animals (including
human beings), and in a still less degree the Carnivores. Aerobic.
Cylindrical cells, 3–4 times as long as broad, united into long
rod-like bodies, which may elongate into long, bent, and twisted
filaments. Not self-motile. Endosporous. Germination takes place
without the throwing off of any spore-membrane (compare Hay-bacillus p.
37 which resembles it). Contagion may take place both by introduction
into wounds, and from the mucous membrane of the intestines or lungs,
both by vegetative cells and by spores; in intestinal anthrax, however,
only by spores. The Bacillus multiplies as soon as it has entered the
blood, and the anthrax disease commences. The Bacilli not only give off
poison, but also deprive the blood of its oxygen. Vegetative cells only
occur in living animals. This species is a _facultative parasite_ which
in the first stage is a saprophyte, and only in this condition forms
spores.
[Illustration: FIG. 32.--_Anthrax bacillus_ (_Bacillus
anthracis_) with red (_b_) and white (_a_) blood-corpuscles.]
[Illustration: FIG. 33.--_Anthrax bacillus._ The formation of the
spores; magnified 450 times.]
_Bacillus tuberculosis_ produces tuberculosis in human beings, also
in domestic animals (_perlsucht_). It is a distinct parasite, but may
also live saprophytically. It is rod-formed, often slightly bent, and
is recognised principally by its action with stains (when stained with
an alkaline solution of methyl-blue or carbolic fuchsin, it retains the
colour for a long time even in solutions of mineral acids, in contrast
with the majority of well-known Bacteria): it probably forms spores
which are able to resist heat, dryness, etc.
_Bacillus lepræ_ produces leprosy; _Bacillus mallei_ produces
glanders; _Bacillus tetani_, tetanus (the tetanus bacillus
is very common in soil; anaerobic); _Bacillus diphtheriæ_,
diphtheria; _Bacillus typhosus_, typhoid fever, etc.
=Pathogenic Spiral Bacteria.= _Spirochæte obermeieri_ (Fig. 24)
produces intermittent fever (febris recurrens); it makes its appearance
in the blood during the attacks of fever, but it is not to be found
during intervals when there is no fever. Obligate parasite.
_Spirillum choleræ asiaticæ_ (_Microspira comma_) without doubt
produces Asiatic cholera; an exceedingly motile spirillum, which is
also found in short, bent rods (known as the “Comma-bacillus”), it
lives in the intestines of those attacked by the disease, and gives off
a strong poison which enters the body. It is easily cultivated as a
saprophyte.
A great many circumstances seem to show that a number of other
infectious diseases (syphilis, small-pox, scarlet-fever, measles,
yellow-fever, etc.) owe their origin to parasitic Bacteria, but this
has not been proved with certainty in all cases.
It has been possible by means of special cultivations (ample supply of
oxygen, high temperature, antiseptic materials) to produce from the
parasitic Bacteria described above (_e.g._ the fowl-cholera and the
anthrax Bacteria) _physiological varieties_ which are distinct from
those appearing in nature and possess a less degree of “virulence,”
_i.e._ produce fever and less dangerous symptoms in those animals
which are inoculated with them. The production of such physiological
varieties has come to be of great practical importance from the fact
that they are used as vaccines, _i.e._ these harmless species produce
in the animals inoculated with them _immunity_ from the malignant
infectious Bacteria from which they were derived. This immunity is
effected by the change of the products of one or more of the Bacteria,
but we do not yet know anything about the way in which they act on
the animal organism. The white blood corpuscles, according to the
Metschnikoff, play the part of “Phagocytes” by absorbing and destroying
the less virulent Bacteria which have entered the blood, and by so
doing they are gradually enabled to overcome those of a more virulent
nature.
[Illustration: FIG. 34.--_a_ and _b_ The same blood-cell of a
Frog: _a_ in the act of engulfing an anthrax-bacillus; _b_ after
an interval of a few minutes when the bacillus has been absorbed.]