Who of us has not, in a partially darkened room, seen the rays of the
sun, as they entered through apertures or chinks in the shutters,
exhibit their track by lighting up the infinitely small corpuscles
contained in the air? Such corpuscles always exist, except in the
atmosphere of lofty mountains, and they constitute the dust of the air.
A microscopic examination of them is a matter of curiosity. Each flock
is a true museum (Fig. 1), wherein we find grains of mineral substances
associated with organic debris, and germs of living organisms, among
which must be mentioned the _microbes_.
Since the splendid researches of Mr. Pasteur and his pupils on
fermentation and contagious diseases, the question of microbes has
become the order of the day.
In order to show our readers the importance of the study of the
microbes, and the results that may be reached by following the
scientific method created by Mr. Pasteur, it appears to us indispensable
to give a summary of the history of these organisms. In the first place,
what is a microbe? Although much employed, the word has not been well
defined, and it would be easy to find several definitions of it. In its
most general sense, the term microbe designates certain colorless algæ
belonging to the family Bacteriaceæ, the principal forms of which are
known under the name of _Micrococcus. Bacterium, Bacillus. Vibrio,
/Spirillum, etc_.
In order to observe these different forms of Bacteriaceæ it is only
necessary to examine microscopically a drop of water in which organic
matter has been macerated, when there will be seen _Micrococci_ (Fig. 2,
I.)looking like spherical granules, _Bacteria_ in the form of very short
rods, _Bacilli_ (Fig. 2, V.), _Vibriones_ (Fig. 2, IV.,) moving their
straight or curved filaments, and _Spirilli_ (Fig. 2, VI.), rolled up
spirally. These varied forms are not absolutely constant, for it often
happens in the course of its existence that a species assumes different
shapes, so that it is difficult to take the form of these algæ as a
basis for classifying them, when all the phases of their development
have not been studied.
The Bacteriaceæ are reproduced with amazing rapidity. If the temperature
is proper, a limpid liquid such as chicken or veal broth will, in a few
hours, become turbid and contain millions of these organisms.
Multiplication is effected through fission, that is to say, each globule
or filament, after elongating, divides into two segments, each of which
increases in its turn, to again divide into two parts, and so on (Fig.
2, I. b). But multiplication in this way only takes place when the
bacteria are placed in a proper nutritive liquid; and it ceases when the
liquid becomes impoverished and the conditions of life become difficult.
It is at this moment that the formation of _spores_ occurs--reproductive
bodies that are destined to permit the algæ to traverse, without
perishing, those phases where life is impossible. The spores are small,
brilliant bodies that form in the center or at the extremity of each
articulation or globule of the bacterium (Fig. 2, II. l), and are set
free through the breaking up of the joints. There are, therefore, two
phases to be distinguished in the life of microbes--that of active life,
during which they multiply with great rapidity, are most active, and
cause sicknesses or fermentations, and that of retarded life, that is to
say, the state, of resting spores in which the organisms are inactive
and consequently harmless. It is curious to find that the resistance to
the two causes of destruction is very different in the two cases.
In the state of active life the bacterides are killed by a temperature
of from 70 to 80 degrees, while the spores require the application of a
temperature of from 100 to 120 degrees to kill them. Oxygen of a high
pressure, which is, as well known from Bert's researches, a poison for
living beings, kills many bacteria in the state of active life, but has
no influence upon their spores.
In a state of active life the bacteriae are interesting to study. The
absence of green matter prevents them from feeding upon mineral matter,
and they are therefore obliged to subsist upon organic matter, just as
do plants that are destitute of chlorophyl (such as fungi, broomrapes,
etc.). This is why they are only met with in living beings or upon
organic substances. The majority of these algae develop very well in the
air, and then consume oxygen and exhale carbonic acid, like all living
beings. If the supply of air be cut off, they resist asphyxia and take
the oxygen that they require from the compounds that surround them. The
result is a complete and rapid decomposition of the organic materials,
or a fermentation. Finally, there are even certain species that die in
the presence of free oxygen, and that can only live by protecting
themselves from contact with this gas through a sort of jelly. These are
ferments, such as _Bacillus amylobacter,_ or butyric ferment, and _B.
septicus_, or ferment of the putrefaction of nitrogenized substances.
[Illustration: FIG. 1.--ATMOSPHERIC DUST.]
These properties explain the regular distribution of bacteria in liquids
exposed to the air. Thus, in water in which plants have been macerated
the surface of the liquid is occupied by _Bacillus subtilis_. which has
need of free oxygen in order to live, while in the bulk of the liquid,
in the vegetable tissues, we find other bacteria, notably _B.
amylobacter_, which lives very well by consuming oxygen in a state of
combination. Bacteria, then, can only live in organic matters, now in
the presence and now in the absence of air.
What we have just said allows us to understand the process of
cultivating these organisms. When it is desired to obtain these algae,
we must take organic matters or infusions of such. These liquids or
substances are heated to at least 120° in order to kill the germs that
they may contain, and this is called "sterilizing." In this sterilized
liquid are then sown the bacteria that it is desired to study, and by
this means they can be obtained in a state of very great purity.
The Bacteriaceae are very numerous. Among them we must distinguish those
that live in inert organic matters, alimentary substances, or debris of
living beings, and which cause chemical decompositions called
fermentations. Such are _Mycoderma aceti_, which converts the alcohol of
fermented beverages into vinegar; _Micrococcus ureae_, which converts
the urea of urine into carbonate of ammonia, and _Micrococcus
nitrificans,_ which converts nitrogenized matters into intrates, etc.
Some, that live upon food products, produce therein special coloring
matters; such are the bacterium of blue milk, and _Micrococcus
prodigiosus_ (Fig. 2, I.), a red alga that lives upon bread and forms
those bloody spots that were formerly considered by the superstitious as
the precursors of great calamities.
[Illustration: Fig. 2.--VARIOUS MICROBES. (Highly magnified.)]
Another group of bacteria has assumed considerable importance in
pathology, and that is the one whose species inhabit the tissues of
living animals, and cause more or less serious alterations therein, and
often death. Most contagious diseases and epidemics are due to algæ of
this latter group. To cite only those whose origin is well known, we may
mention the bacterium that causes charbon, the micrococcus of chicken
cholera, and that of hog measles.
It will be seen from this sketch how important the study of these
organisms is to man, since be must defend his body against their
invasions or utilize them for bringing about useful chemical
modifications in organic matters.
_Our Servants._--We scarcely know what services microbes may render us,
yet the study of them, which has but recently been begun, has already
shown, through the remarkable labors of Messrs. Pasteur, Schloesing and
Muntz, Van Tieghem, Cohn, Koch, etc., the importance of these organisms
in nature. All of us have seen wine when exposed to air gradually sour,
and become converted into vinegar, and we know that in this case the
surface of the liquid is covered with white pellicles called "mother of
vinegar." These pellicles are made up of myriads of globules of
_Mycoderma aceti_. This mycoderm is the principal agent in the
acidification of wine, and it is it that takes oxygen from the air and
fixes it in the alcohol to convert it into vinegar. If the pellicle that
forms becomes immersed in the liquid, the wine will cease to sour.
The vinegar manufacturers of Orleans did not suspect the role of the
mother of vinegar in the production of this article when they were
employing empirical processes that had been established by practice. The
vats were often infested by small worms ("vinegar eals") which disputed
with the mycoderma for the oxygen, killed it through submersion, and
caused the loss of batches that had been under troublesome preparation
for months. Since Mr. Pasteur's researches, the _Mycoderma aceti_ has
been sown directly in the slightly acidified wine, and an excellent
quality of vinegar has thus been obtained, with no fear of an occurrence
of the disasters that accompanied the old process.
Another example will show us the microbes in activity in the earth. Let
us take a pinch of vegetable mould, water it with ammonia compounds, and
analyze it, and we shall find nitrates therein. Whence came these
nitrates? They came from the oxidation of the ammonia compounds brought
about by moistening, since the nitrogen of the air does not seem to
combine under normal conditions with the surrounding oxygen. This
oxidation of ammonia compounds is brought about, as has been shown by
Messrs. Schloesing and Muntz, by a special ferment, the _Micrococcus
nitrificans_, that belongs to the group of Bacteriacæ. In fact, the
vapors of chloroform, which anesthetize plants, also prevent
nitrification, since they anaesthetize the nitric ferment. So, too, when
we heat vegetable humus to 100°, nitrification is arrested, because the
ferment is killed. Finally, we may sow the nitric ferment in calcined
earth and cause nitrification to occur therein as surely as we can bring
about a fermentation in wine by sowing _Mycoderma aceti_ in it.
The nitric ferment exists in all soils and in all latitudes, and
converts the ammoniacal matters carried along by the rain into nitrates
of a form most assimilable by plants. It therefore constitutes one of
the important elements for fertilizing the earth.
Finally, we must refer to the numerous bacteria that occasion
putrefaction in vegetable or animal organisms. These microbes, which
float in the air, fall upon dead animals or plants, develop thereon, and
convert into mineral matters the immediate principles of which the
tissues are composed, and thus continually restore to the air and soil
the elements necessary for the formation of new organic substances.
Thus, _Bacillus amylobacter_ (Fig. 2, II.), as Mr. Van Tieghem has
shown, subsists upon the hydrocarbons contained in plants, and
disorganizes vegetable tissues in disengaging hydrogen, carbonic acid,
and vegetable acids. _Bacterium roseopersicina_ forms, in pools, rosy or
red pellicles that cover vegetable debris and disengage gases of an
offensive odor. This bacterium develops in so great quantity upon low
shores covered with fragments of algæ as to sometimes spread over an
extent of several kilometers. These microbes, like many others,
continuously mineralize organic substances, and thus exhibit themselves
as the indispensable agents of the movement of the matter that
incessantly circulates from the mineral to the organic world, and _vice
versa_.--_Science et Nature._
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Palms sprouted from seeds kept warm by contact of the vessel with the
water boiler of a kitchen range are grown by a man in New York.
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