The bacteriologist is working in a wonderland fully as remote to the
average mind as that ever occupied by the astronomer or psychologist;
and yet it is as real to him as though he were walking through a forest
and noting the different kinds of trees. Such popular doubts as have
been held regarding bacteriology and even the existence of bacteria are
no longer justified. The evidence is too overwhelming not to be accepted
by anyone who has sufficient interest to investigate. The methods used
in bacteriologic studies are to-day giving us information fully as
concise as that obtained by the general botanist in the study of higher
plants. Indeed, the phenomena of bacterial activities and the chemistry
of the products of growth of many species of bacteria have already
received attention not equaled in the study of some of our most useful
plants.
Bacteria are plants; not because of any absolute characteristic that
separates them from animals, but because comparative study shows that
they are more like plants than animals. They are single-celled organisms
and each individual has the prime factors of life, assimilation, growth
and reproduction. Each bacterium is an independent cell and although the
cells in some species remain attached to one another, giving rise to
characteristic groupings, they are mostly detached and free individuals.
Bacteria can increase in numbers to a remarkable extent when favorable
conditions exist. The mother-cell simply splits into two daughter-cells
and these form a generation of four cells, while later generations,
consisting of perhaps one million cells, can in fifteen or twenty
minutes produce two million bacteria. But conditions must be favorable
for this active growth, ample food stuffs, free from other bacteria,
together with moisture and reasonable warmth are most essential. There
are many circumstances constantly at work to prevent an overgrowth of
bacteria; exhaustion of food supply, antagonism of species and fresh air
with sunshine, are the most important. Bacteria are present everywhere
in greater or less numbers, except within the bodies of healthy, growing
plants and animals. It is for this reason that bacteria become so active
and multiply with great rapidity when once established in the tissue
fluids of larger organisms, either before or after they have died. Vital
activities during health prevent the entrance of bacteria into our
bodies. There are, however, times when the association of different
species of bacteria and also the association of bacteria with higher
plants is of mutual advantage. The association of decomposition and
pathogenic bacteria frequently makes it possible for the latter to
infect an animal, when alone it perhaps would not take place. Again, the
growth of certain bacteria within the root-structure of plants greatly
improves their functional activity. The leguminous plants are enabled to
assimilate much larger quantities of nitrogen when associated with
bacteria than when growing alone. No such mutually advantageous
relationships are known to exist between bacteria and animals; the
tendencies are rather destructive, leading to the infectious diseases.
The general biologic function of the bacteria is very important and in a
general way the need of their existence can be much better appreciated
than that of many living beings. Decomposition may be stated as being
their chief functional activity. Decomposition stands before life;
without it the progress of the generations would terminate. The gradual
and ever rapid disappearance of the substance of vegetable and animal
bodies after death makes room for growing life. With an absence of
decomposition the bodies of plants and animals would collect on the
earth and cover it so deeply with organic matter that plants in
particular would be entirely unable to obtain requisite nourishment.
Higher plants having chlorophyll are able to feed on inorganic material,
while bacteria require organic matter to sustain life. Bacterial food is
then derived from the higher forms of life, while these higher forms
feed on the end products of bacterial decomposition, with the addition
of salts from the earth. An evolutionary query might then arise as to
the early conditions in the history of organic life on the earth. It is
certainly a fertile field for the theorist. Accepting the general rule
that simplicity of structure indicates priority, what then was the food
supply of the primordial bacterium before the advent of higher plants to
supply requisite organic matter? We can hardly believe that there was
already in existence sufficient ammonia-bearing compounds of suitable
quality to sustain these lowest organisms until evolutionary conditions
added organisms having the capacity of collecting nitrogen and carbon
from purely inorganic sources. These general facts, as we now see them,
would apparently strengthen the thought that different kinds of
organisms became extant at the same time.
The methods used in bacteriologic study are based on a few very distinct
principles. Successful cultivation of bacteria depends upon a knowledge
of sterilization, preparation of culture media and isolation of species.
It is in fact miniature gardening. A rod of platinum wire is the trowel
and this is kept clean and free from undesirable organisms by heating it
red hot in the gas flame. With it bacteria are lifted from tube or
plate. The culture media required are mostly beef-tea and gelatine
mixtures and are prepared with extreme care as to their composition and
reaction. The decomposition of the culture medium is prevented by
keeping it in test tubes or flasks plugged with cotton and sterilized by
boiling. By means of the cotton plug the air passing in and out of the
tube is filtered and the bacteria floating in the air are caught in the
cotton and cannot get into the tube. It also prevents bacteria from the
culture getting out of the tube and spreading infectious material. Each
test tube represents a little greenhouse, but one that is free from all
life; it is sterile when ready for use. To the media or culture soils in
the tubes the bacteria are transplanted with the platinum rod, and
active growth is obtained by placing the tubes in a suitable
temperature. Such a growth of bacteria in a test tube can contain many
millions of bacteria, while the resulting appearance of growth is due to
the heaping up of the individuals. To the naked eye the cells are
invisible, but the mass is recognized in the same way that one would
know a field of wheat in the distance without being able to see each
separate plant. Species of bacteria are separated by distributing a few
organisms throughout a fluid and then planting upon solid media. The
individual cells then grow in place and produce colonies. These are
separate and distinct to the eye and each contains bacteria, all of the
same kind. From colonies transplantations to tube cultures are made, and
the species is propagated on different media. The observations from such
growths, together with the microscopical study and sometimes inoculation
experiments on animals are the data by which the species is recognized.
Microscopic methods, although somewhat complicated have been so far
developed that some species of bacteria can be as promptly recognized
under the microscope as an acquaintance met upon the street.
Bacteriology is now being studied and investigated as a field of
research in hundreds of laboratories, and in every university in Europe
and America. Bacteriology has added as much to man’s wealth and
happiness as any of the applied sciences. All the methods of
preservation of food depend upon bacteriological principles, while
modern sanitary science is based on the recognition of the cause of
infectious diseases. The presence of specific bacteria in the secretions
or tissues of man and animals is now such a certainty for many diseases
that the work of making bacteriologic diagnoses is in itself an
extensive vocation. Within the next few years every city in America will
have a diagnosis laboratory for infectious diseases. We can safely
predict that the trained bacteriologist will be called upon to stand
between each sick person or animal and the community to direct measures
that will prevent infection of others. Hygienists are learning more
every day as to the exact way in which disease bacteria pass from person
to person, and the reasons for the occurrence of diseases. They have
learned that the accidental and unusual circumstance is least important,
but that there is a regular train of cause and effect, and in the
knowledge of how to break this chain is the key to the proper control of
an epidemic. Veterinary medicine has been able to obtain benefits from
bacteriology much beyond those already so important to human medicine.
This is so because of the persistent prejudice opposed to bacteriology
in medicine, while the veterinarian has been allowed to treat his
patients practically as the experiment animals are treated in the
laboratory.
Bacteriologists are frequently meeting demands made of their science
that are beyond its present stage of progress. It is frequently
forgotten that this is biology whose deductions are always subject to
the variation of growing things, and not chemistry or mathematics, with
their definite determinations and strict limitations. Bacteriology is
now an established science, and it is as competent to render service in
due proportion to its development and with the same integrity as any
biological subject. There are now many known facts in bacteriology that
cannot be made useful because intermediate steps in their study have not
been learned. It will require long series of experiments in some cases,
but when added to the present usefulness of bacteriology the results may
be expected to satisfy the most severe critics.
Adolph Gehrmann.