The Story of Germ Life | Page 4

by Pasteur at first confounded with yeasts.
As a distinct group of organisms they were first distinguished by
Hoffman in 1869, since which date the term bacteria, as applying to
this special group of organisms, has been coming more and more into
use. So difficult were the investigations, that for years there were
hardly any investigators besides Pasteur who could successfully handle
the subject and reach conclusions which could stand the test of time.
For the next thirty years, although investigators and investigations
continued to increase, we can find little besides dispute and confusion
along this line. The difficulty of obtaining for experiment any one kind
of bacteria by itself, unmixed with others (pure cultures), rendered
advance almost impossible. So conflicting were the results that the
whole subject soon came into almost hopeless confusion, and very few
steps were taken upon any sure basis. So difficult were the methods, so
contradictory and confusing the results, because of impure cultures, that
a student of to-day who wishes to look up the previous discoveries in
almost any line of bacteriology need hardly go back of 1880, since he
can almost rest assured that anything done earlier than that was more
likely to be erroneous than correct.
The last fifteen years have, however, seen a wonderful change. The
difficulties had been mostly those of methods of work, and with the
ninth decade of the century these methods were simplified by Robert

Koch. This simplification of method for the first time placed this line of
investigation within the reach of scientists who did not have the genius
of Pasteur. It was now possible to get pure cultures easily, and to obtain
with such pure cultures results which were uniform and simple. It was
now possible to take steps which had the stamp of accuracy upon them,
and which further experiment did not disprove. From the time when
these methods were thus made manageable the study of bacteria
increased with a rapidity which has been fairly startling, and the
information which has accumulated is almost formidable. The very
rapidity with which the investigations have progressed has brought
considerable confusion, from the fact that the new discoveries have not
had time to be properly assimilated into knowledge. Today many facts
are known whose significance is still uncertain, and a clear logical
discussion of the facts of modern bacteriology is not possible. But
sufficient knowledge has been accumulated and digested to show us at
least the direction along which bacteriological advance is tending, and
it is to the pointing out of these directions that the following pages will
be devoted.
WHAT ARE BACTERIA?
The most interesting facts connected with the subject of bacteriology
concern the powers and influence in Nature possessed by the bacteria.
The morphological side of the subject is interesting enough to the
scientist, but to him alone. Still, it is impossible to attempt to study the
powers of bacteria without knowing something of the organisms
themselves. To understand how they come to play an important part in
Nature's processes, we must know first how they look and where they
are found. A short consideration of certain morphological facts will
therefore be necessary at the start.
FORM OF BACTERIA.
In shape bacteria are the simplest conceivable structures. Although
there are hundreds of different species, they have only three general
forms, which have been aptly compared to billiard balls, lead pencils,
and corkscrews. Spheres, rods, and spirals represent all shapes. The
spheres may be large or small, and may group themselves in various

ways; the rods may be long or short, thick or slender; the spirals may
be loosely or tightly coiled, and may have only one or two or may have
many coils, and they may be flexible or stiff; but still rods, spheres, and
spirals comprise all types.
In size there is some variation, though not very great. All are extremely
minute, and never visible to the naked eye. The spheres vary from 0.25
u to 1.5 u (0.000012 to 0.00006 inches). The rods may be no more than
0.3 u in diameter, or may be as wide as 1.5 u to 2.5 u, and in length
vary all the way from a length scarcely longer than their diameter to
long threads. About the same may be said of the spiral forms. They are
decidedly the smallest living organisms which our microscopes have
revealed.
In their method of growth we find one of the most characteristic
features. They universally have the power of multiplication by simple
division or fission. Each individual elongates and then divides in the
middle into two similar halves, each of which then repeats the process.
This method of multiplication by simple division is the distinguishing
mark which separates the bacteria from the yeasts, the latter plants
multiplying by a process known as