The Story of Germ Life | Page 5

budding. Fig. 2 shows these two
methods of multiplication.
While all bacteria thus multiply by division, certain differences in the
details produce rather striking differences in the results. Considering
first the spherical forms, we find that some species divide, as described,
into two, which separate at once, and each of which in turn divides in
the opposite direction, called Micrococcus, (Fig. 3). Other species
divide only in one direction. Frequently they do not separate after
dividing, but remain attached. Each, however, again elongates and
divides again, but all still remain attached. There are thus formed long
chains of spheres like strings of beads, called Streptococci (Fig. 4).
Other species divide first in one direction, then at right angles to the
first division, and a third division follows at right angles to the plane of
the first two, thus producing solid groups of fours, eights, or sixteens
(Fig 5), called Sarcina. Each different species of bacteria is uniform in
its method of division, and these differences are therefore indications of

differences in species, or, according to our present method of
classification, the different methods of division represent different
genera. All bacteria producing Streptococcus chains form a single
genus Streptococcus, and all which divide in three division planes form
another genus, Sarcina, etc.
The rod-shaped bacteria also differ somewhat, but to a less extent. They
almost always divide in a plane at right angles to their longest
dimension. But here again we find some species separating
immediately after division, and thus always appearing as short rods
(Fig. 6), while others remain attached after division and form long
chains. Sometimes they appear to continue to increase in length without
showing any signs of division, and in this way long threads are formed
(Fig. 7). These threads are, however, potentially at least, long chains of
short rods, and under proper conditions they will break up into such
short rods, as shown in Fig. 7a. Occasionally a rod species may divide
lengthwise, but this is rare. Exactly the same may be said of the spiral
forms. Here, too, we find short rods and long chains, or long spiral
filaments in which can be seen no division into shorter elements, but
which, under certain conditions, break up into short sections.
RAPIDITY OF MULTIPLICATION.
It is this power of multiplication by division that makes bacteria agents
of such significance. Their minute size would make them harmless
enough if it were not for an extraordinary power of multiplication. This
power of growth and division is almost incredible. Some of the species
which have been carefully watched under the microscope have been
found under favourable conditions to grow so rapidly as to divide every
half hour, or even less. The number of offspring that would result in the
course of twenty-four hours at this rate is of course easily computed. In
one day each bacterium would produce over 16,500,000 descendants,
and in two days about 281,500,000,000. It has been further calculated
that these 281,500,000,000 would form about a solid pint of bacteria
and weigh about a pound. At the end of the third day the total
descendants would amount to 47,000,000,000,000, and would weigh
about 16,000,000 pounds. Of course these numbers have no

significance, for they are never actual or even possible numbers. Long
before the offspring reach even into the millions their rate of
multiplication is checked either by lack of food or by the accumulation
of their own excreted products, which are injurious to them. But the
figures do have interest since they show faintly what an unlimited
power of multiplication these organisms have, and thus show us that in
dealing with bacteria we are dealing with forces of almost infinite
extent.
This wonderful power of growth is chiefly due to the fact that bacteria
feed upon food which is highly organized and already in condition for
absorption. Most plants must manufacture their own foods out of
simpler substances, like carbonic dioxide (Co2) and water, but bacteria,
as a rule, feed upon complex organic material already prepared by the
previous life of plants or animals. For this reason they can grow faster
than other plants. Not being obliged to make their own foods like most
plants, nor to search for it like animals, but living in its midst, their
rapidity of growth and multiplication is limited only by their power to
seize and assimilate this food. As they grow in such masses of food,
they cause certain chemical changes to take place in it, changes
doubtless directly connected with their use of the material as food.
Recognising that they do cause chemical changes in food material, and
remembering this marvellous power of growth, we are prepared to
believe them capable of producing changes wherever they get a
foothold and begin to grow. Their power of feeding upon complex
organic