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 food and producing chemical changes therein,
together with their marvellous power of assimilating this material
as food, make them agents in Nature of extreme importance.