so
readily explains many of the facts connected with the development and
reproduction of infectious diseases, that it has been unqualifiedly
adopted by a large number of investigators. The proofs of this theory
had not, however, advanced beyond the demonstrations of the presence
of certain forms of bacteria in the pathological changes of a very
limited number of infectious diseases, until February, 1882, when Koch
announced his discovery of the tubercle bacillus, since which time
nearly every disease has its supposed microbe, and the race is,
indeed, swift in which the would-be discoverers press forward with new
germs for public favor.

The term bacteria or microbe refers to particles of matter,
microscopic in size, which belong to the vegetable kingdom, where they
are known as fungi. If we examine a drop of stagnant water under the
microscope, amplifying say four hundred diameters, we see it loaded
with minute bodies, some mere points, others slightly elongated into
rods, all actively in motion and in various positions, a countless
confusion. If evaporation now takes place, all is still. If we now
apply moisture, the dried-up granules will show activity, as though
they had not been disturbed.

All these different organisms have become familiar to us under the
generic term bacteria, which is a very unfortunate application, as it
really applies to only a single class of fungi. Cohn calls them
schizomycetes, and makes the following classifications:

1. _Sphero-bacteria_, or microbes.
2. _Micro-bacteria_, or bacteria.
3. _Desmo-bacteria_, or bacilli.
4. _Spiroteria_, or spirillae.

The _spiro-bacteria_, or micrococci, are the simplest of the fungi,
and appear as minute organisms of spherical form. They multiply by
fission, a single coccus forming two, these two producing four, and so
on. They present a variety of appearances under the microscope. From
single isolated specimens (which under the highest magnifying power
present nothing beyond minute points) you will observe them in pairs,
again in fours, or in clusters of hundreds (forming zooeglea) and still
adhering together, forming chains. When a given specimen is about to
divide, it is seen to elongate slightly, then a constriction is
formed, which deepens until complete fission ensues.

Micrococci possess no visible structure. They consist of a minute
droplet of protoplasm (mycroprotein) surrounded by a delicate cell
membrane. Certain forms are embedded