species, it is necessary to use some names. Bacteria are commonly
given a generic name based upon their microscopic appearance.
There are only a few of these names. Micrococcus, Streptococcus,
Staphylococcus, Sarcina, Bacterium, Bacillus, Spirillum, are all
the names in common use applying to the ordinary bacteria. There
are a few others less commonly used. To this generic name a
specific name is commonly added, based upon some physiological
character. For example, Bacillus typhosus is the name given to the
bacillus which causes typhoid fever. Such names are of great use
when the species is a common and well-known one, but of doubtful
value for less-known species It frequently happens that a
bacteriologist makes a study of the bacteria found in a certain
locality, and obtains thus a long list of species hitherto
unknown. In these cases it is common simply to number these
species rather than name them. This method is frequently
advisable, since the bacteriologist can seldom hunt up all
bacteriological literature with sufficient accuracy to determine
whether some other bacteriologist may not have found the same
species in an entirely different locality. One bacteriologist, for
example, finds some seventy different species of bacteria in
different cheeses. He studies them enough for his own purposes,
but not sufficiently to determine whether some other person may
not have found the same species perhaps in milk or water. He
therefore simply numbers them--a method which conveys no suggestion
as to whether they may be new species or not. This method avoids
the giving of separate names to the same species found by
different observers, and it is hoped that gradually accumulating
knowledge will in time group together the forms which are really
identical, but which have been described by different observers.