be scientific. The most satisfactory designation is
that proposed by Naegeli in 1857, namely "schizomycetes," and it is by this
term that they are usually known among botanists; the less exact term,
however, is also used and is retained in this article since the science is
commonly known as "bacteriology." The first part of this article deals with
the general scientific aspects of the subject, while a second part is
concerned with the medical aspects.

I. THE STUDY OF BACTERIA

The general advances which have been made of late years in the study of
bacteria are clearly brought to mind when we reflect that in the middle of
the 19th century these organisms were only known to a few experts and in a
few forms as curiosities of the microscope, chiefly interesting for their
minuteness and motility. They were then known under the name of
"animalculae," and were confounded with all kinds of other small organisms.
At that time nothing was known of their life-history, and no one dreamed of
their being of importance to man and other living beings, or of their
capacity to produce the profound chemical changes with which we are now so
familiar. At the present day, however, not only have hundreds of forms or
species been described, but our knowledge of their biology has so extended
that we have entire laboratories equipped for their study, and large
libraries devoted solely to this subject. Furthermore, this branch of
science has become so complex that the bacteriological departments of
medicine, of agriculture, of sewage, &c., have become more or less separate
studies.

[Sidenote: Definition.]

The schizomycetes or bacteria are minute vegetable organisms devoid of
chlorophyll and multiplying by repeated bipartitions. They consist of
single cells, which may be spherical, oblong or cylindrical in shape, or of
filamentous or other aggregates of cells. They are characterized by the
absence of ordinary sexual reproduction and by the absence of an ordinary
nucleus. In the two last-mentioned characters and in their manner of
division the bacteria resemble Schizophyceae (Cyanophyceae or blue-green
algae), and the two groups of Schizophyceae and Schizomycetes are usually
united in the class Schizophyta, to indicate the generally received view
that most of the typical bacteria have been derived from the Cyanophyceae.
Some forms, however, such as "Sarcina," have their algal analogues in
Palmellaceae among the green algae, while Thaxter's g