HE PATHOGENIC BACTERIA.

The student, who has conscientiously worked out the methods, etc.,
previously dealt with, is in a position to make accurate observations
and to write precise descriptions of the results of such observations.
He is, therefore, now entrusted with pure cultivations of the various
pathogenic bacteria, in order that he may study the life-history of each
and record the results of his own observations--to be subsequently
corrected or amplified by the demonstrator. In this way he is rendered
independent of text-book descriptions, the statements in which he is
otherwise too liable to take for granted, without personally attempting
to verify their accuracy.

During the course of this work attention must also be directed, as
occasion arises, to such other bacteria, pathogenic or saprophytic, as
are allied to the particular organisms under observation, or so resemble
them as to become possible sources of error, by working them through on
parallel lines--in other words the various bacteria should be studied in
"groups." In the following pages the grouping in use in the author's
elementary classes for medical and dental students and for candidates
for the Public Health service is adopted, since a fairly long experience
has completely vindicated the value and utility of this arrangement, and
by its means a fund of information is obtained with regard to the
resemblances and differences, morphological and cultural, of a large
number of bacteria. The fact that some bacteria appear in more than one
of these groups, so far from being a disadvantage, is a positive gain to
the student, since with repetition alone will the necessary familiarity
with the cultural characters of important bacteria be acquired. The
study of the various groups will of course vary in detail with
individual demonstrators, and with the student's requirements--the
general line it should take is indicated briefly in connection with the
first group only (pages 410-411). This section should be carefully
worked through before the student proceeds to the study of
bacterioscopical analysis.

It is customary to commence the study of the pathogenic bacteria with
the Organisms of Suppuration. This is a large group, for all the
pathogenic bacteria possess the power, under certain conditions, of
initiating purely pyogenic processes in place of or in addition to their
specific lesions, (e. g., Bacillus tuberculosis, Streptococcus
lanceolatus, Bacillu